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  • richardmitnick 7:58 am on July 20, 2017 Permalink | Reply
    Tags: , , , Centauri Dreams, , Nickel 1-meter telescope at Lick Observatory, NIROSETI-Near-Infrared Optical SETI instrument, Optical SETI, Radio SETI, , Shelley Wright, UCSC Lick Observatory   

    From Centauri Dreams: “Making Optical SETI Happen” 

    Centauri Dreams

    July 18, 2017
    Paul Gilster

    Yesterday I made mention of the Schwartz and Townes paper “Interstellar and Interplanetary Communication by Optical Masers,” which ran in Nature in 1961 (Vol. 190, Issue 4772, pp. 205-208). Whereas the famous Cocconi and Morrison paper that kicked off radio SETI quickly spawned an active search in the form of Project Ozma, optical SETI was much slower to develop. The first search I can find is a Russian project called MANIA, in the hands of V. F. Shvartsman and G. M. Beskin, who searched about 100 objects in the early 1970s, finding no significant brightness variations within the parameters of their search.

    If you want to track this one down, you’ll need a good academic library, as it appears in the conference proceedings for the Third Decennial US-USSR Conference on SETI, published in 1993. Another Shvartsman investigation under the MANIA rubric occurred in 1978. Optical SETI did not seem to seize the public’s imagination, perhaps partially because of the novelty of communications through the recently discovered laser. We do see several optical SETI studies at UC-Berkeley’s Leuschner Observatory and Kitt Peak from 1979 to 1981, the work of Francisco Valdes and Robert Freitas, though these were searches for Bracewell probes within the Solar System rather than attempts to pick up laser transmissions from other star systems.

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    Harvard’s Paul Horowitz, a key player in the development of optical SETI. Credit: Harvard University.

    This was an era when radio searches for extraterrestrial technology had begun to proliferate, but despite the advocacy of Townes and others (and three conferences Townes helped create), it wasn’t until the 1990s that optical SETI began to come into its own. Charles Townes himself was involved in a search for laser signals from about 300 nearby stars in the ‘90s, using the 1.7-meter telescope on Mt. Wilson and reported on at the 1993 conference. Stuart Kingsley began an optical SETI search using the 25-centimeter telescope at the Columbus Optical SETI Observatory (COSETI) in 1990, while Gregory Beskin searched for optical signals at the Special Astrophysical Observatory run by the Russian Academy of Sciences in the Caucasus in 1995.

    Optical SETI’s advantages were beginning to be realized, as Andrew Howard (Caltech) commented in a 2004 paper:

    “The rapid development of laser technology since that time—a Moore’s law doubling of capability roughly every year—along with the discovery of many microwave lines of astronomical interest, have lessened somewhat the allure of hydrogen-line SETI. Indeed, on Earth the exploitation of photonics has revolutionized communications technology, with high-capacity fibers replacing both the historical copper cables and the long-haul microwave repeater chains. In addition, the elucidation (Cordes & Lazio 1991) of the consequences to SETI of interstellar dispersion (first seen in pulsar observations) has broadened thinking about optimum wavelengths. Even operating under the prevailing criterion of minimum energy per bit transmitted, one is driven upward to millimetric wavelengths.”

    In the late 90’s, the SETI Institute, as part of a reevaluation of SETI methods, recommended and then co-funded several optical searches including one by Dan Werthimer and colleagues at UC Berkeley and another by a Harvard-Smithsonian team including Paul Horowitz and Andrew Howard. The Harvard-Smithsonian group also worked in conjunction with Princeton University on a detector system similar to the one mounted on Harvard’s 155-centimeter optical telescope. A newer All-Sky Optical SETI (OSETI) telescope, set up at the Oak Ridge Observatory at Harvard and funded by The Planetary Society, dates from 2006.

    4
    http://seti.harvard.edu/oseti/allsky/allsky.htm

    5
    http://www.setileague.org/photos/oseti3.htm

    6
    http://seti.harvard.edu/oseti/

    At Berkeley, the optical SETI effort is led by Werthimer, who had built the laser detector for the Harvard-Smithsonian team. Optical SETI efforts from Leuschner Observatory and Lick Observatory were underway by 1999. Collaborating with Shelley Wright (UC Santa Cruz), Remington Stone (UC Santa Cruz/Lick Observatory), and Frank Drake (SETI Institute), the Berkeley group has gone on to develop new detector systems to improve sensitivity. As I mentioned yesterday, UC-Berkeley’s Nate Tellis, working with Geoff Marcy, has analyzed Keck archival data for 5,600 stars between 2004 and 2016 in search of optical signals.

    Working in the infrared, the Near-Infrared Optical SETI instrument (NIROSETI) is designed to conduct searches at infrared wavelengths. Shelley Wright is the principal investigator for NIROSETI, which is mounted on the Nickel 1-meter telescope at Lick Observatory, seeing first light in March of 2015. The project is designed to search for nanosecond pulses in the near-infrared, with a goal “to search not only for transient phenomena from technological activity, but also from natural objects that might produce very short time scale pulses from transient sources.” The advantage of near-infrared is the decrease in interstellar extinction, the absorption by dust and gas that can sharply impact the strength of a signal.

    7
    Shelley Wright, then a student at UC-Santa Cruz, helped build a detector that divides the light beam from a telescope into three parts, rather than just two, and sends it to three photomultiplier tubes. This arrangement greatly reduces the number of false alarms; very rarely will instrumental noise trigger all three detectors at once. The three-tube detector is in the white box attached here to the back of the 1-meter Nickel Telescope at Lick Observatory. Credit: Seth Shostak.

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    UCSC Lick Observatory Nickel Telescope

    I might also mention METI International’s Optical SETI Observatory at Boquete, Panama. The idea is to put the optical SETI effort in context. With the SETI Institute now raising money for its Laser SETI initiative — all-sky all-the-time — the role of private funding in making optical SETI happen is abundantly clear. And now, of course, we also have Breakthrough Listen, which in addition to listening at radio wavelengths at the Parkes instrument in Australia and the Green Bank radio telescope in West Virginia, is using the Automated Planet Finder at Lick Observatory to search for optical laser transmissions.

    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia



    GBO radio telescope, Green Bank, West Virginia, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Funded by the Breakthrough Prize Foundation, the project continues the tradition of private funding from individuals, institutions (the SETI Institute) and organizations like The Planetary Society to get optical SETI done.

    Centauri Dreams


    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 3:46 pm on July 19, 2017 Permalink | Reply
    Tags: , Centauri Dreams, , , , Ross 128, Seth Shostak SETI Institute Astronomer, SETI Allen Telescope Array, U Chicago Yerkes Observatory   

    From Centauri Dreams: “Keeping an Eye on Ross 128” 

    Centauri Dreams

    July 19, 2017
    Paul Gilster

    1
    A screen shot from Abel Méndez’s lab note titled “Strange Signals from the Nearby Red Dwarf Star Ross 128.” Credit: Planetary Habitability Laboratory/University of Puerto Rico, Arecibo/Aladin Sky Atlas.

    Frank Elmore Ross (1874-1960), an American astronomer and physicist, became the successor to E. E. Barnard at Yerkes Observatory.

    1
    U Chicago Yerkes Observatory

    2
    U Chicago Yerkes Observatory interior

    Barnard, of course, is the discoverer of the high proper motion of the star named after him, alerting us to its proximity.

    3
    http://www.daviddarling.info/encyclopedia/B/BarnardsStar.html

    And as his successor, Ross would go on to catalog over 1000 stars with high proper motion, many of them nearby. Ross 128, now making news for what observers at the Arecibo Observatory are calling “broadband quasi-periodic non-polarized pulses with very strong dispersion-like features,” is one of these, about 11 light years out in the direction of Virgo.

    NAIC/Arecibo Observatory, Puerto Rico, USA

    Any nearby stars are of interest from the standpoint of exoplanet investigations, though thus far we’ve yet to discover any companions around Ross 128. An M4V dwarf, Ross 128 has about 15 percent of the Sun’s mass. More significantly, it is an active flare star, capable of unpredictable changes in luminosity over short periods. Which leads me back to that unusual reception. The SETI Institute’s Seth Shostak described it this way in a post:

    “What the Puerto Rican astronomers found when the data were analyzed was a wide-band radio signal. This signal not only repeated with time, but also slid down the radio dial, somewhat like a trombone going from a higher note to a lower one.”

    And as Shostak goes on to say, “That was odd, indeed.”

    It’s this star’s flare activity that stands out for me as I look over the online announcement of its unusual emissions, which were noted during a ten-minute spectral observation at Arecibo on May 12. Indeed, Abel Mendez, director of the Planetary Habitability Laboratory at Arecibo, cited Type II solar flares first in a list of possible explanations, though his post goes on to note that such flares tend to occur at lower frequencies. An additional novelty is that the dispersion of the signal points to a more distant source, or perhaps to unusual features in the star’s atmosphere. All of this leaves a lot of room for investigation.

    We also have to add possible radio frequency interference (RFI) into the mix, something the scientists at Arecibo are examining as observations continue. The possibility that we are dealing with a new category of M-dwarf flare is intriguing and would have obvious ramifications given the high astrobiological interest now being shown in these dim red stars.

    All of this needs to be weighed as we leave the SETI implications open. The Arecibo post notes that signals from another civilization are “at the bottom of many other better explanations,” as well they should be assuming those explanations pan out. But we should also keep our options open, which is why the news that the Breakthrough Listen initiative has now observed Ross 128 with the Green Bank radio telescope in West Virginia is encouraging.



