First global geologic map of Jupiter’s largest moon Ganymede details an icy world

More than 400 years after its discovery by Galileo, the largest moon in the solar system has finally claimed a spot on the map.A team of scientists led by Wes Patterson of the Johns Hopkins Applied Physics Laboratory (APL), Laurel, Md., and Geoffrey Collins of Wheaton College, Norton, Mass., has produced the first global geologic map of Ganymede, a Galilean moon of Jupiter. Published by the U.S. Geological Survey, the map technically illustrates the varied geologic character of Ganymede’s surface, and is the first complete global geologic map of an icy, outer-planet moon.Patterson, Collins and colleagues used images from NASA’s Voyager and Galileo missions to create the map. It’s only the fourth of its kind covering a planetary satellite; similar maps exist for Earth’s moon as well as Jupiter’s moons Io and Callisto.”By mapping all of Ganymede’s surface, we can more accurately address scientific questions regarding the formation and evolution of this truly unique moon,” says Patterson, a planetary scientist.Since its discovery in January 1610, Ganymede has been the focus of repeated observation, first by Earth-based telescopes, and later by flyby missions and spacecraft orbiting Jupiter. These studies depict a complex icy world whose surface is characterized by the striking contrast between its two major terrain types: the dark, very old, highly cratered regions; and the lighter, somewhat younger (but still ancient) regions marked with an extensive array of grooves and ridges.  With a diameter of 3,280 miles (5,262 kilometers), Ganymede is larger than both planet Mercury and dwarf planet Pluto. It’s also the only satellite in the solar system known to have its own magnetosphere. The map details geologic features of the moon that formed and evolved over much of our solar system’s history. These features record evidence of Ganymede’s internal evolution, its dynamical interactions with the other Galilean satellites, and the evolution of the small bodies that have impacted Ganymede’s surface.The new chart will be a valuable tool for researchers to compare the geologic characters of other icy moons, since almost any type of feature that is found on other icy satellites has a similar feature somewhere on Ganymede. And with a surface over half as large as all the land area on Earth, Ganymede offers a wide variety of locations to observe. …

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Why white dots appear larger than equal size black dots: How Galileo’s visual illusion works in the mind’s eye

Scientists have studied a visual illusion first discovered by Galileo Galilei, and found that it occurs because of the surprising way our eyes see lightness and darkness in the world. Their results advance our understanding of how our brains are wired for seeing white versus black objects.The work was done by Jens Kremkow and collaborators in the laboratories of Jose Manuel Alonso and Qasim Zaidi at the State University of New York College of Optometry. It will be published on February 10 of 2014 in the Proceedings of the National Academy of Sciences.Galileo was puzzled by the fact that the appearance of the planets depended on whether one looked with the naked eye or with a telescope. Viewed directly, planets seemed “expanded” and had “a radiant crown,” which made Venus looked eight to ten times larger than Jupiter even though Jupiter was four times larger. Though Galileo realized this size illusion was not created by the object — but by his eyes — he did not understand why or how.He mused, “Either because their light is refracted in the moisture that covers the pupil, or because it is reflected from the edges of the eyelids and these reflected rays are diffused over the pupil, or for some other reason.” Generations of scientists following Galileo continued to assume the illusion was caused by blur or similar optical effects. However, though blur can distort size, it does not explain why Venus looks larger than Jupiter with the naked eye. Hermann von Helmholtz — the venerable 19th Century German physician-physicist — was the first to realize that something else was needed to explain the illusion, as he described in his Treatise on Physiological Optics.Only now, with Kremkow and colleagues’ new study, has science finally zoomed in and illuminated the scope of the problem. It’s a feature of how we see everything, no less. By examining the responses of neurons in the visual system of the brain — to both light stimuli and dark stimuli — the neuroscientists discovered that, whereas dark stimuli result in a faithful neural response that accurately represents their size, light stimuli on the contrary result in non-linear and exaggerated responses that make the stimulus look larger. So white spots on a black background look bigger than same-sized black spots on white background, and Galileo’s glowing stellar objects are not really as big as they might appear to the unaided eye.This effect is responsible for how we see everything from textures and faces — based on their dark parts in bright daylight — to why it is easier to read this very page with black-on-white lettering, rather than white-on-black (a well known, and until now, unexplained phenomenon). …

