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  • richardmitnick 3:37 pm on April 25, 2017 Permalink | Reply
    Tags: Astronomers detect dozens of new quasars and galaxies, Astronomy, , , , NOAJ,   

    From NAOJ via phys.org: “Astronomers detect dozens of new quasars and galaxies” 

    NAOJ

    NAOJ

    phys.org

    April 25, 2017
    Tomasz Nowakowski

    1
    Reduced spectra of the first set of eight quasars and possible quasars discovered in this work, displayed in decreasing order of redshift. The object name and the estimated redshift are indicated at the top left corner of each panel. The blue dotted lines mark the expected positions of the Lyα and N V λ1240 emission lines, given the redshifts. The spectra were smoothed using inverse-variance weighted means over 3 – 9 pixels (depending on the S/N), for display purposes. The bottom panel displays a sky spectrum, as a guide to the expected noise. Credit: Matsuoka et al., 2017.

    A team of astronomers led by Yoshiki Matsuoka of the National Astronomical Observatory of Japan (NAOJ) has detected a treasure trove of new high-redshift quasars (or quasi-stellar objects) and luminous galaxies. The newly found objects could be very important for our understanding of the early universe. The findings were presented Apr. 19 in a paper published on arXiv.org.

    High-redshift quasars and galaxies (at redshift higher than 5.0) are useful probes of the early universe in many respects. They offer essential clues on the evolution of the intergalactic medium, quasar evolution, early supermassive black hole growth, as well as evolution of galaxies through cosmic times. Generally speaking, they enable scientists to study the universe when it looked much different than it does today.

    Recently, Matsuoka’s team has presented the results from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which uses multi-band photometry data provided by the Hyper Suprime-Cam (HSC) Subaru Strategic Program (SSP) survey.

    NAOJ Subaru Hyper Suprime Camera

    HSC is a wide-field camera installed on the Subaru 8.2 m telescope located at the summit of Maunakea, Hawaii and operated by NAOJ.

    NAOJ/Subaru Telescope at Mauna Kea Hawaii, USA

    The researchers selected nearly 50 photometric candidates from the HSC-SSP source catalog and then observed them with spectrographs on the Subaru Telescope and the Gran Telescopio Canarias (GTC), located on the island on the Canary Island of La Palma, Spain.

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain

    The observations resulted in the identification of 24 new quasars and eight new luminous galaxies at redshift between 5.7 and 6.8.

    “We took optical spectra of 48 candidates with GTC/OSIRIS and Subaru/FOCAS, and newly discovered 24 quasars and 8 luminous galaxies at 5.7 < z ≤ 6.8," the paper reads.

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    GTC/OSIRIS

    4
    Subaru/FOCAS

    According to the study, the newly detected quasars have lower luminosity than most of the previously known high-redshift quasi-stellar objects, in contrast to the new galaxies, which have extremely high luminosity when compared to other galaxies found at similar redshift.

    The quasar with the highest redshift (6.8) described in the paper received designation J1429 − 0104, while the one with the lowest redshift (5.92) was named J0903 + 0211. Among the new galaxies, J1628 + 4312 was found at the highest redshift (6.03) and J2237 − 0006 at the lowest (5.77). J2237 − 0006 is also the most luminous newly found galaxy.

    Meanwhile, the researchers revealed that the SHELLQs project continues, and more new quasars are being discovered, which will be reported in forthcoming papers.

    “Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ∼ 6, are ongoing,” they wrote in the paper.

    The authors also noted that they plan to conduct follow-up observations of the newly discovered quasars and galaxies at various wavelengths from sub-millimeter/radio to X-ray. Several of these objects have already been observed with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, near-infrared spectrographs on the Gemini telescope, located in Hawaii and the Very Large Telescope (VLT), also in Chile.

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

    Gemini/North telescope at Mauna Kea, Hawaii, USA

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

    See the full article here .

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    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

    NAOJ Subaru Telescope

    NAOJ Subaru Telescope interior
    Subaru

    ALMA Array
    ALMA

    sft
    Solar Flare Telescope

    Nobeyama Radio Telescope - Copy
    Nobeyama Radio Observatory

    Nobeyama Solar Radio Telescope Array
    Nobeyama Radio Observatory: Solar

    Misuzawa Station Japan
    Mizusawa VERA Observatory

    NAOJ Okayama Astrophysical Observatory Telescope
    Okayama Astrophysical Observatory

    The National Astronomical Observatory of Japan (NAOJ) is an astronomical research organisation comprising several facilities in Japan, as well as an observatory in Hawaii. It was established in 1988 as an amalgamation of three existing research organizations – the Tokyo Astronomical Observatory of the University of Tokyo, International Latitude Observatory of Mizusawa, and a part of Research Institute of Atmospherics of Nagoya University.

    In the 2004 reform of national research organizations, NAOJ became a division of the National Institutes of Natural Sciences.

     
  • richardmitnick 2:56 pm on April 25, 2017 Permalink | Reply
    Tags: , Astronomy, , , Spinning up massive classical bulges in spiral galaxies   

    From astrobites: “Spinning up massive classical bulges in spiral galaxies” 

    Astrobites bloc

    Astrobites

    Apr 25, 2017
    Sandeep Kumar Kataria – guest writer

    Title: Spin-up of massive classical bulges during secular evolution
    Authors: Kanak Saha, Ortwin Gerhard, and Inma Martinez-Valpuesta
    First Author’s Institution: Inter-University Center for Astronomy and Astrophysics, Pune
    1
    Status: Accepted for publication in Astronomy & Astrophysics, open access

    Introduction:

    The mass of spiral galaxies is mainly distributed in three components: the classical bulge (ClB), disc, and surrounding dark matter halo.

    Dark matter halo Image credit: Virgo consortium / A. Amblard / ESA

    Classical bulges are the central building blocks of many early-type spiral galaxies (see the Astrobites Guide to Galaxy Types). These bulges might have formed as a result of collisions between galaxies in the early universe or various other processes mentioned in this paper. It is believed that initially the motion of stars in ClBs is disordered, so the ClB does not rotate. The authors of this paper see an interesting problem to ponder: in the present day, there is an observed net rotation of stars in classical bulges. The origin of this rotation is still to be understood in detail.