    GBO radio telescope, Green Bank, West Virginia, USA

    No evidence of the emissions Arecibo detected has turned up in the Breakthrough Listen data. We’re waiting for follow-up observations from Arecibo, which re-examined the star on the 16th, and Mendez in an update noted that the SETI Institute’s Allen Telescope Array had also begun observations.

    SETI/Allen Telescope Array situated at the Hat Creek Radio Observatory, 290 miles (470 km) northeast of San Francisco, California, USA

    Seth Shostak tells us that the ATA has thus far collected more than 10 hours of data, observations which may help us determine whether the signal has indeed come from Ross 128 or has another source.

    “We need to get all the data from the other partner observatories to put all things together for a conclusion,” writes Mendez. “Probably by the end of this week.”
    [Shostak]

    Or perhaps not, given the difficulty of detecting the faint signal and the uncertainties involved in characterizing it. If you’re intrigued, an Arecibo survey asking for public reactions to the reception is now available.

    I also want to point out that Arecibo Observatory is working on a new campaign to observe stars like Ross 128, the idea being to characterize their magnetic environment and radiation. One possible outcome of work like that is to detect perturbations in their emissions that could point to planets — planetary magnetic fields could conceivably affect flare activity. That’s an intriguing way to look for exoplanets, and the list being observed includes Barnard’s Star, Gliese 436, Ross 128, Wolf 359, HD 95735, BD +202465, V* RY Sex, and K2-18.

    A final note: Arecibo is now working with the Red Dots campaign in coordination with other observatories to study Barnard’s Star, for which there is some evidence of a super-Earth mass planet. More on these observations can be found in this Arecibo news release.

    ESO Red Dots Campaign

    Centauri Dreams


    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 5:20 pm on July 18, 2017 Permalink | Reply
    Tags: Bernard's Star, Centauri Dreams, , , Paul Gilster   

    From Red Dots: “Dreaming Peter van de Kamp’s dream” 

    Red Dots

    7.18.17
    by Paul Gilster, writer and author of “Centauri Dreams”
    Edited by Zaira M. Berdiñas

    1

    The Red Dots campaign to study Proxima Centauri, Barnard’s Star and Ross 154 gives us a cannily chosen set of targets. All red dwarfs much smaller than the Sun, these stars offer us the opportunity of atmospheric analysis of any planets discovered there by future space-and ground-based instruments because all are close. At 4.2 light years, Proxima Centauri is nearest to the Sun, but Barnard’s Star is a scant 6 light years out, making it the closest known star other than the three Alpha Centauri stars. Ross 154 comes in at just under 10 light years, still very much in the local neighborhood in astronomical terms.

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    The proper motion of Barnard’s Star between the years 1991 and 2007, an indication of its proximity to our own Solar System. No image credit.

    But it is not just their proximity that makes these stars interesting. We’d like to know how stars like this age, considering that young M-dwarfs can show strong flare activity. All three of these stars do, with Proxima Centauri and Ross 154 being catalogued as UV Ceti stars; i.e., stars that produce major flares every few days. Barnard’s Star is of a variable category known as BY Draconis, stars that show starspots, variations in luminosity and other activity.

    So consider the spread here. Proxima Centauri is thought to be about 4.85 billion years old, while Barnard’s Star is perhaps twice that. Ross 154, however, shows a high rate of rotation — 3.5 ± 1.5 km/s — that indicates a younger star, perhaps one less than a billion years old. Thus we have three stars and possible planets at markedly different stages of development, giving us the ability to take a deeper look into flare activity on M-dwarfs as they age, and to assess flare effects on planetary habitability, assuming Barnard’s Star and Ross 154 do have planets. We’ll also be investigating the prospects for multiple planets around Proxima Centauri itself.

    Barnard’s Star has already produced its own share of notoriety. Working at the Sproul Observatory (Swarthmore College, Pennsylvania), astronomer Peter van de Kamp examined 2,413 photographic plates of the star taken between 1916 and 1962. The astronomer observed what he believed to be a telltale wobble in the motion of Barnard’s Star that fit the profile of a planet about 1.6 times Jupiter’s mass in an orbit at 4.4 AU [1]. He would later suggest the possibility of two gas giants here [2], and by 1973, Oliver Jensen (University of British Columbia) and Tadeusz Ulrych had upped the number to three [3].

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    Peter van de Kamp (right) and the the 61 cm Sproul refracting telescope (left) he used in his work on Barnard’s Star.

    If confirmed, these would have been the first planets ever detected outside our Solar System, but it was not to be. Follow-up studies by George Gatewood (University of Pittsburgh) and John Hershey (also at the Sproul Observatory) found systematic errors in van de Kamp’s work. The culprit: Lens adjustments to the Swarthmore instrument that were later confirmed by Hershey when he found an identical wobble in the M-dwarf Gliese 793 [4]. Subsequent work by Gatewood and, later, Jieun Choi (UC Berkeley) would be able to detect no planets [5],[6].

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    Figure from Gatewood & Eichhorn that shows the disagreement between their data (black dots) and the model fitted by Van de Kamp using the data from the Sproul Observatory (dashed line).

    Peter van de Kamp’s tool was astrometry, meaning he used precise measurements in the proper motion of the star to look for the presence of planets, finding minute variations on photographic plates that were consistent with the hypothesis. His observational skills and persistence were rightly praised, but errors in his instrument negated what would have been a major discovery.

    So what do we have today? We can rule out gas giants at Barnard’s Star thanks to continuing Doppler monitoring, but we can’t yet rule out small rocky planets of the kind we are now turning up around other M-dwarfs in data from the Kepler mission.

    NASA/Kepler Telescope

    Kepler has shown us that planets of a few times Earth-mass are not uncommon, while a 2013 study by Ravi Kopparapu (Pennsylvania State) found that about half of all M-dwarfs should have Earth-size planets in the habitable zone[7]. What might Red Dots uncover around this tantalizingly close star?

    It was Peter van de Kamp’s work that helped the energetic team of starship designers behind the British Interplanetary Society’s Project Daedalus choose Barnard’s Star as their destination. And physicist Robert Forward, no stranger to fiction, would use a planetary system around Barnard’s Star as the setting for his novel ​Rocheworld​ (1984). The system is reached by a lightsail beamed by a laser array, a concept not unfamiliar to today’s Breakthrough Starshot (read the article by Avi Loeb), which envisions sending small sails by laser to Proxima Centauri.

    How fitting, then, that Red Dots should home in on this interesting system, along with a return to Proxima Centauri and a deep exploration of Ross 154 as well. Red dwarf stars like these account for as much as 80 percent of the stars in our galaxy. The new campaign will let us see, in real time, no less, just how this inspiring search of nearby dwarfs proceeds.

    References:

    van de Kamp, P. “Astrometric study of Barnard’s star from plates taken with the 24-inch Sproul refractor”, Astronomical Journal, 68, 515, (1963).
    van de Kamp, P. “Alternate dynamical analysis of Barnard’s star”, Astronomical Journal, 74, 757, (1969).
    Jensen, O. G. & Ulrych, T. “An analysis of the perturbations on Barnard’s Star”, Astronomical Journal, 78, 1104, (1973).
    Hershey, J. L. “Astrometric analysis of the field of AC +65 6955 from plates taken with the Sproul 24-inch refractor”, Astronomical Journal, 78, 421, (1973).
    Gatewood, G. & Eichhorn, H. “An unsuccessful search for a planetary companion of Barnard’s star BD +4 3561”, Astronomical Journal, 78, 769, (1973).
    Choi, J. et al. “Precise Doppler Monitoring of Barnard’s Star”, Astrophysical Journal, 764, 131, (2013).
    Kopparapu, R. K. “A Revised Estimate of the Occurrence Rate of Terrestrial Planets in the Habitable Zones around Kepler M-dwarfs”, Astrophysical Journal, 767, L8, (2013).

    See the full article here .

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    Red dots is a project to attempt detection of the nearest terrestrial planets to the Sun. Terrestrial planets in temperate orbits around nearby red dwarf stars can be more easily detected using Doppler spectroscopy, hence the name of the project.

    ESO 3.6m telescope & HARPS at LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    ESO/HARPS at La Silla

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

     
  • richardmitnick 9:45 am on July 13, 2017 Permalink | Reply
    Tags: "Planetary mass binary", , , , , Centauri Dreams, , L7 dwarf 2MASS J11193254–1137466, TW Hydrae Association   

    From Centauri Dreams: “A Binary ‘Rogue’ Planet?” 

    Centauri Dreams

    July 12, 2017
    Paul Gilster

    “Planetary mass binary” is an unusual term, but one that seems to fit new observations of what was thought to be a brown dwarf or free-floating large Jupiter analog, and now turns out to be two objects, each of about 3.7 Jupiter masses. That puts them into planet-range when it comes to mass, as the International Astronomical Union normally considers objects below the minimum mass to fuse deuterium (13 Jupiter masses) to be planets. This is the lowest mass binary yet discovered.

    A team led by William Best (Institute for Astronomy, University of Hawaii) went to work on the L7 dwarf 2MASS J11193254–1137466 with the idea of determining what they assumed to be the single object’s mass and age. It was through observations with the Keck II telescope in Hawaii that they discovered the binary nature of their target.


