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  • SwRI scientists find evidence for early planetary shake-up
    Sonntag, 16.09.2018, 21:17:56 Uhr
    SwRI scientists find evidence for early planetary shake-up San Antonio TX (SPX) Sep 11, 2018 -
    Scientists at Southwest Research Institute studied an unusual pair of asteroids and discovered that their existence points to an early planetary rearrangement in our solar system.These bodies, called Patroclus and Menoetius, are targets of NASA's upcoming Lucy mission. They are around 70 miles wide and orbit around each other as they collectively circle the Sun. They are the only large binary known in the population of ancient bodies referred to as the Trojan asteroids. The two swarms of Trojans orbit at roughly the same distance from the Sun as Jupiter, one swarm orbiting ahead of, and the other trailing, the gas giant."The Trojans were likely captured during a dramatic period of dynamic instability when a skirmish between the solar system's giant planets - Jupiter, Saturn, Uranus and Neptune - occurred," said SwRI Institute Scientist Dr. David Nesvorny. He is the lead author of the paper, "Evidence for Very Early Migration of the Solar System Planets from the Patroclus-Menoetius Binary Jupiter Trojan," published in Nature Astronomy."This shake-up pushed Uranus and Neptune outwards, where they encountered a large primordial population of small bodies thought to be the source of today's Kuiper Belt objects, which orbit at the edge of the solar system. "Many small bodies of this primordial Kuiper Belt were scattered inwards, and a few of those became trapped as Trojan asteroids."A key issue with this solar system evolution model, however, has been when it took place. In this paper, scientists demonstrate that the very existence of the Patroclus-Menoetius pair indicates that the dynamic instability among the giant planets must have occurred within the first 100 million years of the solar system formation.Recent models of small body formation suggest that these types of binaries are leftovers of the very earliest times of our solar system, when pairs of small bodies could form directly from a collapsing cloud of "pebbles.""Observations of today's Kuiper Belt show that binaries like these were quite common in ancient times," said Dr. William Bottke, director of SwRI's Space Studies Department, who coauthored the paper. "Only a few of them now exist within the orbit of Neptune. The question is how to interpret the survivors."Had the instability been delayed many hundreds of millions of years, as suggested by some solar system evolution models, collisions within the primordial small-body disk would have disrupted these relatively fragile binaries, leaving none to be captured in the Trojan population.Earlier dynamical instabilities would have left more binaries intact, increasing the likelihood that at least one would have been captured in the Trojan population. The team created new models that show that the existence of the Patroclus-Menoetius binary strongly indicates an earlier instability.This early dynamical instability model has important consequences for the terrestrial planets, particularly regarding the origin of large impact craters on the Moon, Mercury and Mars that formed approximately 4 billion years ago. The impactors that made these craters are less likely to have been flung in from the outer regions of the Solar System. This could imply they were made by small-body leftovers of the terrestrial planet formation process.This work underscores the importance of the Trojan asteroids in illuminating the history of our solar system. Much more will be learned about Patroclus-Menoetius binary when NASA's Lucy mission, led by SwRI scientist and paper coauthor Dr. Hal Levison, surveys the pair in 2033, culminating a 12-year mission to tour both Trojan swarms.