    One of the authors of this paper has explained in earlier work that low-mass classical bulges spin up by absorbing angular momentum from galactic bars. The bar has a pattern speed, which is a measure of the collective rotation of a family of orbits of stars in the bar. Angular momentum exchange from the bar mainly occurs at resonances in the disc. These are locations where the difference between disc’s rotation speed and the bar pattern speed have specific ratios with radial oscillations of the stars in the disc. These resonances can be thought of as analogous to resonances in an organ pipe, the natural frequency of which corresponds to waves with wavelengths which match the length of the organ pipe. Let’s see how the authors approach the solution of the rotation problem in ClBs.

    Experiments with galaxy models using computers:

    The authors of this paper try to explain net rotations in Massive ClBs using N-Body simulations.

    2

    First, models of galaxies having non-rotating classical bulges of different masses and sizes are generated using well known techniques such that these models are not unstable. One of the well known classical parameters of local stability is the Toomre Parameter. This parameter measures the ratio between inward gravitational pull on stars at a particular point, and the radial motions of stars at that point. If these motions are sufficiently strong, the gravitational pull will be insufficient to overcome them and the disc will be locally stable. All the models, after evolution, form bars of different sizes according to the initial value of the Toomre parameter. Further, the point of interest lies in understanding how these bars transfer angular momentum to ClBs.

    Studying Bulge Kinematics from experiments:

    4
    Figure 1a. Top row – surface density maps of the model with the highest mass ClB at different times during its evolution. Second to fourth rows – line-of-sight velocity (left) and velocity dispersion (right) maps at different times. These images are taken at 90° projection (edge-on view) and the major axis of the bar is aligned with the x-axis. Clear signatures of rotation are seen at 4 Gyr. The colour bar at the top represents density, middle the velocity, and bottom the velocity dispersion.
    Figure 1b. Rotation, velocity dispersion, and local V/σ radial profiles for the four ClBs in the models.

    The authors notice changes in orbital configuration due to angular momentum transfer by the bar. From Figure 1a it can be noticed that the rotational component in the outer part of the bulge increases over time. It can also be seen that the central part of bulge becomes ‘hot’ and slightly rounder. Here ‘hot’ means that orbits of stars become more disordered and their velocity dispersion (σ) increases. Figure 1b shows radial profiles of rotation and dispersion of stars in the bulge at 4 Gyr for a few of the simulated models. It can be deduced that ClBs rotate faster in their outer parts. However, comparing simulated rotation data of ClBs with observations is no easy task: observational rotation data contains stars both in bulges and bars and distinguishing which they belong to at a single moment in time is challenging.

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    Figure 2a. Top row: distribution of bulge stars with frequency (Ω − ΩB)/κ at different times throughout the secular evolution in the model with the lowest bulge mass. Bottom row: net change in the angular momentum of the selected stars with respect to the previous time. The vertical dotted lines indicate the most important resonances (from left to right): −1:1, 4:1, 3:1, 5:2, and 2:1. As time progresses, more stars are trapped by the 2:1 resonance of the bar with the stellar disc. However, most of the angular momentum transfer occurs through the 5:2 resonance.
    Figure 2b. Here the top and bottom rows represent same entities as in the previous figure but for the models with the highest mass ClBs. As with the low mass Classical bulges most of the angular momentum transfer occurs via the 5:2 resonance.

    The Spin-up process in Massive Classical Bulges:

    After simulating galaxy models with various types of ClBs, the authors conclude that specific angular momentum (angular momentum per unit mass) transfer by the bar is the same for ClBs with low and high mass. Most of the angular momentum transfer from the disc to the bulge occur at particular locations (resonances) which are shown in Figures 2a and 2b. This phenomenon lead to density wakes (alignments of stars in the bulge with the bar) in the bulge. In the simulations density wakes are not so aligned with the bar in the low-mass ClBs but are completely aligned with the high mass ClBs by the end of simulation. The authors also find that outer parts of the bulge experience significant amount of rotation. In addition, the orbits in low-mass bulges are well-ordered, but the ones in high-mass bulges are more disordered. At the end of the simulation all models have a bar with a ‘box’ shape, suggesting that composite bulges (ClB + Boxy Bar) should be common in galaxies. Finally the authors conclude that massive ClBs, like low mass ClBs, are affected by angular momentum exchange with the bar. The spin up process is more prominent when the bar is larger than the ClB.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:29 pm on April 25, 2017 Permalink | Reply
    Tags: Astronomy, , , , ,   

    From Eos: “What to Expect from Cassini’s Final Views of Titan” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    20 April 2017
    JoAnna Wendel

    1
    A view of Saturn’s moon Titan accompanied by its third largest moon, Dione. The Cassini spacecraft captured this image of Titan using its narrow-angle camera in 2011, from about 2.3 million kilometers away. Scientists will soon say goodbye to future images like this one as Cassini’s mission comes to an end in September. Credit: NASA/JPL-Caltech/Space Science Institute

    NASA/ESA/ASI Cassini Spacecraft

    Since the Cassini spacecraft entered Saturn’s orbit in 2004 and dropped a probe onto its largest moon, Titan, scientists have been captivated. Titan’s icy surface is dotted with lakes and seas, its equator wrapped in a field of dunes. Its rainstorms are eerily Earth-like, and its atmosphere swells with prebiotic chemistry.

    But in a few short months, Cassini will vaporize in Saturn’s atmosphere, and scientists will wave goodbye to studying Titan up close.


    Published on Apr 4, 2017
    The final chapter in a remarkable mission of exploration and discovery, Cassini’s Grand Finale is in many ways like a brand new mission. Twenty-two times, NASA’s Cassini spacecraft will dive through the unexplored space between Saturn and its rings. What we learn from these ultra-close passes over the planet could be some of the most exciting revelations ever returned by the long-lived spacecraft. This animated video tells the story of Cassini’s final, daring assignment and looks back at what the mission has accomplished.
    For more about the making of this video, including the science behind the imagery, see the feature at https://saturn.jpl.nasa.gov/news/3016&#8230;
    The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. For more information about Cassini’s Grand Finale, please visit https://saturn.jpl.nasa.gov/grandfinale

    “It’s going to be a very emotional next several months,” said Elizabeth “Zibi” Turtle, a planetary scientist at Johns Hopkins University’s Applied Physics Laboratory (JHUAPL) in Laurel, Md. Turtle, along with about 60 other scientists inside and outside the Cassini mission, gathered at NASA’s Goddard campus in Greenbelt, Md., in early April for the fourth Titan Through Time workshop.

