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  • richardmitnick 12:59 pm on May 23, 2019 Permalink | Reply
    Tags: "NASA Astrobiology Researchers Identify Features That Could Be Used to Detect Life-Friendly Climates on Other Worlds", , , , , Exomoons, ,   

    From NASA Goddard Space Flight Center: “NASA Astrobiology Researchers Identify Features That Could Be Used to Detect Life-Friendly Climates on Other Worlds” 

    NASA Goddard Banner
    From NASA Goddard Space Flight Center

    Bill Steigerwald /
    NASA Goddard Space Flight Center, Greenbelt, Maryland
    301-286-8955 /
    william.a.steigerwald@nasa.gov /

    Nancy Jones
    NASA Goddard Space Flight Center, Greenbelt, Maryland

    Scientists may have found a way to tell if alien worlds have a climate that is suitable for life by analyzing the light from these worlds for special signatures that are characteristic of a life-friendly environment. This technique could reveal the inner edge of a star’s habitable zone, the region around a star where liquid water could exist on the surface of a rocky planet.

    Artist rendering of a red dwarf or M star, with three exoplanets orbiting. About 75 percent of all stars in the sky are the cooler, smaller red dwarfs. Credits: NASA/JPL-Caltech

    “Habitable planets by definition have water on their surfaces,” said Eric Wolf of the University of Colorado, Boulder. “However, water can come in the forms of ocean, ice, snow, vapor, or cloud. Each of these forms of water have very different effects on climate. However, each form also has specific effects that we may be able to detect on these planets, and use to determine whether or not a planet may have a habitable climate state.” Wolf is lead author of a paper on this research published May 22 in The Astrophysical Journal.

    Location determines value of real estate on Earth and in the cosmos as well. If a planet or planetary body is too close to its host star, the star’s intense light and heat cause the planet’s oceans to evaporate and eventually be lost to space. This climate state, called a “runaway greenhouse,” can be seen in our solar system on Venus, the next planet closer to the Sun than Earth. Venus is almost the same size as Earth and may have had oceans, but they vanished long ago as the planet’s proximity to the Sun caused a runaway greenhouse state. Now the parched surface of Venus swelters under an atmosphere about 100 times the pressure of Earth’s, with temperatures hot enough to melt lead. Conversely, if a planet or other planetary body is too far away from its host star, the oceans freeze, as can be seen in the icy moons of the outer solar system like Europa and Enceladus.

    This image shows a view of the trailing hemisphere of Jupiter’s ice-covered satellite, Europa, in approximate natural color. Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. This crater has been provisionally named “Pwyll” for the Celtic god of the underworld. Europa is about 3,160 kilometers (1,950 miles) in diameter, or about the size of Earth’s moon. This image was taken on September 7, 1996, at a range of 677,000 kilometers (417,900 miles) by the solid state imaging television camera onboard the Galileo spacecraft during its second orbit around Jupiter. The image was processed by Deutsche Forschungsanstalt fuer Luftund Raumfahrt e.V., Berlin, Germany. NASA/JPL/DLR

    NASA’s Cassini spacecraft captured this view as it neared icy Enceladus for its closest-ever dive past the moon’s active south polar region. The view shows heavily cratered northern latitudes at top, transitioning to fractured, wrinkled terrain in the middle and southern latitudes. The wavy boundary of the moon’s active south polar region — Cassini’s destination for this flyby — is visible at bottom, where it disappears into wintry darkness. This view looks towards the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 23 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 28, 2015. The view was acquired at a distance of approximately 60,000 miles (96,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 45 degrees. Image scale is 1,896 feet (578 meters) per pixel.National Aeronautics and Space Administration (NASA) / Jet Propulsion Laboratory (JPL)

    Liquid water on a planet is a big deal because it’s necessary for life as we know it. Where there is liquid water, there may be life. The range where the distance is right for a climate that allows liquid water to persist on a planet’s surface is called the star’s “habitable zone”.

    Since we don’t have the ability to travel to planets around other stars (exoplanets) due to their enormous distances from us, we are limited to analyzing the light from exoplanets to search for a signal that the climate might be habitable. By separating this light into its component colors, or spectrum, scientists can identify the constituents of an exoplanet’s atmosphere, since different compounds emit and absorb distinct wavelengths (i.e. colors) of light. An exoplanet’s spectrum resembles a wavy line with peaks where the colors are bright and valleys where colors are dim. The researchers simulated an exoplanet’s emitted infrared spectrum, which is the heat-energy given out by an exoplanet, either due to its internal heat and/or the exoplanet heated by the star and then re-radiated. Infrared light is invisible to the human eye but detectable with special cameras and instruments on telescopes.

    In the new work, the researchers found that the appearance of the spectrum changes in distinct, signature ways for each climate state. “Different climate states — cold, warm and ‘runaway greenhouse’ which is very warm — have different amount of water-vapor in the atmosphere,” said Ravi Kopparapu, a co-author of the paper at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “Different amounts of water vapor cause changes in the emitted radiation from the exoplanet, which changes the ‘spectra’, i.e., how much energy is emitted from each color and therefore how bright each color appears.”

    In the simulations, exoplanets much colder than Earth can still be habitable because they have small amounts of liquid water when these planets orbit close to the star. An ideal habitable exoplanet case is “temperate” with temperatures about the same as our Earth, and has elevated amounts of water vapor in the atmosphere compared to a cold exoplanet. The runaway greenhouse state has even more atmospheric water vapor. The findings raise the possibility that hot and moist climates, like a runaway greenhouse state, can potentially be identifiable in the appearance of the spectrum of exoplanets, and by observing how the spectrum changes as the exoplanet orbits its host star. According to Kopparapu, if correct, this gives a way to find the inner edge of the habitable zone with observations, which so far has only been simulated with climate models. The team is proposing a method to test this with observations.

    The idea of using an exoplanet’s emission and reflection spectrum to assess habitability has been proposed before. In the new work, the team simulated the spectra from exoplanets around a variety of stars smaller and fainter than our Sun, called M and K stars. They found specific features that could differentiate a runaway greenhouse state from habitable states, and hence, could be used to locate the inner edge of the habitable zone. The team used a 3-D climate model from the National Center for Atmospheric Research, called the Community Atmosphere Model, and modified it to suit for habitable exoplanets, naming it “ExoCAM”.