    Keck Observatory, Mauna Kea, Hawaii, USA

    The separation between the two objects is about 3.9 AU, based upon the assumption that the binary is around 160 light years away, the distance of the grouping of stars called the TW Hydrae Association.

    Let’s pause on this for a moment. The TW Hydrae Association has come up in these pages in the past, as a so-called ‘moving group’ that contains stars that share a common origin, and thus are similar in age and travel through space together. Moving groups are obviously useful — if astronomers can determine that a star is in one, then its age and distance can be inferred from the other stars in the group. Best and colleagues determined from key factors like sky position, proper motion, and radial velocity that there was about an 80 percent chance that 2MASS J11193254–1137466AB is a member of the TW Hydrae Association.

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    Keck images of 2MASS J11193254–1137466 reveal that this object is actually a binary system. A similar image of another dwarf, WISEA J1147-2040, is shown at bottom left for contrast: this one does not show signs of being a binary at this resolution. Credit: Best et al. 2017.

    Determining a brown dwarf’s age is tricky business because these objects cool continuously as they age, which means that brown dwarfs of different masses and ages can wind up with the same luminosity. The authors point out that this mass-age-luminosity degeneracy makes it hard to figure out their characteristics without knowing at least two of the three parameters. Membership in a moving group like the TW Hydrae Association gives us an age of about 10 million years but also provides mass estimates from evolutionary models.

    And a binary system hits the jackpot, for now we can study the orbits of the two objects to work out model-independent masses, which is how Best drilled down to the 3.7 Jupiter mass result for each binary member here. The authors consider the binary a benchmark for tests of evolutionary and atmospheric models of young planets, and go on to speculate about its possible origins:

    “The isolation of 2MASS J1119−1137AB strongly suggests that it is a product of normal star formation processes, which therefore must be capable of making binaries with ≲ 5 MJup components. 2MASS J1119−1137AB could be a fragment of a higher-order system that was ejected via dynamical interactions (Reipurth & Mikkola 2015 ApJ), although the lack of any confirmed member of TWA within 10° (projected separation ≈ 5 pc) of 2MASS J1119−1137 makes this scenario unlikely. Formation of very low mass binaries in extended massive disks around Sun-like stars followed by ejection into the field has been proposed by, e.g., Stamatellos & Whitworth (2009), but disks of this type have not been observed.”

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    The positions of 2MASS J11193254–1137466A and B on a color-magnitude diagram for ultracool dwarfs. The binary components lie among the faintest and reddest planetary-mass L dwarfs. Credit: Best et al. 2017.

    So there is much to learn here. An object’s composition, temperature and formation history all come into play when determining whether it is a brown dwarf or a planet, and some definitions of brown dwarf take us below the 13 Jupiter mass criteria. But at 3.7 Jupiter masses, these objects clearly warrant the authors’ careful tag of “planetary mass binary.”

    The paper is Best et al., The Young L Dwarf 2MASS J11193254−1137466 Is a Planetary-mass Binary, Astrophysical Journal Letters Vol. 843, No. 1 (23 June 2017).

    Centauri Dreams


    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 3:13 pm on July 11, 2017 Permalink | Reply
    Tags: , , , Centauri Dreams, , Cornelia crater, , , Haulani Crater, Marcia crater, , Terrain Clues to Ice in the Outer System, The human expansion into the Solar System will demand our being able to identify sources of water, Vesta   

    From Centauri Dreams: “Terrain Clues to Ice in the Outer System” 

    Centauri Dreams

    July 11, 2017
    Paul Gilster

    The human expansion into the Solar System will demand our being able to identify sources of water, a skill we’re honing as explorations continue. On Mars, for example, the study of so-called ‘pitted craters’ has been used as evidence that the low latitude regions of the planet, considered its driest, nonetheless have a layer of underlying ice. The Dawn spacecraft discovered similar pitted terrain on Vesta, as you can see in the image below.

    NASA/Dawn Spacecraft

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    These enhanced-color views from NASA’s Dawn mission show an unusual “pitted terrain” on the floors of the craters named Marcia (left) and Cornelia (right) on the giant asteroid Vesta. The views show that the physical properties or composition of the material in which these pits form is different from crater to crater. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/JHUAPL.

    Vesta’s Marcia crater contains the largest number of pits on the asteroid. The 70-kilometer feature is also one of the youngest craters found there. So what accounts for this kind of terrain? Perhaps the water that formed the pits came from Vesta itself. Another possibility: Low-speed collisions with carbon-rich meteorites could have deposited hydrated materials on the surface, to be released in the heat of subsequent high-speed collisions within the asteroid belt. An explosive degassing into space could explain such pothole-like depressions.

    But Dawn wasn’t through when it left Vesta, and what it has found at Ceres is proving invaluable at understanding what appears to be a common marker of volatile-rich material. In new work from Hanna Sizemore [Geophysical Reseach Letters] (Planetary Science Institute) and colleagues, we learn that Ceres is home to the same kind of pitted terrain. As Sizemore notes:

    “Now, we’ve found this same type of morphological feature on Ceres, and the evidence suggests that ice in the Cerean subsurface dominated the formation of pits there. Finding this type of feature on three different bodies suggests that similar pits might be found on other asteroids we will explore in the future, and that pitted materials may mark the best places to look for ice on those asteroids.”

    2
    Haulani Crater, Ceres, showing abundant pitted materials on the crater floor. Similar pitted materials have previously been identified on Mars and Vesta, and are associated with rapid volatile release following impact. Their discovery on Ceres indicates pitted materials may be a common morphological indicator of volatile-rich materials in the asteroid belt. Haulani Crater is 34 km in diameter. Color indicates topography. Credit: NASA/MPS/PSI/Thomas Platz.

    Sizemore’s team studied the formation of pitted craters on Ceres through numerical models that explored the role of water ice and other volatiles. The morphological similarities between the Ceres features and what has been found on Mars and Vesta are striking. With water ice evidently significant in pit development on two asteroids and a planet, similar terrains will be of clear interest for future missions in terms of in situ resource utilization.

    4
    Pitted terrain on Mars as seen by HiRISE aboard the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.

    Centauri Dreams


    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 4:40 pm on July 4, 2017 Permalink | Reply
    Tags: , , , Centauri Dreams, ,   

    From Centauri Dreams: “M-Dwarf Habitability: New Work on Flares” 

    Centauri Dreams

    July 4, 2017
    Paul Gilster

    The prospects for life around M-dwarf stars, always waxing and waning depending on current research, have dimmed again with the release of new work [Accepted in ApJ]from Christina Kay (NASA/GSFC) and colleagues. As presented at the National Astronomy Meeting at the University of Hull (UK), the study takes on the question of space weather and its effect on habitability.

    We know that strong solar flares can disrupt satellites and ground equipment right here on Earth. But habitable planets around M-dwarfs — with liquid water on the surface — must orbit far closer to their star than we do. Proxima Centauri b, for example, is roughly 0.05 AU from its small red host (7,500,000 km), while all seven of the TRAPPIST-1 planets orbit much closer than Mercury orbits the Sun. What, then, could significant flare activity do to such vulnerable worlds?

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    ESO Red Dots Campaign

    ESO Pale Red Dot project

    The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

    ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile interior

    ESO Belgian robotic Trappist-South National Telescope at Cerro La Silla, Chile

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    Artist’s impression of HD 189733b, showing the planet’s atmosphere being stripped by the radiation from its parent star. Credit: Ron Miller.

    Working with Merav Opher and Marc Kornbleuth (both at Boston University), Kay has homed in on coronal mass ejections (CMEs), the vast upheavals that throw stellar plasma into nearby space. While red dwarf stars are significantly cooler than our G-class Sun, their CMEs are thought to be far stronger because of their enhanced magnetic fields. From the paper:

    “Stellar activity tends to increase with the size of the stellar convection envelope (West et al. 2004) and stellar rotation rates (Mohanty et al. 2002; West et al. 2015), although the activity saturates for sufficiently high rotational velocity (Delfosse et al. 1998). For mid- to late-type M dwarfs (M4 to M8.5) the activity saturates at higher rotational velocities than for early-type M dwarfs, and above M9 the activity levels decrease significantly (Mohanty et al. 2002). Accordingly, most M dwarf stars will have significantly enhanced stellar activity as compared to the Sun.”

    A strong planetary magnetic field could counteract at least some of the resulting flare activity, but even there a possibility of strong erosion of the atmosphere remains. And if the planet is tidally locked, some recent work suggests little to no magnetic field can be expected.

    The paper outlines the process when a CME hits a nearby planet. One problem is extreme ultraviolet and X-ray flux (XUV) which can heat the upper atmosphere and perhaps ionize it. If such radiation gets through to the surface, it can damage any potential life-forms there. While it turns out that an M-dwarf habitable zone planet receives an order of magnitude less XUV flux than Earth when the star is quiet, the flux jumps as high as 100 times Earth’s during the star’s frequent flare activity.

    Significant CME activity also makes the planet much less likely to retain its atmosphere as a shield for life on the surface. A CME compresses whatever magnetosphere the planet has, and in extreme cases, say the authors, can exert enough pressure to shrink the magnetosphere to the point where the atmosphere can be seriously eroded.

    Modeling an Astrospheric Current Sheet

    Kay’s team modeled the effects of theoretical CMEs on the red dwarf V374 Pegasi, using a tool Kay developed for CME modeling called ForeCAT. They found that the strong magnetic fields of the star produce CMEs that can reach the so-called Astrospheric Current Sheet, where the background magnetic field is at its minimum. The same effect occurs with our Sun, when solar CMEs are deflected by magnetic forces toward the minimum magnetic energy.

