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16

Science and Information / Hubble finds planet orbiting pair of stars

« on: January 15, 2017, 08:31:44 PM »

Astronomers using NASA's Hubble Space Telescope, and a trick of nature, have confirmed the existence of a planet orbiting two stars in the system OGLE-2007-BLG-349, located 8,000 light-years away towards the center of our galaxy.

The planet orbits roughly 300 million miles from the stellar duo, about the distance from the asteroid belt to our sun. It completes an orbit around both stars roughly every seven years. The two red dwarf stars are a mere 7 million miles apart, or 14 times the diameter of the moon's orbit around Earth.

The Hubble observations represent the first time such a three-body system has been confirmed using the gravitational microlensing technique. Gravitational microlensing occurs when the gravity of a foreground star bends and amplifies the light of a background star that momentarily aligns with it. The particular character of the light magnification can reveal clues to the nature of the foreground star and any associated planets.

The three objects were discovered in 2007 by an international collaboration of five different groups: Microlensing Observations in Astrophysics (MOA), the Optical Gravitational Lensing Experiment (OGLE), the Microlensing Follow-up Network (MicroFUN), the Probing Lensing Anomalies Network (PLANET), and the Robonet Collaboration. These ground-based observations uncovered a star and a planet, but a detailed analysis also revealed a third body that astronomers could not definitively identify.

"The ground-based observations suggested two possible scenarios for the three-body system: a Saturn-mass planet orbiting a close binary star pair or a Saturn-mass and an Earth-mass planet orbiting a single star," explained David Bennett of the NASA Goddard Space Flight Center in Greenbelt, Maryland, the paper's first author.

The sharpness of the Hubble images allowed the research team to separate the background source star and the lensing star from their neighbors in the very crowded star field. The Hubble observations revealed that the starlight from the foreground lens system was too faint to be a single star, but it had the brightness expected for two closely orbiting red dwarf stars, which are fainter and less massive than our sun. "So, the model with two stars and one planet is the only one consistent with the Hubble data," Bennett said.

Bennett's team conducted the follow-up observations with Hubble's Wide Field Planetary Camera 2. "We were helped in the analysis by the almost perfect alignment of the foreground binary stars with the background star, which greatly magnified the light and allowed us to see the signal of the two stars," Bennett explained.

Kepler has discovered 10 other planets orbiting tight binary stars, but these are all much closer to their stars than the one studied by Hubble.

Now that the team has shown that microlensing can successfully detect planets orbiting double-star systems, Hubble could provide an essential role in this new realm in the continued search for exoplanets.

The team's results have been accepted for publication in The Astronomical Journal.

17

Science and Information / Colorful demise of a sun-like star

« on: January 15, 2017, 08:31:19 PM »

This image, taken by the NASA/ESA Hubble Space Telescope, shows the colorful "last hurrah" of a star like our sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow.

The burned-out star, called a white dwarf, is the white dot in the center. Our sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years.

Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers called them the name because through small telescopes they resembled the disks of the distant planets Uranus and Neptune. The planetary nebula in this image is called NGC 2440. The white dwarf at the center of NGC 2440 is one of the hottest known, with a surface temperature of more than 360,000 degrees Fahrenheit (200,000 degrees Celsius).

The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bowtie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.

The material expelled by the star glows with different colors depending on its composition, its density and how close it is to the hot central star. Blue samples helium; blue-green oxygen, and red nitrogen and hydrogen.

18

Science and Information / New low-mass objects could help refine planetary evolution

« on: January 15, 2017, 08:30:52 PM »

When a star is young, it is often still surrounded by a primordial rotating disk of gas and dust, from which planets can form. Astronomers like to find such disks because they might be able to catch the star partway through the planet formation process, but it's highly unusual to find such disks around brown dwarfs or stars with very low masses. New work from a team led by Anne Boucher of Université de Montréal, and including Carnegie's Jonathan Gagné and Jacqueline Faherty, has discovered four new low-mass objects surrounded by disks.

The results will be published by The Astrophysical Journal.

Three of the four objects discovered by these researchers are quite small, somewhere between only 13 and 18 times the mass of Jupiter. The fourth has about 120 times Jupiter's mass. (For comparison the Sun is just over 1,000 times more massive than Jupiter.)

"Finding disks in low-mass systems is really interesting to us, because objects that exist at the lower limit of what defines a star and that still have disks that indicate planet formation can tell us a lot about both stellar and planetary evolution," said first author Boucher, who works at her university's Institute for Research on Exoplanets (iREx).

In a planet-forming disk, the dust grains collide and aggregate to form pebbles, which grow into boulders, and so on, increasing in size through planetesimals, planetary embryos, and finally rocky terrestrial planets (some of which then become the cores for gas giant planets). Astronomers are able to identify these types of planet-birthing disks, because the star heats up the surrounding dust, which affects the way it looks using a telescope with an infrared camera.

However, some disks indicate that planet formation isn't ongoing, but has already finished. These disks are made up of the debris left behind by all the collisions during planet formation and by subsequent collisions of the newly formed planets. Eventually these dusty remains are swept away. But until that happens, a cooler, thinner ring of dust surrounds the star.

Some disks even represent an intermediate stage between the planet-forming and dusty remnant phases.

It's important for astronomers to try to distinguish between these different types of disks, because then they can better chart the way planetary systems, including our own Solar System, are born and change over time.