    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 2:11 pm on January 13, 2017 Permalink | Reply
    Tags: , , , Exomoons, , The Impact of Stars on Moons   

    From AAS NOVA: ” The Impact of Stars on Moons” 


    American Astronomical Society
    13 January 2017
    Susanna Kohler

    Artist’s illustration of exomoons orbiting an exoplanet. A new study examines a way that exomoons might become unbound from their planets. [NASA/JPL-Caltech]

    In other solar systems, the radiation streaming from the central star can have a destructive impact on the atmospheres of the star’s close-in planets. A new study suggests that these exoplanets may also have a much harder time keeping their moons.

    Where Are the Exomoons?

    Moons are more common in our solar system than planets by far (just look at Jupiter’s enormous collection of satellites!) — and yet we haven’t made a single confirmed discovery of a moon around an planet outside of our solar system. Is this just because moons have smaller signals and are more difficult to detect? Or might there also be a physical reason for there to be fewer moons around the planets we’re observing?

    Led by Ming Yang, a team of scientists from Nanjing University in China have explored one mechanism that could limit the number of moons we might find around exoplanets: photoevaporation.

    Artist’s illustration of the process of photoevaporation, in which the atmosphere of a planet is stripped by radiation from its star. [NASA Goddard SFC]

    Effects of Radiation

    Photoevaporation is a process by which the harsh high-energy radiation from a star blasts a close-in planet, imparting enough energy to the atoms of the planet’s atmosphere for those atoms to escape. As the planet’s atmosphere gradually erodes, significant mass loss occurs on timescales of tens or hundreds of millions of years.

    How might this process affect such a planet’s moons? To answer this question, Yang and collaborators used an N-body code called MERCURY to model solar systems in which a Neptune-like planet at 0.1 AU gradually loses mass. The planet starts out with a large system of moons, and the team tracks the moons’ motions to determine their ultimate fates.

    Escaping Bodies

    Evolution of the planet mass (top) in a simulation containing 500 small moons. The evolution of the semimajor axes of the moons (middle) and their eccentricities (bottom) are shown, with three example moons, starting at different radii, highlighted in blue, red and green. The black dotted line shows how the critical semimajor axis for stability evolves with time as the planet loses mass. [Yang et al. 2016]

    Yang and collaborators find that the photoevaporation process has a critical impact on whether or not the moons remain in stable orbits. As the photoevaporation drives mass loss of the planet, the planet’s gravitational influence shrinks and the orbits of its exomoons expand and become more eccentric. Eventually these orbits can reach critical values where they’re no longer stable, often resulting in systems with only one or no surviving moons.

    The team finds that even in the best-case scenario of only small moons, no more than roughly a quarter of them survive the simulation still in orbit around their planet. In simulations that include larger moons further out, the system is even more likely to become unstable as the planet loses mass, with more moons ultimately escaping.

    What happens to the moons that escape? Some leave the planet–moon system to become planet-like objects that remain in orbit around the host star. Others are smashed to bits when they collide with other moons or with the planet. And some can even escape their entire solar system to become a free-floating object in the galaxy!

    Based on their simulations, the authors speculate that exomoons are less common around planets that are close to their host stars (<0.1 AU). Furthermore, exomoons are likely less common in solar systems around especially X-ray-luminous stars (e.g., M dwarfs) that can more easily drive photoevaporation. For these reasons, our best chances for finding exomoons in future missions will be around stars that are more Sun-like, orbiting planets that aren’t too close to their hosts.

    Ming Yang et al, 2016 ApJ 833 7. doi:10.3847/0004-637X/833/1/7

    See the full article here .

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  • richardmitnick 2:16 pm on November 25, 2016 Permalink | Reply
    Tags: , , , Exomoons,   

    From Forbes: “The Hunt For Extrasolar Moons Heats Up” 


    Forbes Magazine

    Nov 21, 2016
    Bruce Dorminey

    Super-earths have been the exoplanet-hunting flavor of the last decade, but the moons of extrasolar planets could still be a good bet for finding extant life around some far-flung star. Problem is, to date, such moons have been observationally out of reach.

    A hypothetical rendition of the Blue Moon created by “Frizaven” on the 3D Space Simulator Celestia, via Wikipedia.

    Yet if the European Space Agency (ESA) launches its ARIEL (Atmospheric Remote-sensIng Exoplanet Large-survey) mission by 2025, there remains a small chance that the spacecraft might actually spot a moon around a relatively hot, giant extrasolar planet. That is, one circling one of the roughly 500 stars the mission would survey. Or so says David Waltham, a University of London geophysicist.

    Despite years of sifting through data for their signature, to date, no exomoons have been confirmed. That’s arguably more of a testament to the rudimentary nature of our planet-hunting technology than a dearth of earth-sized moons around giant planets circling other sun-like stars.

    “At the moment, we simply don’t know whether earth-sized moons exist,” Waltham, author of Lucky Planet: Why Earth is Exceptional and What that Means for Life in the Universe, told me.

    The current search for exomoons, uses data from planets transiting across the face of their parent stars, the so-called transit method; as well as data from surveys to look for the telltale stellar wobble caused by an exoplanet in orbit around its host star.

    Planet transit. NASA/Ames
    Planet transit. NASA/Ames

    Such surveys sometimes even look for the wobble of an exoplanet caused by an orbiting exomoon.

    ARIEL will look for “transit time variations” (TTVs) in the exoplanets it finds, says Waltham. That is, small variations of less than a minute in the exact timing of a planet as it transits across the face of its parent star. Such transit variations could, in theory, be caused by the gravitational effect of a moon on its host planet; causing the planet to wobble around the planet-moon center of gravity.

    “Attempts to spot moon-generated TTVs in Kepler data have so far failed because the data is too noisy to allow such small effects to be seen,” said Waltham. “My hope had been that since ARIEL data will be from bright stars, the data would be less noisy and allow moons to be found.”

    But Waltham plans on looking for ARIEL’s transit time variations anyway.

    “Exomoons are unlikely around the majority of target planets for ARIEL but, if a few of the targeted planets orbit sun-sized stars, I might get lucky,” said Waltham.

    On another front, using data from NASA’s Kepler Space Telescope, the ongoing “Hunt for Exomoons with Kepler” (HEK) Project, led by Columbia University astronomer David Kipping, is continuing. Kipping and colleagues note that our own moon — only about 1% of earth’s mass — would be very hard to detect from light years away. But their search is still sensitive to statistically detecting an Earth-Moon combination for about one in every eight extrasolar planets they study.