  • New Exoplanet Discovered by Team Led by Canadian Student
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    New Exoplanet Discovered by Team Led by Canadian Student Montreal, Canada (SPX) Sep 10, 2018 -
    Wolf 503b, an exoplanet twice the size of Earth, has been discovered by an international team of Canadian, American and German researchers using data from NASA's Kepler Space Telescope. The find is described in a new study whose lead author is Merrin Peterson, an Institute for Research on Exoplanets (iREx) graduate student who started her master's degree at Universite de Montreal (UdeM) in May.Wolf 503b is about 145 light-years from Earth in the Virgo constellation; it orbits its star every six days and is thus very close to it, about 10 times closer than Mercury is to the Sun."The discovery and confirmation of this new exoplanet was very rapid, thanks to the collaboration that I and my advisor, Bjorn Benneke, are a part of," Peterson said. "In May, when the latest release of Kepler K2 data came in, we quickly ran a program that allowed us to find as many interesting candidate exoplanets as possible. Wolf 503b was one of them."The program the team used identifies distinct, periodic dips that appear in the light curve of a star when a planet passes in front of it. In order to better characterize the system Wolf 503b is part of, the astronomers first obtained a spectrum of the host star at the NASA Infrared Telescope Facility.This confirmed the star is an old 'orange dwarf,' slightly less luminous than the Sun but about twice as old, and allowed a precise determination of the radius of both the star and its companion.To confirm the companion was indeed a planet and to avoid making a false positive identification, the team obtained adaptive optics measurements from Palomar Observatory and also examined archival data. With these, they were able to confirm that there were no binary stars in the background and that the star did not have another, more massive companion that could be interpreted as a transiting planet.Wolf 503b is interesting, firstly, because of its size. Thanks to the Kepler telescope, we know that most of the planets in the Milky Way that orbit close to their stars are about as big as Wolf 503b, somewhere between that the size of the Earth and Neptune (which is 4 times bigger than Earth). Since there is nothing like them in our solar system, astronomers wonder whether these planets are small and rocky 'super-Earths' or gaseous mini versions of Neptune.One recent discovery also shows that there are significantly fewer planets that are between 1.5 and 2 times the size of Earth than those either smaller or larger than that. This drop, called the Fulton gap, could be what distinguishes the two types of planets from each other, researchers say in their study of the discovery, published in 2017."Wolf 503b is one of the only planets with a radius near the gap that has a star that is bright enough to be amenable to more detailed study that will better constrain its true nature," explained Bjorn Benneke, a UdeM professor and member of iREx and CRAQ."It provides a key opportunity to better understand the origin of this radius gap as well as the nature of the intriguing populations of 'super-Earths' and 'sub-Neptunes' as a whole."The second reason for interest in the Wolf 503b system is that the star is relatively close to Earth, and thus very bright. One of the possible follow-up studies for bright stars is the measurement of their radial velocity to determine the mass of the planets in orbit around them. A more massive planet will have a greater gravitational influence on its star, and the variation in line-of-sight velocity of the star over time will be greater.The mass, together with the radius determined by Kepler's observations, gives the bulk density of the planet, which in turn tells us something about its composition. For example, at its radius, if the planet has a composition similar to Earth, it would have to be about 14 times its mass. If, like Neptune, it has an atmosphere rich in gas or volatiles, it would be approximately half as massive.Because of its brightness, Wolf 503 will also be a prime target for the upcoming James Webb Space Telescope. Using a technique called transit spectroscopy, it will be possible to study the chemical content of the planet's atmosphere, and to detect the presence of molecules like hydrogen and water. This is crucial to verify if it is similar to that of the Earth, Neptune or completely different from the atmospheres of planets in our solar system.Similar observations can't be made of most planets found by Kepler, because their host stars are usually much fainter. As a result, the bulk densities and atmospheric compositions of most exoplanets are still unknown."By investigating the nature of Wolf 503b, we'll understand more about the structure of planets near the radius gap and more generally about the diversity of exoplanets present in our galaxy," said Peterson. "I look forward to learning more about it."Research Report: "A 2 Earth Radius Planet Orbiting the Bright Nearby K-Dwarf Wolf 503," Merrin S. Peterson et al., 2018, to appear in the Astronomical Journal
  • Youngest Accretion Disk Detected in Star Formation
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Youngest Accretion Disk Detected in Star Formation Taipei, Taiwan (SPX) Sep 07, 2018 -