The research team was able to determine that the disks surrounding their four newly discovered low-mass objects were all likely in a phase of planet forming. None were in the dusty aftermath phase.

Even more interesting, two of the objects are possibly between 42 and 45 million years old. This would make them the oldest objects surrounded by active disk systems ever found.

"There is still so much to learn about disks around low-mass objects such as these four," concluded Gagné, who is also a iREx collaborator. "Hopefully, we can conduct further research on them and be able to narrow down what kind of activity is happening in them and whether or not they would be good targets for future planet hunters."

The other co-authors are: David Lafrenière and René Doyon of Université de Montréal, and Lison Malo of the Canada-France-Hawaii Telescope.

This work was supported by Fonds de Recherche du Québec -- Nature et Technologies, the Natural Science and Engineering Research Council of Canada, and the Centre de Recherche en Astrophysique du Québec.

19

Science and Information / Spiral arms in protoplanetary disk: They're not just for galaxies any more

« on: January 15, 2017, 08:30:32 PM »

Astronomers have found distinct spiral arms in the disk of gas and dust surrounding the young star Elias 2-27. While similar features have been observed on the surfaces of such disks before, this is the first time they have been identified within the disk, where planet formation takes place. Structures such as these could either indicate the presence of a newly formed planet, or else create the necessary conditions for a planet to form. As such, the results are a crucial step towards a better understanding how planetary systems like our Solar system came into being. The results have been published in the journal Science.

An international team of astronomers has obtained the first image of a spiral structure seen in thermal dust emission coming from a protoplanetary disk, the potential birthplace of a new Solar System. Such structures are thought to play a key role in allowing planets to form around young stars. The researchers used the international observatory ALMA to image the disk around the young star Elias 2-27, in the constellation Ophiuchus, at a distance of about 450 light-years from Earth.

The group is led by Laura Pérez, an Alexander von Humboldt Research Fellow from the Max Planck Institute for Radio Astronomy in Bonn, and includes Hendrik Linz and Thomas Henning from the Max Planck Institute for Astronomy in Heidelberg.

Disks: Birthplace of Planets

Planets are formed in disks of gas and dust around newborn stars. But while this general concept goes way back, astronomers have only recently gained the ability to observe such disks directly. One early example is the discovery of disk silhouettes in front of extended emission in the Orion Nebula by the Hubble Space Telescope in the 1990s, the so-called proplyds. The ability to observe not only each disk as a whole, but also its sub-structure, is more recent still. Gaps in a protoplanetary disks, in the form of concentric rings, were first observed with ALMA in 2014.

These new observations are of particular interest to anyone interested in the formation of planets. Without structures such as this giant spiral, planets might not been able to form in the first place! The reason is as follows: In a smooth disk, planets can only grow step by step. Dust particles within the gas of the disk occasionally collide and clump together, and by successive collisions, ever larger particles, grains, and eventually solid bodies form.

But as soon as such bodies reach a size of about one meter, drag by the surrounding gas of the disk will make them migrate inwards, towards the star, on a time scale of 1000 years or shorter. The time needed for such bodies to collect sufficient mass by successive collisions, eventually reaching a size where gas drag becomes a negligible influence, is much larger than that.

No structure, no planets

So how can bodies larger than about a meter form in the first place? Without a good explanation, we could not understand how planetary systems, including our own solar system, came into being in the first place.

There are several possible mechanisms that would allow primordial rocks to grow larger more quickly, until they finally reach a size were mutual gravitational attraction forms them into full-size planets. "The observed spirals in Elias 2-27 are the first direct evidence for the shocks of spiral density waves in a protoplanetary disk", says Laura M. Pérez from MPIfR, the leading author of the paper. "They show that density instabilities are possible within the disk, which can eventually lead to strong disk inhomogeneities and further planet formation." Such instabilities are not confined to the scale of planet formation. In fact, the best-known example are density waves in disk galaxies, which create the spectacular spiral arms of spiral galaxies.

In regions of increased density, as those corresponding to the observed density waves, planet formation could proceed much faster, both due to those region's gravity and due to the more confined space, which would make collisions of grains or rocks more probable. In this way, the problem of how to go beyond meter or ten-meter size objects could be solved.

On the other hand, planets that have already started forming within a disk can launch spiral waves in the disk as they orbit their host stars. Distinguishing those two roles of spiral and other features -- consequences of planet formation, or the cause of it? -- will require a deeper understanding of such features, which in turn requires high-resolution images that show details of these structures.

Understanding the diversity of planets

Thomas Henning, director at the Max Planck Institute for Astronomy (MPIA) and one of the scientists involved, says: "For years, we couldn't discern details in the disks around young stars. Now we see them in all their beauty and diversity, including the spiral structure we just found. This will help us improve our understanding of planet formation."

Hendrik Linz (MPIA) adds: "Over the last two decades, astronomers have found an astounding variety of exoplanets. In order to explain this variety, we need to understand the early phases of planet formation -- and the strikingly detailed ALMA pictures will help us with that!"

A specific example: The two sweeping spiral arms in Elias 2-27 extend more than 10 billion kilometers away from the newborn star, at a larger distance than the location of the Kuiper Belt in our Solar System. "The presence of spiral density waves at these extreme distances may help explain puzzling observations of extrasolar planets at similar far-away locations," Pérez notes, "such planets cannot form in-situ under our standard picture of planet formation."