    As for an earth-sized moon around a large planet?

    The project notes that statistically they would be sensitive to detecting one such exomoon for every three extrasolar planets surveyed.

    Our own anomalously large moon is about as inhospitable as they come. Most habitable planetary bodies require some sort of active geophysical tectonics or atmospheric recycling, which are usually not a feature of smaller bodies. And the only known moon with a substantial atmosphere, remains the Saturn’s moon of Titan, some 0.4 earth radii in size.

    Thus, what’s the next ground- or space-based effort to detect exomoons?

    Waltham says exomoon detection using transit timing variations will be very hard from the ground but it may be possible to see their direct transit signature using the next generation of very-large telescopes. But he says that NASA’s planned James Webb Space Telescope (JWST) due for launch in 2018, has the best chance of finding the first exomoons.

    NASA/ESA/CSA Webb Telescope annotated
    NASA/ESA/CSA Webb Telescope annotated

    As for the percentage of known exoplanetary systems that might also harbor habitable exomoons?

    “The statistics suggest that if earth-sized exomoons were really common, we’d probably have spotted one by now ,” Duncan Forgan, an astronomer at the U.K.’s University of St. Andrews, told me.

    Getting anything like a spectrum — which might tell us about the moon’s atmosphere or surface composition — will require much bigger telescopes than anything currently planned, Waltham says.

    However, Forgan says the biggest issue with exomoon bio-signatures is that if astronomers do get an exomoon spectrum, for the foreseeable future, they’ll probably be looking at it combined with its host planet’s spectrum as well.

    “There’s actually a worrying feature of this blending, which might convince us of habitability when the opposite is true,” said Forgan.

    Waltham says the best chance of detecting an exomoon is to look at a long-period, medium-sized planet orbiting a bright star. However, he cautions, astronomers would need to look for many decades to see enough transits to detect such long-period planets.

    Meanwhile, Kipping told me that there may still be some exomoon candidates in Kepler data of hundreds of extrasolar planets that he and colleagues are currently analyzing. But he says he is holding off on revealing more until their work is further along.

    See the full article here .

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  • richardmitnick 9:41 am on June 8, 2016 Permalink | Reply
    Tags: , , , Exomoons   

    From CosmosUp: “Hunting Extraterrestrial Life On Exomoons” 

    CosmosUp bloc


    08, Jun 2016
    No writer credit found

    In the past two decades, astronomers have detected more than 2000 exoplanets, the first of these detections were gas giants as massive as Jupiter that are so close to the host that they are heated to high temperature in order of 2,000°C; but now, for the first time, astronomers are getting down to the regime of potentially habitable Earth-like worlds.

    The goal of space exploration has always been the same, to try to answer the oldest scientific question: are we alone in the universe?

    Why limit ourselves to exoplanets? The search for alien life doesn’t end with them; Increasingly, astrobiologists watch the moons in our own solar system for the hint of biology, if the so-called exomoons can also have potential life then it will be more habitable moons than planets within the cosmos.

    But first, just as a reminder: an exomoon is simply a moon which orbits an exoplanet and remember, an exoplanet is a planet which orbits other star than the sun, so these exomoons are just moons going around planets around stars other than the sun.

    So far, we haven’t discovered and confirmed exomoons but we know thousands of exoplanets, so we are sure exomoons are there, we simply lack the sensitivity to detect them — to date, there are only three exomoon candidates.

    Exomoons’ idea is really interesting, there is no reason why you couldn’t have an Earth-like world as moon going around a massive planet as Jupiter and, don’t forget, exomoons doesn’t depend on how far away from the heat of their star they are.

    Remember the world of Pandora in the epic movie Avatar? Well, that wasn’t an exoplanet, it was in fact a moon orbiting a massive exoplanet.

    Our solar system has some fascinating moons orbiting Jupiter and Saturn that, may not look like the SF rain-forest moon of Pandora, but they do have vast sub-surface oceans beneath their frozen crusts — the water is heated to a liquid by tidal forces squeezing the insides of the moon creating a heat source — no sunlight required!

    “Moons have separate energy sources,

    René Heller, an astrophysicist at the Origins Institute at McMaster University, said.

    While the habitability of terrestrial planets is mostly determined by stellar illumination, moons also receive reflected stellar light from the planet as well as thermal emission from the planet itself.”


    The first challenge in studying exomoons is to actually find one. For detection, current techniques mostly focus on light curve analysis. The concept is that the exomoon alters the light curve in a specific and identifiable way.

    Other methods also have been proposed, such as direct imaging, radial velocity measurements, microlensing, or pulsar timing.

    Today, scientists use Kepler to search for moons orbiting alien planets, with a project called the Hunt for Exomoons with Kepler (HEK), the first systematic search for exomoons. Astronomers simulate billions of possible star-planet-moon arrangements using NASA’s Pleiades Supercomputer.

    NASA Advanced Supercomputing Center Pleiades Supercomputer
    NASA SGI Advanced Supercomputing Center Pleiades Supercomputer

    They then compare the results with actual data taken with Kepler telescope, if one of the simulated combinations matches the Kepler data, that area warrants further exploration.

    “For each planet where we don’t discover an exomoon, we are able to say how massive a moon is excluded by the current data, telling us about our sensitivity,

    said David Kipping at the Harvard-Smithsonian Center for Astrophysics, lead astronomer of HEK.

    Signs of life on an exomoon could be as simple as some form of primitive biology. And life on one moon could mean life on many more. If such habitable moons are possible, then there could even be more habitable moons than habitable planets.”

    New perspective for alien life on exomoons

    Occultation light curves of exomoons may give information on their albedo, or reflection coefficient, and hence indicate the presence of ice cover on the surface. Icy moons might have subsurface oceans thus these may potentially be habitable.

    In a new work, uploaded on arxiv servers, astronomers applied some simple calculations for different stellar masses and compared the flux drop caused by the moon’s occultation and thus they found that the albedo estimation by their method is not feasible for moons of solar-like stars, but small M dwarfs are better candidates for such measurements.

    Although most search projects focus on solar-like stars, M dwarfs as targets should also be considered, because of more than 70% of the stars are of M spectral type.

    But in theory, red dwarf stars, which are smaller and cooler than the sun, tend not to produce particularly massive gas giant planets so it is possible that no large exomoons are present around them.