    There, presenters covering Titan from its interior all the way to the top of its thick atmosphere reminded us that before Cassini’s September demise, there’s still plenty of fun in store.

    On 22 April, for example, the spacecraft will sideswipe Titan and skim its ionosphere a little less than 1000 kilometers away from its surface. This flyby, designated T-126, will be Cassini’s last close trip to Titan. After 22 April, Cassini’s subsequent flybys of Titan will be from hundreds of thousands of kilometers away while it swings in and out of Saturn’s rings.

    In the past 13 years, “Titan went from being a mystery, which is exciting, to being a frontier to explore,” Turtle said. With these last views of Titan—both near and far—scientists hope to see the bottom of its lakes, improve their maps of the north pole, and even spot some storm clouds.

    A Strange Surface

    Cassini didn’t give us our first glimpse of Titan. That came from the Voyager spacecraft, which passed by Saturn in 1980 and 1981. But Voyager couldn’t see down to Titan’s surface: Those views came only with Cassini and the short-lived Huygens probe.

    NASA/Voyager 1

    ESA/Huygens Probe from Cassini landed on Titan

    During Cassini’s fourth flyby in 2005, its radar instrument revealed wind-swept dunes wrapping around Titan’s equator. Dunes are exciting because they “can be an instantaneous marker for climate and wind,” said Jani Radebaugh, a planetary scientist at Brigham Young University in Provo, Utah. A dune’s shape can, on Earth at least, reveal which way the wind is blowing.

    However, as with most things on Titan, even the discovery of dunes raised more questions. Currently, the sand looks like it’s moving one direction, but climate models show the wind is blowing in a different direction, Radebaugh said. And when observations and models don’t match up, scientists know that they should search for more clues.

    Dunes aren’t the only unexpected feature dotting Titan’s cold landscape. Early in the mission, scientists also discovered dark patches of liquid: lakes and seas. Thanks to Cassini’s infrared spectrometer and other instruments, scientists know that these lakes are filled with liquid methane, ethane, other more complex hydrocarbons, and possibly nitrogen.

    What’s more, scientists recently spotted waves on the surface of Punga Mare, a northern lake, which can tell them something about Titan’s winds and whether a future submarine exploration mission would splash or splat.

    3
    Punga Mar is a lake in the north polar region of Titan, the planet Saturn’s largest moon. After Kraken Mare and Ligeia Mare, it is the third largest known body of liquid on Titan. It is composed of liquid hydrocarbons (mainly methane and ethane). Located almost adjacent to the north pole at 85.1° N, 339.7° W, it measures roughly 380 km (236 mi) across, greater than the length of Lake Victoria on Earth. Its namesake is Punga, in Māori mythology ancestor of sharks, rays and lizards and a son of Tangaroa, the god of the sea.

    4
    A mosaic of Titan’s north polar lakes and seas stitched together from Cassini’s radar images from 2004 to 2013. Scientists are hoping that the final close-up flyby, T-126, will help them understand features on Titan’s lake beds. Credit: NASA/JPL-Caltech/ASI/USGS

    High Hopes for T-126

    Thus far, however, the angle of Titan flybys hasn’t allowed the spacecraft to see the bottoms of Titan’s smaller lakes.

    Scientists hope that T-126 will change that, said Marco Mastrogiuseppe, a telecommunications engineer at Sapienza University in Rome. During the last close flyby, Cassini scientists will aim its radar at the northern lakes to peek at their depths.

    T-126 could also help illuminate the lakes’ origins, Mastrogiuseppe said. Could they form like sinkholes on Earth, where rain and groundwater dissolve rock from above and below? Or could there be a tectonic origin, perhaps involving rifts opening basins and liquid rushing in? Scientists also suspect there could be a subsurface network connecting the lakes and seas, but they aren’t yet sure.

    Zooming Out to the Big Picture

    Even Cassini’s subsequent far-off flybys, from hundreds of thousands of kilometers away, will help scientists better understand the lakes and seas, said Conor Nixon, a planetary scientist at NASA’s Goddard Space Flight Center and one of the original cofounders of the Titan Through Time workshops.

    From up close, the radar can show scientists small patches in high resolution as the spacecraft zooms by, but it can’t get wide shots of the entire region. Imagine driving by a house at 100 kilometers per hour and snapping a picture. There isn’t much time to get a complete view. But driving by from 100 kilometers away, you’d have more time to snap multiple pictures, Nixon said.

    Similarly, during the faraway flybys, Cassini will sail over Titan’s north pole and spend hours capturing radar images of the entire region, Nixon said. These images will allow scientists to improve their maps and watch for changes along the lakes’ and seas’ shorelines.

    An Active Atmosphere

    As a scientist who works with Cassini’s remote sensing instruments, Turtle actually prefers the faraway flybys. The reason is because, from farther away, Cassini’s infrared mapping instrument and high-resolution camera can also capture a more complete profile of the atmosphere, Turtle said.

    And Titan’s atmosphere is quite the mystery. Titan is the only large moon in the solar system swaddled in a thick atmosphere, and the Huygens probe revealed that it’s dominated by nitrogen, like Earth’s. Likewise, Titan is the only other body in the solar system with liquid on its surface. Plus, Titan boasts liquid cycling akin to Earth’s hydrologic cycle, although in Titan’s case, it’s primarily methane that gets evaporated, condenses in the atmosphere, and precipitates as rainstorms that erode and shape the surface.

    But scientists have no idea how Titan’s atmosphere got there or what replenishes its nitrogen and its methane, another major constituent of the atmosphere. One particularly surprising find from Cassini was the upper atmosphere’s complex organic molecules, Turtle said. No one expected to see benzene rings or long, complex chains of hydrogen and carbon.

    Another surprising find in Titan’s upper atmosphere was heavy ions, said Sarah Hörst, an atmospheric chemist at Johns Hopkins University in Baltimore, Md. Heavy ions are key ingredients to prebiotic chemistry, which means Titan’s atmosphere could hold clues to life-generating chemistry.

    A Future Window into Titan’s Skies

    In May, scientists will recruit an Earth-based system to help them observe Titan’s atmosphere. Nixon and his team have scheduled time to observe Titan using the Atacama Large Millimeter/submillimeter Array (ALMA) observatory in northern Chile’s Atacama Desert.

