Stretched-out solid exoplanets

An artist’s impression of a stretched rocky planet in orbit around a red dwarf star. So close to the star, there is a difference in the strength of the gravitational field on each side of the planet, stretching it significantly.
Credit: Shivam Sikroria

Astronomers could soon be able to find rocky planets stretched out by the gravity of the stars they orbit, according to a group of researchers in the United States. The team, led by Prabal Saxena of George Mason University, describe how to detect these exotic worlds in a paper in the journal Monthly Notices of the Royal Astronomical Society.

Since the first discovery in 1993, more than 1800 planets have been found in orbit around stars other than our Sun. These 'exoplanets' are incredibly diverse, with some gaseous like Jupiter and some mostly rocky like the Earth. The worlds also orbit their stars at very different distances, from less than a million km to nearly 100 billion km away. Planets that are very close to their stars experience harsh conditions, often with very high temperatures (>1000 degrees Celsius) and significant stretching from the tidal forces resulting from the stellar gravitational field. This is most obvious with planets with a large atmosphere (so-called 'hot Jupiters') but harder to see with the rockier objects.

Prabal and his team modelled cases where the planets are in orbit close to small red dwarf stars, much fainter than our Sun, but by far the most common type of star in the Galaxy. The planets' rotation is locked, so the worlds keep the same face towards the stars they orbit, much like the Moon does as it moves around the Earth. According to the scientists, in these circumstances the distortion of the planets should be detectable in transit events, where the planets moves in front of their stars and blocks out some of their light.

If astronomers are able to find these extreme exoplanets, it could give them new insights into the properties of Earth-like planets as a whole. Prabal comments, "Imagine taking a planet like the Earth or Mars, placing it near a cool red star and stretching it out. Analysing the new shape alone will tell us a lot about the otherwise impossible to see internal structure of the planet and how it changes over time."

The subtle signals from stretched rocky planets could be found by some current telescopes, and certainly by much more powerful observatories like the James Webb Space Telescope (JWST) and the European Extremely Large Telescope (E-ELT) that are due to enter service in the next few years.

Source: Royal Astronomical Society (RAS)

Water vapor on Rosetta's target comet significantly different from that found on Earth

First measurements of comet’s water ratio. Credit: Copyright Spacecraft: ESA/ATG medialab; Comet: ESA/Rosetta/NavCam; Data: Altwegg et al. 2014

ESA's Rosetta spacecraft has found the water vapour from its target comet to be significantly different to that found on Earth. The discovery fuels the debate on the origin of our planet's oceans.

The measurements were made in the month following the spacecraft's arrival at Comet 67P/Churyumov-Gerasimenko on 6 August. It is one of the most anticipated early results of the mission, because the origin of Earth's water is still an open question.

One of the leading hypotheses on Earth's formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. But, today, two thirds of the surface is covered in water, so where did it come from?
In this scenario, it should have been delivered after our planet had cooled down, most likely from collisions with comets and asteroids. The relative contribution of each class of object to our planet's water supply is, however, still debated.

The key to determining where the water originated is in its 'flavour', in this case the proportion of deuterium -- a form of hydrogen with an additional neutron -- to normal hydrogen.

This proportion is an important indicator of the formation and early evolution of the Solar System, with theoretical simulations showing that it should change with distance from the Sun and with time in the first few million years.

One key goal is to compare the value for different kinds of object with that measured for Earth's oceans, in order to determine how much each type of object may have contributed to Earth's water.

Comets in particular are unique tools for probing the early Solar System: they harbour material left over from the protoplanetary disc out of which the planets formed, and therefore should reflect the primordial composition of their places of origin.

But thanks to the dynamics of the early Solar System, this is not a straightforward process. Long-period comets that hail from the distant Oort cloud originally formed in Uranus-Neptune region, far enough from the Sun that water ice could survive.

They were later scattered to the Solar System's far outer reaches as a result of gravitational interactions with the gas giant planets as they settled in their orbits.

Conversely, Jupiter-family comets like Rosetta's comet were thought to have formed further out, in the Kuiper Belt beyond Neptune. Occasionally these bodies are disrupted from this location and sent towards the inner Solar System, where their orbits become controlled by the gravitational influence of Jupiter.

Indeed, Rosetta's comet now travels around the Sun between the orbits of Earth and Mars at its closest and just beyond Jupiter at its furthest, with a period of about 6.5 years.

Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth's water, in observations made by ESA's Herschel mission in 2011.

By contrast, meteorites originally hailing from asteroids in the Asteroid Belt also match the composition of Earth's water. Thus, despite the fact that asteroids have a much lower overall water content, impacts by a large number of them could still have resulted in Earth's oceans.

It is against this backdrop that Rosetta's investigations are important. Interestingly, the D/H ratio measured by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, or ROSINA, is more than three times greater than for Earth's oceans and for its Jupiter-family companion, Comet Hartley 2. Indeed, it is even higher than measured for any Oort cloud comet as well.

"This surprising finding could indicate a diverse origin for the Jupiter-family comets -- perhaps they formed over a wider range of distances in the young Solar System than we previously thought," says Kathrin Altwegg, principal investigator for ROSINA and lead author of the paper reporting the results in the journal Science this week.

"Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth's oceans."

"We knew that Rosetta's in situ analysis of this comet was always going to throw up surprises for the bigger picture of Solar System science, and this outstanding observation certainly adds fuel to the debate about the origin of Earth's water," says Matt Taylor, ESA's Rosetta project scientist.

"As Rosetta continues to follow the comet on its orbit around the Sun throughout next year, we'll be keeping a close watch on how it evolves and behaves, which will give us unique insight into the mysterious world of comets and their contribution to our understanding of the evolution of the Solar System."