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One planet, two stars: New research shows how circumbinary planets form

Luke Skywalker’s home planet Tatooine would have formed far from its current location in the Star Wars universe, a new University of Bristol study into its real world counterparts, observed by the Kepler space telescope, suggests.Like the fictional Star Wars planet, Kepler-34(AB)b is a circumbinary planet, so-called because its orbit encompasses two stars. There are few environments more extreme than a binary star system in which planet formation can occur. Powerful gravitational perturbations from the two stars on the rocky building blocks of planets lead to destructive collisions that grind down the material. So, how can the presence of such planets be explained?In research published this week in Astrophysical Journal Letters, Dr Zoe Leinhardt and colleagues from Bristol’s School of Physics have completed computer simulations of the early stages of planet formation around the binary stars using a sophisticated model that calculates the effect of gravity and physical collisions on and between one million planetary building blocks.They found that the majority of these planets must have formed much further away from the central binary stars and then migrated to their current location.Dr Leinhardt said: “Our simulations show that the circumbinary disk is a hostile environment even for large, gravitationally strong objects. Taking into account data on collisions as well as the physical growth rate of planets, we found that Kepler 34(AB)b would have struggled to grow where we find it now.”Based on these conclusions for Kepler-34, it seems likely that all of the currently known circumbinary planets have also migrated significantly from their formation locations — with the possible exception of Kepler-47 (AB)c which is further away from the binary stars than any of the other circumbinary planets.Stefan Lines, lead author of the study, said: “Circumbinary planets have captured the imagination of many science-fiction writers and film-makers — our research shows just how remarkable such planets are. Understanding more about where they form will assist future exoplanet discovery missions in the hunt for earth-like planets in binary star systems.”Story Source:The above story is based on materials provided by University of Bristol. Note: Materials may be edited for content and length.

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Oldest solar twin identified: New clues to help solve lithium mystery

Aug. 28, 2013 — A team led by astronomers in Brazil has used ESO’s Very Large Telescope to study the oldest solar twin known to date. Located 250 light-years away, the star HIP 102152 is more like the Sun than any other solar twin — except that it is nearly four billion years older. This older twin may be host to rocky planets and gives us an unprecedented chance to see how the Sun will look when it ages.Astronomers have only been observing the Sun with telescopes for 400 years — a tiny fraction of the Sun’s age of 4.6 billion years. It is very hard to study the history and future evolution of our star, but we can do this by hunting for rare stars that are almost exactly like our own, but at different stages of their lives. Now astronomers have identified a star that is essentially an identical twin to our Sun, but 4 billion years older — almost like seeing a real version of the twin paradox in action [1].Jorge Melendez (Universidade de São Paulo, Brazil), the leader of the team and co-author of the new paper explains: “For decades, astronomers have been searching for solar twins in order to know our own life-giving Sun better. But very few have been found since the first one was discovered in 1997. We have now obtained superb-quality spectra from the VLT and can scrutinise solar twins with extreme precision, to answer the question of whether the Sun is special.”The team studied two solar twins [2] — one that was thought to be younger than the Sun (18 Scorpii) and one that was expected to be older (HIP 102152). They used the UVES spectrograph on the Very Large Telescope (VLT) at ESO’s Paranal Observatory to split up the light into its component colours so that the chemical composition and other properties of these stars could be studied in great detail. They found that HIP 102152 in the constellation of Capricornus (The Sea Goat) is the oldest solar twin known to date. …

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Free-floating planets may be born free

Aug. 20, 2013 — Tiny, round, cold clouds in space have all the right characteristics to form planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free.Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such “rogue planets,” which don’t orbit around a star, must have been ejected from existing planetary systems.New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own.A team of astronomers from Sweden and Finland used several telescopes to observe the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn).They collected observations in radio waves with the 20-metre telescope at Onsala Space Observatory in Sweden, in submillimetre waves with APEX in Chile, and in infrared light with the New Technology Telescope (NTT) at ESO’s La Silla Observatory in Chile.”The Rosette Nebula is home to more than a hundred of these tiny clouds — we call them globulettes,” says Gösta Gahm, astronomer at Stockholm University, who led the project.”They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of planetary mass, less than 13 times Jupiter’s mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment,” he says.”We found that the globulettes are very dense and compact, and many of them have very dense cores. That tells us that many of them will collapse under their own weight and form free-floating planets. The most massive of them can form so-called brown dwarfs,” says team member Carina Persson, astronomer at Chalmers University of Technology.Brown dwarfs, sometimes called failed stars, are bodies whose mass lies between that of planets and stars.The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80 000 kilometres per hour.”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars. They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre,” explains Minja Mäkelä, astronomer at the University of Helsinki.According to Gösta Gahm and his team, the tiny dark clouds are being thrown out of the Rosette Nebula. …