    An international team led by Chin-Fei Lee at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA) has discovered a very small accretion disk formed around one of the youngest protostars, with the Atacama Large Millimeter/submillimeter Array (ALMA).This discovery poses a constraint on current theory of disk formation stronger than before, by pushing the disk formation time by a factor of a few earlier. Moreover, a compact rotating outflow has been detected. It may trace a disk wind carrying away angular momentum from the disk and thus facilitate the disk formation."ALMA is so powerful that it can resolve an accretion disk with a radius as small as 15 astronomical units (AU)," says Chin-Fei Lee at ASIAA."Since this disk is about a few times younger than the previously resolved youngest disk, our result has provided a stronger constraint on current theory of disk formation by pushing the disk formation time by a factor of a few earlier.Moreover, together with the previous results of the older disks, our disk result favors a model where the disk radius grows linearly with the protostellar mass, and thus supporting the 'early-start, slow-growth' scenario against the 'slow-start, rapid-growth' scenario for accretion disk formation around protostars."HH 211 is one of the youngest protostellar systems in Perseus at a distance of about 770 light-years. The central protostar has an age of only about 10,000 years (which is about 2 millionths of the age of our Sun) and a mass of less than 0.05 solar mass. It drives a powerful bipolar jet and thus must accrete material efficiently.Previous search at a resolution of about 50 AU only found a hint of a small dusty disk near the protostar. Now with ALMA at a resolution of 7 AU, which is about 7 times finer, the dusty disk at submillimeter wavelength not only has been detected but also spatially resolved.It is a nearly edge-on accretion disk feeding the central protostar and has a radius of about 15 AU. The disk is thick, indicating that the submillimeter light emitting grains have yet to settle to the midplane. Unlike the previously resolved older edge-on disk HH 212 which appears as a large "hamburger," this younger edge-on disk appears as a small "bun."Thus, it seems that an edge-on disk will grow from a small "bun" to a large "hamburger" in a later phase. Moreover, a compact rotating outflow has been detected, and it may trace a disk wind carrying away angular momentum from the disk and thus facilitate the disk formation.The observations open up an exciting possibility of directly detecting and characterizing small disks around the youngest protostars through high-resolution imaging with ALMA, which provides strong constraints on theories of disk formation and thus the feeding process in star formation.Research Report: "ALMA Observations of the Very Young Class 0 Protostellar System HH 211-mms: A 30-au Dusty Disk with a Disk-Wind Traced by SO?"
  • A Direct-Imaging Mission to Study Earth-like Exoplanets
    Sonntag, 16.09.2018, 21:17:56 Uhr
    A Direct-Imaging Mission to Study Earth-like Exoplanets Washington DC (SPX) Sep 06, 2018 -
    To answer significant questions about planetary systems, such as whether our solar system is a rare phenomenon or if life exists on planets other than Earth, NASA should lead a large direct imaging mission - an advanced space telescope - capable of studying Earth-like exoplanets orbiting stars similar to the Sun, says a new congressionally mandated report by the National Academies of Sciences, Engineering, and Medicine.The study of exoplanets - planets outside our solar system that orbit a star - has seen remarkable discoveries in the past decade. The report identifies two overarching goals in this field of science:* To understand the formation and evolution of planetary systems as products of star formation and characterize the diversity of their architectures, composition, and environments.* To learn enough about exoplanets to identify potentially habitable environments and search for scientific evidence of life on worlds orbiting other stars.Based on these goals, the committee that authored the report found that our current knowledge of the range of characteristics of planets outside the solar system is substantially incomplete. A holistic approach to studying habitability in exoplanets, using both theory and observations, will ultimately be required to search for evidence of past and present life elsewhere in the universe.While the committee recognized that developing a direct imaging capability will require large financial investments and a long timescale to see results, the effort will foster the development of the scientific community and technological capacity to understand myriad worlds. To detect a system analogous to our own Earth-Sun system, the report recommends using instruments that enable direct imaging of an exoplanet by blocking the light emitted by the parent stars - such as a coronagraph or starshade.In addition, ground-based astronomy - enabled by two U.S.