Source: ESA

How to estimate the magnetic field of an exoplanet

Artist's interpretation of Planet HD 209458b. Scientists have now estimated the value of the magnetic moment of the planet HD 209458b. Credit: NASA/ESA/CNRS/Alfred Vidal-Madjar

Scientists developed a new method which allows to estimate the magnetic field of a distant exoplanet, i.e., a planet, which is located outside the Solar system and orbits a different star. Moreover, they managed to estimate the value of the magnetic moment of the planet HD 209458b.The group of scientists including one of the researchers of the Lomonosov Moscow State University (Russia) published their article in the Science magazine.

In the two decades which passed since the discovery of the first planet outside the Solar system, astronomers have made a great progress in the study of these objects. While 20 years ago a big event was even the discovery of a new planet, nowadays astronomers are able to consider their moons, atmosphere and climate and other characteristics similar to the ones of the planets in the Solar system. One of the important properties of both solid and gaseous planets is their possible magnetic field and its magnitude. On Earth it protects all the living creatures from the dangerous cosmic rays and helps animals to navigate in space.

Kristina Kislyakova of the Space Research Institute of the Austrian Academy of Sciences in Graz together with an international group of physicists for the first time ever was able to estimate the value of the magnetic moment and the shape of the magnetosphere of the exoplanet HD 209458b. Maxim Khodachenko, a researcher at the Department of Radiation and computational methods of the Skobeltsyn Institute of Nuclear Physics of the Lomonosov Moscow State University, is also one of the authors of the article. He also works at the Space Research Institute of the Austrian Academy of Sciences.

Planet HD 209458b (Osiris) is a hot Jupiter, approximately one third larger and lighter than Jupiter. It is a hot gaseous giant orbiting very close to the host star HD 209458. HD 209458b accomplishes one revolution around the host star for only 3.5 Earth days. It has been known to astronomers for a long time and is relatively well studied. In particular, it is the first planet where the atmosphere was detected. Therefore, for many scientists it has become a model object for the development of their hypotheses.

Scientists used the observations of the Hubble Space Telescope of the HD 209458b in the hydrogen Lyman-alpha line at the time of transit, when the planet crosses the stellar disc as seen from Earth. At first, the scientists studied the absorption of the star radiation by the atmosphere of the planet. Afterwards they were able to estimate the shape of the gas cloud surrounding the hot Jupiter, and, based on these results, the size and the configuration of the magnetosphere.

"We modeled the formation of the cloud of hot hydrogen around the planet and showed that only one configuration, which corresponds to specific values of the magnetic moment and the parameters of the stellar wind, allowed us to reproduce the observations," explained Kristina Kislyakova.

To make the model more accurate, scientists accounted for many factors that define the interaction between the stellar wind and the atmosphere of the planet: so-called charge exchange between the stellar wind and the neutral atmospheric particles and their ionization, gravitational effects, pressure, radiation acceleration, and the spectral line broadening.

At present, scientists believe that the size of the atomic hydrogen envelope is defined by the interaction between the gas outflows from the planet and the incoming stellar wind protons. Similarly to Earth, the interaction of the atmosphere with the stellar wind occurs above the magnetosphere. By knowing the parameters of an atomic hydrogen cloud, one can estimate the size of the magnetosphere by means of a specific model.

Since direct measurements of the magnetic field of exoplanets are currently impossible, the indirect methods are broadly used, for example, using the radio observations. There exist a number of attempts to detect the radio emission from the planet HD 209458b. However, because of the large distances the attempts to detect the radio emission from exoplanets have yet been unsuccessful.

"The planet's magnetosphere was relatively small beeing only 2.9 planetary radii corresponding to a magnetic moment of only 10% of the magnetic moment of Jupiter," explained Kislyakova, a graduate of the Lobachevsky State University of Nizhny Novgorod. According to her, it is consistent with the estimates of the effectiveness of the planetary dynamo for this planet.

"This method can be used for every planet, including Earth-like planets, if there exist an extended high energetic hydrogen envelope around them," summarized Maxim Khodachenko.

Source: Lomonosov Moscow State University

Planet forming around star about 335 light years from Earth

An artist's conception of the young massive star HD100546 and its surrounding disk. A planet forming in the disk has cleared the disk within 13AU of the star, a distance comparable to that of Saturn from the sun. As gas and dust flows from the circumstellar disk to the planet, this material surrounds the planet as a circumplanetary disk (inset). These rotating disks are believed to be the birthplaces of planetary moons, such as the Galilean moons that orbit Jupiter. While they are theoretically predicted to surround giant planets at birth, there has been little observational evidence to date for circumplanetary disks outside the solar system. Brittain et al. (2014) report evidence for an orbiting source of carbon monoxide emission whose size is consistent with theoretical predictions for a circumplanetary disk. Observations over 10 years trace the orbit of the forming planet from behind the near side of the circumstellar disk in 2003 to the far side of the disk in 2013. These observations provide a new way to study how planets form. Credit: P. Marenfeld & NOAO/AURA/NSF

Dr. John Carr, a scientist at the U.S. Naval Research Laboratory (NRL), is part of an international team that has discovered what they believe is evidence of a planet forming around a star about 335 light years from Earth. This research is published in the August 20th issue of The Astrophysical Journal.

Carr and the other research team members set out to study the protoplanetary disk around a star known as HD 100546, and as sometimes happens in scientific inquiry, it was by "chance" that they stumbled upon the formation of the planet orbiting this star. A protoplanetary disk, or circumstellar disk, is a very large disk of material orbiting a newly formed star out of which a planetary system may form. The team was studying the warm gas in this disk using a technique called spectro-astrometry, which allows astronomers to detect small changes in the position of moving gas.

The researchers discovered an "extra" source of gaseous emission from carbon monoxide molecules that could not be explained by the protoplanetary disk alone. By tracking the changes in velocity and position of this extra emission over the years of the observations, they were able to show that it is orbiting around the young star. The distance from the star is somewhat larger than the distance of Saturn from the Sun. The evidence suggests that they are observing hot gas that surrounds an orbiting young planet. Carr points out that rather than seeing the planet directly, they are detecting the gas as it swirls around and onto the forming planet.