    But based on the discovered exoplanets currently 68 M dwarfs are known to have 96 exoplanets, from which the heaviest planet’s mass is 62 Jupiter masses (Mj), 20 other exoplanets have at least 10 Jupiter-masses, and there are 13 other planets that are heavier than 1 MJ (source: exoplanet.eu, January 2016). So, the average mass of the exoplanets of the 68 M dwarfs is 4.8 MJ.

    Moons of smaller stars seem to be easier to detect, if their stellar distance is smaller. In addition, the smaller the star, the closer the snowline located, meaning that rocky bodies can stay icy even if they are orbiting the star in a closer orbit.

    The vicinity to the star makes the body brighter, thus an icy exomoon is easier to detect in occultation close to the snowline of an M dwarf, than at the snowline of a solar-like star.

    So, based on these observations, astronomers assume that geometric albedo above around 0.7 (for reference, Europa with 1.02 and Enceladus with 1.38 geometric albedo) indicates some ice, often water ice, with relatively young surface, and higher albedo might suggest freshly fallen water ice crystals — thus may potentially be habitable or at least could be considered as favorable environments for life.

    “We predict that the first albedo estimations of exomoons will probably be made for large icy moons around the snowline of M type main sequence stars.”

    concluded astronomers.

    With the next generation of telescopes expected soon to be launched, the exomoons might not be able to hide for much longer.

    See the full article here .

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  • richardmitnick 11:25 am on March 9, 2016 Permalink | Reply
    Tags: , , , Exomoons   

    From astrobites: “Searching for Exo-Ios” 

    Astrobites bloc


    Mar 9, 2016
    David Wilson

    Title: On the radio detection of multiple-exomoon systems due to plasma torus sharing
    Authors: J. P. Noyola, S. Satyal, Z.E. Musielak
    First Author’s Institution: The Department Physics, University of Texas at Arlington
    Status: Accepted by the Astrophysical Journal.

    Io Moon of Jupiter NASA
    The volcanic surface of Jupiter’s moon Io. Could similar worlds be detectable around exoplanets? Image Credit: NASA

    Moons appear to be everywhere in the Solar system. Six out of the eight major planets have at least one, and the two largest gas giants have dozens. Astronomers expect that the thousands of exoplanets discovered in recent years are no different, with most of them hosting their own system of mini-worlds.

    However, despite several years of searching, we’ve yet to find an exomoon. This isn’t really surprising, as discovering exoplanets themselves took a step change in the capabilities of astronomical equipment, and confirming an exoplanet is still by no means routine. Exomoons, which by definition are smaller than their host planets, are even harder to detect. Many techniques have been suggested, such as looking for changes in the shape of the transit of a planet in front of its star, or finding strange patterns in exo-planetary rings, but so far no method has borne fruit.

    The authors of today’s paper suggest a new way to find them. Instead of the optical telescopes favoured by exoplanet searches, Noyola et al. turn to the giant radio telescopes. They suggest that they could be able to detect signals from extrasolar equivalents of one of the Solar system’s most extreme objects: Jupiter’s moon, Io.

    Similar in size to Earth’s moon, Io is the closest of the four Galilean satellites to Jupiter. The gravitational interactions between Io, Jupiter, and the neighbouring moon Europa squeeze and heat up Io’s interior, making it the most volcanically active object in the Solar system.

    As material is blasted out of Io, some of it is caught up in Jupiter’s powerful magnetic field lines. The electrons in this material move around the magnetic field lines in a spiral pattern, producing cyclotron radiation in the form of a stream of radio waves. This radiation is much stronger that what Jupiter itself emits at the same frequencies.

    Io isn’t the only moon that does this. Similar, albeit weaker, emissions are produced by several other moons of both Jupiter and Saturn. Based on this commonality, the authors suggest that radio emissions from exomoons may be common and detectable.

    Could we detect an exo-Io? The authors start by calculating the signal from Io were it one light year away. They find a signal of 0.0027 Janskys, which is faint, but well within the capabilities of current telescopes. Of course, most exoplanet systems are tens to hundreds of light years away. The authors point out that the bias in exoplanet detection methods towards giant planets works in their favour, as the maximum theoretical sizes of moon, magnetic field and radio emission all scale with the mass of the host planet. Such emission would also vary as the exomoon travelled around its host, revealing the moon’s orbital period.

    With the method established, the authors go on to suggest that it might be possible to find multiple exomoons with this technique. The large signal from Io is a result of the material produced by its volcanic activity. Moons which are further out experience less tidal force and therefore less volcanism, so the radio signals are much smaller. However, the authors suggest that an Io-like exomoon (an exo-Io) could “donate” material to a nearby moon, should they be close enough together.

    This would work via simple orbital mechanics. Volcanoes facing in the direction of the exo-Io’s motion would give the material they ejected a boost, sending it into a higher orbit. There, it could run into the next moon out and be gravitationally captured. The outer moon could then start its own interactions with the host planet’s magnetosphere. As the orbital period of the outer moon is longer, the resulting radio emission would vary on a different time scale to the initial exo-Io, allowing the two signals to be distinguished.

    The authors show that this detection method would have uses beyond just finding multiple exomoons. The orbital periods of two moons can be used to find either the mass or radius of the host planet, which may unobtainable via more traditional techniques. Further more, two moons allows the masses of the moons themselves to be found. A complete picture of the system could be built up, just from radio emissions.

    The race is on to find an exomoon. As the authors conclude here, the first detection might just be made with a radio telescope.

    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 11:41 am on February 18, 2016 Permalink | Reply
    Tags: , , Exomoons,   

    From The Conversation: “Eying exomoons in the search for E.T.” 

    The Conversation

    February 18, 2016
    Bryan Gaensler
    Director, Dunlap Institute for Astronomy and Astrophysics, University of Toronto

    U Toronto Dunlap bloc

    Maxwell Hamilton, CC BY

    When I was young, the only planets we knew about were the ones in our own solar system.

    Astronomers presumed that many of the other stars in the night sky had planets too, but this was sheer speculation. We could never know for sure, the thinking went, because such planets were ridiculously small and faint. To ever see or study them seemed a complete impossibility. “Extrasolar planets,” or “exoplanets,” were a staple of science fiction, but not of professional astrophysics.