-led telescopes - will also play a pivotal role in studying planet formation and potentially terrestrial worlds, the report says. The future Giant Magellan Telescope (GMT) and proposed Thirty Meter Telescope (TMT) would allow profound advances in imaging and spectroscopy - absorption and emission of light - of entire planetary systems. They also could detect molecular oxygen in temperate terrestrial planets in transit around close and small stars, the report says.The committee pointed out that the technology roadmap to enable the full potential of GMT and TMT in the study of exoplanets is in need of investments, and should leverage the existing network of U.S. centers and laboratories. To that end, the report recommends that the National Science Foundation invest in both telescopes and their exoplanet instrumentation to provide all-sky access to the U.S. community.While missions like Kepler spacecraft have characterized a remarkable population of planets relatively close to their stars, our knowledge of worlds in the outer reaches of the universe is woefully lacking, the committee said. The report says WFIRST, the large space-based mission that received the highest priority in the Academies' 2010 decadal survey, will play two extremely valuable roles: first, it will permit a survey of planets farther from their stars than surveyed by Kepler and other missions. Second, it will enable a large direct imaging mission.Although the radial velocity method - which measures the shift of the star as it orbits the center of mass of the planet system - will continue to provide essential mass and orbit information, its measurements are currently limited by variations in the surface of the star and imperfect calibration of the instruments, the report says.New instruments installed on large telescopes, substantial allocations of observing time, and collaboration between observers as well as theorists are some of the requirements for progress. To develop these methods and facilities for measuring the masses of temperate terrestrial planets orbiting Sun-like stars, NASA and NSF should establish a strategic initiative in Extremely Precise Radial Velocities.In addition, NASA should create a mechanism to systematically collect data on exoplanet atmospheres early in the James Webb Space Telescope mission. The committee also recommended building on the model of NASA's interdisciplinary collaboration initiative - Nexus for Exoplanet Science System - by supporting a cross-divisional research effort inviting proposals for interdisciplinary research.The committee called on NASA to support a robust individual investigator program that includes grants for theoretical, laboratory, and ground-based telescopic investigations to fully realize the scientific payoff of exoplanet missions.The report also recognizes that discrimination and harassment exist in the scientific workforce and can affect the exoplanet research community, posing barriers to the participation of people from certain demographic groups. To maximize scientific potential and opportunities for excellence, institutions and organizations should take concrete steps to eliminate discrimination and harassment and to proactively recruit and retain scientists from underrepresented groups.
  • Rutgers scientists identify protein that may have existed when life began
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Rutgers scientists identify protein that may have existed when life began New Brunswick NJ (SPX) Sep 04, 2018 -
    How did life arise on Earth? Rutgers researchers have found among the first and perhaps only hard evidence that simple protein catalysts - essential for cells, the building blocks of life, to function - may have existed when life began.Their study of a primordial peptide, or short protein, is published in the Journal of the American Chemical Society.In the late 1980s and early 1990s, the chemist Gunter Wachtershauser postulated that life began on iron- and sulfur-containing rocks in the ocean. Wachtershauser and others predicted that short peptides would have bound metals and served as catalysts of life-producing chemistry, according to study co-author Vikas Nanda, an associate professor at Rutgers' Robert Wood Johnson Medical School.Human DNA consists of genes that code for proteins that are a few hundred to a few thousand amino acids long. These complex proteins - needed to make all living-things function properly - are the result of billions of years of evolution.When life began, proteins were likely much simpler, perhaps just 10 to 20 amino acids long. With computer modeling, Rutgers scientists have been exploring what early peptides may have looked like and their possible chemical functions, according to Nanda.The scientists used computers to model a short, 12-amino acid protein and tested it in the laboratory. This peptide has several impressive and important features. It contains only two types of amino acids (rather than the estimated 20 amino acids that synthesize millions of different proteins needed for specific body functions), it is very short and it could have emerged spontaneously on the early Earth in the right conditions.The metal cluster at the core of this peptide resembles the structure and chemistry of iron-sulfur minerals that were abundant in early Earth oceans. The peptide can also charge and discharge electrons repeatedly without falling apart, according to Nanda, a resident faculty member at the Center for Advanced Technology and Medicine."Modern proteins called ferredoxins do this, shuttling electrons around the cell to promote metabolism," said senior author Professor Paul G. Falkowski, who leads Rutgers' Environmental Biophysics and Molecular Ecology Laboratory. "A primordial peptide like the one we studied may have served a similar function in the origins of life."Falkowski is the principal investigator for a NASA-funded ENIGMA project led by Rutgers scientists that aims to understand how protein catalysts evolved at the start of life. Nanda leads one team that will characterize the full potential of the primordial peptide and continue to develop other molecules that may have played key roles in the origins of life.With computers, Rutgers scientists have smashed and dissected nearly 10,000 proteins and pinpointed four "Legos of life" - core chemical structures that can be stacked to form the innumerable proteins inside all organisms.The small primordial peptide may be a precursor to the longer Legos of life, and scientists can now run experiments on how such peptides may have functioned in early-life chemistry.Research paper