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

    The May observation will match up with one of the closer of the distant Cassini flybys, Nixon said, and will allow scientists to look for an even wider range of molecules in Titan’s atmosphere. This is because some molecules can be viewed only in certain wavelengths, beyond the capabilities of Cassini’s instruments. Using ALMA will allow researchers to see molecules that might be invisible to Cassini.

    This simultaneous observation will give scientists a benchmark set of data that will allow them to continue to observe Titan’s atmosphere decades into the future, Nixon said, while they look for more prebiotic signatures, like sulfur, or a molecule called vinyl cyanide that could form cell-like membranes in Titan’s liquid oceans and lakes.

    A Portal to Data

    Even after Cassini ends, scientists will still be digging for clues, said astronomer Trina Ray from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. Ray, along with her colleagues at JPL, has made it her mission to ensure that future scientists can use the mountains of data that Cassini has beamed to Earth.

    Cassini scientists upload their raw data into an online database called the Planetary Data System, which scientists even outside the mission can use. But these data aren’t necessarily formatted in an intuitive way for those scientists, Ray said. So she cofounded a group that is puzzling out ways to help future scientists interpret Titan data specifically. She presented at the Titan Through Time workshop to solicit input from scientists studying Titan about how to aggregate all the data.

    One of the ideas is to build a Cassini “master timeline,” Ray said, a narrative that could help guide future scientists through the mission. This timeline would include more than times, dates, and instrument information: It would include details about the intent of an activity. Why was Cassini’s camera pointing here; why was the infrared instrument pointed there?

    Ray and her team have also considered a strategy that would incorporate Titan data into a ready-to-use platform like Mars Trek, an interactive, publicly available map that layers data from various Mars missions and their landing sites. Mars Trek users can toggle between layers, explore the different sites, and save and share what they’ve found with others. Ray imagines a similar map for Titan, where scientists or users could flip through layers of data from Cassini’s different instruments.

    Mysteries Within Mysteries

    In the subsequent seven flybys of Titan before the end of Cassini, Turtle and her team will be looking for clouds over the moon’s northern hemisphere. All the climate models predict that large storm clouds should form over Titan’s high northern latitudes as Titan enters its long summer. But so far, no clouds have appeared, another sign that the hunt for clues isn’t over.

    “Titan has really been teasing us with the clouds,” Turtle said.

    Turtle may not glimpse the elusive clouds. And maybe T-126 won’t provide answers to long-standing questions about Titan’s lakes. The end of Cassini’s mission means no more sniffing the atmosphere with spectrometers, no more close-up images of meandering dunes, and no new views of its mysterious seas.

    But the workshop ended optimistically, with scientists turning their focus to a future Titan mission. Perhaps a drone-like quadcopter could fly around Titan’s surface, researchers mused, taking data from multiple research sites. Or a submarine could swim through a sea.

    And whatever new information comes to light will inevitably generate more questions.

    “That’s the other thing that’s been really fun about [studying Titan]: mysteries within mysteries,” Turtle said.

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
  • richardmitnick 9:21 am on April 25, 2017 Permalink | Reply
    Tags: Astronomy, , , , , SwRI-led team discovers lull in Mars’ giant impact history   

    From SwRI: “SwRI-led team discovers lull in Mars’ giant impact history” 

    SwRI bloc

    Southwest Research Institute

    April 25, 2017
    No writer credit

    1
    Mars bears the scars of five giant impacts, including the ancient giant Borealis basin (top of globe), Hellas (bottom right), and Argyre (bottom left). An SwRI-led team discovered that Mars experienced a 400-million-year lull in impacts between the formation of Borealis and the younger basins. Image Courtesy of University of Arizona/LPL/Southwest Research Institute

    From the earliest days of our solar system’s history, collisions between astronomical objects have shaped the planets and changed the course of their evolution. Studying the early bombardment history of Mars, scientists at Southwest Research Institute (SwRI) and the University of Arizona have discovered a 400-million-year lull in large impacts early in Martian history.

    This discovery is published in the latest issue of Nature Geoscience in a paper titled, “A post-accretionary lull in large impacts on early Mars.” SwRI’s Dr. Bill Bottke, who serves as principal investigator of the Institute for the Science of Exploration Targets (ISET) within NASA’s Solar System Exploration Research Virtual Institute (SSERVI), is the lead author of the paper. Dr. Jeff Andrews-Hanna, from the Lunar and Planetary Laboratory in the University of Arizona, is the paper’s coauthor.

    “The new results reveal that Mars’ impact history closely parallels the bombardment histories we’ve inferred for the Moon, the asteroid belt, and the planet Mercury,” Bottke said. “We refer to the period for the later impacts as the ‘Late Heavy Bombardment.’ The new results add credence to this somewhat controversial theory. However, the lull itself is an important period in the evolution of Mars and other planets. We like to refer to this lull as the ‘doldrums.’”

    The early impact bombardment of Mars has been linked to the bombardment history of the inner solar system as a whole. Borealis, the largest and most ancient basin on Mars, is nearly 6,000 miles wide and covers most of the planet’s northern hemisphere. New analysis found that the rim of Borealis was excavated by only one later impact crater, known as Isidis. This sets strong statistical limits on the number of large basins that could have formed on Mars after Borealis. Moreover, the preservation states of four youngest large basins — Hellas, Isidis, Argyre, and the now-buried Utopia — are strikingly similar to that of the larger, older Borealis basin. The similar preservation states of Borealis and these younger craters indicate that any basins formed in-between should be similarly preserved. No other impact basins pass this test.

    “Previous studies estimated the ages of Hellas, Isidis, and Argyre to be 3.8 to 4.1 billion years old,” Bottke said. “We argue the age of Borealis can be deduced from impact fragments from Mars that ultimately arrived on Earth. These Martian meteorites reveal Borealis to be nearly 4.5 billion years old — almost as old as the planet itself.”

    The new results reveal a surprising bombardment history for the red planet. A giant impact carved out the northern lowlands 4.5 billion years ago, followed by a lull of approximately 400 million years. Then another period of bombardment produced giant impact basins between 4.1 and 3.8 billion years ago. The age of the impact basins requires two separate populations of objects striking Mars. The first wave of impacts was associated with formation of the inner planets, followed by a second wave striking the Martian surface much later.