Through modeling carried out by Dr. Sean Brittain, a Clemson University astrophysicist and the lead author on the paper, and with additional data gathered by the team to confirm their initial hypothesis, they were able to investigate the extra emission as it orbited the star. The authors concluded that a likely explanation for the observations is a small circumplanetary disk of hot gas orbiting a forming planet. The candidate planet would be a gas giant at least three times the mass of Jupiter. The theory is that material from the large protoplanetary disk feeds into the circumplanetary disk, which then feeds onto the growing planet. Hence, a circumplanetary disk plays a mediating role in the growth of the planet. The remnants of a circumplanetary disk could also give birth to moons, such as those seen around Jupiter in our solar system. As Carr explains, a novel aspect of this new evidence for planet formation is the possible detection of a circumplanetary disk.

The team's study is based on four sets of observations gathered in 2003, 2006, 2010, and 2013. They used the Gemini Observatory and the Very Large Telescope at the European Southern Observatory, both located in Chile. The Gemini Observatory consists of twin 8.1-meter diameter optical/infrared telescopes located on mountains in Hawaii and Chile. The VLT is not just one telescope, but an array of four, each with a main mirror of 8.2 meters in diameter. The data were collected using high-resolution infrared spectrographs that allowed precise measurements of the motions of molecular gas surrounding the star.

"These results provide a rare opportunity," Carr says, "to study planet formation in action. Our analysis strongly suggests we are observing a disk of hot gas that surrounds a forming giant planet in orbit around the star. While such circumplanetary disks have been theorized to surround giant planets at birth and to control the flow of gas onto the growing planet, these findings are the first observational evidence for their existence. If our interpretation is correct, we are essentially seeing a planet caught in the act of formation."

Looking ahead, the team would like to continue to monitor the motion of the planet and obtain additional data to better define the properties of the circumplanetary disk. They predict that the planet and its disk will disappear from view in about two years time when they become hidden by the inner edge of the circumstellar disk. So, if the team's model is correct, the signature of the orbiting planet will not be seen for another 15 years until its orbit brings it back into view.

Source: Naval Research Laboratory

Jupiter's moons remain slightly illuminated, even in eclipse

A schematic image of the model to show that the Galilean satellites eclipsed in Jovian shadow are illuminated by scattered sunlight by the haze in the Jovian upper atmosphere. The size and the distance of the satellites are not to the scale. This process is similar to one that causes red color of the Earth’s Moon during its total eclipse. Credit: NASA, JAXA, Tohoku University

Astronomers using the Subaru Telescope and Hubble Space Telescope have found that Jupiter's Galilean satellites (Io, Europa, Ganymede, and Callisto) remain slightly bright (up to one millionth of their normal state) even when in the Jovian shadow and not directly illuminated by the Sun. The effect is particularly pronounced for Ganymede and Callisto. The finding was made by researchers at Tohoku University, Institute of Space and Astronautical Science/Japan Aerospace Exploration Agency (ISAS/JAXA), National Astronomical Observatory of Japan (NAOJ), and elsewhere.

The mechanism of this phenomenon is still under investigation, but the researchers suggest that indirect forward scattering of sunlight by hazes in the upper Jovian atmosphere could be the reason for the illumination. This effect is similar to the one that causes Earth's moon to look red during a total lunar eclipse.

The type of continuous observations of the Galilean satellites in eclipse made by the Japanese team also provides a much better basis for studying the hazes in Jupiter's atmosphere, which are difficult to study otherwise (Note 1). In addition, this detailed study method for a planetary atmosphere will provide new insights about the atmospheres of exoplanets, which are only beginning to be studied.

Dr. Tsumura Kohji (FRIS, Tohoku University), the PI on the project, explained that this unexpected finding is really the outcome of attempts to measure diffuse light from the distant universe. "It is a serendipitous discovery made as a by-product of a cosmological study," he said. "It is very interesting that it provides us a new method to investigate the atmosphere of Jupiter and of exoplanets. I will keep studying from nearby space (the solar system and exoplanets) out to the farthest universe through this project."

The research team started its observations with the Subaru Telescope in February of 2012. 
The idea was to detect the diffuse light from the most distant parts of the universe. To do this, team members planned to use the Galilean satellites in eclipse as "occulters" to block distant background emissions. This would allow an extremely accurate separation of the background light from the very bright foreground radiation from our solar system (known as the zodiacal light).

The team assumed that the Galilean satellites would be "dark" while in Jupiter's shadow, and the difference in brightness[??] between the dark satellite as an occulter and its surrounding sky would allow the team to determine the still-unknown level of background emission from the distant universe. Instead, they found an unexpected surprise: Ganymede and Callisto were still somewhat "bright" (illuminated) even when eclipsed (relative to the expected level of near-zero). Their eclipsed luminosity was one millionth of their un-eclipsed brightness, which is low enough that this phenomenon has been undetected until now.

To understand why the Galileans remain ever-so-slightly bright even when they're in eclipse, the project team of astronomers and planetary scientists considered several theories based on their multi-band observational data, including data from Spitzer Space Telescope. The most plausible is that the Galilean satellites are still illuminated during eclipse by sunlight that is scattered by hazes in the Jovian upper atmosphere. By comparison, the sunlight refracted in the atmosphere does not contribute to the illumination during the eclipse.

Although Jupiter is a familiar planet, there are many unresolved issues about its atmosphere. One example is the origin of the cloud particles composing Jupiter's banded appearance. The cloud particles are assumed to grow from tiny particles called aerosols or hazes. Researchers expect that those hazes form somewhere in the upper part of Jupiter's atmosphere, which is very difficult to observe. The unexpected discovery of haze-induced brightening of the Galileans provides a new way to study the mysterious part of Jupiter's atmosphere. In addition, since astronomers usually observe the planets in our solar system by reflected sunlight, one of the unique aspects of these new observations at Jupiter is that observers can precisely measure the transmitted sunlight through the planetary atmosphere (Note 2).