  • Water worlds could support life, study says
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Water worlds could support life, study says Chicago IL (SPX) Sep 03, 2018 -
    The conditions for life surviving on planets entirely covered in water are more fluid than previously thought, opening up the possibility that water worlds could be habitable, according to a new paper from the University of Chicago and Pennsylvania State University.The scientific community has largely assumed that planets covered in a deep ocean would not support the cycling of minerals and gases that keeps the climate stable on Earth, and thus wouldn't be friendly to life.But the study, published Aug. 30 in The Astrophysical Journal, found that ocean planets could stay in the "sweet spot" for habitability much longer than previously assumed. The authors based their findings on more than a thousand simulations."This really pushes back against the idea you need an Earth clone - that is, a planet with some land and a shallow ocean," said Edwin Kite, assistant professor of geophysical sciences at UChicago and lead author of the study.As telescopes get better, scientists are finding more and more planets orbiting stars in other solar systems. Such discoveries are resulting in new research into how life could potentially survive on other planets, some of which are very different from Earth - some may be covered entirely in water hundreds of miles deep.Because life needs an extended period to evolve, and because the light and heat on planets can change as their stars age, scientists usually look for planets that have both some water and some way to keep their climates stable over time.The primary method we know of is how Earth does it. Over long timescales, our planet cools itself by drawing down greenhouse gases into minerals and warms itself up by releasing them via volcanoes.But this model doesn't work on a water world, with deep water covering the rock and suppressing volcanoes.Kite, and Penn State coauthor Eric Ford, wanted to know if there was another way. They set up a simulation with thousands of randomly generated planets, and tracked the evolution of their climates over billions of years."The surprise was that many of them stay stable for more than a billion years, just by luck of the draw," Kite said. "Our best guess is that it's on the order of 10 percent of them."These lucky planets sit in the right location around their stars. They happened to have the right amount of carbon present, and they don't have too many minerals and elements from the crust dissolved in the oceans that would pull carbon out of the atmosphere.They have enough water from the start, and they cycle carbon between the atmosphere and ocean only, which in the right concentrations is sufficient to keep things stable."How much time a planet has is basically dependent on carbon dioxide and how it's partitioned between the ocean, atmosphere and rocks in its early years," said Kite. "It does seem there is a way to keep a planet habitable long-term without the geochemical cycling we see on Earth."The simulations assumed stars that are like our own, but the results are optimistic for red dwarf stars, too, Kite said. Planets in red dwarf systems are thought to be promising candidates for fostering life because these stars get brighter much more slowly than our sun - giving life a much longer time period to get started.The same conditions modeled in this paper could be applied to planets around red dwarfs, they said: Theoretically, all you would need is the steady light of a star.Research paper
  • Little star sheds light on young planets
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Little star sheds light on young planets Tokyo, Japan (SPX) Sep 05, 2018 -
    Astronomers from the Department of Physics at the University of Tokyo discovered a dense disk of material around a young star, which may be a precursor to a planetary system. Their research could vastly improve models of how solar systems form, which would tell us more about our own place in the cosmos.Early in 2017, Assistant Professor Yoko Oya gave graduate student Yuki Okoda some recent complex data on a nearby star with which she could begin her Ph.D. Little did she realize that what she would find could unlock not only the secrets of how planets form but possibly her career as a professional astronomer.The star in question (only known by its catalog number IRAS 15398-3359) is small, young and relatively cool for a star. It's diminutive stature means the weak light it shines can't even reach us through a cloud of gas and dust that surrounds it. But this doesn't stop inquisitive minds from exploring the unknown.In 2013, Oya and her collaborators used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile to observe the star in submillimeter wavelengths, as that kind of light can penetrate the dust cloud - for reference, red light is around 700 nanometers. A painstaking analysis revealed some interesting nebulous structures, despite the images they worked from being difficult to comprehend."The greatest academic