High-resolution observations

The young star Elias 2-27 targeted by the new ALMA observations is a member of a much larger star-forming region known as the ρ-Ophiuchus star-forming complex. Elias 2-27 is estimated to have formed about a million years ago; a very short time, compared to the age of our Sun of 4.6 billion years.

The star was already known to have a circumstellar disk, but judging by previous observations (at resolutions showing details in the range of 0.6″-1.1″) this appeared to bea featureless, axisymmetric disk. The new ALMA observations with a spatial resolution of 0.24'' were made in the millimeter wave regime, at a wavelength of 1.3 millimeters. They trace the thermal emission from dust grains, which may make up between 1 and 10% (by mass) of protoplanetary disks.

In this way, astronomers were able to trace a gigantic spiral pattern at distances between about 100 astronomical units (that is, 100 times the average distance of the Sun from the Earth) and 300 astronomical units away from the central star. The interaction with a planet that has already formed and is now orbiting within the disk is one plausible explanation for these spiral features.

ALMA detected a narrow band in the disk with significantly less dust, but such a small gap is not consistent with the large planet needed to create the observed spiral arms. On the other hand, the disk's own gravity causes instabilities which can trigger the formation of the spiral pattern. Taking into account estimates for the total mass of the disk, and the shape and symmetry of the spiral pattern, the authors consider this possibility as also likely.

As similar observations with ALMA become increasingly common, and more and more detailed images showing inhomogeneous structures in disk density become available, astronomers should be able to investigate the properties of such features, to eventually define their role in the planetary formation process.

20

Science and Information / Planet formation: The death of a planet nursery?

« on: January 15, 2017, 08:30:06 PM »

When the maps appeared at the end of March, experts were electrified. The images revealed an orange-red disk pitted with circular gaps that looked like the grooves in an old-fashioned long-playing record. But this was no throwback to the psychedelic Sixties. It was a detailed portrait of a so-called protoplanetary disk, made up of gas and dust grains, associated with a young star -- the kind of structure out of which planets could be expected to form. Not only that, the maps showed that the disk around the star known as TW Hydrae exhibits several clearly defined gaps. Astronomers speculated that these gaps might indicate the presence of protoplanets, which had pushed away the material along their orbital paths. And to make the story even more seductive, one prominent gap is located at approximately the same distance from TW Hydrae as Earth is from the Sun -- raising the possibility that this putative exoplanet could be an Earth-like one.

Now an international team led by Professor Barbara Ercolano at LMU's Astronomical Observatory has compared the new observations with theoretical models of planet formation. The study indicates that the prominent gap in the TW Hydrae system is unlikely to be due to the action of an actively accreting protoplanet. Instead, the team attributes the feature to a process known as photoevaporation. Photoevaporation occurs when the intense radiation emitted by the parent star heats the gas, allowing it to fly away from the disk. But although hopes of a new exo-Earth orbiting in the inner gap of TW Hydrae may themselves have evaporated, the system nevertheless provides the opportunity to observe the dissipation of a circumstellar disk in unprecedented detail. The new findings appear in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

Only 175 light-years from Earth

The dusty disk that girdles TW Hydrae has long been a favored object of observation. The star lies only 175 light-years from Earth, and is it relatively young (around 106 years old). Moreover, the disk is oriented almost perpendicular to our line of sight, affording a well-nigh ideal view of its structure. The spectacular images released in March were made with the Atacama Large Millimeter/submillimeter Array (ALMA), an array of detectors in the desert of Northern Chile. Together, they form a radiotelescope with unparalleled resolving power that can detect the radiation from dust grains in the millimeter size range.

Photoevaporation is one of the major forces that shape the fate of circumstellar disks. Not only can it destroy such disks -- which typically have a life expectancy of around 10 million years -- it can also stop young planets being drawn by gravity and by the interaction with the surrounding disc gas into their parent star. The gaps caused by the action of photoevaporation on the disk, park the planets at their location by removing the gas, allowing the small dusty clumps to grow into fully fledged planets and steering them into stable orbits. However, in the case of the TW Hydrae system, Barbara Ercolano believes that the inner gap revealed by the ALMA maps is not caused by a planet, but represents an early stage in the dissipation of the disk. This view is based on the fact that many characteristic features of the disk around TW Hydrae, such as the distance between the gap and the star, the overall mass accretion rate, and the size and density distributions of the particles, are in very good agreement with the predictions of her photoevaporation model.

21

Science and Information / Researchers discover effect of rare solar wind on earth's radiation belts

« on: January 15, 2017, 08:29:43 PM »

Researchers from the University of New Hampshire have captured unique measurements of the Van Allen radiation belts, which circle Earth, during an extremely rare solar wind event. The findings, which have never been reported before, may be helpful in protecting orbiting telecommunication and navigational satellites, and possibly future astronauts, by helping to more accurately predict space conditions near Earth, as well as around more remote planets.​

The study was published in the journal Nature Communications.

The UNH researchers used data from more than 10 spacecrafts, including information from a UNH-led instrument on board NASA's Van Allen Probes twin satellites, to get measurements of both Earth's inner and outer Van Allen radiation belts, two donut-shaped regions of high-energy particles trapped by Earth's magnetic field, during the uncommon solar wind conditions. The results revealed valuable information of unexpected and dramatic changes in the radiation belts allowing scientists to explore the effect of similar conditions around other Earth-like planets at other stars.