This new method of studying the upper atmosphere of Jupiter via transmitted sunlight provides a basis for the study of other planetary systems. Exoplanet discoveries now occur quite regularly and atmospheres around some of them have been investigated using "transit observations" (when the exoplanet passes between us and the host star, resulting in the star becoming slightly dimmer). In such observations, some characteristics of the exoplanet's atmosphere are revealed as host starlight passes through it. This is the same situation seen with Jupiter and its Galilean satellites, and makes studies of transmitted sunlight of the planets in our solar system essential for comparison.

The observations for this project were very challenging because the Galilean satellites (while eclipsed) are extremely faint and they are located next to the incredibly bright disk of Jupiter. In addition, the eclipses only happen at very specific times, and Jupiter and the satellites are continuously in motion during the observations. The complexity of the situation requires the observation procedure to be much more sophisticated. This new discovery required thorough preparations by the project team and conscientious support by the operations staff.

Source: National Astronomical Observatory of Japan

Jupiter's Great Red Spot is smaller than ever seen before

Jupiter's monster storm, the Great Red Spot, was once so large that three Earths would fit inside it. But new measurements by NASA's Hubble Space Telescope reveal that the largest storm in our solar system has downsized significantly. The Great Red Spot, which has been raging for at least a hundred years, is only the width of one Earth. What is happening? One possibility is that some unknown activity in the planet's atmosphere may be draining energy and weakening the storm, causing it to shrink. The Hubble images were taken in 1995, 2009, and 2014. Credit: mage: NASA, ESA, and A. Simon (GSFC);Science: A. Simon (GSFC), G. Orton (JPL), J. Rogers (Univ. of Cambridge, UK), and M. Wong and I. de Pater (Univ. of California, Berkeley);Acknowledgment: C. Go, H. Hammel (SSI, Boulder, and AURA), and R. Beebe (NMSU)

Jupiter's trademark Great Red Spot -- a swirling anticyclonic storm feature larger than Earth -- has shrunken to the smallest size ever measured. Astronomers have followed this downsizing since the 1930s. Jupiter's Great Red Spot is a churning anticyclonic storm.

"Recent Hubble Space Telescope observations confirm that the Great Red Spot (GRS) is now approximately 10,250 miles across, the smallest diameter we've ever measured," said Amy Simon of NASA's Goddard Space Flight Center in Greenbelt, Maryland. Historic observations as far back as the late 1800s gauged the GRS to be as big as 25,500 miles on its long axis. The NASA Voyager 1 and Voyager 2 flybys of Jupiter in 1979 measured the GRS to be 14,500 miles across.

Starting in 2012, amateur observations revealed a noticeable increase in the spot's shrinkage rate. The GRS's "waistline" is getting smaller by 580 miles per year. The shape of the GRS has changed from an oval to a circle. The cause behind the shrinking has yet to be explained.

"In our new observations it is apparent that very small eddies are feeding into the storm," said Simon. "We hypothesized that these may be responsible for the sudden change by altering the internal dynamics and energy of the Great Red Spot."

Simon's team plans to study the motions of the small eddies and also the internal dynamics of the GRS to determine if these eddies can feed or sap momentum entering the upwelling vortex.

In the comparison images on the right, the Hubble photo at top was taken in 1995, when the long axis of the GRS was estimated to be 13,020 miles across. In the 2009 photo the GRS was measured at 11,130 miles across.

The full disk image of Jupiter on the left was taken on April 21, 2014, with Hubble's Wide Field Camera 3.

Source: Space Telescope Science Institute (STScI)

Jupiter's moon Ganymede may harbor 'club sandwich' of oceans and ice

This artist's concept of Jupiter's moon Ganymede, the largest moon in the solar system, illustrates the "club sandwich" model of its interior oceans. Credit: NASA/JPL-Caltech

The largest moon in our solar system, a companion to Jupiter named Ganymede, might have ice and oceans stacked up in several layers like a club sandwich, according to new NASA-funded research that models the moon's makeup.

Previously, the moon was thought to harbor a thick ocean sandwiched between just two layers of ice, one on top and one on bottom.

"Ganymede's ocean might be organized like a Dagwood sandwich," said Steve Vance of NASA's Jet Propulsion Laboratory in Pasadena, Calif., explaining the moon's resemblance to the "Blondie" cartoon character's multi-tiered sandwiches. The study, led by Vance, provides new theoretical evidence for the team's "club sandwich" model, first proposed last year. The research appears in the journal Planetary and Space Science.

The results support the idea that primitive life might have possibly arisen on the icy moon. Scientists say that places where water and rock interact are important for the development of life; for example, it's possible life began on Earth in bubbling vents on our sea floor. Prior to the new study, Ganymede's rocky sea bottom was thought to be coated with ice, not liquid -- a problem for the emergence of life. The "club sandwich" findings suggest otherwise: the first layer on top of the rocky core might be salty water.

"This is good news for Ganymede," said Vance. "Its ocean is huge, with enormous pressures, so it was thought that dense ice had to form at the bottom of the ocean. When we added salts to our models, we came up with liquids dense enough to sink to the sea floor."

NASA scientists first suspected an ocean in Ganymede in the 1970s, based on models of the large moon, which is bigger than Mercury. In the 1990s, NASA's Galileo mission flew by Ganymede, confirming the moon's ocean, and showing it extends to depths of hundreds of miles. The spacecraft also found evidence for salty seas, likely containing the salt magnesium sulfate.

Previous models of Ganymede's oceans assumed that salt didn't change the properties of liquid very much with pressure. Vance and his team showed, through laboratory experiments, how much salt really increases the density of liquids under the extreme conditions inside Ganymede and similar moons. It may seem strange that salt can make the ocean denser, but you can see for yourself how this works by adding plain old table salt to a glass of water. Rather than increasing in volume, the liquid shrinks and becomes denser. This is because the salt ions attract water molecules.