    At the Sun, the Heliospheric Current Sheet — the local analog to a different star’s Astrospheric Current Sheet — is a field that extends along the Sun’s equatorial plane in the heliosphere and is shaped by the effect of the Sun’s rotating magnetic field on the plasma in the solar wind. The HCS separates regions of the solar wind where the magnetic field points toward or away from the Sun.

    Let’s dwell on that for a moment. Here’s what a NASA fact sheet has to say about the Heliospheric Current Sheet:

    “The sun’s magnetic field permeates the entire solar system called the heliosphere. All nine planets orbit inside it. But the biggest thing in the heliosphere is not a planet, or even the sun. It’s the current sheet — a sprawling surface where the polarity of the sun’s magnetic field changes from plus (north) to minus (south). A small electrical current flows within the sheet, about 10−10 A/m². The thickness of the current sheet is about 10,000 km near the orbit of the Earth. Due to the tilt of the magnetic axis in relation to the axis of rotation of the sun, the heliospheric current sheet flaps like a flag in the wind. The flapping current sheet separates regions of oppositely pointing magnetic field, called sectors.”

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    The Heliospheric Current Sheet results from the influence of the Sun’s rotating magnetic field on the plasma in the interplanetary medium (solar wind). The wavy spiral shape has been likened to a ballerina’s skirt. The new work uses a software modeling package called ForeCAT to study interactions between CMEs and the Astrospheric Current Sheet around the red dwarf V374 Pegasi. Credit: NASA GSFC.

    Kay and team have modeled the Astrospheric Current Sheet expected to be found around M-dwarfs like V374 Pegasi. The authors find that upon reaching the ACS, CMEs become ‘trapped’ along it. Planets can dip into and out of the ACS as they orbit. A CME moving out into the Astrospheric Current Sheet around an M-dwarf can cancel out a habitable zone planet’s local magnetic field, opening the world to devastating flare effects. The upshot:

    “We expect that rocky exoplanets cannot generate sufficient magnetic field to shield their atmosphere from mid-type M dwarf CMEs… We expect that the minimum magnetic field strength will change with M dwarf spectral type as the amount of stellar activity and stellar magnetic field strength change, and that early-type M dwarfs would be more likely to retain an atmosphere than mid or late-type M dwarfs.”

    The authors calculate that a mid-type M-dwarf planet would need a minimum planetary magnetic field between tens to hundreds of Gauss to retain an atmosphere, values that are far higher than Earth’s (0.25 to 0.65 gauss). CME impacts as numerous as five per day could occur for planets near the star’s Astrospheric Current Sheet. The only mitigating factor is that the rate decreases for planets in inclined orbits. The paper notes:

    “The sensitivity to the inclination is much greater for the mid-type M dwarf exoplanets due to the extreme deflections to the Astrospheric Current Sheet. For low inclinations we find a probability of 10% whereas the probability decreases to 1% for high inclinations. From our estimation of 50 CMEs per day, we expect habitable mid-type M dwarf exoplanets to be impacted 0.5 to 5 times per day, 2 to 20 times the average at Earth during solar maximum. The frequency of CME impacts may have significant implications for exoplanet habitability if the impacts compress the planetary magnetosphere leading to atmospheric erosion.”

    So we have much to learn about M-dwarfs. In particular, how accurate is the ForeCAT model in developing the CME scenario around such stars? As we examine such modeling, we have to keep in mind that magnetic field strength will change with the type of M-dwarf we are dealing with. Based on this research, only early M-dwarfs are likely to maintain an atmosphere.

    The paper is Kay, Opher and Kornbleuth, Probability of CME Impact on Exoplanets Orbiting M Dwarfs and Solar-Like Stars.

    Centauri Dreams

    See the full article here .

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    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 3:40 pm on June 30, 2017 Permalink | Reply
    Tags: , , , , , , Centauri Dreams, Cosmic Modesty’ in a Fecund Universe, , ,   

    From Centauri Dreams: “‘Cosmic Modesty’ in a Fecund Universe” 

    Centauri Dreams

    8

    June 30, 2017
    Paul Gilster

    I came across the work of Chin-Fei Lee (Academia Sinica Institute of Astronomy and Astrophysics, Taiwan) when I had just read Avi Loeb’s essay Cosmic Modesty. Loeb (Harvard University) is a well known astronomer, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics and a key player in Breakthrough Starshot.

    Breakthrough Starshot Initiative

    Breakthrough Starshot

    ESO 3.6m telescope & HARPS at LaSilla, 600 km north of Santiago de Chile at an altitude of 2400 metres.

    SPACEOBS, the San Pedro de Atacama Celestial Explorations Observatory is located at 2450m above sea level, north of the Atacama Desert, in Chile, near to the village of San Pedro de Atacama and close to the border with Bolivia and Argentina

    SNO Sierra Nevada Observatory is a high elevation observatory 2900m above the sea level located in the Sierra Nevada mountain range in Granada Spain and operated maintained and supplied by IAC

    Teide Observatory in Tenerife Spain, home of two 40 cm LCO telescopes

    Observatori Astronòmic del Montsec (OAdM), located in the town of Sant Esteve de la Sarga (Pallars Jussà), 1,570 meters on the sea level

    Bayfordbury Observatory,approximately 6 miles from the main campus of the University of Hertfordshire

    [And, don’t forget Breakthrough Listen

    Breakthrough Listen Project

    1

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA



    GBO radio telescope, Green Bank, West Virginia, USA


    CSIRO/Parkes Observatory, located 20 kilometres north of the town of Parkes, New South Wales, Australia

    His ‘cosmic modesty’ implies we should accept the idea that humans are not intrinsically special. Indeed, given that the only planet we know that hosts life has both intelligent and primitive lifeforms on it, we should search widely, and not just around stars like our Sun.

    More on that in a moment, because I want to intertwine Loeb’s thoughts with recent work by Chin-Fei Lee, whose team has used the Atacama Large Millimeter/submillimeter Array (ALMA) to detect organic molecules in an accretion disk around a young protostar. The star in question is Herbig-Haro (HH) 212, an infant system (about 40,000 years old) in Orion about 1300 light years away. Seen nearly edge-on from our perspective on Earth, the star’s accretion disk is feeding a bipolar jet. This team’s results, to my mind, remind us why cosmic modesty seems like a viable course, while highlighting the magnitude of the question.

    What Lee’s team has found at HH 212 is an atmosphere of complex organic molecules associated with the disk. Methanol (CH3OH) is involved, as is deuterated methanol (CH2DOH), methanethiol (CH3SH), and formamide (NH2CHO), which the researchers see as precursors for producing biomolecules like amino acids and sugars. “They are likely formed on icy grains in the disk and then released into the gas phase because of heating from stellar radiation or some other means, such as shocks,” says co-author Zhi-Yun Li of the University of Virginia.

    1
    Image: Jet, disk, and disk atmosphere in the HH 212 protostellar system. (a) A composite image for the HH 212 jet in different molecules, combining the images from the Very Large Telescope (McCaughrean et al. 2002) and ALMA (Lee et al. 2015).

    ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Orange image shows the dusty envelope+disk mapped with ALMA. (b) A zoom-in to the central dusty disk. The asterisk marks the position of the protostar. A size scale of our solar system is shown in the lower right corner for comparison. (c) Atmosphere of the accretion disk detected with ALMA. In the disk atmosphere, green is for deuterated methanol, blue for methanethiol, and red for formamide. Credit: ALMA (ESO/NAOJ/NRAO)/Lee et al.

    Every time I read about finds like this, I think about the apparent ubiquity of life’s materials — here we’re seeing organics at the earliest phases of a stellar system’s evolution. The inescapable conclusion is that the building blocks of living things are available from the outset to be incorporated in the planets that emerge from the disk. That certainly doesn’t count as a detection of life, but it does remind us of how frequently the ingredients of life manage to appear.

    In that context, Avi Loeb’s thoughts on cosmic modesty ring true. We’ve been able to extract some statistical conclusions from the Kepler instrument’s deep stare that let us infer there are more Earth-mass planets in the habitable zones of their stars in the observable universe than there are grains of sand on all the Earth’s beaches. Something to think about as you read this on your beach vacation and gaze from the sand beneath your feet to the ocean beyond.

    But are most living planets likely to occur around G-class stars like our Sun? Loeb reminds us that red dwarf stars like Proxima Centauri b and TRAPPIST-1, both of which made headlines in the past year because of their conceivably habitable planets, are long-lived, with lifetimes as long as 10 trillion years. Our Sun’s life, by comparison, is a paltry 10 billion years. Long after the Sun has turned into a white dwarf after its red giant phase, living things could still have a habitat around Proxima Centauri and TRAPPIST-1. Says Loeb:

    “I therefore advise my wealthy friends to buy real estate on Proxima b, because its value will likely go up dramatically in the future. But this also raises an important scientific question: “Is life most likely to emerge at the present cosmic time near a star like the sun?” By surveying the habitability of the universe throughout cosmic history from the birth of the first stars 30 million years after the big bang to the death of the last stars in 10 trillion years, one reaches the conclusion that unless habitability around low-mass stars is suppressed, life is most likely to exist near red dwarf stars like Proxima Centauri or TRAPPIST-1 trillions of years from now.”