"What makes this very exciting is that this type of interaction between the sun and a planet rarely happens for Earth but it's believed to be a frequent occurrence for other Earth-like extrasolar planets," said Noé Lugaz, a research associate professor at UNH's Institute for the Study of Earth, Oceans, and Space (EOS), and lead author of the study. "Since the closest of these extrasolar planets is several light years away, these measurements help give us a sense of the radiation conditions that might be occurring around some of those distant worlds, that will never be visited in our lifetime."

Earth is embedded in the always-expanding atmosphere of the sun, called the solar wind, which blows past planets to the edge of the solar system. Typically, the solar wind is supersonic, faster than the speed of sound. When the solar wind encounters planets, like Earth, a shock wave is created that slows the wind down and deflects it around the planet. However, during the unusual episode, which was caused by the passage of a solar eruption over Earth, the data recorded by the researchers showed the solar wind became subsonic, or slower than the speed of sound. During this interval is when the researchers recorded measurements of the Van Allen radiations belts, and found that the outer belt was not as calm as expected. Two unusual phenomena occurred; a long-lasting electron drop in Earth's radiation belts and large oscillations in the magnetic field.

"This is the first time detailed measurements of Earth's radiation belts have ever been recorded during such rare conditions," said Harlan Spence, director of EOS at UNH and a co-author of the study. "There have only been a handful of these solar wind events since the beginning of space exploration."

When the Van Allen belts were first discovered in the 1950s they were thought to be relatively stable structures, but subsequent observations have shown they are dynamic and mysterious. Unlocking these mysteries could be valuable for newer technologies like telecommunication and GPS satellites which spend most of their time in the Van Allen belts.

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Science and Information / Chaos in cosmos: System of two stars with three planet-forming discs of gas

« on: January 15, 2017, 08:29:21 PM »

A star with a ring of planets orbiting around it -- that is the picture we know from our own solar system and from many of the thousands of exoplanets observed in recent years. But now researchers from the Niels Bohr Institute have discovered a system consisting of two stars with three rotating planet-forming accretion discs around them. It is a binary star where each star has its own planet-forming disc and in addition, there is one large shared disc. All three planet-forming discs are misaligned in relation to one another. The spectacular results are published in the scientific journal, Astrophysical Journal Letters.

A solar system is formed by a large cloud of gas and dust. The cloud of gas and dust condenses and eventually becomes so compact that it collapses into a ball of gas in the centre. Here the pressure heats up the matter and creates a glowing ball of gas, a star. The remainder of the gas and dust cloud rotates as a disc around the newly formed star. In this rotating disc of gas and dust, the material begins to accumulate and form larger and larger clumps, which finally become planets.

Often it is not just one, but two stars that are formed in the dense cloud of gas and dust. This is called a binary star and they are held together by their mutual gravity and orbit in a path around each other. About half of all stars are binary stars and they can each have a rotating disc of gas and dust.

Never before seen

But now the researchers have observed something highly unusual: a binary star with not just two, but three rotating gas discs.

"The two newly formed stars are both the size of our sun and they each have a rotating disc of gas and dust similar to the size of our solar system. In addition, they have a shared disc that is much larger and crosses over the other two discs. All three discs are staggered and this breaks with everything we have seen so far," says Christian Brinch, assistant professor in the research group Astrophysics and Planetary Science and the Niels Bohr International Academy at the Niels Bohr Institute, University of Copenhagen.

The stars were observed with the large international telescope, the Atacama Large Millimeter Array (ALMA) in northern Chile by an international team of researchers from Denmark, England and the Netherlands. The stars are about 400 light years away from the Earth. The stars are about 100-200,000 years old and planet formation may already have started. They cannot see this. But when they can see the accretion discs, it is because they are still mostly made up of gases.

Tumble around

"What we can observe is the gas itself, because the molecules are excited by the heat from the stars and therefore emit light in the infrared and microwave range. By studying the wavelength of the light you can see whether the light source is moving farther away or is getting closer. If the light shifts towards red wavelengths it is moving farther away, while blue shift light is moving closer and thus we can see that the three planet-forming discs are almost 'tumbling around' and are skewed relative to each other," explains Christian Brinch.

The researchers do not know why it is not a 'nice' system where the rotating discs of gas lie flat in relation to each other. Perhaps the formation occurred in a particularly turbulent manner.

"We will use computer simulations to try to understand the physics of the formation process. Perhaps it is a dynamic process of formation, which happens often and then it corrects itself later on. We will try to clarify this. We will also apply for more observation time on the ALMA telescope to study the planet-forming discs in even higher resolution to get more detailed information about their chemical composition," says Jes Jørgensen, associate professor in the research group Astrophysics and Planetary Science at the Niels Bohr Institute and Centre for Star and Planet Formation, University of Copenhagen.

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Science and Information / Tatooine worlds orbiting two suns often survive violent escapades of aging stars

« on: January 15, 2017, 08:28:58 PM »

Planets that revolve around two suns may surprisingly survive the violent late stages of the stars' lives, according to new research out of the NASA Goddard Space Flight Centre and York University. The finding is surprising because planets orbiting close to a single sun, like Mercury and Venus in our solar system, would be destroyed when the aging star swells into a red giant.

Led by Veselin Kostov at the NASA Goddard Space Flight Centre, in collaboration with York University master's student Keavin Moore and Professor Ray Jayawardhana, the study found that planets orbiting two (binary) stars -- also referred to as circumbinary planets or "Tatooine worlds" after the iconic planetary home of Luke Skywalker in Star Wars -- often escape death and destruction by moving out to wider orbits.