The models get more complicated when the different forms of ice are taken into account. The ice that floats in your drinks is called "Ice I." It's the least dense form of ice and lighter than water. But at high pressures, like those in crushingly deep oceans like Ganymede's, the ice crystal structures become more compact. "It's like finding a better arrangement of shoes in your luggage -- the ice molecules become packed together more tightly," said Vance. The ice can become so dense that it is heavier than water and falls to the bottom of the sea. The densest and heaviest ice thought to persist in Ganymede is called "Ice VI."

By modeling these processes using computers, the team came up with an ocean sandwiched between up to three ice layers, in addition to the rocky seafloor. The lightest ice is on top, and the saltiest liquid is heavy enough to sink to the bottom. What's more, the results demonstrate a possible bizarre phenomenon that causes the oceans to "snow upwards." As the oceans churn and cold plumes snake around, ice in the uppermost ocean layer, called "Ice III," could form in the seawater. When ice forms, salts precipitate out. The heavier salts would thus fall downward, and the lighter ice, or "snow," would float upward. This "snow" melts again before reaching the top of the ocean, possibly leaving slush in the middle of the moon sandwich.

"We don't know how long the Dagwood-sandwich structure would exist," said Christophe Sotin of JPL. "This structure represents a stable state, but various factors could mean the moon doesn't reach this stable state.

Sotin and Vance are both members of the Icy Worlds team at JPL, part of the multi-institutional NASA Astrobiology Institute based at the Ames Research Center in Moffett Field, Calif.

The results can be applied to exoplanets too, planets that circle stars beyond our sun. Some super-

Earths, rocky planets more massive than Earth, have been proposed as "water worlds" covered in oceans. Could they have life? Vance and his team think laboratory experiments and more detailed modeling of exotic oceans might help find answers.

Ganymede is one of five moons in our solar system thought to support vast oceans beneath icy crusts. The other moons are Jupiter's Europa and Callisto and Saturn's Titan and Enceladus. The European Space Agency is developing a space mission, called JUpiter ICy moons Explorer or JUICE, to visit 
Europa, Callisto and Ganymede in the 2030s. NASA and JPL are contributing to three instruments on the mission, which is scheduled to launch in 2022 (see http://www.jpl.nasa.gov/news/news.php?release=2013-069).

Other authors of the study are Mathieu Bouffard of Ecole Normale Supérieure de Lyon, France, and Mathieu Choukroun, also of JPL and the Icy World team of the NASA Astrobiology Institute. JPL is managed by the California Institute of Technology in Pasadena for NASA.

Source: nasa

Artist impression of the debris disc and planets around the star known as Gliese 581, superimposed on Herschel PACS images at 70, 100 and 160 micrometre wavelengths. The line drawing superimposed on the Herschel image gives a schematic representation of the location and orientation of the star, planets and disc, albeit not to scale. Credit: Image courtesy of European Space Agency (ESA)

Using ESA's Herschel space observatory, astronomers have discovered vast comet belts surrounding two nearby planetary systems known to host only Earth-to-Neptune-mass worlds. The comet reservoirs could have delivered life-giving oceans to the innermost planets.

In a previous Herschel study, scientists found that the dusty belt surrounding nearby star Fomalhaut must be maintained by collisions between comets.

In the new Herschel study, two more nearby planetary systems -- GJ 581 and 61 Vir -- have been found to host vast amounts of cometary debris.

Herschel detected the signatures of cold dust at 200ºC below freezing, in quantities that mean these systems must have at least 10 times more comets than in our own Solar System's Kuiper Belt.

GJ 581, or Gliese 581, is a low-mass M dwarf star, the most common type of star in the Galaxy. Earlier studies have shown that it hosts at least four planets, including one that resides in the 'Goldilocks Zone' -- the distance from the central sun where liquid surface water could exist.

Two planets are confirmed around G-type star 61 Vir, which is just a little less massive than our Sun.

The planets in both systems are known as 'super-Earths', covering a range of masses between 2 and 18 times that of Earth.

Interestingly, however, there is no evidence for giant Jupiter- or Saturn-mass planets in either system.

The gravitational interplay between Jupiter and Saturn in our own Solar System is thought to have been responsible for disrupting a once highly populated Kuiper Belt, sending a deluge of comets towards the inner planets in a cataclysmic event that lasted several million years.

"The new observations are giving us a clue: they're saying that in the Solar System we have giant planets and a relatively sparse Kuiper Belt, but systems with only low-mass planets often have much denser Kuiper belts," says Dr Mark Wyatt from the University of Cambridge, lead author of the paper focusing on the debris disc around 61 Vir.

"We think that may be because the absence of a Jupiter in the low-mass planet systems allows them to avoid a dramatic heavy bombardment event, and instead experience a gradual rain of comets over billions of years."

"For an older star like GJ 581, which is at least two billion years old, enough time has elapsed for such a gradual rain of comets to deliver a sizable amount of water to the innermost planets, which is of particular importance for the planet residing in the star's habitable zone," adds Dr Jean-Francois Lestrade of the Observatoire de Paris who led the work on GJ 581.

However, in order to produce the vast amount of dust seen by Herschel, collisions between the comets are needed, which could be triggered by a Neptune-sized planet residing close to the disc.

"Simulations show us that the known close-in planets in each of these systems cannot do the job, but a similarly-sized planet located much further from the star -- currently beyond the reach of current detection campaigns -- would be able to stir the disc to make it dusty and observable," says Dr Lestrade.

"Herschel is finding a correlation between the presence of massive debris discs and planetary systems with no Jupiter-class planets, which offers a clue to our understanding of how planetary systems form and evolve," says Göran Pilbratt, ESA's Herschel project scientist.

Source: European Space Agency (ESA)

Dwarf planet Haumea shines with crystalline ice

The tiny and strange planet Haumea moves beyond the orbit of Neptune. Credit: SINC/José Antonio Peñas

The fifth dwarf planet of the solar system, Haumea, and at least one of its two satellites, are covered in crystalline water-ice due to the tidal forces between them and the heat of radiogenic elements. This is the finding of an international research study using observations from the VLT telescope at the European Southern Observatory in Chile.