    SSERVI is a virtual institute headquartered at NASA’s Ames Research Center in Mountain View, California. Its members are distributed among universities and research institutes across the United States and around the world. SSERVI is working to address fundamental science questions and issues that can help further human exploration of the solar system.

    For more information, contact Deb Schmid, (210) 522-2254, Communications Department, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.

    See the full article here .

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    SwRI Campus

    Southwest Research Institute (SwRI) is an independent, nonprofit applied research and development organization. The staff of nearly 2,800 specializes in the creation and transfer of technology in engineering and the physical sciences. SwRI’s technical divisions offer a wide range of technical expertise and services in such areas as engine design and development, emissions certification testing, fuels and lubricants evaluation, chemistry, space science, nondestructive evaluation, automation, mechanical engineering, electronics, and more.

     
  • richardmitnick 8:45 am on April 25, 2017 Permalink | Reply
    Tags: An old star learns new tricks, AR Scorpii white dwarf star, Astronomy, , , ,   

    From COSMOS: “An old star learns new tricks” 

    Cosmos Magazine bloc

    COSMOS

    25 April 2017
    Alan Duffy

    1

    The strange object AR Scorpii. In this unique double star a rapidly spinning white dwarf star (right) powers electrons up to almost the speed of light. M. Garlick/University of Warwick, ESA/Hubble

    When textbooks are proven wrong, we scientists can’t help but celebrate. So let’s raise a glass to the white dwarf!

    We have always dismissed these aged fellows as defunct relics of a sun-sized star. Now one has surprised us. Instead of going off gently into that good night, it is zapping the universe with a spinning beam of radiation. For astrophysicists like me, this is like hearing a retired centenarian has entered the world heavyweight boxing championships and is punching with the best of them.

    This unexpected behavior was reported in a January issue of Nature Astronomy by David Buckley at the South African Astronomical Observatory and colleagues from the University of Warwick.

    The white dwarf, AR Scorpii, and a larger companion star (a red dwarf) are located 380 light years away. Separated from each other by just three times the distance between the Earth and Moon, they orbit each other every four hours.

    Till now, if you had have asked me to describe the typical life story of a white dwarf, my explanation would have gone something like this.

    Fast-forward the next five billion years to see the Sun age before your very eyes. Its surface reddens and bloats as fusion reactions relocate to the outer layers; its shapely edges blur as its atmosphere drifts off into space. Now known as a red giant, it engulfs Mercury and Venus, almost certainly Earth and possibly Mars.

    At the end of those five billion years, the Sun’s nuclear fusion furnace has used up its fuel. Absent the outward pressure, it collapses under its own gravity.

    The result is an Earth-sized object – about one millionth its original size. After 10 billion years of fusion, the Sun is gone, the remaining carbon atoms crushed till they form a near-perfect lattice akin to a diamond. Each teaspoon’s worth of material equals a ton in mass.

    It is now a white dwarf. Though the star’s surface continues to glow white hot at more than 100,000 Kelvin, it is effectively dead, slowly fading to leave a black dwarf, with no more role to play in the evolution of the galaxy.

    AR Scorpii, however, is different. Rather than fading away, it has been acting more like a lighthouse, spinning on its axis every two minutes and emitting a tightly focused beam of radiation along its magnetic poles. Like a giant dynamo, the beam is powered by a magnetic field a 100 million times that of Earth’s.

    In emitting its regular rotating beam, AR Scorpii is behaving like a pulsar, albeit a slow one. These cosmic beacons usually spin with a period of seconds rather than minutes and were previously thought to be powered only by neutron stars, the end state of a star with a mass at least three times that of the Sun. Even more dense than a white dwarf, a teaspoonful of neutron star weighs a billion tonnes.

    Even more unusually, the beams from the feisty AR Scorpii tear across the face of its companion star, accelerating material to close to the speed of light and causing it to shine measurably brighter.

    Just how AR Scorpii acquired the superpowers of a neutron star is a mystery that has astrophysicists bemused. White dwarves are not supposed to be able to do this! Only neutron stars were thought to be able to power the pulsars seen in their thousands across the galaxy. Now we know different.

    This isn’t the first time researchers have suggested a white dwarf might not just be a silent senior citizen. In 2008, Japanese astrophysicist Yukikatsu Terada and colleagues published an article in the Publications of the Astronomical Society of Japan that showed the rapidly rotating white dwarf AE Aquarii was pulsating X-rays.

    See the full article here .

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  • richardmitnick 7:32 am on April 25, 2017 Permalink | Reply
    Tags: Astronomy, , , Heliosphere, Heliotail, ,   

    From Goddard: “NASA’s Cassini, Voyager Missions Suggest New Picture of Sun’s Interaction with Galaxy” 

    NASA Goddard Banner
    NASA Goddard Space Flight Center

    April 24, 2017
    Sarah Frazier
    sarah.frazier@nasa.gov
    NASA’s Goddard Space Flight Center, Greenbelt, Md.

    New data from NASA’s Cassini mission, combined with measurements from the two Voyager spacecraft and NASA’s Interstellar Boundary Explorer, or IBEX, suggests that our sun and planets are surrounded by a giant, rounded system of magnetic field from the sun — calling into question the alternate view of the solar magnetic fields trailing behind the sun in the shape of a long comet tail.

    NASA/Voyager 1

    NASA/ESA/ASI Cassini Spacecraft

    NASA/IBEX

    The sun releases a constant outflow of magnetic solar material — called the solar wind — that fills the inner solar system, reaching far past the orbit of Neptune. This solar wind creates a bubble, some 23 billion miles across, called the heliosphere. Our entire solar system, including the heliosphere, moves through interstellar space. The prevalent picture of the heliosphere was one of comet-shaped structure, with a rounded head and an extended tail. But new data covering an entire 11-year solar activity cycle show that may not be the case: the heliosphere may be rounded on both ends, making its shape almost spherical. A paper on these results was published in Nature Astronomy on April 24, 2017.

    “Instead of a prolonged, comet-like tail, this rough bubble-shape of the heliosphere is due to the strong interstellar magnetic field — much stronger than what was anticipated in the past — combined with the fact that the ratio between particle pressure and magnetic pressure inside the heliosheath is high,” said Kostas Dialynas, a space scientist at the Academy of Athens in Greece and lead author on the study.