The paper, "Tatooine's Future: The Eccentric Response of Kepler's Circumbinary Planets to Common-Envelope Evolution of their Host Stars," has been accepted for publication in The Astrophysical Journal.

"This is very different from what will happen in our own solar system a few billion years from now, when our Sun starts to evolve and expand to such a tremendous size that it will engulf the inner planets, like Mercury and Venus and possibly Earth too, faster than they can migrate out to larger orbits," says Kostov. "It seems that if we had a second star in the center of our solar system, things might go differently."

Binary star systems are ubiquitous in the Universe and consist of two stars that orbit around a common center of gravity. If the two stars are close enough to each other, when one starts evolving and expanding into a giant, they exchange material and spiral towards each other resulting in their sharing a common atmosphere (also called a common envelope). The binary star system ends up losing a large amount of mass, or might be destroyed in a supernova explosion.

"Given the exciting recent discoveries of planets circling binary stars, some with orbits similar in size to that of Mercury around the Sun, we were curious to explore the ultimate fate of these Tatooine worlds," says Jayawardhana. "We found that many such planets are likely to survive the messy and violent late stages of their stars' lives by moving farther out."

The team, which also included Daniel Tamayo of the Canadian Institute for Theoretical Astrophysics and Stephen Rinehart of NASA Goddard, simulated the fate of nine circumbinary planets recently discovered by NASA's Kepler mission. They found that the planets will predominantly survive the common envelope phase -- even those orbiting very close to their stars. In addition, the planets can migrate to farther orbits similar to what it would be like if Venus moved out to where Uranus orbits our Sun. In some cases, planets can even reach more than twice the distance to Pluto.

Interestingly, when there are multiple planets orbiting a binary star, some can be ejected from the system, while others can switch places or even collide with their stars.

"The reconfiguration can be quite dramatic when there are several planets," says Moore. "Although all of the known circumbinary planets are gas giants, it is possible that somewhere out there is a terrestrial circumbinary planet that migrates to an orbit that now makes the planet potentially habitable for a little while."

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Science and Information / Possible formation site of icy giant planet spotted

« on: January 15, 2017, 08:28:35 PM »

A number of extrasolar planets have been found in the past two decades and now researchers agree that planets can have a wide variety of characteristics. However, it is still unclear how this diversity emerges. Especially, there is still debate about how the icy giant planets, such as Uranus and Neptune, form.

To take a close look at the planet formation site, a research team led by Takashi Tsukagoshi at Ibaraki University, Japan, observed the young star TW Hydrae. This star, estimated to be 10 million years old, is one of the closest young stars to the Earth. Thanks to the proximity and the fact that its axis of rotation points roughly in the Earth's direction, giving us a face-on-view of the developing planetary system, TW Hydrae is one of the most favorable targets for investigating planet formation.

Past observations have shown that TW Hydrae is surrounded by a disk made of tiny dust particles. This disk is the site of planet formation. Recent ALMA observations revealed multiple gaps in the disk. Some theoretical studies suggest that the gaps are evidence of planet formation.

The team observed the disk around TW Hydrae with ALMA in two radio frequencies. Since the ratio of the radio intensities in different frequencies depends on the size of the dust grains, researchers can estimate the size of dust grains. The ratio indicates that smaller, micrometer-sized, dust particles dominate and larger dust particles are absent in the most prominent gap with a radius of 22 astronomical units.

Why are smaller dust particles selectively located in the gap in the disk? Theoretical studies have predicted that a gap in the disk is created by a massive planet, and that gravitational interaction and friction between gas and dust particles push the larger dust out from the gap, while the smaller particles remain in the gap. The current observation results match these theoretical predictions.

Researchers calculated the mass of the unseen planet based on the width and depth of the 22 au gap and found that the planet is probably a little more massive than the Neptune. "Combined with the orbit size and the brightness of TW Hydrae, the planet would be an icy giant planet like Neptune," said Tsukagoshi.

Following this result, the team is planning further observations to better understand planet formation. One of their plans is to observe the polarization of the radio waves. Recent theoretical studies have shown that the size of dust grains can be estimated more precisely with polarization observations. The other plan is to measure the amount of gas in the disk. Since gas is the major component of the disk, the researchers hope to attain a better estimation of the mass of the forming planet.

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Science and Information / First Pluto, now this: Discovery of first binary-binary calls solar system forma

« on: January 15, 2017, 08:28:13 PM »

Everything we know about the formation of solar systems might be wrong, says University of Florida astronomy professor Jian Ge and his postdoc, Bo Ma. They've discovered the first "binary-binary" -- two massive companions around one star in a close binary system, one so-called giant planet and one brown dwarf, or "failed star" The first, called MARVELS-7a, is 12 times the mass of Jupiter, while the second, MARVELS-7b, has 57 times the mass of Jupiter.

Astronomers believe that planets in our solar system formed from a collapsed disk-like gaseous cloud, with our largest planet, Jupiter, buffered from smaller planets by the asteroid belt. In the new binary system, HD 87646, the two giant companions are close to the minimum mass for burning deuterium and hydrogen, meaning that they have accumulated far more dust and gas than what a typical collapsed disk-like gaseous cloud can provide. They were likely formed through another mechanism. The stability of the system despite such massive bodies in close proximity raises new questions about how protoplanetary disks form. The findings, which are now online, will be published in the November issue of the Astronomical Journal.