The tiny and strange planet Haumea moves beyond the orbit of Neptune. It has the shape of a flattened rugby ball and is around 2,000 km long. It spins completely in less than four hours, at one of the fastest rotation speeds in the solar system. The crystallised water that covers this planet and its two satellites (Hi'iaka and Namaka) makes them shine in the darkness of space.

Now an international research team has confirmed that 75% of Haumea and 100% of Hi'iaka (which is around 400 km in diameter) are covered with crystallised water-ice (with an ordered structure) and not, as would have been expected, with amorphous ice disorganised due to solar radiation. The study suggests that the planet is made up of a frozen outer layer and an internal section made up of between 88% and 97% rock (with a density of 3.5 g/cm3).

"Since solar radiation constantly destroys the crystalline structure of ice on the surface, energy sources are required to keep it organised. The two that we have taken into consideration are that able to generate radiogenic elements (potassium-40, thorium-232 and uranium-238) from the inside, and the tidal forces between Haumea and its satellites (as seen between Earth and the Moon)," Benoit Carry, co-author of the study and a researcher at the ESAC Centre of the European Space Agency (ESA) in Madrid (Spain), said.

The researcher also highlights other peculiarities of Haumea: "Its orbital plane is inclined at 28º with respect to the usual plane of planets in the solar system, the orbits of its satellites are not on the same plane either -- which is very unusual -- and the entire system belongs to a single family within the frozen objects in the Kuiper Belt (at a distance of between 4.5 billion and more than 15 billion kilometres from the Sun)."

According to the scientists, the two satellites could have been created by another object smashing into Haumea, which could also have originated the rapid rotation of the dwarf planet (3.9 hours) and have moulded it into its rugby ball shape. Some numerical models have demonstrated that this could be caused by a fairly tangential impact.

Observations from the SINFONI instrument of the Very Large Telescope (VLT), the enormous telescope of the European Southern Observatory (ESO) in Chile, were used in order to carry out the study, which has been published in the journal Astronomy & Astrophysics. ESO astronomer Christophe Dumas led this study from the observatory.
"SINFONI is an integral field spectrometer that provides 'data cubes' in which two of the dimensions are spatial (like those of any flat image), while the third is spectral, meaning that each layer of the cube is an image taken with a different wave size," explains Carry.

The mystery of Haumea

The scientist acknowledges that the precise orbits and sizes of the dwarf planet are still not known (they are operating with approximate scales of around 2,000 x 1,500 x 1,000 km) nor are those of its satellites. In reality, these are two very distant bright points of light, the data for which are obtained indirectly.

In the case of the tiny Namaka (around 200 km in diameter), the signal at the time it was observed was so weak that it was impossible to obtain information about its surface, although new data on its orbit were gathered. Meanwhile, the models for the tidal forces of this strange system are also improving.

Another of the mysteries of Haumea is the presence of a dark, reddish spot, which contrasts with the whitish colour of the planet. "My interpretation of the infrared photometry is that this area could be a richer source of crystalline water-ice than the rest of the surface," Pedro Lacerda, co-discoverer of the spot and an astronomer at Queen's University in Belfast (United Kingdom), said. The researcher does not rule out the possibility of some kind of irradiated mineral or organic matter having caused this colouration.

Haumea is the fifth dwarf planet in the solar system along with Pluto, Ceres, Eris and Makemake. Its existence was confirmed in 2005, when it was called 2003 EL61 (from the international nomenclature code: year of first observation, half and order number).

Two teams of astronomers contested the discovery. The first group was led by the Spanish researcher José Luis Ortiz Moreno from the Institute of Astrophysics of Andalusia (CSIC), while the other was led by the astrophysicist Michael E. Brown from the California Institute of Technology (Caltech, USA).

In the end, the International Astronomical Union decided to accept the discovery by the Spanish team, but named the strange dwarf planet and its satellites according to names suggested by the American team. In Hawaiian mythology, Haumea is the goddess of fertility and birth, and Hi'iaka and Namaka are two of her daughters.

Source: Plataforma SINC

NASA-funded FOXSI to observe X-rays from Sun

The Focusing Optics X-ray Solar Imager, or FOXSI, mission launched for the first time in November 2012, as shown here. It will fly again on a sounding rocket for a 15-minute flight in December 2014 to observe hard X-rays from the sun. Credit: NASA/FOXSI

An enormous spectrum of light streams from the sun. We're most familiar with the conventional visible white light we see with our eyes from Earth, but that's just a fraction of what our closest star emits. NASA regularly watches the sun in numerous wavelengths because different wavelengths provide information about different temperatures and processes in space. Looking at all the wavelengths together helps to provide a complete picture of what's occurring on the sun over 92 million miles away -- but no one has been able to focus on high energy X-rays from the sun until recently.

In early December 2014, the Focusing Optics X-ray Solar Imager, or FOXSI, mission will launch aboard a sounding rocket for a 15-minute flight with very sensitive hard X-ray optics to observe the sun. This is FOXSI's second flight -- now with new and improved optics and detectors. FOXSI launched previously in November 2012. The mission is led by Säm Krucker of the University of California in Berkeley.

Due to launch from White Sands Missile Range in New Mexico, on Dec. 9, 2014, FOXSI will be able to collect six minutes worth of data during the 15-minute flight. Sounding rockets provide a short trip for a relatively low price -- yet allow scientists to gather robust data on various things, such as X-ray emission, which cannot be seen from the ground as they are blocked by Earth's atmosphere.

"Hard X-rays are a signature of particles accelerating on the sun," said Steven Christe, the project scientist for FOXSI at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The sun accelerates particles when it releases magnetic energy. The biggest events like solar flares release giant bursts of energy and send particles flying, sometimes directed towards Earth. But the sun is actually releasing energy all the time and that process is not well-understood."