    1
    New data from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions show that the heliosphere — the bubble of the sun’s magnetic influence that surrounds the inner solar system — may be much more compact and rounded than previously thought. The image on the left shows a compact model of the heliosphere, supported by this latest data, while the image on the right shows an alternate model with an extended tail. The main difference is the new model’s lack of a trailing, comet-like tail on one side of the heliosphere. This tail is shown in the old model in light blue.
    Credits: Dialynas, et al. (left); NASA (right)

    An instrument on Cassini, which has been exploring the Saturn system over a decade, has given scientists crucial new clues about the shape of the heliosphere’s trailing end, often called the heliotail. When charged particles from the inner solar system reach the boundary of the heliosphere, they sometimes undergo a series of charge exchanges with neutral gas atoms from the interstellar medium, dropping and regaining electrons as they travel through this vast boundary region. Some of these particles are pinged back in toward the inner solar system as fast-moving neutral atoms, which can be measured by Cassini.

    “The Cassini instrument was designed to image the ions that are trapped in the magnetosphere of Saturn,” said Tom Krimigis, an instrument lead on NASA’s Voyager and Cassini missions based at Johns Hopkins University’s Applied Physics Laboratory in Laurel, Maryland, and an author on the study. “We never thought that we would see what we’re seeing and be able to image the boundaries of the heliosphere.”

    2
    Many other stars show tails that trail behind them like a comet’s tail, supporting the idea that our solar system has one too. However, new evidence from NASA’s Cassini, Voyager and Interstellar Boundary Explorer missions suggest that the trailing end of our solar system may not be stretched out in a long tail. From top left and going counter clockwise, the stars shown are LLOrionis, BZ Cam and Mira. Credits: NASA/HST/R.Casalegno/GALEX

    Because these particles move at a small fraction of the speed of light, their journeys from the sun to the edge of the heliosphere and back again take years. So when the number of particles coming from the sun changes — usually as a result of its 11-year activity cycle — it takes years before that’s reflected in the amount of neutral atoms shooting back into the solar system.

    Cassini’s new measurements of these neutral atoms revealed something unexpected — the particles coming from the tail of the heliosphere reflect the changes in the solar cycle almost exactly as fast as those coming from the nose of the heliosphere.

    “If the heliosphere’s ‘tail’ is stretched out like a comet, we’d expect that the patterns of the solar cycle would show up much later in the measured neutral atoms,” said Krimigis.

    3
    5
    4
    The heliosphere is the bubble-like region of space dominated by the Sun, which extends far beyond the orbit of Pluto. Plasma “blown” out from the Sun, known as the solar wind, creates and maintains this bubble against the outside pressure of the interstellar medium, the hydrogen and helium gas that permeates the Milky Way Galaxy. The solar wind flows outward from the Sun until encountering the termination shock, where motion slows abruptly. The Voyager spacecraft have actively explored the outer reaches of the heliosphere, passing through the shock and entering the heliosheath, a transitional region which is in turn bounded by the outermost edge of the heliosphere, called the heliopause. The overall shape of the heliosphere is controlled by the interstellar medium through which it is traveling, as well as the Sun, and is not perfectly spherical.[1] The limited data available and unexplored nature[2] of these structures have resulted in many theories.
    Wikipedia.

    But because patterns from solar activity show just as quickly in tail particles as those from the nose, that implies the tail is about the same distance from us as the nose. This means that long, comet-like tail that scientists envisioned may not exist at all — instead, the heliosphere may be nearly round and symmetrical.

    A rounded heliosphere could come from a combination of factors. Data from Voyager 1 show that the interstellar magnetic field beyond the heliosphere is stronger than scientists previously thought, meaning it could interact with the solar wind at the edges of the heliosphere and compact the heliosphere’s tail.

    The structure of the heliosphere plays a big role in how particles from interstellar space — called cosmic rays — reach the inner solar system, where Earth and the other planets are.

    “This data that Voyager 1 and 2, Cassini and IBEX provide to the scientific community is a windfall for studying the far reaches of the solar wind,” said Arik Posner, Voyager and IBEX program scientist at NASA Headquarters in Washington, D.C., who was not involved with this study.

    “As we continue to gather data from the edges of the heliosphere, this data will help us better understand the interstellar boundary that helps shield the Earth environment from harmful cosmic rays.”

    See the full article here.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.


    NASA/Goddard Campus

     
  • richardmitnick 4:57 pm on April 24, 2017 Permalink | Reply
    Tags: Astronomy, , , , , Where Is Spitzer Now?   

    From Spitzer: “Where Is Spitzer Now?” 

    NASA Spitzer Telescope

    Spitzer

    1

    Current Observation Details
    Target Name NGC1385
    RA 3:37:28.32
    Declination -24:30: 4.60
    Program Name SPIRITS1 1
    Principal Investigator Kasliwal
    AOT iracmapp
    Start Time 2017-04-24 21:43:34 UTC
    Duration of Observation 29.39

    How To Read The Details
    Target Name
    This is the name of the object being observed by Spitzer. The name appears as it was input by the observer, and will usually appear as a unique, universally accepted catalog designation rather than a “name” in the traditional sense of the word.
    RA
    These are the coordinates in the sky where the object is located. They work much like longitude and latitude on Earth. RA is the object’s position along the equator, and Declination is its position north or south (positive numbers are the northern sky, and negative numbers are the southern sky).
    Declination
    These are the coordinates in the sky where the object is located. They work much like longitude and latitude on Earth. RA is the object’s position along the equator, and Declination is its position north or south (positive numbers are the northern sky, and negative numbers are the southern sky).
    Program Name
    When astronomers are granted observing time on Spitzer, their planned observations are defined under a unique program name. Each program has specific goals and objectives, such as the various Legacy Science programs, whose objective is to create a substantial and coherent database of archived observations that can be used by subsequent Spitzer researchers.
    Principal Investigator
    This is the name of the scientist who leads the team of people who are making the observation on Spitzer.
    AOT
    This is the specific observing mode that Spitzer is using for its observation. Spitzer has three different instruments (IRAC – The Infrared Array Camera, IRS – The Infrared Spectrograph, and MIPS – The Multiband Imaging Photometer for Spitzer), all of which can be used in several different ways.
    Start Time
    The time that the observation began. The times are given in UTC (also known as Greenwich Mean Time), which is 8 hours ahead of Pacific Standard Time (7 hours ahead of Pacific Daylight Time).
    Duration of Observation

    Different observations require different amounts of time to gather all the data. Some observations can be quite quick, and some can take hours.