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Free-floating planets may be born free

Aug. 20, 2013 — Tiny, round, cold clouds in space have all the right characteristics to form planets with no parent star. New observations, made with Chalmers University of Technology telescopes, show that not all free-floating planets were thrown out of existing planetary systems. They can also be born free.Previous research has shown that there may be as many as 200 billion free-floating planets in our galaxy, the Milky Way. Until now scientists have believed that such “rogue planets,” which don’t orbit around a star, must have been ejected from existing planetary systems.New observations of tiny dark clouds in space point out another possibility: that some free-floating planets formed on their own.A team of astronomers from Sweden and Finland used several telescopes to observe the Rosette Nebula, a huge cloud of gas and dust 4600 light years from Earth in the constellation Monoceros (the Unicorn).They collected observations in radio waves with the 20-metre telescope at Onsala Space Observatory in Sweden, in submillimetre waves with APEX in Chile, and in infrared light with the New Technology Telescope (NTT) at ESO’s La Silla Observatory in Chile.”The Rosette Nebula is home to more than a hundred of these tiny clouds — we call them globulettes,” says Gösta Gahm, astronomer at Stockholm University, who led the project.”They are very small, each with diameter less than 50 times the distance between the Sun and Neptune. Previously we were able to estimate that most of them are of planetary mass, less than 13 times Jupiter’s mass. Now we have much more reliable measures of mass and density for a large number of these objects, and we have also precisely measured how fast they are moving relative to their environment,” he says.”We found that the globulettes are very dense and compact, and many of them have very dense cores. That tells us that many of them will collapse under their own weight and form free-floating planets. The most massive of them can form so-called brown dwarfs,” says team member Carina Persson, astronomer at Chalmers University of Technology.Brown dwarfs, sometimes called failed stars, are bodies whose mass lies between that of planets and stars.The study shows that the tiny clouds are moving outwards through the Rosette Nebula at high speed, about 80 000 kilometres per hour.”We think that these small, round clouds have broken off from tall, dusty pillars of gas which were sculpted by the intense radiation from young stars. They have been accelerated out from the centre of the nebula thanks to pressure from radiation from the hot stars in its centre,” explains Minja Mäkelä, astronomer at the University of Helsinki.According to Gösta Gahm and his team, the tiny dark clouds are being thrown out of the Rosette Nebula. …

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Snow in an infant solar system: A frosty landmark for planet and comet formation

July 18, 2013 — A snow line has been imaged in a far-off infant solar system for the very first time. The snow line, located in the disc around the Sun-like star TW Hydrae, promises to tell us more about the formation of planets and comets, the factors that decide their composition, and the history of the Solar System.The results are published today in Science Express.Astronomers using the Atacama Large Millimeter/submillimeter Array have taken the first ever image of the snow line in an infant solar system. On Earth, snow lines form at high altitudes where falling temperatures turn the moisture in the air into snow. This line is clearly visible on a mountain, where the snow-capped summit ends and the rocky face begins.The snow lines around young stars form in a similar way, in the distant, colder reaches of the dusty discs from which solar systems form. Starting from the star and moving outwards, water (H2O) is the first to freeze, forming the first snow line. Further out from the star, as temperatures drop, more exotic molecules can freeze and turn to snow, such as carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO). These different snows give the dust grains a sticky outer coating and play an essential role in helping the grains to overcome their usual tendency to break up in collisions, allowing them to become the crucial building blocks of planets and comets. The snow also increases how much solid matter is available and may dramatically speed up the planetary formation process.Each of these different snow lines — for water, carbon dioxide, methane and carbon monoxide — may be linked to the formation of particular kinds of planets [1]. Around a Sun-like star in a solar system like our own, the water snow line would correspond to a distance between the orbits of Mars and Jupiter, and the carbon monoxide snow line would correspond to the orbit of Neptune.The snow line spotted by ALMA is the first glimpse of the carbon monoxide snow line, around TW Hydrae, a young star 175 light-years away from Earth. Astronomers believe this budding solar system shares many of the same characteristics of the Solar System when it was just a few million years old.”ALMA has given us the first real picture of a snow line around a young star, which is extremely exciting because of what it tells us about the very early period in the history of the Solar System,” said Chunhua “Charlie” Qi (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) one of the two lead authors of the paper. …