Scientists want to understand these energy releases both because they contribute to immense explosions on the sun that can send particles and energy toward Earth, but also because that energy helps heat up the sun's atmosphere to temperatures of millions of degrees -- 1,000 times hotter than the surface of the sun itself. Observing many wavelengths of light allows us to probe different temperatures within the sun's atmosphere. Looking for hard X-rays, is not only one of the best ways to measure the highest temperatures, up to tens of millions of degrees, but it also helps track accelerated particles.

The sensitivity of the FOXSI instrument means the team can investigate very faint events on the sun, including tiny energy releases commonly known as nanoflares. Nanoflares are thought to occur constantly, but are so small that we can't see them with current telescopes. Spotting hard X-rays with FOXSI would be a confirmation that these small flares do exist. Moreover, it would suggest that nanoflares behave in a similar fashion as larger flares, accelerating particles in much the same way that big flares do.

"It's not necessarily true that these small flares accelerate particles. Perhaps they are just small heating events and the physics is different," said Christe. "That's one of the things we're trying to figure out."

Viewing such faint events requires extra sensitive optics. FOXSI carries something called grazing-incidence optics -- built by NASA's Marshall Space Flight Center in Huntsville, Alabama -- that are unlike any previous ones launched into space for solar observations. 

Techniques to collect and observe high energy X-rays streaming from the sun have been hampered by the fact that these wavelengths cannot be focused with conventional lenses the way visible light can be. When X-rays encounter most materials, including a standard glass lens, they usually pass right through or are absorbed. Such lenses can't, therefore, be used to adjust the X-ray's path and focus the incoming beams. So X-ray telescopes have previously relied on imaging techniques that don't use focusing. This is effective when looking at a single bright event on the sun, such as the large burst of X-rays from a solar flare, but it doesn't work as well when searching for many faint events simultaneously.

The FOXSI instrument makes use of mirrors that can successfully cause x-rays to reflect -- as long as the x-ray mirrors are nearly parallel to the incoming X-rays. Several of these mirrors in combination help collect the X-ray light before funneling it to the detector. This focusing makes faint events appear brighter and crisper.

The FOXSI launch is scheduled for Dec. 9 between 2 and 3 pm EST. The shutter door on the optics system opens up after the payload reaches an altitude of 90 miles, one minute after launch. FOXSI then begins six minutes of observing the sun. After the observations, the door on the optics system closes. The rocket deploys a parachute and the instruments float down to the ground in the hopes of being used again.

The FOXSI mission made it through this process successfully once before, when it flew in 2012. On its first flight, the telescope successfully viewed a flare in progress. On this second flight, the team has updated some of the optics to be more sensitive and has removed insulation blankets that blocked some of the X-rays during the last flight. They also upgraded some of the detectors with new detectors built by the Japanese Aerospace 

Exploration Agency using a new detector material. Last time they used silicon and this time they are using cadmium telluride.

Such refurbishing illustrates a key value of sounding rockets: Making adjustments to the instruments on relatively low-cost flights has great benefit for future missions. By testing FOXSI on a sounding rocket, it can be perfected to use on a larger satellite with even larger, more sensitive optics.

In addition to developing technology, these low-cost missions help train students and young scientists.

"Sounding rockets are a great way for students to be heavily involved in every aspect of a space mission, from electronics testing to observational planning," said Lindsay Glesener, 

FOXSI's project manager at the University of California in Berkeley, who was also a graduate student during FOXSI's first flight. "Development on low-cost missions is the way that,scientists, engineers, and even the telescopes get prepared to work on an eventual satellite mission."

FOXSI is a collaboration between the United States and the Japanese Aerospace Exploration Agency. FOXSI is supported through NASA's Sounding Rocket Program at the Goddard Space Flight Center's Wallops Flight Facility in Virginia. NASA's Heliophysics Division manages the sounding rocket program.

Source:  NASA/Goddard Space Flight Center

Sun sizzles in high-energy X-rays

X-rays stream off the sun in this image showing observations from by NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken by NASA's Solar Dynamics Observatory (SDO).
Credit: NASA/JPL-Caltech/GSFC

For the first time, a mission designed to set its eyes on black holes and other objects far from our solar system has turned its gaze back closer to home, capturing images of our sun. NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR, has taken its first picture of the sun, producing the most sensitive solar portrait ever taken in high-energy X-rays.

NuSTAR will give us a unique look at the sun, from the deepest to the highest parts of its atmosphere," said David Smith, a solar physicist and member of the NuSTAR team at University of California, Santa Cruz.

Solar scientists first thought of using NuSTAR to study the sun about seven years ago, after the space telescope's design and construction was already underway (the telescope launched into space in 2012). Smith had contacted the principal investigator, Fiona Harrison of the California Institute of Technology in Pasadena, who mulled it over and became excited by the idea.

"At first I thought the whole idea was crazy," says Harrison. "Why would we have the most sensitive high energy X-ray telescope ever built, designed to peer deep into the universe, look at something in our own back yard?" Smith eventually convinced Harrison, explaining that faint X-ray flashes predicted by theorists could only be seen by NuSTAR.

While the sun is too bright for other telescopes such as NASA's Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors. The sun is not as bright in the higher-energy X-rays detected by NuSTAR, a factor that depends on the temperature of the sun's atmosphere.
This first solar image from NuSTAR demonstrates that the telescope can in fact gather data about sun. And it gives insight into questions about the remarkably high temperatures that are found above sunspots -- cool, dark patches on the sun. Future images will provide even better data as the sun winds down in its solar cycle.

"We will come into our own when the sun gets quiet," said Smith, explaining that the sun's activity will dwindle over the next few years.