HD 87646's primary star is 12 percent more massive than our sun, yet is only 22 astronomical units away from its secondary, a star about 10 percent less massive than our sun, roughly the distance between the sun and Uranus in our solar system. An astronomical unit is the mean distance between the center of the Earth and our sun, but in cosmic terms, is a relatively short distance. Within such a short distance, two giant companions are orbiting the primary star at about 0.1 and 1.5 astronomical units away. For such large companion objects to be stable so close together defies our current popular theories on how solar systems form.

The planet-hunting Doppler instrument W.M. Keck Exoplanet Tracker, or KeckET, developed by a team led by Ge at the Sloan Digital Sky Survey telescope at Apache Point Observatory in New Mexico, is unusual in that it can simultaneously observe dozens of celestial bodies. Ge says this discovery would not have been possible without a multiple-object Doppler measurement capability such as KeckET to search for a large number of stars to discover a very rare system like this one. The survey of HD 87646 occurred in 2006 during the pilot survey of the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) of the SDSS-III program, and Ge led the MARVELS survey from 2008 to 2012. It has taken eight years of follow-up data collection through collaboration with over 30 astronomers at seven other telescopes around the world and careful data analysis, much of which was done by Bo Ma, to confirm what Ge calls a "very bizarre" finding.

The team will continue to analyze data from the MARVELS survey.

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Science and Information / Curious tilt of the Sun traced to undiscovered planet

« on: January 15, 2017, 08:27:52 PM »

Planet Nine the undiscovered planet at the edge of the solar system that was predicted by the work of Caltech's Konstantin Batygin and Mike Brown in January 2016 appears to be responsible for the unusual tilt of the Sun, according to a new study.

The large and distant planet may be adding a wobble to the solar system, giving the appearance that the Sun is tilted slightly.

"Because Planet Nine is so massive and has an orbit tilted compared to the other planets, the solar system has no choice but to slowly twist out of alignment," says Elizabeth Bailey, a graduate student at Caltech and lead author of a study announcing the discovery.

All of the planets orbit in a flat plane with respect to the Sun, roughly within a couple degrees of each other. That plane, however, rotates at a six-degree tilt with respect to the Sun giving the appearance that the Sun itself is cocked off at an angle. Until now, no one had found a compelling explanation to produce such an effect. "It's such a deep-rooted mystery and so difficult to explain that people just don't talk about it," says Brown, the Richard and Barbara Rosenberg Professor of Planetary Astronomy.

Brown and Batygin's discovery of evidence that the Sun is orbited by an as-yet-unseen planet that is about 10 times the size of Earth with an orbit that is about 20 times farther from the Sun on average than Neptune's changes the physics. Planet Nine, based on their calculations, appears to orbit at about 30 degrees off from the other planets' orbital plane in the process, influencing the orbit of a large population of objects in the Kuiper Belt, which is how Brown and Batygin came to suspect a planet existed there in the first place.

"It continues to amaze us; every time we look carefully we continue to find that Planet Nine explains something about the solar system that had long been a mystery," says Batygin, an assistant professor of planetary science.

Their findings have been accepted for publication in an upcoming issue of the Astrophysical Journal, and will be presented this week at the American Astronomical Society's Division for Planetary Sciences 48th annual meeting, held jointly in Pasadena, California, with the 11th European Planetary Science Congress.

The tilt of the solar system's orbital plane has long befuddled astronomers because of the way the planets formed: as a spinning cloud slowly collapsing first into a disk and then into objects orbiting a central star.

Planet Nine's angular momentum is having an outsized impact on the solar system based on its location and size. A planet's angular momentum equals the mass of an object multiplied by its distance from the Sun, and corresponds with the force that the planet exerts on the overall system's spin. Because the other planets in the solar system all exist along a flat plane, their angular momentum works to keep the whole disk spinning smoothly.

Planet Nine's unusual orbit, however, adds a multi-billion-year wobble to that system. Mathematically, given the hypothesized size and distance of Planet Nine, a six-degree tilt fits perfectly, Brown says.

The next question, then, is how did Planet Nine achieve its unusual orbit? Though that remains to be determined, Batygin suggests that the planet may have been ejected from the neighborhood of the gas giants by Jupiter, or perhaps may have been influenced by the gravitational pull of other stellar bodies in the solar system's extreme past.

For now, Brown and Batygin continue to work with colleagues throughout the world to search the night sky for signs of Planet Nine along the path they predicted in January. That search, Brown says, may take three years or more.

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Science and Information / More evidence for ninth planet roming Solar System's outer fringes

« on: January 15, 2017, 08:27:29 PM »

As the search for a hypothetical, unseen planet far, far beyond Neptune's orbit continues, research by a team of the University of Arizona provides additional support for the possible existence of such a world and narrows the range of its parameters and location.

Led by Renu Malhotra, a Regents' Professor of Planetary Sciences in the UA's Lunar and Planetary Lab, the team found that the four Kuiper Belt Objects with the longest known orbital periods revolve around the Sun in patterns most readily explained by the presence of a hypothetical "Planet Nine" approximately ten times the mass of Earth. Malhotra is presenting the results at the joint 48th meeting of the Division for Planetary Sciences of the American Astronomical Society and 11th European Planetary Science Congress in Pasadena, California.