    It’s hard to believe that there was once such a simple time. The first definitive detection of an exoplanet was in 1991, identified by the tiny wobbles experienced by the parent star as its exoplanet swung around it. Since then, the field has exploded. There are now around 1,600 confirmed exoplanets, with almost 4,000 other known candidates. There are exoplanets smaller than Mercury, and others many times bigger than Jupiter. Their orbits around their parent stars range from a few hours to hundreds of years. And the ones we know about are just a tiny fraction of the approximately 100 billion exoplanets we now believe are spread throughout our Milky Way galaxy.

    But while the golden age of exoplanets has barely begun, an exciting additional chapter is also taking shape: the hunt for exomoons.

    Beyond Earth-like planets to exomoons

    An exomoon is a moon orbiting a planet, which in turn is orbiting another star. You may not have ever heard of exomoons before now. But if you’re a fan of films such as “Avatar,” “Return of the Jedi” or “Prometheus,” this should be familiar territory: in all three cases, most of the action takes place on an exomoon.

    But what about real life? How many exomoons do we know of? At the moment, zero.

    But the race is on to find the real-life analogs of Endor and Pandora.

    You might think searching for tiny rocks orbiting distant planets around faint stars hundreds or thousands of light years away is the ultimate example of an obscure academic pursuit. But exomoons are poised to become a big deal.

    The whole reason exoplanets are exciting is that they’re a path to answering one of the grandest questions of all: “Are we alone?” As we find more and more exoplanets, we eagerly ask whether life could exist there, and whether this planet is anything like Earth. However, so far we’ve yet to find an exact match to Earth, nor can we yet really know for sure whether any exoplanet, Earth-like or otherwise, hosts life.
    Enter exomoons in the search for life

    There are several reasons why exomoons, these little distant worlds, may be the key to finding life elsewhere in the universe.

    First, there’s the stark reality that life on Earth may not have happened at all without the starring role played by our own moon.

    The Earth’s axis is tilted by 23.5 degrees relative to its motion around the sun. This tilt gives us seasons, and because this tilt is relatively small, seasons on Earth are mild: most places never get impossibly hot or unbearably cold. One thing that has been crucial for life is that this tilt has stayed the same for very long periods: for millions of years, the angle of tilt has varied by only a couple of degrees.

    What has kept the Earth so steady? The gravity of our moon.

    In contrast, Mars only has two tiny moons, which have negligible gravity. Without a stabilizing influence, Mars has gradually tumbled back and forth, its tilt ranging between 0 and 60 degrees over millions of years. Extreme changes in climate have resulted. Any Martian life that ever existed would have found the need to continually adapt very challenging.

    Without our moon, the Earth, too, would likely have been subject to chaotic climate conditions, rather than the relative certainty of the seasons that stretches back deep into the fossil record.

    The gravity of the moon also produces the Earth’s tides. Billions of years ago, the ebb and flow of the oceans produced an alternating cycle of high and low salt content on ancient rocky shores. This recurring cycle could have enabled the unique chemical processes needed to generate the first DNA-like molecules.

    Exomoons might have Earth-like environments

    Overall, as we continue to hunt for another Earth somewhere out there, it seems likely that a twin of Earth, but without a moon accompanying it, would not look familiar. Finding exomoons is a key part of finding somewhere like here.

    Meanwhile, we shouldn’t be discouraged by the fact that most exoplanets found so far are bloated gaseous beasts, with hostile environments unlikely to support life as we know it. What we don’t know yet, crucially, is whether these exoplanets have moons. This prospect is exciting, because exomoons are expected to be smaller rocky or icy bodies, possibly hosting oceans and atmospheres.

    This is hardly speculation: Titan (a moon of Saturn) has a thick atmosphere even denser than Earth’s, while underground oceans are thought to exist on Enceladus (another moon of Saturn) and on Europa and Ganymede (both moons of Jupiter). Thus, if there is any other life out there somewhere, it may well not be found on a distant planet, but on a distant moon.

    The hunt is on. While exomoons are too faint to see directly, astronomers are deploying ingenious indirect techniques in their searches. Those moons are assuredly out there by the billions – and soon we will find them. It won’t be too much longer before these tiny worlds help us answer huge questions.

    See the full article here .

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  • richardmitnick 7:21 am on March 28, 2015 Permalink | Reply
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    From CfA: “HEK – Hunt for Exomoons with Kepler 

    Smithsonian Astrophysical Observatory
    Smithsonian Astrophysical Observatory


    Undated, but 2013
    No Writer Credit

    NASA Kepler Telescope


    The Hunt for Exomoons with Kepler, or HEK, is an astronomy project designed to search for observational evidence of exomoons (extrasolar moons). The “exo” part of the word simply means that the moon lies outside of our own solar system. Because the nearest star to us is several light years away, the stars which we look at in our hunt are in the range of 10’s to 1000’s of light years away. So far, no-one has ever found an exomoon but there has never been a systematic search for their existence before. HEK will therefore test the hypothesis that moons exist in other solar systems aside from our own. Our primary mission is to determine the occurrence rate of large moons around viable planets hosts, which we denote with the symbol η☾.


    Why should we care about exomoons? Perhaps, the most fundamental reason is life. Science fiction writers and film makers have long toyed with the idea of moons teaming with life, such as the moon “Pandora” in the recent film Avatar (pictured). But this is not just science fiction- astrobiologists believe that Europa, Titan and Enceladus (the moons of Jupiter and Saturn) are potentially viable homes for some form of primitive biology. Sadly though, there are no moons in our own solar system which offer truly Earth-like conditions such as that depicted in Avatar.

    But could there be a vast population of habitable exomoons out there just waiting for us to find them? If such habitable moons are possible, then there could even be more habitable moons than habitable planets. Planet-based life could even be a rarity in the Galaxy! HEK cannot tell us whether life inhabits exomoons or not, but the first step is to establish whether moons big enough to support a biosphere exist or not. HEK will hopefully answer this question.


    Another important implication of moons is that aside from being habitable themselves, they also may affect the habitability of any planets they orbit. For example, the Moon (pictured) is thought to stabilize the axial tilt of the Earth which is beneficial to the climate and habitability of our planet. If the Moon wasn’t there, would our planet still have complex life (like us) on it? With just one known example, the Earth-Moon system, it is difficult to make this determination. But HEK will seek evidence of exomoons around habitable-zone planets in order to say whether planets in the habitable-zone of their host star frequently have large moons or not.