    ESO Pale Red Dot project

    ESO Red Dots Campaign

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    The TRAPPIST-1 star, an ultracool dwarf, is orbited by seven Earth-size planets (NASA).

    ESO Belgian robotic Trappist National Telescope at Cerro La Silla, Chile interior

    ESO Belgian robotic Trappist-South National Telescope at Cerro La Silla, Chile

    But of course, one of the reasons for missions like TESS (Transiting Exoplanet Survey Satellite),

    NASA/TESS

    is to begin to understand the small rocky worlds around nearby red dwarfs, and to determine whether there are factors like tidal lock or stellar flaring that preclude life there. For that matter, do the planets around Proxima and TRAPPIST-1 have atmospheres? There too the answer will be forthcoming, assuming the James Webb Space Telescope is deployed successfully and can make the needed assessment of these worlds.

    NASA/ESA/CSA Webb Telescope annotated

    ” …very advanced civilizations [Loeb continues] could potentially be detectable out to the edge of the observable universe through their most powerful beacons. The evidence for an alien civilization might not be in the traditional form of radio communication signals. Rather, it could involve detecting artifacts on planets via the spectral edge from solar cells, industrial pollution of atmospheres, artificial lights or bursts of radiation from artificial beams sweeping across the sky.”

    Changes to the traditional view of SETI abound as we explore these new pathways. In any case, our technologies for making such detections have never been as advanced, and work across the exoplanetary spectrum, such as the findings of Chin-Fei Lee and colleagues, urges us on as we try to relate our own civilization to a universe in which it is hardly the center. As Loeb reminds us, we are orbiting a galaxy that itself moves at ~0.001c relative to the cosmic rest frame, one of perhaps 100 billion galaxies in the observable universe.

    Either alternative — we are alone, or we are not — changes everything about our perspective, and encourages us to deepen the search for simple life (perhaps detected in exoplanetary atmospheres through its biosignatures) as well as conceivable alien civilizations. Embracing Loeb’s cosmic modesty, we press on under the assumption that life’s emergence is not uncommon, and that refining the search to learn the answer is a civilizational imperative.

    See the full article here .

    Please help promote STEM in your local schools.

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    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 2:32 pm on June 9, 2017 Permalink | Reply
    Tags: , , , Centauri Dreams, ,   

    From Centauri Dreams: “Planet Formation around TRAPPIST-1” 

    Centauri Dreams

    June 9, 2017
    Paul Gilster

    Just how did the seven planets around TRAPPIST-1 form? This is a system with seven worlds each more or less the size of the Earth orbiting a small red dwarf. If these planets formed in situ, an unusually dense disk would have been required, making planet migration the more likely model. But if the planets migrated from beyond the snowline, how do we explain their predominantly rocky composition? And what mechanisms are at work in this system to produce seven planets all of approximately the same size?

    New work out of the University of Amsterdam attempts to resolve the question through a different take on planet formation, one that involves the migration not of planets but planetary building blocks in the form of millimeter to centimeter-sized particles. Chris Ormel (University of Amsterdam) and team note that thermal emission from pebbles like these has been observed around other low-mass stars and even brown dwarfs. The researchers believe these migrating particles become planetary embryos as they reach the snowline, which at TRAPPIST-1 occurs at about 0.1 AU.

    Once within the snowline, the embryos would grow by the accretion of rocky pebbles from the inner circumstellar disk, with inward migration eventually stopping at the inner edge of the disk. A key assumption here is that the planets of TRAPPIST-1 formed sequentially rather than simultaneously, a novel concept indeed. So let me go to the paper at this point:

    “In our model we assume that the H2O iceline is the location where the midplane solids-to-gas ratio exceeds unity, triggering streaming instabilities and spawning the formation of planetesimals. These planetesimals merge into a planetary embryo, whose growth is aided by icy pebble accretion. Once its mass becomes sufficiently large, it migrates interior to the H2O iceline by type I migration, where it continues to accrete (now dry) pebbles until it reaches the pebble isolation mass.”

    The process then begins again for a second planet:

    “After some time, a second embryo forms at the snowline, which follows a similar evolutionary path as its predecessor. Even though the inner planet’s growth could be reduced by its younger siblings’ appetite for pebbles, it always remains ahead in terms of mass. Planet migration stalls at the inner disk edge, where the planets are trapped in resonance.”

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    Image: Astronomers from the University of Amsterdam (the Netherlands) present a new model for how seven earth-sized planets could have been formed in the planetary system Trappist-1. The crux is at the line where ice changes to water. Credit and copyright: NASA/R. Hurt/T. Pyle. And please note this JPL news release on the artists who produced this image [https://sciencesprings.wordpress.com/2017/06/08/from-jpl-the-art-of-exoplanets/] . All too often, artists like Tim Pyle and Robert Hurt receive scant attention in the stories that run their work. It’s excellent to see their background and methods explained.

    The TRAPPIST-1 planets, indeed, form what the authors call ‘a resonant convoy,’ with the outer planets ‘pushing’ on the inner ones. The paper’s numerical simulations produce the observed planetary system with the exception that a 3:2 mean motion resonance emerges among planets b and c, as well as among c and d. Although neither pair is presently at the 3:2 MMR, the authors argue that during the disk dispersion phase of the system’s formation, the 3:2 MMRs of these pairs were broken, leaving us with the overall architecture we see today.

    The paper’s most radical contention is that planets have assembled at a specific location, the snowline, as opposed to forming in situ or migrating from their formation regions beyond the snowline. Clearly, many questions remain, including how the streaming instabilities induced at the snowline operate in the presence of planetary embryos. The paper does, however, make a prediction: If a giant planet forms rapidly at the snowline, it should end the flux of pebbles to the inner disk, depriving it of planet-building material. From the paper:

    “Hence, we expect a dichotomy: when giant planet formation fails, pebbles can drift across the iceline to aid the growth of super-Earths and mini-Neptunes. Conversely, when a giant planet forms at the iceline we expect a dearth of planetary building blocks in the inner disk. Therefore, the close-in super-Earth population found by Kepler and the cold Jupiter populations found chiefly by radial velocity surveys should be anti-correlated – a prediction that could be tested with future exoplanet surveys.”

    The paper is Ormel et al., Formation of Trappist-1 and other compact systems, accepted at Astronomy & Astrophysics (abstract). A preprint is available, but be aware that a number of internal references are not yet filled in, another reason not to assume that preprints necessarily mirror the final paper.

    3

    See the full article here .

    Please help promote STEM in your local schools.

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    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 1:45 pm on June 2, 2017 Permalink | Reply
    Tags: , , , Centauri Dreams, , Griffith Observatory, Jeff Nosanov, , Solar sail, SSEARS: Background of a NIAC Study   

    From Centauri Dreams: “SSEARS: Background of a NIAC Study” 

    Centauri Dreams

    June 2, 2017
    Paul Gilster

    I always keep an eye on what’s going on at the NASA Innovative Advanced Concepts office, which is where I ran into Jeff Nosanov’s Phase I study for a solar sail called Solar System Escape Architecture for Revolutionary Science. At the Jet Propulsion Laboratory, Jeff managed flight mission proposals and supported the radio isotope power program. He now lives in Washington DC, a technology entrepreneur whose fascination with spacecraft design has never diminished. In the essay below, Jeff explains the background of his first NIAC award (a second, PERIapsis Subsurface Cave Optical Explorer, would lead to Phase I and Phase II grants), and gives us an idea of the ins and outs of making ideas into reality at NIAC and JPL. For more, the website nosanov.com is about to go online, as is Jeff’s own podcast, about which more soon.

    By Jeff Nosanov

    1

    It’s an honor and a privilege to be asked to write about my near-interstellar mission work for the Tau Zero Foundation. Marc’s book and Paul’s writing were very inspiring to me as I began working at JPL and dove into the interstellar mission community. This article will describe my journey to JPL, the process of proposing the mission concept, and the experience of managing the project. The mission concept itself can be read about here.

    In summary, SSEARS (Solar System Escape Architecture for Revolutionary Science) is a solar sail-based mission to return to the heliopause (the edge of the solar system) to continue the Voyager science.

    2
    https://science.nasa.gov/science-news/science-at-nasa/2008/31jul_solarsails

    The driving goal was to determine the fastest possible propulsion method to return to the outer solar system. We concluded that it was possible to get there in about 18 years (half the time it took Voyager) using a very large solar sail system. How did we get to this point? I’ll start at the beginning.

    A Child’s View

    One of my favorite childhood photos was taken at the Griffith Observatory in Los Angeles.

    3

    I don’t quite remember this event, but I do strongly remember a later one, my visit at age 5 in 1987 around the time of the Voyager 2 Neptune encounter.

    NASA Voyager 2

    My dad took me there to look through the big telescope at Neptune, and told me of the spacecraft that was nearing the ice giant planet.

    I distinctly remember the “mind blown” moment of realization that such things were possible. I also learned that day about JPL, the NASA lab just a few dozen miles from the Griffith Observatory where the Voyagers, and so many other spacecraft, were built.

    I didn’t know it until much later but that event turned me into a space guy. I also recall a conversation with my dad from around that time in which he told me that we can visit other planets, but not other stars. That stuck with me.