According to the researchers' calculations, such a hypothetical planet would complete one orbit around the Sun roughly every 17,000 years and, at its farthest point from our central star, it would swing out more than 660 astronomical units, with one AU being the average distance between Earth and the Sun.

Scientists think that objects in the Kuiper Belt, a vast region of dwarf planets and icy rocks populating the fringes of our solar system beyond the orbit of Neptune, dance mostly to the tune of the giant planets, Saturn, Jupiter, Uranus and Neptune, influenced by their gravity either directly or indirectly.

However, there are a few known Kuiper Belt objects (KBOs) that are unlikely to be significantly perturbed by the known giant planets in their current orbits. Referred to as "extreme KBOs" (eKBOs) by the authors, all of these have extremely large orbital eccentricities, in other words, they get very close to the Sun at one point on their orbital journey, only to swing far out into space once they pass the Sun, on long elliptical orbits that take these strange mini worlds hundreds of AUs away from the Sun.

"We analyzed the data of these most distant Kuiper Belt objects," Malhotra said, "and noticed something peculiar, suggesting they were in some kind of resonances with an unseen planet."

In their paper, "Corralling a Distant Planet with Extreme Resonant Kuiper Belt Objects," Malhotra and her co-authors, Kathryn Volk and Xianyu Wang, point out peculiarities of the orbits of the extreme KBOs that went unnoticed until now: they found that the orbital period ratios of these objects are close to ratios of small whole numbers. An example of this would be one KBO traveling around the Sun once while another takes twice as long, or three times as long, or four times as long etc., but not, say, 2.7 times as long.

According to the authors, such ratios could arise most naturally if the extreme KBOs' orbital periods are in small whole number ratios with a massive planet, which would help to stabilize the highly elliptical orbits of eKBOs.

The findings bolster previous work by other scientists that showed that six of those bodies travel on highly eccentric orbits whose long axes all point in the same direction. This clustering of orbital parameters of the most distant KBOs suggested a large, planetary size body shepherding their orbits.

Another paper published earlier this year presented the results of numerical simulations providing a range of possibilities for the mass and orbit for such a hypothetical planet, that could account for the observed clustering of eKBO orbits.

"Our paper provides more specific estimates for the mass and orbit that this planet would have, and, more importantly, constraints on its current position within its orbit," Malhotra said.

The team's calculations also suggest two likely orbital planes for the planet: one moderately close to the mean plane of the solar system and near the mean plane of the four eKBOs at about 18 degrees, and one steeper plane, inclined at about 48 degrees.

While the results provide additional support for the idea of a potential "Planet Nine" and lay out possible scenarios, the authors stress that their paper should not be considered definitive proof of the planet's existence.

For one, the very far and faint KBOs haven't been observed for very long, and given their minuscule apparent motion along their immensely long journeys around the Sun, the estimates for their closeness to whole number ratios of orbital periods come with uncertainties that can be narrowed down only through more observations.

The authors also note that the long orbital timescales in this region of the outer solar system may allow formally unstable orbits to persist for very long times, possibly even to the age of the solar system, without the help of orbital resonances. In this scenario, orbits whose orderly parameters appear as testimony to the stabilizing influence of an unseen planet may in fact be in the process of deterioration but haven't been observed long enough for it to show.

Future observations and studies into the dynamical lifetimes of non-resonant planet-crossing orbits in the far regions of the outer solar system could help to further test the case for the existence and whereabouts of a ninth planet, Malhotra and her co-authors write.

Note: The above press release was issued by University of Arizona to coincide with a presentation at the joint 48th annual meeting of the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS) and 11th annual European Planetary Science Congress (EPSC).

28

Science and Information / Probing giant planets' dark hydrogen

« on: January 15, 2017, 08:22:54 PM »

Hydrogen is the most-abundant element in the universe. It's also the simplest--sporting only a single electron in each atom. But that simplicity is deceptive, because there is still so much we have to learn about hydrogen.

One of the biggest unknowns is its transformation under the extreme pressures and temperatures found in the interiors of giant planets, where it is squeezed until it becomes liquid metal, capable of conducting electricity. New work published in Physical Review Letters by Carnegie's Alexander Goncharov and University of Edinburgh's Stewart McWilliams measures the conditions under which hydrogen undergoes this transition in the lab and finds an intermediate state between gas and metal, which they're calling "dark hydrogen."

On the surface of giant planets like Jupiter, hydrogen is a gas. But between this gaseous surface and the liquid metal hydrogen in the planet's core lies a layer of dark hydrogen, according to findings gleaned from the team's lab mimicry.

Using a laser-heated diamond anvil cell to create the conditions likely to be found in gas giant planetary interiors, the team probed the physics of hydrogen under a range of pressures from 10,000 to 1.5 million times normal atmospheric pressure and up to 10,000 degrees Fahrenheit.

They discovered this unexpected intermediate phase, which does not reflect or transmit visible light, but does transmit infrared radiation, or heat.

"This observation would explain how heat can easily escape from gas giant planets like Saturn," explained Goncharov.

They also found that this intermediate dark hydrogen is somewhat metallic, meaning it can conduct an electric current, albeit poorly. This means that it could play a role in the process by which churning metallic hydrogen in gas giant planetary cores produces a magnetic field around these bodies, in the same way that the motion of liquid iron in Earth's core created and sustains our own magnetic field.

"This dark hydrogen layer was unexpected and inconsistent with what modeling research had led us to believe about the change from hydrogen gas to metallic hydrogen inside of celestial objects," Goncharov added.