    Finally, the third important reason to try and find exomoons is that they can teach us a lot about how planets, moons and solar systems form and evolve. The solar system is billions of years old and so we have only been observing it for a very short fraction of that time – therefore a major challenge in planetary astronomy is work out how our own solar system formed and evolved over all that time we weren’t looking. A significant piece of this puzzle is how moons form and evolve. Taking the example of the Earth-Moon system once again, the Moon is thought to have formed through a giant collision between the primordial Earth and a Mars-sized planet which drifted too close (pictured). This enormous collision broke up the smaller planet into a disc of vaporized rock which slowly coalesced into what we now call the Moon. This extraordinary tale is our best guess for how the Moon formed but we have no idea as to whether this happens all the time in other solar systems or whether the Earth-Moon system is somehow a freak in the Universe. Only by detecting a population of planet-moon systems can be hope to answer whether the Earth-Moon system is unique and so whether solar systems like our own reside in the cosmos.


    Principal Investigator: David Kipping
    David Kipping wrote his PhD thesis on the subject of exomoon detection theory at University College London and has single-authored numerous papers on the topic. David devised two new methods to detect exomoons in the form of TDV-V and TDV-TIP (velocity and transit-impact-parameter induced transit duration variations, respectively). These tools are critical in assessing a moon’s mass and sense of orbital motion (prograde or retrograde).

    David is now a Donald Menzel fellow at the Harvard College Observatory, where the HEK project servers perform round the clock automated searches for exomoons.

    Co-Investigator: Gáspár Bakos
    Assoc. Prof. Bakos of Princeton University founded the HATNet project (Hungarian Automated Telescope NETwork), which is one the most successful transiting planet hunting surveys to date. Gáspár’s expertise range from instrumentation, to programming, from observations to theory and we are fortunate to have these talents for HEK.

    Co-Investigator: Lars Buchhave
    Dr. Lars Buchhave, based at the Neils Bohr Institute in Copenhagen, obtains stellar spectra for the HEK project as well as his own projects. These spectra are then used to refine the stellar parameters and look for the stellar wobble caused by the presence of a planet. By combining this data with the Kepler photometry, HEK can not only confirm candidates, but also dynamically measure the masses and radii of the entire system.

    Co-Investigator: Joel Hartman
    Joel is an Associate Research Scholar at Princeton and has been instrumental in the success of the HAT project, founded by Prof. Bakos. Joel has recently begun investigating novel non-parametric methods to look for exomoons and provides invaluable support in the interpretation of light curve signals, as well characterizing the host stars.

    Co-Investigator: Chelsea (Xu) Huang
    Chelsea is a graduate student at Princeton University interested in the analysis Kepler light curve data. Chelsea has developed an independent processing pipeline of the Kepler data which HEK uses in certain cases to vet moon candidate signals. This independent check, including pixel-level diagnostics, allows us to verify potential signals are astrophysical rather than instrumental in nature.

    Co-Investigator: David Nesvorný
    Based at the Southwest Research Institute in Colorado, Dr. David Nesvorny is a dynamist who has written pivotal papers in fields ranging from Kuiper belt objects to moons, from exoplanets to asteroids. David’s expertise is crucial to the HEK project. Frequently, the dynamical perturbations which can signal the presence of a moon could also be confused with a perturbing planet. David will interrogate the hypothesis of a perturbing planet in such cases, to help us understand the true nature of the planetary system.

    Co-Investigator: Allan Schmitt
    Allan Schmitt joined the HEK project via PlanetHunters.org. This dedicated group of non-professional astronomers inspect Kepler light curves for signs of other planets not found by the automated planet-hunting tools of Kepler. In a similar vein, Allan leads the visual inspection effort on these data for exomoon signals. Exomoon signals are much trickier to spot than new planets but a trained and patient human eye is a powerful tool.

    Co-Investigator: Guillermo Torres
    Located at the Harvard-Smithsonian Center for Astrophysics, Guillermo Torres is a world renown expert in the analysis and validation of planetary transits and the determination of accurate stellar parameters who joined the HEK project in fall 2014. These expertise aid the HEK project greatly, providing a second check as to the nature of candidate signals and also providing physical parameters for the star which affects the planet and moon terms too.

    See the full article here.

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    About CfA

    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy. The long relationship between the two organizations, which began when the SAO moved its headquarters to Cambridge in 1955, was formalized by the establishment of a joint center in 1973. The CfA’s history of accomplishments in astronomy and astrophysics is reflected in a wide range of awards and prizes received by individual CfA scientists.

    Today, some 300 Smithsonian and Harvard scientists cooperate in broad programs of astrophysical research supported by Federal appropriations and University funds as well as contracts and grants from government agencies. These scientific investigations, touching on almost all major topics in astronomy, are organized into the following divisions, scientific departments and service groups.

  • richardmitnick 9:41 am on February 3, 2015 Permalink | Reply
    Tags: , , Exomoons,   

    From NASA: “NASA Supercomputer Assists the Hunt for Exomoons” 



    NASA Advanced Supercomputing Division Pictorial

    NASA Advanced Supercomputing Division header

    Artist’s impression of a hypothetical Earth-like moon around a Saturn-like exoplanet.

    A team of 21st-century explorers working on the Hunt for Exomoons with Kepler (HEK) project, based at Harvard University, are searching for exomoons using data from NASA’s Kepler mission and the Pleiades supercomputer at the NASA Advanced Supercomputing (NAS) facility at NASA’s Ames Research Center.

    NASA Kepler Telescope

    NASA Advanced Supercomputing Center Pleiades Supercomputer

    The discovery of exomoons—moons situated beyond our own solar system—would add to the growing list of celestial objects detected by the Kepler telescope that could potentially harbor life in some form.

    In the quest to find the first exomoon, HEK astronomers led by David Kipping at the Harvard-Smithsonian Center for Astrophysics have devised a unique, systematic computational approach that requires 5.2 million processor hours on Pleiades. Using their in-house LUNA light curve modeling algorithm and a massively parallel sampling algorithm called MultiNest, the project team simulates billions of possible star-planet-moon configurations and compares the results to the actual Kepler data to look for a good match. So far, the team has surveyed 56 of about 400 identified Kepler planet candidates that could have a detectable exomoon.