    As a child it is easy to have a fairly distorted view of what NASA actually is, and what it does. It’s tempting to imagine something out of Star Trek, with wild and amazing technologies in development all around. In reality, only a small part of NASA, the NASA Innovative Advanced Concepts Program (NIAC), embodies that exciting vision, as I discovered as an adult.

    Working at JPL

    About 22 years later I started working at JPL on January 4th, 2010. Suddenly the greatest deep space exploration playground was opened to me. I was extremely eager, giddy even, to learn about this work and discover how I could contribute. I began to learn everything I could about everything I could access. I spent many hours reading books in the library (especially Frontiers of Propulsion Science) and talking to as many people, especially senior people, as possible. I especially stalked the Voyager program people.

    5

    My general knowledge about how NASA missions are developed, selected, funded, built, and operated grew. I began to pay attention to RFPs (Requests for Proposals) and BAAs (Broad Agency Announcements) that came through the daily emails. I eventually pieced together the realization that anyone could propose concepts (at nearly any stage of development) to various programs within NASA. But how to possibly find the right combination of ambition, team, capability, vision, most importantly a receptive NASA program?

    I spent many hours with program managers, scientists and engineers learning about the current challenges and capabilities in deep space exploration. I was extremely grateful at the time, but in retrospect I have even greater appreciation for the time spent with me. It was only through the kind support of managers, engineers, scientists and many others that I developed the general background knowledge to attempt the work that became my project.

    Eventually I came to learn about the NIAC program. That program exists to fund revolutionary concepts that significantly increase exploration capability. This is distinct from the majority of NASA projects, which largely seek to minimize technological risk. The NIAC program exists as a way to ensure that investments in promising, ambitious technology get made, and to reduce technological stagnation as the risk-minimizing forcing functions of most other NASA programs run their course.

    Stalking Voyager

    I knew I wanted to make a dent in interstellar flight, so I spent a lot of time with people from the Voyager program. I tried to learn everything I could about the mission to develop a mission concept that would be worth doing scientifically. Around this time NASA had been planning to fund a technology demonstration mission for a concept called SunJammer. This was to be a solar sail mission to a Lagrange point, using the sail for propulsion and station-keeping.

    LaGrange Points map. NASA

    I decided that a NIAC-worthy proposal would be to start with just how large we could reasonably build a solar sail, and then see how fast such a system could reach the heliopause with a scientifically valuable payload.

    I approached Ed Stone at Caltech with child-like reverence.

    Stone was project scientist for Voyager and a former director of JPL itself. I wanted to ask him what he would do to follow Voyager if he had a limitless budget. To my surprise he accepted my meeting request, and we had several meetings in which he outlined a scientific payload designed entirely for the heliopause region. This became the “mission” that the hypothetical giant solar sail propulsion system would uniquely enable.

    Writing the Proposal

    JPL has several systems in place to help people write successful proposals. Each proposal opportunity announcement from NASA results in a mentoring and guidance resource from the responsible JPL program office. I took great advantage of this resource for the first few proposals of my career and it has made a world of difference.

    The theme across many proposals for many agencies in my experience is the importance of genuine, exciting storytelling. Thinking back, that was all I had for my first effort! The process of writing the proposal exposed me to a great many inner workings of JPL including program management, costing, and even obtaining submission authority. I doggedly, perhaps obsessively, followed the process to ensure that all the rules were followed and I felt a deep sense of relief and excitement once the proposal was fully submitted. However, I did not have any way of estimating my chances for success due to my lack of experience. I moved on with my regular work and hoped.

    Months later I got a most unexpected phone call telling me that my proposal had been selected! I was over the moon, and I felt something very powerful for the first time: My ideas are good and are worth pursuing. I felt a change in responsibility. The proposal development process was partly for my own personal satisfaction and growth. It was a wonderful experience. Now, having been selected, I had the privilege of having the responsibility of discovering something new about the universe and our place in it.

    Outcome

    One of the important lessons I learned is to keep the long term goal in mind. In our case, this specifically meant figuring out the fastest possible way back to the heliopause with a science payload worth taking there. It turned out that we could get there in 18 years with a 250m x 250m solar sail and a “Voyager on steroids” payload.

    This rendering shows our vision for the spacecraft, and a small part of the solar sail behind it.

    6

    Towards the end of the study I made another appointment with Ed Stone. I told him what we had learned. He looked me in the eye and said “Wow.” I’d like to imagine that in that one moment he was the 5 year old looking at the sky, his mind bursting with possibilities, instead of me.

    Impact

    We ultimately submitted a proposal for Phase 2. Unfortunately intervening events ended the possibility in the foreseeable future for significant progress on our work. We had relied upon the NASA excitement in the SunJammer program to chart the course for solar sail work. That program was cancelled and so we did not have a path forward to advance the technology, and without that potential synergy it seemed that a NIAC phase 2 award was unlikely.

    Still, I was satisfied and inspired by our results. I must conclude that the relative impact, in the grand scheme of things, of our study was small, perhaps incremental. However the experience drastically changed my goals and ambition. Ultimately my study is one of many that attempted to explore the limits of what human ingenuity and curiosity can achieve.

    Conclusion

    I became a father on May 4, 2012 in the middle of the study period. This event fundamentally changed the way I think about space exploration and my own role in it. I enjoyed bringing my son to the Griffith Observatory for many reasons. During the Griffith Observatory visit in which this photo of my son was taken I recalled my dad’s statement that we can travel to other planets but not other stars. As of June 2nd, 2017 now that is still true…

    7
    … but we’re working on it.

    8

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
  • richardmitnick 4:51 pm on May 26, 2017 Permalink | Reply
    Tags: , , , , Centauri Dreams, Centauris Alpha Beta Proxima, , Dr. Greg Matloff, Near-term interstellar probe   

    From Centauri Dreams: “Near-Term Interstellar Probes: Some Gentle Suggestions” 

    Centauri Dreams

    May 26, 2017
    Paul Gilster

    When Greg Matloff’s “Solar Sail Starships: Clipper Ships of the Galaxy” appeared in JBIS in 1981, the science fictional treatments of interstellar sails I had been reading suddenly took on scientific plausibility. Later, I would read Robert Forward’s work, and realize that an interstellar community was growing in space agencies, universities and the pages of journals. Since those days, Matloff’s contributions to the field have kept coming at a prodigious rate, with valuable papers and books exploring not only how we might reach the stars but what we can do in our own Solar System to ensure a bright future for humanity. In today’s essay, Greg looks at interstellar propulsion candidates and ponders the context provided by Breakthrough Starshot, which envisions small sailcraft moving at 20 percent of the speed of light, bound for Proxima Centauri. What can we learn from the effort, and what alternatives should we consider as we ponder the conundrum of interstellar propulsion?

    Dr. Greg Matloff
    Marc Millis, Paul Gilster and their associates of the Tau Zero Foundation are to be congratulated on the recent award of a $500,000 NASA grant to investigate the prospects for a near-term interstellar probe. As one of the co-authors of The Starlight Handbook, the author of Deep-Space Probes and many interstellar related papers, a former NASA consultant in this field and an Advisor to Project Starshot, I would like to offer some gentle and very personal suggestions about how to best spend this money. Since it is unlikely that I can attend this year’s Tennessee Valley Interstellar Workshop, I have elected to submit these concepts to Centauri Dreams.

    Motivation

    The basic reason for an early interstellar endeavor is knowledge acquisition. Data acquired by a star-probe en route to its destination includes in situ measurements of the interstellar medium including ions, neutral atoms, dust grains and cosmic rays. Of particular interest to designers of eventual human-carrying star arks is measurements of the directionality of high-Z cosmic rays. If these originate from discrete sources in and beyond our galaxy rather than being omni-directional, the problem of shielding a space ark will be more readily solved.

    Another possible function of such a probe is extra-galactic astrometry. If the probe carries a telescope, the very-long baseline observations possible when pairing with solar-system instruments during interstellar cruise should yield valuable data regarding distances and kinematics of extra-galactic objects.

    During the interstellar transfer after the probe’s distance from the Sun exceeds 550 AU, the Sun’s Gravitational Focus can be applied to obtain greatly amplified images of astrophysical objects occulted by the Sun. Trajectory deviations farther along the probe’s interstellar track might indicate the presence of elusive dark matter.

    Upon arrival in the destination planetary system, investigation of planets within the target star’s habitable zone will be the highest priority. Does life evolve on any water-rich world within the liquid-water temperature range, if that world has an atmosphere? Or are special conditions such as a massive satellite a requisite?

    If living planets are commonplace, do technology and civilization naturally evolve? Because we have received no unambiguous signals from hypothetical advanced extraterrestrial civilizations and intelligent ETs are apparently rare or non-existent in our solar system, our early interstellar robots should be configured to investigate the “Eerie Silence” (as Paul Davies has dubbed it) and Fermi’s Paradox (“where is everybody?”). Do advanced ETs perhaps evolve in a non-technological direction, or do they generally self-destruct? Or do they generally elect to remain radio silent and not engage in interstellar exploration and colonization?

    Destination

    I will next consider the probable destination for a probe that we might conceivably launch in the 2050-2100 time frame. Our early probes should almost certainly be directed towards the nearest stars—the Proxima/Alpha Centauri triple star system.