    See the full article here .

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    The Spitzer Space Telescope is a NASA mission managed by the Jet Propulsion Laboratory located on the campus of the California Institute of Technology and part of NASA’s Infrared Processing and Analysis Center.

    NASA image

    NASA JPL Icon

    Caltech Logo

     
  • richardmitnick 4:03 pm on April 24, 2017 Permalink | Reply
    Tags: Astronomy, Astrophotography, , , ,   

    From Liverpool: “Shooting for the stars: capturing the beauty of science through astrophotography” 

    Liverpool John Moores University

    1
    Thor’s Helmet is a planetary nebula. Nothing to do with planets, it is actually a shell of gas being thrown off from an old star towards the end of its life cycle. Planetary nebulae are wonderfully varied in shape and colour. This image was originally obtained with the Liverpool Telescope for BBC Sky At Night.

    2-metre Liverpool Telescope at La Palma in the Canary Islands

    3
    Castell Alun High School captured the Messier 27 through the NSO.

    National Solar Observatory at Kitt Peak in Arizona

    One of the best planetary nebulae to observe on the NSO, it almost fills the field of view, providing a spectacular image with vast detail. The image was produced by combining observations in the blue, visual and red filters using NSO’s 3-colour image tool.

    5
    The Crab Nebula is a supernova remnant, the expanding cloud of gas and dust from a catastrophically exploding star. Chinese astronomers witnessed this explosion in 1054 and we still see the remnant cloud now. To the human eye, it would be faint pink. Scientific instruments do not necessarily ‘see’ colours the same way as our eyes and allow astronomers to bring out details that a true colour image might not reveal.

    When thinking about the types of photographs that capture the beauty of science, a stunning landscape or an animal in its natural habitat might come to mind. But when it comes to images from telescopes, we might not immediately consider these as anything more than the collection of scientific data. Beyond their significance in helping us to discover more about our universe, the images of galaxies, planets and stars are also appreciated purely for aesthetic reasons. For many amateur and professional astrophotographers capturing the shapes and colours of the universe is just as important as capturing scientific data. In fact, most astronomical images for general viewing have been modified from their original form. An astrophotographer’s goal in this case is to bring out the best of the image – to find the art within the science.

    Robert Smith, creator of the “Iridis” image which won the Robotic Scope Special Prize at the Insight Astronomy Photographer of the Year competition, sums up the concept of science as art/art as science:

    “We often hear about the idea of representing scientific data in an appealing way as an expression of art, but why not look at it the other way around; ‘art as science’? Astrophotography is not just a matter of making science look pretty, it shows us that beauty actually is science. The winners of this competition were obviously selected because they were beautiful, striking or interesting, but each and every one is also an expression of astrophysical processes and could be the basis of a science seminar in their own right. It is physics that creates that beauty. Looking at the swirling gas in a nebula or the aurorae, you are literally seeing maths and physics.”

    Robert is an astronomer at the Astrophysics Research Institute (ARI) at LJMU and captured the award-winning image from ARI’s very own Liverpool Telescope. As the world’s largest fully robotic telescope, the Liverpool Telescope is responsible for a wide range of images which, in addition to their obvious importance scientifically, are also interesting and beautiful as pieces of art in their own right.

    Astronomers were among the first to embrace photography, with the first images of the sun captured on daguerreotypes, an early photographic imaging process, in the 1840s.

    Users of the Liverpool Telescope not only include researchers at LJMU but because it is remotely operated, it is available to astronomers from around the world. Schools and colleges across the UK and Ireland also get involved in capturing astronomical images. As a part of ARI’s educational outreach programmes, the National Schools’ Observatory (NSO) makes it possible for schoolchildren to study the night sky for themselves via the Telescope. Almost 4,000 schools have already participated with students making well over 100,000 astronomical observations from the classroom. A couple examples of the photos from NSO can be found on this page, but feel free to take a look at more on the NSO website.

    ______________________________________________________________________

    How do you photograph a night sky?

    Make sure it’s a clear night and find a place as far away from light pollution as you can. With a manual camera, try setting 25 second exposure, f/2.8, ISO 1600 (you can experiment with these settings). You’ll need a tripod to keep your camera stable during the exposure. Modern smartphones can produce impressive results as well. There are free apps available to download that automatically take a series of short exposures for you and add them together to create a long night-time photo.

    If you have access to a telescope, you can hold your smartphone up to the eyepiece of the telescope and take your shot, this is known as afocal photography – where the lens takes the place of the human eye.

    There are plenty of tips for getting started in astrophotography, just do a search online and you’ll be exposed to a wealth of information.
    ______________________________________________________________________

    See the full article here .

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    3

    Liverpool John Moores University is a public research university[6] in the city of Liverpool, England. It has 21,875 students, of which 18,375 are undergraduate students and 3,500 are postgraduate, making it the 33rd largest university in the UK by total student population.

    The university can trace its origins to the Liverpool Mechanics’ School of Arts, established in 1823 making it a contestant as the third-oldest university in England; this later merged to become Liverpool Polytechnic. In 1992, following an Act of Parliament the Liverpool Polytechnic became what is now Liverpool John Moores University.

    It is a member of the University Alliance, a mission group of British universities which was established in 2007.[9] and the European University Association.

     
  • richardmitnick 2:04 pm on April 24, 2017 Permalink | Reply
    Tags: , Astronomy, , , , Is TRAPPIST-1 Really Moonless?, Worlds Without Moons   

    From AAS NOVA: ” Worlds Without Moons” 

    AASNOVA

    American Astronomical Society

    24 April 2017
    Susanna Kohler

    1
    Many exoplanets are expected to host moons — but can planets in compact systems orbiting close to their host stars do so? [NASA/JPL-Caltech]

    Many of the exoplanets that we’ve discovered lie in compact systems with orbits very close to their host star. These systems are especially interesting in the case of cool stars where planets lie in the star’s habitable zone — as is the case, for instance, for the headline-making TRAPPIST-1 system.

    But other factors go into determining potential habitability of a planet beyond the rough location where water can remain liquid. One possible consideration: whether the planets have moons.