    Surveying the remaining 340 planet candidates would require about 50,000 hours of processing time per object and would take nearly a decade to complete on smaller computers. Utilizing NASA’s powerful Pleiades system—which performs over 3 quadrillion calculations per second—will speed up this computationally expensive process, reducing the processing time to 30,000 hours per object. Over the next two years, the team will survey the remaining candidates for exomoons by performing photo-dynamical analysis of the public data from Kepler, consuming about 10 million processor hours on Pleiades. Their results will be used to determine the occurrence rate of Earth-like moons.

    See the full article here.

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    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

  • richardmitnick 9:58 am on January 27, 2015 Permalink | Reply
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    From Wired: “Why We’re Looking for Alien Life on Moons, Not Just Planets” 

    Wired logo


    Marcus Woo

    An artist’s depiction of what a moon around another planet may look like. JPL-Caltech/NASA

    Think “moon” and you probably envision a desolate, cratered landscape, maybe with an American flag and some old astronaut footprints. Earth’s moon is no place for living things. But that isn’t necessarily true for every moon. Whirling around Saturn, Enceladus spits out geysers of water from an underground ocean. Around Jupiter, Europa has a salty, subsurface sea and Titan has lakes of ethane and methane. A handful of the roughly 150 moons in the solar system have atmospheres, organic compounds, ice, and maybe even liquid water. They all seem like places where something could live—albeit something weird.




    So now that the Kepler space telescope has found more than 1,000 planets—data that suggest the Milky Way galaxy could contain a hundred billion worlds—it makes sense to some alien-hunters to concentrate not on them but on their moons.

    NASA Kepler Telescope

    The odds for life on these so-called exoplanets look a lot better—multiply that hundred billion by 150 and you get a lot of places to look for ET. “Because there are so many more moons than planets, if life can get started on moons, then that’s going to be a lot of lively moons,” says Seth Shostak, an astronomer at the SETI Institute.

    Even better, more of those moons might be in the habitable zone, the region around a star where liquid water can exist. That’s one reason Harvard astronomer David Kipping got interested in exomoons. He says about 1.7 percent of all stars similar to the sun have a rocky planet in their habitable zones. But if you’re talking about planets made out of gas, like Saturn and Jupiter, that number goes up to 9.2 percent. Gaseous planets don’t have the solid surfaces that astronomers think life needs, but their moons might.

    So far, no one has found a moon outside the solar system yet. But people like Kipping are looking hard. He leads a project called the Hunt for Exomoons with Kepler, the only survey project dedicated to finding moons in other planetary systems. The team has looked at 55 systems, and this year they plan to add 300 more. “It’s going to be a very big year for us,” Kipper says.

    Finding moons isn’t easy. Kepler was designed to find planets—the telescope watches for dips in starlight when a planet passes in front of its star. But if a moon accompanies that planet, it could further lessen that starlight, called a light curve. A moon’s gravitational tug also causes the planet to wobble, a subtle motion that scientists can measure.

    In their search, Kipping’s team sifts through more than 4,000 potential planets in Kepler’s database, identifying 400 that have the best chances of hosting a detectable moon. They then use a supercomputer to simulate how a hypothetical moon of every possible size and orientation would orbit each of the 400 planets. The computer simulations produce hypothetical light curves that the astronomers can then compare to the real Kepler data. The real question, Kipping says, isn’t whether moons exist—he’s pretty sure they do—but how big they are. If the galaxy is filled with big moons about the same size as Earth or larger, then the researchers might find a dozen such moons in the Kepler data. But if it turns out that the universe doesn’t make moons that big, and they’re as small as the moons in our solar system, then the chances of detecting a moon drop.

    According to astronomer Gregory Laughlin of the University of California, Santa Cruz, the latter case may be more likely. “My gut feeling is that because the moon formation process seems so robust in our solar system, I would expect a similar thing is going on in an exoplanetary system,” he says. Which means it’ll be tough for Kipping’s team to find anything, even though they’re getting better at detecting the teeny ones—in one case, down to slightly less than twice the mass of the solar system’s largest moon, Ganymede.


    Whether anything can live on those moons is a whole other story. Even if astronomers eventually detect a moon, determining whether it’s habitable (with an atmosphere, water, and organic compounds)—let alone actually inhabited—would be extremely difficult. The starlight reflected off the planet would be overwhelming. Current and near-future telescopes won’t be able to discern much of anything in detail at all—which is why some researchers aren’t optimistic about Kipping’s ideas. “I just don’t see any great path to characterize the moons,” says Jonathan Fortney, an astronomer at UC Santa Cruz.

    Even Kipping acknowledges that it’s impossible to place any odds on whether he’ll actually find an exomoon. Still, thanks to improvements in detecting smaller moons and the 300 additional planets to analyze, Kipping says he’s optimistic. “It would be kind of surprising if we don’t find anything at all,” he says.

    See the full article here.

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  • richardmitnick 3:29 pm on October 20, 2014 Permalink | Reply
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    From astrobio.net: ” Exomoons Could Be Abundant Sources Of Habitability” 

    Astrobiology Magazine

    Astrobiology Magazine

    Oct 20, 2014
    Elizabeth Howell

    With about 4,000 planet candidates from the Kepler Space Telescope data to analyze so far, astronomers are busy trying to figure out questions about habitability. What size planet could host life? How far from its star does it need to be? What would its atmosphere need to be made of?

    NASA Kepler Telescope

    Look at our own solar system, however, and there’s a big gap in the information we need. Most of the planets have moons, so surely at least some of the Kepler finds would have them as well. Tracking down these tiny worlds, however, is a challenge.

    Europa is one of the moons in our solar system that could host life. What about beyond the solar system? Credit: NASA/JPL/Ted Stryk

    A new paper in the journal Astrobiology, called Formation, Habitability, and Detection of Extrasolar Moons, goes over this mostly unexplored field of extrasolar research. The scientists do an extensive literature review of what is supposed about moons beyond the Solar System, and they add intriguing new results.

    A wealth of moons exist in our own solar system that could host life. Icy Europa, which is circling Jupiter, was recently discovered to have plumes of water erupting from its surface. Titan, in orbit around Saturn, is the only known moon with an atmosphere, and could have the precursor elements to life in its hydrocarbon seas that are warmed by Saturn’s heat. Other candidates for extraterrestrial hosts include Jupiter’s moons Callisto and Ganymede, as well as Saturn’s satellite Enceladus.