With NuSTAR's high-energy views, it has the potential to capture hypothesized nanoflares -- smaller versions of the sun's giant flares that erupt with charged particles and high-energy radiation. Nanoflares, should they exist, may explain why the sun's outer atmosphere, called the corona, is sizzling hot, a mystery called the "coronal heating problem." The corona is, on average, 1.8 million degrees Fahrenheit (1 million degrees Celsius), while the surface of the sun is relatively cooler at 10,800 Fahrenheit (6,000 degrees Celsius). It is like a flame coming out of an ice cube. Nanoflares, in combination with flares, may be sources of the intense heat.

If NuSTAR can catch nanoflares in action, it may help solve this decades-old puzzle.

"NuSTAR will be exquisitely sensitive to the faintest X-ray activity happening in the solar atmosphere, and that includes possible nanoflares," said Smith.
What's more, the X-ray observatory can search for hypothesized dark matter particles called axions. Dark matter is five times more abundant than regular matter in the universe. Everyday matter familiar to us, for example in tables and chairs, planets and stars, is only a sliver of what's out there. While dark matter has been indirectly detected through its gravitational pull, its composition remains unknown.

It's a long shot, say scientists, but NuSTAR may be able spot axions, one of the leading candidates for dark matter, should they exist. The axions would appear as a spot of X-rays in the center of the sun.

Meanwhile, as the sun awaits future NuSTAR observations, the telescope is continuing with its galactic pursuits, probing black holes, supernova remnants and other extreme objects beyond our solar system.

NuSTAR is a Small Explorer mission led by Caltech and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington. The spacecraft was built by Orbital Sciences Corporation, Dulles, Virginia. Its instrument was built by a consortium including Caltech; JPL; the University of California, Berkeley; Columbia University, New York; NASA's Goddard Space Flight Center, Greenbelt, Maryland; the Danish Technical University in Denmark; Lawrence Livermore National Laboratory, Livermore, California; ATK Aerospace Systems, Goleta, California; and with support from the Italian Space Agency (ASI) Science Data Center.

NuSTAR's mission operations center is at UC Berkeley, with the ASI providing its equatorial ground station located at Malindi, Kenya. The mission's outreach program is based at Sonoma State University, Rohnert Park, California. NASA's Explorer Program is managed by Goddard. JPL is managed by Caltech for NASA.

Source: NASA

Magnetic fields frozen into meteorite grains tell a shocking tale of solar system birth

Magnetic field lines (green) weave through the cloud of dusty gas surrounding the newborn Sun. In the foreground are asteroids and chondrules, the building blocks of chondritic meteorites. While solar magnetic fields dominate the region near the Sun, out where the asteroids orbit, chondrules preserve a record of varying local magnetic fields. Credit: Science

The most accurate laboratory measurements yet made of magnetic fields trapped in grains within a primitive meteorite are providing important clues to how the early solar system evolved. The measurements point to shock waves traveling through the cloud of dusty gas around the newborn Sun as a major factor in solar system formation.

The results appear in a paper published Nov. 13 in the journal Science. The lead author is graduate student Roger Fu of MIT, working under Benjamin Weiss; Steve Desch of Arizona State University's School of Earth and Space Exploration is a co-author of the paper.

"The measurements made by Fu and Weiss are astounding and unprecedented," says Desch. 
"Not only have they measured tiny magnetic fields thousands of times weaker than a compass feels, they have mapped the magnetic fields' variation recorded by the meteorite, millimeter by millimeter."

Construction debris
It may seem all but impossible to determine how the solar system formed, given it happened about 4.5 billion years ago. But making the solar system was a messy process, leaving lots of construction debris behind for scientists to study.

Among the most useful pieces of debris are the oldest, most primitive and least altered type of meteorites, called the chondrites (KON-drites). Chondrite meteorites are pieces of asteroids, broken off by collisions, that have remained relatively unmodified since they formed at the birth of the solar system. They are built mostly of small stony grains, called chondrules, barely a millimeter in diameter.

Chondrules themselves formed through quick melting events in the dusty gas cloud -- the solar nebula -- that surrounded the young sun. Patches of the solar nebula must have been heated above the melting point of rock for hours to days. Dustballs caught in these events made droplets of molten rock, which then cooled and crystallized into chondrules.

Tiny magnets
As chondrules cooled, iron-bearing minerals within them became magnetized like bits on a hard drive by the local magnetic field in the gas. These magnetic fields are preserved in the chondrules even down to the present day.

The chondrule grains whose magnetic fields were mapped in the new study came from a meteorite named Semarkona, after the place in India where it fell in 1940. It weighed 691 grams, or about a pound and a half.

The scientists focused specifically on the embedded magnetic fields captured by "dusty" olivine grains that contain abundant iron-bearing minerals. These had a magnetic field of about 54 microtesla, similar to the magnetic field at Earth's surface, which ranges from 25 to 65 microtesla.

Coincidentally, many previous measurements of meteorites also implied similar field strengths. But it is now understood that those measurements detected magnetic minerals contaminated by Earth's magnetic field, or even from hand magnets used by meteorite collectors.

"The new experiments," Desch says, "probe magnetic minerals in chondrules never measured before. They also show that each chondrule is magnetized like a little bar magnet, but with 'north' pointing in random directions."

This shows, he says, they became magnetized before they were built into the meteorite, and not while sitting on Earth's surface.

Shocks and more shocks
"My modeling for the heating events shows that shock waves passing through the solar nebula is what melted most chondrules," Desch explains. Depending on the strength and size of the shock wave, the background magnetic field could be amplified by up to 30 times.
He says, "Given the measured magnetic field strength of about 54 microtesla, this shows the background field in the nebula was probably in the range of 5 to 50 microtesla."

There are other ideas for how chondrules might have formed, some involving magnetic flares above the solar nebula, or passage through the sun's magnetic field. But those mechanisms require stronger magnetic fields than what is measured in the Semarkona samples.

This reinforces the idea that shocks melted the chondrules in the solar nebula at about the location of today's asteroid belt, which lies some two to four times farther from the sun than Earth now orbits.

Desch says, "This is the first really accurate and reliable measurement of the magnetic field in the gas from which our planets formed."

Source: Arizona State University