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In bitter cold subglacial lake, surprising life goes on

July 5, 2013 — Lake Vostok, buried under a glacier in Antarctica, is so dark, deep and cold that scientists had considered it a possible model for other planets, a place where nothing could live.However, work by Dr. Scott Rogers, a Bowling Green State University professor of biological sciences, and his colleagues has revealed a surprising variety of life forms living and reproducing in this most extreme of environments. A paper published June 26 in PLOS ONE (Public Library of Science) details the thousands of species they identified through DNA and RNA sequencing.”The bounds on what is habitable and what is not are changing,” Rogers said.This is the fourth article the group has published about its Lake Vostok investigations. The team included Dr. Paul Morris, biology, who with Scott and doctoral student Yury Shtarkman conducted most of the genetic analyses; former doctoral students Zeynep Koçer, now with the Department of Infectious Diseases, Division of Virology, at St. Jude’s Research Hospital in Memphis, performed most of the laboratory work; Ram Veerapaneni, now at BGSU Firelands, Tom D’Elia, now at Indian River State College in Florida, and undergraduate student Robyn Edgar, computer science.Their work was supported by several grants, including two from the National Science Foundation, one from U.S. Department of Agriculture and one from the BGSU Faculty Research Committee. Together, the amount dedicated to the project was more than $250,000.When thinking about Lake Vostok, you have to think big. The fourth-deepest lake on Earth, it is also the largest of the 400-some subglacial lakes known in Antarctica. The ice that has covered it for the past 15 million years is now more than two miles deep, creating tremendous pressure in the lake. …

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Three planets in habitable zone of nearby star — Gliese 667c

June 25, 2013 — A team of astronomers has combined new observations of Gliese 667C with existing data from HARPS at ESO’s 3.6-metre telescope in Chile, to reveal a system with at least six planets. A record-breaking three of these planets are super-Earths lying in the zone around the star where liquid water could exist, making them possible candidates for the presence of life. This is the first system found with a fully packed habitable zone.Gliese 667C is a very well-studied star. Just over one third of the mass of the Sun, it is part of a triple star system known as Gliese 667 (also referred to as GJ 667), 22 light-years away in the constellation of Scorpius (The Scorpion). This is quite close to us — within the Sun’s neighbourhood — and much closer than the star systems investigated using telescopes such as the planet-hunting Kepler space telescope.Previous studies of Gliese 667C had found that the star hosts three planets with one of them in the habitable zone. Now, a team of astronomers led by Guillem Anglada-Escudé of the University of Göttingen, Germany and Mikko Tuomi of the University of Hertfordshire, UK, has reexamined the system. They have added new HARPS observations, along with data from ESO’s Very Large Telescope, the W.M. Keck Observatory and the Magellan Telescopes, to the already existing picture [1]. The team has found evidence for up to seven planets around the star [2].These planets orbit the third fainter star of a triple star system. Viewed from one of these newly found planets the two other suns would look like a pair of very bright stars visible in the daytime and at night they would provide as much illumination as the full Moon. …

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Unfrozen mystery: H2O reveals a new secret