29

Science and Information / Hubble confirms new dark spot on Neptune

« on: January 15, 2017, 08:22:37 PM »

New images obtained on May 16, 2016, by NASA's Hubble Space Telescope confirm the presence of a dark vortex in the atmosphere of Neptune. Though similar features were seen during the Voyager 2 flyby of Neptune in 1989 and by the Hubble Space Telescope in 1994, this vortex is the first one observed on Neptune in the 21st century.

The discovery was announced on May 17, 2016, in a Central Bureau for Astronomical Telegrams (CBAT) electronic telegram by University of California at Berkeley research astronomer Mike Wong, who led the team that analyzed the Hubble data.

Neptune's dark vortices are high-pressure systems and are usually accompanied by bright "companion clouds," which are also now visible on the distant planet. The bright clouds form when the flow of ambient air is perturbed and diverted upward over the dark vortex, causing gases to likely freeze into methane ice crystals. "Dark vortices coast through the atmosphere like huge, lens-shaped gaseous mountains," Wong said. "And the companion clouds are similar to so-called orographic clouds that appear as pancake-shaped features lingering over mountains on Earth."

Beginning in July 2015, bright clouds were again seen on Neptune by several observers, from amateurs to astronomers at the W. M. Keck Observatory in Hawaii. Astronomers suspected that these clouds might be bright companion clouds following an unseen dark vortex. Neptune's dark vortices are typically only seen at blue wavelengths, and only Hubble has the high resolution required for seeing them on distant Neptune.

In September 2015, the Outer Planet Atmospheres Legacy (OPAL) program, a long-term Hubble Space Telescope project that annually captures global maps of the outer planets, revealed a dark spot close to the location of the bright clouds, which had been tracked from the ground. By viewing the vortex a second time, the new Hubble images confirm that OPAL really detected a long-lived feature. The new data enabled the team to create a higher-quality map of the vortex and its surroundings.

Neptune's dark vortices have exhibited surprising diversity over the years, in terms of size, shape, and stability (they meander in latitude, and sometimes speed up or slow down). They also come and go on much shorter timescales compared to similar anticyclones seen on Jupiter; large storms on Jupiter evolve over decades.

Planetary astronomers hope to better understand how dark vortices originate, what controls their drifts and oscillations, how they interact with the environment, and how they eventually dissipate, according to UC Berkeley doctoral student Joshua Tollefson, who was recently awarded a prestigious NASA Earth and Space Science Fellowship to study Neptune's atmosphere. Measuring the evolution of the new dark vortex will extend knowledge of both the dark vortices themselves, as well as the structure and dynamics of the surrounding atmosphere.

The team, led by Wong, also included the OPAL team (Wong, Amy Simon, and Glenn Orton), UC Berkeley collaborators (Imke de Pater, Joshua Tollefson, and Katherine de Kleer), Heidi Hammel (AURA), Statia Luszcz-Cook (AMNH), Ricardo Hueso and Agustin Sánchez-Lavega (Universidad del Pais Vasco), Marc Delcroix (Société Astronomique de France), Larry Sromovsky and Patrick Fry (University of Wisconsin), and Christoph Baranec (University of Hawaii).

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Science and Information / ‘Building blocks for life' may originate in space

« on: January 15, 2017, 08:22:15 PM »

Amino acids are the building blocks for life on earth. They may originate in space and reach the earth via comets and meteorites. Daniël Paardekooper examined part of this hypothesis. PhD defence on 5 July.

In 2014 the Rosetta space probe reached a comet that is orbiting in our solar system. A small lander vehicle detected the presence of glycine on the comet, an unexpected discovery as the glycine molecule is an amino acid. Amino acids form the basis for proteins, and are an essential element of all life on earth. But how did these amino acids come to be present on earth?

Piggybacking on meteorites

'The discovery of glycine on the comet seems to indicate that amino acids are formed in space,' comments PhD candidate Daniël Paardekooper. 'It seems likely that these amino acids are able to enrich planetary biological matter by piggy-backing on meteorites.' Paardekooper set up a lab experiment in the Sackler Laboratory for Astrophysics to study this hypothesis.

Complex molecules

Paardekooper looked specifically at the conditions that are prevalent in dark instellar nebulae. Nebulae are clouds of gas, plasma and cold matter that occur in all galaxies. After millions of years, ice crusts form on these particles. The ice consists not only of water, but also of other frozen components, such as methane and methanol. These molecules can disintegrate if they are irradiated by high-energy light particles -- and there are plenty of these in space. Once they have disintegrated, the fragments interreact with one another and form larger and more complex molecules.

Fats and sugars

Paardekooper shows in his lab study that chemical reactions between separate particles can indeed take place on icy surfaces, comparable with the extreme circumstances in dark clouds. Paardekooper was able to produce fats and sugars in his experimental set-up. The expectation is that even more complex amino acids can originate on icy dust particles, although Paardekooper did not manage this last step. 'That will be the subject of my successor's dissertation.'

Unanswered

This does not confirm the hypothesis that amino acids reach the earth via comets and meteorites. There are questions that still have to be answered, such as whether they are able to survive a journey through the earth's atmosphere, or a crash landing on the earth's surface. Paardekooper: 'Somehow or other, the building blocks of life are present throughout the universe. That makes it more likely that other planets also meet the conditions for the origin of life.'