    Supporting Habitability

    2
    Locations of equality between the Hill and Roche radius for five different potential moon densities. The phase space allows for planets of different semi-major axes and stellar host masses. Two example systems are shown, Kepler-80 and TRAPPIST-1, with dots representing the planets within them. [Kane 2017]

    Earth’s Moon is thought to have been a critical contributor to our planet’s habitability. The presence of a moon stabilizes its planet’s axial tilt, preventing wild swings in climate as the star’s radiation shifts between the planet’s poles and equator. But what determines if a planet can have a moon?

    A planet can retain a moon in a stable orbit anywhere between an outer boundary of the Hill radius (beyond which the planet’s gravity is too weak to retain the moon) and an inner boundary of the Roche radius (inside which the moon would be torn apart by tidal forces). The locations of these boundaries depend on both the planet’s and moon’s properties, and they can be modified by additional perturbative forces from the host star and other planets in the system.

    In a new study, San Francisco State University scientist Stephen R. Kane modeled these boundaries for planets specifically in compact systems, to determine whether such planets can host moons to boost their likelihood of habitability.

    3
    Allowed moon density as a function of semimajor axis for the TRAPPIST-1 system, for two different scenarios with different levels of perturbations. The vertical dotted lines show the locations of the six innermost TRAPPIST-1 planets. [Kane 2017]

    Challenge of Moons in Compact Systems

    Kane found that compact systems have a harder time supporting stable moons; the range of radii at which their moons can orbit is greatly reduced relative to spread-out systems like our own. As an example, Kane calculates that if the Earth were in a compact planetary system with a semimajor axis of 0.05 AU, its Hill radius would shrink from being 78.5 times to just 4.5 times its Roche radius — greatly narrowing the region in which our Moon would be able to reside.

    4
    Image of the Moon as it transits across the face of the Sun, as viewed from the Stereo-B spacecraft (which is in an Earth-trailing orbit). [NASA]

    Kane applied his models to the TRAPPIST-1 system as an example, demonstrating that it’s very unlikely that many — if any — of the system’s seven planets would be able to retain a stable moon unless that moon were unreasonably dense.

    Is TRAPPIST-1 Really Moonless?

    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

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

    How do these results fit with other observations of TRAPPIST-1? Kane uses our Moon as an example again: if we were watching a transit of the Earth and Moon in front of the Sun from a distance, the Moon’s transit depth would be 7.4% as deep as Earth’s. A transit of this depth in the TRAPPIST-1 system would have been detectable in Spitzer photometry of the system — so the fact that we didn’t see anything like this supports the idea that the TRAPPIST-1 planets don’t have large moons.

    On the other hand, smaller moons (perhaps no more than 200–300 km in radius) would have escaped detection. Future long-term monitoring of TRAPPIST-1 with observatories like the James Webb Space Telescope or 30-meter-class ground-based telescopes will help constrain this possibility, however.

    Citation

    Stephen R. Kane 2017 ApJL 839 L19. doi:10.3847/2041-8213/aa6bf2

    There are further referenced articles of interest on the full article.

    See the full article here .

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  • richardmitnick 10:08 am on April 24, 2017 Permalink | Reply
    Tags: Astronomy, , , , , What's The Largest Planet In The Universe?, What's the upper limit to planetary size?   

    From Ethan Siegel: “What’s The Largest Planet In The Universe?” 

    Ethan Siegel
    Apr 24, 2017

    1
    ATG medialab, ESA

    There’s a large difference between a planet and a star, but some planets can be significantly larger than anything we find in our own Solar System.

    In our Solar System, Jupiter is the largest planet we have, but what’s the upper limit to planetary size?

    2
    Lunar and Planetary Institute

    Jupiter may be the largest and most massive planet in the Solar System, but adding more mass to it would only make it smaller.

    If you get too much mass together in a single object, its core will fuse lighter elements into heavier ones.

    3
    NASA, ESA, and G. Bacon (STScI)

    It takes about 75-80 times as much mass as Jupiter to initiate hydrogen burning in the core of an object, but the line between a planet and a star is not so simple.

    At about eighty times the mass of Jupiter, you’ll have a true star, burning hydrogen into helium.

    4
    NASA/JPL-Caltech/UCB

    Brown dwarfs, between about 13-80 solar masses, will fuse deuterium+deuterium into helium-3 or tritium, remaining at the same approximate size as Jupiter but achieving much greater masses. Note the Sun is not to scale and would be many times larger.

    5

    Gliese 229 is a red dwarf star, and is orbited by Gliese 229b, a brown dwarf, that fuses deuterium only. Although Gliese 229b is about 20 times the mass of Jupiter, it’s only about 47% of its radius.

    This line — between a gas giant and a brown dwarf — defines the most massive planet.

    6
    Chen and Kipping, 2016, via https://arxiv.org/pdf/1603.08614v2.pdf

    Planetary size peaks at a mass between that of Saturn and Jupiter, with heavier and heavier worlds getting smaller until true nuclear fusion ignites and a star is born.

    In terms of physical size, however, brown dwarfs are actually smaller than the largest gas giants.

    7
    NASA Ames / W. Stenzel; Princeton University / T. Morton

    Jupiter may only be about 12 times Earth’s diameter, but the largest planets of all are actually less massive than Jupiter, with more massive ones shrinking as more mass is added.

    Above a certain mass, the atoms inside large planets will begin to compress so severely that adding more mass will actually shrink your planet.

    8
    Wikimedia Commons user MarioProtIV

    The exoplanet Kepler-39b is one of the most massive ones known, at 18 times the mass of Jupiter, placing it right on the border between planet and brown dwarf. In terms of radius, however, it’s only 22% larger than Jupiter.

    This happens in our Solar System, explaining why Jupiter is three times Saturn’s mass, but only 20% physically larger.

    9
    Wikimedia Commons user Kelvinsong

    A cutaway of Jupiter’s interior. If all the atmospheric layers were stripped away, the core would appear to be a rocky Super-Earth. Planets that formed with fewer heavy elements can be a lot larger and less dense than Jupiter.

    But many solar systems have planets made out of much lighter elements, without large, rocky cores inside.

    10
    NASA/ESA Hubble

    WASP-17b is one of the largest planets confirmed not to be a brown dwarf. Discovered in 2009, it is twice the radius of Jupiter, but only 48.6% of the mass. Many other ‘puffy’ planets are comparably large, but none are yet significantly larger.

    As a result, the largest planets can be up to twice as big as Jupiter before becoming stars.

    See the full article here .

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    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
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