    Centauris Alpha Beta Proxima 27, February 2012. Skatebiker

    This system, which is estimated to be about 6 billion years old, consists of two central Sun-like stars (Alpha A and Alpha B) and a red dwarf companion (Proxima). Alpha A and B orbit their common center of mass in an elliptical orbit with a period of about 80 years. At their closest (periapsis), Alpha A and Alpha B are separated by about 9 Astronomical Units. At their farthest (apoapsis), their separation is in excess of 30 AU. Each of the central Centauri suns could have planets orbiting within their habitable zones. Alpha A/B Centauri is about 4.27 light years from the Sun.

    Proxima Centauri is a bit closer at 4.24 light years from the Sun. It is quite possible (but not definite) that this star is gravitationally bound to the Alpha A/B even though its current separation from Alpha A/B is about 15,000 Astronomical Units.. During the summer of 2016, the discovery of a planet with a probable mass 30% greater than Earth orbiting Proxima Centauri within that star’s habitable zone was announced. A less-than-poetic designation for this planet is Proxima b Centauri.

    Although several research teams are investigating the possibility of habitable worlds attending Alpha A or Alpha B Centauri, the discovery of Proxima b was totally unexpected. Since the nearest star to the Sun has a probable planet orbiting within its habitable zone, it is reasonable to conclude that such worlds are very common in our galaxy.

    Achievable Interstellar Transit Duration

    Our early extrasolar probes— Pioneer 10/11, Voyager 1/2, and New Horizons— don’t really count as starships.

    NASA Pioneer 10

    NASA/Voyager 1

    NASA/New Horizons spacecraft

    Yes, they have left or will eventually leave our solar system and move freely through the Milky Way galaxy. But their propulsion systems—chemical rockets combined with giant-planet gravity assists are not effective enough for true star voyaging. Even the fastest of these would require about 70,000 years to reach Proxima/Alpha Centauri if it happened to be pointing in the right direction (which it isn’t).

    A human colony ship, often called an interstellar ark or world ship, could probably be designed using near-term technology such that it could survive a millennial journey to our nearest stellar neighbor. But such a long travel time for a robotic probe would be difficult to sell to the scientific community since most research participants would prefer to see some results within their lifetimes.

    So the Breakthrough Initiatives project Breakthrough Starshot pushes technology to its limits on numerous fronts in order to design a starcraft capable of traversing the enormous distance between the Sun and Proxima/Alpha Centauri in about 20 years.

    Everything about Starshot is enormously challenging. A hyperthin sail with dimensions up to a few meters on a side must be generated.

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    Image: Artist’s concept of the Breakthrough Starshot sail under beamed acceleration. Credit: Breakthrough Initiatives.

    It must have near perfect reflectivity, high emissivity, low areal mass thickness and very high melting point. This is necessary for it to survive a several minute exposure to a 50-100 GW laser beam without melting. By the way, it must also have enormous tensile strength in order to support the nano-payload during the acceleration process. The sail must also be configured to maintain stability within the beam.

    The laser array would likely be mounted atop a Southern Hemisphere mountain, in order to point at Alpha Centauri. Adaptive optics must be used not only to compensate for the effects of Earth’s atmosphere but to insure that the beam completely fills the sail during the acceleration process at distances measured in millions of kilometers. Also, since a single continuous wave 50-100 GW laser is somewhat beyond current capabilities, thousands of smaller lasers must be synced together to produce the beam.

    Assuming that the sail survives the acceleration process, it must possess ample on-board intelligence to perform several tasks independent of Mission Control. First, it should reorient itself to travel edge-on rather than broadside through interstellar space. This is necessary to reduce the effects of dust grain impacts. Although interstellar dust is rare in our galactic vicinity, even a single grain moving at 0.2c (60,000 kilometers per second) relative to the sail has an enormous wallop.

    But we’re not done yet. Approaching Proxima/Alpha Centauri, the sail must reorient itself once again to allow its instrument suite to survey the environment of the destination stars and to send the results towards Earth. A very tall order indeed for a ~gram-massed nano payload.

    None of the above challenges present physical impossibilities. The question is whether they can all be achieved in a single nano-spacecraft within the next few decades.

    So any NASA-funded interstellar initiative intended for possible implementation within the next few decades should not attempt to duplicate the goals of Project Starshot. Rather than a 20-year travel duration, a 100-year flight time might be more realizable in the near term. Mission planners need to realize that even this is quite a challenge. A 100-200 year travel duration might be a reasonable goal.

    Proposed Propulsion Systems

    Many propulsion systems have been proposed to enable interstellar exploration and colonization. Only a few have any hope of being feasible in the near term. Before we get to the near-term possibilities, it might be nice to review some of the more exotic suggestions.

    Space Warps, Wormholes, and Hyperdrives

    It would indeed be lovely if one of these devices emerged from the realms of science fiction and Hollywood special effects into the real world. Then we could wander the star lanes with the same dispatch that we book a flight to Europe.

    Unfortunately, all of these short-cuts through space-time require either enormous amounts of energy, exotic forms of matter or new physics. It seems wise to continue research in these possibilities. There is no telling when or if a breakthrough might occur. But it would be unwise to hold our collective breaths.

    Thrust Machines

    In the 1960’s, we were treated to the famous Dean Drive. Now engineers in several international locations are testing the Shawyer EM Drive. These and similar devices apparently violate one of the basic laws of classical mechanics: Conservation of Linear Momentum. Although excess unidirectional thrust seems to be generated by the EM Drive, Marc Millis has described in this blog numerous possible causes for this effect that do not violate this law.

    Before any proposed thrust machine can be seriously considered for application to interplanetary or interstellar propulsion, it must demonstrate excess thrust in outer space conditions. Two venues for preliminary in-space tests are stratospheric balloons and sub-orbital rockets. If these succeed, a follow-on demonstration would be a dedicated cubesat containing the device deployed in Low Earth Orbit.

    The Matter/Antimatter Rocket

    This physically possible interstellar propulsion system utilizes total conversion of matter to energy in the reaction between matter and antimatter. Sadly, we are a very long way from the capability of creating the necessary mass of antimatter in a reasonable time frame. If we applied humanity’s best antimatter factory (the Large Hadron Collider) to the the task of full-time antimatter production, we might have a gram of the stuff after 100 million years.

    Another problem is storing the antimatter. Charged sub-atomic particles can be stored in Penning Traps for periods of weeks. These devices use crossed electric and magnetic fields to contain the particles. If applied in space travel, how would the trap’s fields compensate for variable spacecraft acceleration? Also, might stray cosmic rays heat and divert the anti-ions so that they explosively interact with the walls of the containment vessel?

    Perhaps it’s a good thing that application matter-antimatter technology does not seem a near-term possibility. Our security would be jeopardized enormously (and probably terminally) if terrorists could smuggle city-killing weapons in thimble-sized containers.

    Ramjets and EM Sails

    By far the most elegant of physically possible interstellar spacecraft is Robert Bussard’s fusion ramjet. This craft utilizes an electromagnetic (EM) scoop to collect interstellar hydrogen over a large area and redirect the plasma to a proton-proton fusion reactor. Energized fusion products (helium nuclei) are exhausted out the rear of the craft. An ideal ramjet, accelerating at 1g could reach near-optic velocities in about a year Earth time. Because of relativistic effects, the craft could cross the galaxy within the crew’s lifetime, according to on-board clocks.

    Sadly, there are a few problems with the proton-fusing ramjet. First and most significant is the difficulty of igniting the proton-proton thermonuclear reaction. This reaction, which powers main sequence stars such as our Sun, is many orders of magnitude more difficult to ignite than the fusion reactions we currently experiment with. One way around this is to consider lower performance ramjet alternatives such as the ram-augmented interstellar rocket (RAIR) that carries on-board fusion fuel and uses scooped protons as additional reaction mass.

    But even that approach is limited by the limitations of EM scoops that have been suggested to date. Most (including those considered by this author) function better as proton reflectors or drag sails—very good for interstellar deceleration but not too effective for achieving high velocities. The one exception to this is Brice Cassenti’s toroidal scoop, suggested in the late 1990’s. But because this scoop utilizes an array of superconducting wires projected in front of the spacecraft, only accelerations of the order 0.01 g are possible.

    In the near future, the best we can likely hope for to apply ramjet technology is in-space experiments using electric and magnetic sails to reflect the solar wind. This might encourage the perfection of both an interplanetary propulsion option requiring no on-board fuel and experimental tests of an approach to interstellar deceleration.

    Beamed Propulsion

    It is unclear whether Project Starshot’s imaginative enterprise will be successful. Even if a beam projector is located on a high mountain, it is not known how rapidly it can be adjusted to compensate for atmospheric turbulence. Another unknown is whether the beam-steering mechanism will be efficient enough to keep the beam output directed at Alpha/Proxima Centauri for several minutes. Finally, much analysis is required to insure that the beam is centered on the sail and fills the sail during the acceleration process.

    Any funded consideration of interstellar probes would be wise, however, to investigate terrestrial and in-space experiments to demonstrate the utility of beamed propulsion. These could be far less ambitious and expensive than the Project Starshot concepts.

    For example, imagine two cubesats launched simultaneously into Low Earth Orbit. One contains a wafer sail. Its neighbor deploys a very low-power laser or maser projector. The beam is focused on the unfurled sail. It should be possible to monitor both sail acceleration and stability in the beam.

    Another possibility is to repeat an experiment originally planned for the failed Planetary Society Cosmos-1 Earth-orbiting solar-photon sail. After the sail is unfurled, a microwave beam from a terrestrial radio telescope could be focused on the sail. If sail stability and acceleration can be demonstrated, this will advance the possibility of Earth-escape by low-orbit photon sails as well as furthering the cause of interstellar travel.