challenge I've faced was trying to make sense of grainy images. It's extremely difficult to know exactly what you're really looking at." says Okoda. "But I felt compelled to explore the nature of the structures Dr. Oya had seen with ALMA, so I came up with a model to explain them."The model she produced came as a surprise to Okoda and her colleagues, but it fit the data perfectly. It describes a dense disk of material that consists of gas and dust from the cloud that surrounds the star. This has never before been seen around such a young star.The disk is a precursor to a protoplanetary disk, which is far denser still and eventually becomes a planetary system in orbit around a star."We can't say for sure this particular disk will coalesce into a new planetary system," explains Oya. "The dust cloud may be pushed away by stellar winds or it might all fall into the star itself, feeding it in the process. What's exciting is how quickly this might happen."The star is small at around 0.7 percent the mass of our sun, based on observations of the mass of the surrounding cloud. It could grow to as large as 20 percent in just a few tens of thousands of years, a blink of the eye on the cosmic scale."I hope our observations and models will enhance knowledge of how solar systems form," says Okoda. "My research interests involve young protostellar objects, and the implication that protoplanetary disks could form earlier than expected really excites me."Okoda began this project a year-and-a-half ago to hone her skills as an astronomer, but mirroring the young star she observed, the practice evolved quickly and became a full research project, which will hopefully earn her a Ph.D. from the University of Tokyo.The observations and resultant model were only possible thanks to advancements in radio astronomy with observatories such as ALMA. The team was lucky that the plane of the disk is level with our own solar system as this means the starlight ALMA sees passes through enough of the gas and dust to divulge important characteristics of it."We were also lucky to be given time with ALMA to carry out our observations. Only about 20 percent of applications actually go ahead," explains Oya. "With highly specialized astronomical instruments, there is much competition for time. My hope is our success will inspire a new generation of astronomers in Japan to reach for the stars."Research Report: "The Co-evolution of Disks and Stars in Embedded Stages: The Case of the Very-low-mass Protostar IRAS 15398-3359"
  • Scientist develops database for stellar-exoplanet "exploration"
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Scientist develops database for stellar-exoplanet "exploration" San Antonio TX (SPX) Aug 30, 2018 -
    A Southwest Research Institute scientist is using big data to help the scientific community characterize exoplanets, particularly alien worlds orbiting nearby stars. Of particular interest are exoplanets that could harbor life."At first scientists focused on temperatures, looking for exoplanets in the 'Goldilocks zone' - neither too close nor too far from the star, where liquid water could exist," said Dr. Natalie Hinkel, a planetary astrophysicist at SwRI. "But the definition of habitability is evolving beyond liquid water and a cozy temperature."The planets also need the building blocks for life (such as hydrogen, carbon, nitrogen, oxygen, and phosphorus) as well as a rocky composition (including elements such as iron, silicon, and magnesium) for a planet to be habitable. Plus, active geochemical cycles are necessary to distribute these elements around the world. As seen on Earth, a protective atmosphere is also a necessity for life."With current technology, we can't measure the composition of an exoplanet's surface, much less its interior," Hinkel said."But we can measure the abundance of elements in a star spectroscopically, studying how light interacts with the elements in a star's upper layers. Using these data, scientists can infer what a star's orbiting planets are made of, using stellar composition as a proxy for its planets."Hinkel built a publicly available database, called the Hypatia Catalog, to help researchers explore thousands of stars, as well as potential star-exoplanet systems, observed over the last 35 years.It's the largest database of stars and their elements for the population within 500 light-years of our Sun. At last count, Hypatia had stellar chemical abundance data on 6,156 stars, 365 of which are known to host planets. The database also catalogs 72 stellar elements from hydrogen to lead."The Hypatia Catalog and other large databases of stellar chemical abundances open up a new age of exoplanet exploration," Hinkel said. She was part of a team of scientists that recently modeled water in planets orbiting the nearby star TRAPPIST-1."We found that a few of the planets, including one in the habitable zone, are likely 'water worlds,' composed of 5-25% water, which would strongly affect their habitability. By comparison, Earth has 0.02% water."Next, Hinkel is working with a variety of machine learning algorithms to explore the unseen ways the presence of a planet may influence the chemistry of the host star.The American Scientist September-October issue included an article by Hinkel titled "Big Data on Exoplanet Composition," featuring the Hypatia Catalog. Hinkel named the catalog after one of her scientific heroines, a leading mathematician and astronomer in the late 300s, early 400s - the only woman known to have had this level of scientific influence in her time.Research Report: "Big Data on Exoplanet Composition"