    Lead author René Heller, an astrophysicist at the Origins Institute at McMaster University, in Ontario, Canada, said some exomoons could be even better candidates for life than many exoplanets.

    “Moons have separate energy sources,” he said. “While the habitability of terrestrial planets is mostly determined by stellar illumination, moons also receive reflected stellar light from the planet as well as thermal emission from the planet itself.”

    Moreover, a planet like Jupiter — which hosts most of the moons in the Solar System that could support life — provides even more potential energy sources, he added. The planet is still shrinking and thereby converts gravitational energy into heat, so that it actually emits more light than it receives from the Sun, providing yet more illumination. Besides that, moons orbiting close to a gas giant are flexed by the planet’s gravity, providing potential tidal heating as an internal, geological heat source.

    Triton’s odd, melted appearance hint that the moon was captured and altered by Neptune. Credit: NASA

    Finding the first exomoon

    The first challenge in studying exomoons outside our Solar System is to actually find one. Earlier this year, NASA-funded researchers reported the possible discovery of such a moon, but this claim was ambiguous and can never be confirmed. That’s because it appeared as a one-time event, when one star passed in front of another, acting as a sort of gravitational lens that amplified the background star. Two objects popped out in the gravitational lens in the foreground — either a planet and a star, or a planet and an extremely heavy exomoon.

    For his part, Heller is convinced that exomoons are lurking in the Kepler data, but they have not been discovered yet. Only one project right now is dedicated to searching for exomoons, and is led by David Kipping at the Canadian Space Agency. His group has published several papers investigating 20 Kepler planets and candidates in total. The big restriction to their efforts is computational power, as their simulations require supercomputers.

    Another limiting factor is the number of observatories that can search for exomoons. To detect them, at least a handful of transits of the planet-moon system across their common host star would be required to absolutely make sure that the companion is a moon, Heller said. Also, the planet with the moon would have to be fairly far from its star, and decidedly not those close-in hot Jupiters that take only a few days to make an orbit. In that zone, the gravitational drag of the star would fatally perturb any moon’s orbit.

    Heller estimates that a telescope would need to stare constantly at the same patch of sky for several hundred days, minimum, to pick up an exomoon. Kepler fulfilled that obligation in spades with its four years of data gazing at the same spot in the sky, but astronomers will have to wait again for that opportunity.

    Because two of Kepler’s gyroscopes (pointing devices) have failed, Kepler’s new mission will use the pressure of the Sun to keep it steady. But it can only now point to the same region of the sky for about 80 days at at time because the telescope will periodically need to be moved so as not to risk placing its optics too close to the Sun.

    NASA’s forthcoming Transiting Exoplanet Survey Satellite [TESS} is only expected to look at a given field for 70 days. Further into the future, the European Space Agency’s PLAnetary Transits and Oscillations of stars (PLATO) will launch in 2024 for what is a planned six-year mission looking at several spots in the sky.



    “PLATO is the next step, with a comparable accuracy to Kepler but a much larger field of view and hopefully a longer field of view coverage,” Heller said.

    Clues in our solar system

    Thousands of exoplanets and exoplanet candidates have been discovered, but astronomers are still searching for exomoons. Credit: ESA – C. Carreau

    Heller characterizes moons as an under-appreciated feature of extrasolar planetary systems. Just by looking around us in the Solar System, he says, astronomers have been able to make crucial explanations about how the moons must have formed and evolved together with their planets. Moons thus carry information about the substructure of planet evolution, which is not accessible by planet observations alone.

    The Earth’s moon, for example, was likely formed when a Mars-sized object collided with the proto-Earth and produced a debris disk. Over time, that debris coalesced into our moon.

    While Heller says the literature mostly focuses on collision scenarios between an Earth-sized object and a Mars-sized object, he doesn’t see any reason why crashes on a bigger scale might not happen. Perhaps an Earth-sized object crashed into an object that was five times the mass of Earth, producing an extrasolar Earth-Earth binary planet system, he suggests.

    Another collision scenario likely took place at Uranus. The gas giant’s rotation is tilted about 90 degrees in its orbit around the Sun. In other words, it is rolling on its side. More intriguing, its two dozen moons follow Uranus’ rotational equator, and they do not orbit in the same plane as Uranus’ track around the Sun. This scenario suggests that Uranus was hit multiple times by huge objects instead of just once, Heller said.

    Examining mighty Jupiter’s moons gives astronomers a sense of how high temperatures were in the disk that formed the gas giant and its satellites, Heller added. Ganymede, for example, is an icy moon. Models indicate that beyond Ganymede’s orbit (at about 15 Jupiter radii) it is sufficiently cold for water to pass from the gas to the solid (ice) stage, so the regular moons in these regions are very water-rich compared to the inner, mostly rocky moons Io and Europa.

    “It sounds a bit technical, but we couldn’t have this information about planetary accretion if we did not have the moons today to observe,” Heller said.

    Some moons could also have been captured, such as Neptune’s large moon, Triton. The moon orbits in a direction opposite to other moons in Neptune‘s system (and in fact, opposite to the direction of other large moons in the Solar System.) Plus, its odd terrain suggests that it used to be a free-floating object that was captured by Neptune’s gravity. Neptune is so huge that it raised tides within the moon, reforming its surface.

    Even comparing the different types of moons around planets in the Solar System reveals different timescales of formation. Jupiter includes four moons similar in size to Earth’s moon (Europa, Callisto, Ganymede and Io), while the next largest planet in our solar system, Saturn, only has one large moon called Titan. Astronomers believe Saturn has only one large moon because the gas that formed objects in our solar system was more plentiful in Jupiter’s system to provide material for the moons to form.

    The gas abundance happened as a consequence of the huge gas giant creating a void in the material surrounding our young Sun, pulling the material in for its moons. Saturn was not quite large enough to do this, resulting in fewer large moons.

    More strange situations could exist beyond our solar system’s boundaries, but it will take a dedicated search to find exomoons. Once they are discovered, however, they will allow planet formation and evolution studies on a completely new level.

    This research was supported in part by the Natural Sciences and Engineering Research Council of Canada (NSERC), the Center for Exoplanets and Habitable Worlds, which is supported by the Pennsylvania State University, the Pennsylvania Space Grant Consortium, the National Science Foundation (NSF) the NASA Astrobiology Institute.

    See the full article here.


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