    Theoretical researchers might also expand the concept of particle-beam propulsion. Because electrically charged sub-atomic particles carry significantly more linear momentum than photons, it would be interesting to develop an understanding of particle-beam collimation over interplanetary and interstellar distances.

    But there is a geopolitical obstacle to the construction of a ~gigawatt laser-, maser-, or particle-beam projector in space. Such a device could be applied to accelerating a starship or diverting an Earth-threatening asteroid; it could also be construed as a weapon.

    If such an enormous beam projector could be constructed in space and could maintain its aim for decades, a hybrid interstellar propulsion system might ultimately become feasible. This is the laser ramjet. In such a vehicle, interstellar ions collected by a Cassenti EM scoop could be accelerated by energy beamed from the solar system.

    Fission-Electric Propulsion

    Nuclear fission has been an available energy source for more than 70 years. The solar-electric rocket (or ion drive) has been used successfully on several interplanetary probes. One reasonable approach to interstellar travel is to remove the solar panels and connect the ion drive’s thruster to a nuclear-fission reactor. In such a device, the reactor energy output would ionize propellant atoms (or molecules) and accelerate the resulting ions out the rear of the spacecraft.

    There are at least three factors limiting interstellar application of fission-electric propulsion. One is propellant availability. To reduce thruster erosion, the inert gas xenon is used as propellant in most current solar-electric drives. Applying this approach to the much more massive fuel requirement of an interstellar probe would likely far exceed the annual terrestrial production rate of xenon. Alternative propellants should be investigated.

    Then there is the matter of geopolitics. Many citizens of our planet would be somewhat unnerved if one of the major space powers began to store the large amount of fissionable material required in Low Earth Orbit during construction of the massive probe. One way around this is to construct the probe as an international project, similar to that applied to creation and operation of the International Space Station.

    Technology is another limitation. Present day ion thrusters are limited to exhaust velocities of about 100 kilometers per second. So a nuclear-electric rocket launched using current technology might require 10,000 years to reach Alpha/Proxima Centauri.

    Exhaust velocity must be raised to at least 1000 kilometers/second to propel a “1000-year ark”, as discussed by Les Shepherd in his 1952-vintage JBIS paper on interstellar travel. To reduce probe flight time to 100 years or so, the ion-exhaust velocity must be increased by another order of magnitude.

    Another required improvement to implement ion-propelled interstellar travel is the reduction of the propulsion system’s specific mass (kilograms/kilowatts). As my late friend, the UK propulsion expert Dr. David Fearn once told me, such a reduction is challenging but ultimately not impossible.

    Thermonuclear Fusion Rockets

    There are two major types of fusion under development. Magnetic fusion, which confines the reacting plasma in EM fields, seems to always be a few decades in the future. Some have quipped that it is the energy source and the propulsion system of the future and always will be.

    Small scale inertial fusion confines and compresses micropellets using crossed electron or laser beams. Large scale inertial fusion—the hydrogen bomb—accomplishes confinement and heating reactants using fission charges, and has of course been operational for more than 60 years.

    Large scale inertial-fusion propulsion was first investigated during the early space age by NASA and the US Department of Defense in the original Project Orion. The first demonstration in a scientific journal of the near-term feasibility of large-scale interstellar travel was Freeman Dyson’s original paper on an interstellar Orion in the October 1968 issue of Physics Today. Assuming propulsion by exploding hydrogen bombs, Dyson demonstrated that the US and USSR Cold War nuclear arsenals were sufficient to dispatch thousands of migrants on colonization ships. The estimated duration of one-way voyages to Alpha/Proxima Centauri was 130-1,300 years.

    In an ideal world, the former Cold War adversaries would be glad to donate their now-obsolete thermonuclear arsenals to the worthy cause of promoting an interstellar diaspora. Sadly, we do not live in such a world.

    Even if nuclear “devices” would be donated to the worthy cause of interstellar exploration/colonization, there are a few technical difficulties to contend with. Unless we can master aneutronic fusion reactions such as the boron-proton scheme, it must be demonstrated that spacecraft structures can survive periodic high-energy thermal-neutron doses.

    Application of fusion micro pellets also has a number of technical issues. First, there is the problem of fuel availability. To reduce neutron irradiation on ship structures, the Daedalus study of the British Interplanetary Society (BIS) considered a Deuterium-Helium3 fusion fuel cycle. The problem is that Helium3 is very rare on Earth. To construct a Daedalus craft, cosmic helium sources must be tapped—perhaps the lunar regolith, atmospheres of giant planets or the solar wind.

    The BIS follow-up to Daedalus, called Icarus, uses a Deuterium-Tritium fuel cycle. Here, it might be necessary to breed Tritium in nuclear fission reactors.

    Some engineering issues must be addressed before Daedalus/Icarus-type pulsed fusion ships can become operational. What are the acoustic effects of repeated fusion ignitions within the reaction chamber? Will the walls of the reaction chamber be damaged if laser- or electron-beams miss a fuel pellet?

    Another significant issue is the enormous size of inertial fusion ships. Even if payload mass can be drastically reduced, the beam projectors, reaction chamber and associated gear are massive.

    One suggestion to reduce the mass of an inertial-fusion propelled spacecraft is worthy of future study. That is Johndale Solem’s Medusa concept. In Medusa, the massive reaction chamber is replaced by a hyper-thin, high-melting-point, radiation-tolerant sail. Fusion charges are ignited within this flexible canopy, which is connected to the payload by strong cables.

    The Solar-Photon Sail

    There are several reasons why photon sails have emerged as the near-term interstellar propulsion system of choice. First, small photon sails have been unfurled and operated in Earth orbit and interplanetary space.

    Second, the photon sail can be scaled with the payload. A payload-on-a-chip requires a small sail. If the payload is small enough, sail and payload can be deployed from a small cubesat. Sail deployment and integration with payload can therefore be based upon current operational experience.

    But today’s multi-layer solar-photon sails are not really capable of interstellar travel. Even if sail acceleration is combined with giant-planet gravity assists, it seems clear that Alpha/Proxima Centauri travel times less than 10,000 years will be difficult to achieve.

    The best we can expect from current solar-photon sails is exploration of the heliopause at around 550 AU, the Sun’s gravity focus at >550 AU, and the inner reaches of the Sun’s Oort Comet Cloud.

    In all likelihood, interstellar probes launched by solar-photon sails will never be as fast as those launched by laser-photon or maser-photon sails. The reason for this is that solar irradiance is an inverse square phenomenon—acceleration at Jupiter is 1/25 that at Earth’s solar orbit. A collimated and accurately aimed beam could maintain sail acceleration over much greater distances.

    But the advantage of solar-photon over beam-photon sails is that mission designers need not concern themselves with the beam-projection system. The solar constant should not vary too much for the foreseeable future.

    So a number of researchers have evaluated the possibility of all-metal sails, dielectric sails, carbon nanotube sails and mesh sails. But the ultimate sail material might be a molecular monolayer such as graphene.

    Graphene is a hyper-strong layer of carbon, one molecule thick. Its melting point is in excess of 4,000 K and it is impermeable to many gases. In the visible spectral range, graphene is essentially transparent. Its fractional visible absorption is 0.023. As I describe in a 2012 JBIS paper, combination with other materials can increase reflectivity to about 0.05 and absorption to ~0.4. Graphene sails carrying robotic payloads and unfurled near the Sun seem capable of reaching Alpha/Proxima Centauri in a few centuries. Because human-carrying arks are limited to ~3g accelerations, these larger ships require about 1,000 years to reach these stars if they are propelled by graphene sails.

    But here is where Project Starshot can play a very major role. In order to reach ~0.2c in a ~50 GW laser beam without melting, the sail reflectivity to laser light must be very high. Perhaps this can be achieved with an appropriate mesh-like meta material. Or perhaps the reflectivity of molecular monolayers such as graphene can be greatly increased.

    After the Project Starshot workshop last August, participants produced draft Requests For Proposals (RFPs). I have discussed the possibility of increasing graphene reflectivity with theoretical condensed-matter researchers at my home institution (CUNY). It is quite possible that they will submit a proposal in response to the RFP when it is issued.

    If monolayer reflectivity can be greatly increased, it will be necessary to demonstrate that this action does not adversely affect monolayer tensile strength so that the wafer sail is strong enough to support the payload during a very close solar approach. It will also be necessary to demonstrate that sail and payload can survive the very hostile environment encountered near the Sun.

    A solar-photon sail will likely never achieve the ~0.2c interstellar velocity of the laser-boosted Project Starshot sail. But, just possibly, solar-photon-sail terminal velocities capable of making the journey to Alpha/Proxima Centauri in a century or so may not be totally infeasible.

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    See the full article here .

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    Tracking Research into Deep Space Exploration

    Alpha Centauri and other nearby stars seem impossible destinations not just for manned missions but even for robotic probes like Cassini or Galileo. Nonetheless, serious work on propulsion, communications, long-life electronics and spacecraft autonomy continues at NASA, ESA and many other venues, some in academia, some in private industry. The goal of reaching the stars is a distant one and the work remains low-key, but fascinating ideas continue to emerge. This site will track current research. I’ll also throw in the occasional musing about the literary and cultural implications of interstellar flight. Ultimately, the challenge may be as much philosophical as technological: to reassert the value of the long haul in a time of jittery short-term thinking.

     
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