June 10, 2013 — Using revolutionary new techniques, a team led by Carnegie’s Malcolm Guthrie has made a striking discovery about how ice behaves under pressure, changing ideas that date back almost 50 years. Their findings could alter our understanding of how the water molecule responds to conditions found deep within planets and could have implications for energy science.Their work is published in the Proceedings of the National Academy of Sciences.When water freezes into ice, its molecules are bound together in a crystalline lattice held together by hydrogen bonds. Hydrogen bonds are highly versatile and, as a result, crystalline ice reveals a striking diversity of at least 16 different structures.In all of these forms of ice, the simple H2O molecule is the universal building block. However, in 1964 it was predicted that, under sufficient pressure, the hydrogen bonds could strengthen to the point where they might actually break the water molecule apart. The possibility of directly observing a disassociated water molecule in ice has proven a fascinating lure for scientists and has driven extensive research for the last 50 years. In the mid-1990s several teams, including a Carnegie group, observed the transition using spectroscopic techniques. However, these techniques are indirect and could only reveal part of the picture.A preferred method is to “see” the hydrogen atoms-or protons-directly. This can be done by bouncing neutrons off the ice and then carefully measuring how they are scattered. However, applying this technique at high enough pressures to see the water molecule dissociate had simply not been possible in the past. Guthrie explained that: “you can only reach these extreme pressures if your samples of ice are really small. …

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‘Dust trap’ around young star solves long-standing planet formation mystery

June 6, 2013 — Astronomers using the new Atacama Large Millimeter/submillimeter Array (ALMA) have imaged a region around a young star where dust particles can grow by clumping together. This is the first time that such a dust trap has been clearly observed and modelled. It solves a long-standing mystery about how dust particles in discs grow to larger sizes so that they can eventually form comets, planets and other rocky bodies. The results are published in the journal Science on 7 June 2013.Astronomers now know that planets around other stars are plentiful. But they do not fully understand how they form and there are many aspects of the formation of comets, planets and other rocky bodies that remain a mystery. However, new observations exploiting the power of ALMA are now answering one of the biggest questions: how do tiny grains of dust in the disc around a young star grow bigger and bigger — to eventually become rubble, and even boulders well beyond a metre in size?Computer models suggest that dust grains grow when they collide and stick together. However, when these bigger grains collide again at high speed they are often smashed to pieces and sent back to square one. Even when this does not happen, the models show that the larger grains would quickly move inwards because of friction between the dust and gas and fall onto their parent star, leaving no chance that they could grow even further.Somehow the dust needs a safe haven where the particles can continue growing until they are big enough to survive on their own [1]. Such “dust traps” have been proposed, but there was no observational proof of their existence up to now.Nienke van der Marel, a PhD student at Leiden Observatory in the Netherlands, and lead author of the article, was using ALMA along with her co-workers, to study the disc in a system called Oph-IRS 48 [2]. They found that the star was circled by a ring of gas with a central hole that was probably created by an unseen planet or companion star. …

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Lightest exoplanet to be directly observed so far? Faint object moves near bright star

June 3, 2013 — A team of astronomers using ESO’s Very Large Telescope has imaged a faint object moving near a bright star. With an estimated mass of four to five times that of Jupiter, it would be the least massive planet to be directly observed outside the Solar System. The discovery is an important contribution to our understanding of the formation and evolution of planetary systems.Although nearly a thousand exoplanets have been detected indirectly — most using the radial velocity or transit methods [1] — and many more candidates await confirmation, only a dozen exoplanets have been directly imaged. Nine years after ESO’s Very Large Telescope captured the first image of an exoplanet, the planetary companion to the brown dwarf 2M1207, the same team has caught on camera what is probably the lightest of these objects so far [2][3].”Direct imaging of planets is an extremely challenging technique that requires the most advanced instruments, whether ground-based or in space,” says Julien Rameau (Institut de Planetologie et d’Astrophysique de Grenoble, France), first author of the paper announcing the discovery. “Only a few planets have been directly observed so far, making every single discovery an important milestone on the road to understanding giant planets and how they form.”In the new observations, the likely planet appears as a faint but clear dot close to the star HD 95086. A later observation also showed that it was slowly moving along with the star across the sky. This suggests that the object, which has been designated HD 95086 b, is in orbit around the star. Its brightness also indicates that it has a predicted mass of only four to five times that of Jupiter.The team used NACO, the adaptive optics instrument mounted on one of the 8.2-metre Unit Telescopes of ESO’s Very Large Telescope (VLT). This instrument allows astronomers to remove most of the blurring effects of the atmosphere and obtain very sharp images. The observations were made using infrared light and a technique called differential imaging, which improves the contrast between the planet and dazzling host star.The newly discovered planet orbits the young star HD 95086 at a distance of around 56 times the distance from Earth to the Sun, twice the Sun-Neptune distance. …

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