  • Infant exoplanet weighed by Hipparcos and Gaia
    Sonntag, 16.09.2018, 21:17:56 Uhr
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    Infant exoplanet weighed by Hipparcos and Gaia Paris (ESA) Aug 23, 2018 -
    The mass of a very young exoplanet has been revealed for the first time using data from ESA's star mapping spacecraft Gaia and its predecessor, the quarter-century retired Hipparcos satellite.Astronomers Ignas Snellen and Anthony Brown from Leiden University, the Netherlands, deduced the mass of the planet Beta Pictoris b from the motion of its host star over a long period of time as captured by both Gaia and Hipparcos.The planet is a gas giant similar to Jupiter but, according to the new estimate, is 9 to 13 times more massive. It orbits the star Beta Pictoris, the second brightest star in the constellation Pictor.The planet was only discovered in 2008 in images captured by the Very Large Telescope at the European Southern Observatory in Chile. Both the planet and the star are only about 20 million years old - roughly 225 times younger than the Solar System. Its young age makes the system intriguing but also difficult to study using conventional methods."In the Beta Pictoris system, the planet has essentially just formed," says Ignas."Therefore we can get a picture of how planets form and how they behave in the early stages of their evolution. On the other hand, the star is very hot, rotates fast, and it pulsates."This behaviour makes it difficult for astronomers to accurately measure the star's radial velocity - the speed at which it appears to periodically move towards and away from the Earth.Tiny changes in the radial velocity of a star, caused by the gravitational pull of planets in its vicinity, are commonly used to estimate masses of exoplanets. But this method mainly works for systems that have already gone through the fiery early stages of their evolution.In the case of Beta Pictoris b, upper limits of the planet's mass range had been arrived at before using the radial velocity method. To obtain a better estimate, the astronomers used a different method, taking advantage of Hipparcos' and Gaia's measurements that reveal the precise position and motion of the planet's host star in the sky over time."The star moves for different reasons," says Ignas."First, the star circles around the centre of the Milky Way, just as the Sun does. That appears from the Earth as a linear motion projected on the sky. We call it proper motion. And then there is the parallax effect, which is caused by the Earth orbiting around the Sun. Because of this, over the year, we see the star from slightly different angles."And then there is something that the astronomers describe as 'tiny wobbles' in the trajectory of the star across the sky - minuscule deviations from the expected course caused by the gravitational pull of the planet in the star's orbit. This is the same wobble that can be measured via changes in the radial velocity, but along a different direction - on the plane of the sky, rather than along the line of sight."We are looking at the deviation from what you expect if there was no planet and then we measure the mass of the planet from the significance of this deviation," says Anthony. "The more massive the planet, the more significant the deviation."To be able to make such an assessment, astronomers need to observe the trajectory of the star for a long period of time to properly understand the proper motion and the parallax effect.The Gaia mission, designed to observe more than one billion stars in our Galaxy, will eventually be able to provide information about a large amount of exoplanets. In the 22 months of observations included in Gaia's second data release, published in April, the satellite has recorded the star Beta Pictoris about thirty times. That, however, is not enough."Gaia will find thousands of exoplanets, that's still on our to-do list," says Timo Prusti, ESA's Gaia project scientist. "The reason that the exoplanets can be expected only late in the mission is the fact that to measure the tiny wobble that the exoplanets are causing, we need to trace the position of stars for several years."Combining the Gaia measurements with those from ESA's Hipparcos mission, which observed Beta Pictoris 111 times between 1990 and 1993, enabled Ignas and Anthony to get their result much faster. This led to the first successful estimate of a young planet's mass using astrometric measurements."By combining data from Hipparcos and Gaia, which have a time difference of about 25 years, you get a very long term proper motion," says Anthony."This proper motion also contains the component caused by the orbiting planet. Hipparcos on its own would not have been able to find this planet because it would look like a perfectly normal single star unless we had measured it for a much longer time."Now, by combining Gaia and Hipparcos and looking at the difference in the long term and the short term proper motion, we can see the effect of the planet on the star."The result represents an important step towards better understanding the processes involved in planet formation, and anticipates the exciting exoplanet discoveries that will be unleashed by Gaia's future data releases.Research Report: "The mass of the young planet Beta Pictoris b through the astrometric motion of its host star," by I. Snellen and A. Brown is published in Nature Astronomy, 20 August 2018.
  • Infant exoplanet weighed by Hipparcos and Gaia
    Sonntag, 16.09.2018, 21:17:56 Uhr
    Weitere Links:
    Infant exoplanet weighed by Hipparcos and Gaia Paris (ESA) Aug 24, 2018 -
    The mass of a very young exoplanet has been revealed for the first time using data from ESA's star mapping spacecraft Gaia and its predecessor, the quarter-century retired Hipparcos satellite.Astronomers Ignas Snellen and Anthony Brown from Leiden University, the Netherlands, deduced the mass of the planet Beta Pictoris b from the motion of its host star over a long period of time as captured by both Gaia and Hipparcos.The planet is a gas giant similar to Jupiter but, according to the new estimate, is 9 to 13 times more massive. It orbits the star Beta Pictoris, the second brightest star in the constellation Pictor.The planet was only discovered in 2008 in images captured by the Very Large Telescope at the European Southern Observatory in Chile. Both the planet and the star are only about 20 million years old - roughly 225 times younger than the Solar System. Its young age makes the system intriguing but also difficult to study using conventional methods."In the Beta Pictoris system, the planet has essentially just formed," says Ignas. "Therefore we can get a picture of how planets form and how they behave in the early stages of their evolution. On the other hand, the star is very hot, rotates fast, and it pulsates."This behaviour makes it difficult for astronomers to accurately measure the star's radial velocity - the speed at which it appears to periodically move towards and away from the Earth. Tiny changes in the radial velocity of a star, caused by the gravitational pull of planets in its vicinity, are commonly used to estimate masses of exoplanets. But this method mainly works for systems that have already gone through the fiery early stages of their evolution.In the case of Beta Pictoris b, upper limits of the planet's mass range had been arrived at before using the radial velocity method. To obtain a better estimate, the astronomers used a different method, taking advantage of Hipparcos' and Gaia's measurements that reveal the precise position and motion of the planet's host star in the sky over time."The star moves for different reasons," says Ignas. "First, the star circles around the centre of the Milky Way, just as the Sun does. That appears from the Earth as a linear motion projected on the sky. We call it proper motion. And then there is the parallax effect, which is caused by the Earth orbiting around the Sun. Because of this, over the year, we see the star from slightly different angles."And then there is something that the astronomers describe as 'tiny wobbles' in the trajectory of the star across the sky - minuscule deviations from the expected course caused by the gravitational pull of the planet in the star's orbit. This is the same wobble that can be measured via changes in the radial velocity, but along a different direction - on the plane of the sky, rather than along the line of sight."We are looking at the deviation from what you expect if there was no planet and then we measure the mass of the planet from the significance of this deviation," says Anthony. "The more massive the planet, the more significant the deviation."To be able to make such an assessment, astronomers need to observe the trajectory of the star for a long period of time to properly understand the proper motion and the parallax effect.The Gaia mission, designed to observe more than one billion stars in our Galaxy, will eventually be able to provide information about a large amount of exoplanets. In the 22 months of observations included in Gaia's second data release, published in April, the satellite has recorded the star Beta Pictoris about thirty times. That, however, is not enough."Gaia will find thousands of exoplanets, that's still on our to-do list," says Timo Prusti, ESA's Gaia project scientist. "The reason that the exoplanets can be expected only late in the mission is the fact that to measure the tiny wobble that the exoplanets are causing, we need to trace the position of stars for several years."Combining the Gaia measurements with those from ESA's Hipparcos mission, which observed Beta Pictoris 111 times between 1990 and 1993, enabled Ignas and Anthony to get their result much faster. This led to the first successful estimate of a young planet's mass using astrometric measurements."By combining data from Hipparcos and Gaia, which have a time difference of about 25 years, you get a very long term proper motion," says Anthony."This proper motion also contains the component caused by the orbiting planet. Hipparcos on its own would not have been able to find this planet because it would look like a perfectly normal single star unless we had measured it for a much longer time."Now, by combining Gaia and Hipparcos and looking at the difference in the long term and the short term proper motion, we can see the effect of the planet on the star."The result represents an important step towards better understanding the processes involved in planet formation, and anticipates the exciting exoplanet discoveries that will be unleashed by Gaia's future data releases.Research Report: "The mass of the young planet Beta Pictoris b through the astrometric motion of its host star," by I. Snellen and A. Brown is published in Nature Astronomy, 20 August 2018.
http://www.spacedaily.com/Exo_Worlds.xml
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