The mountains likely formed no more than 100 million years ago — mere youngsters relative to the 4.56-billion-year age of the solar system — and may still be in the process of building, says Geology, Geophysics and Imaging (GGI) team leader Jeff Moore of NASA’s Ames Research Center in Moffett Field, California.. That suggests the close-up region, which covers less than one percent of Pluto’s surface, may still be geologically active today.

Moore and his colleagues base the youthful age estimate on the lack of craters in this scene. Like the rest of Pluto, this region would presumably have been pummeled by space debris for billions of years and would have once been heavily cratered — unless recent activity had given the region a facelift, erasing those pockmarks.

“This is one of the youngest surfaces we’ve ever seen in the solar system,” says Moore.

Unlike the icy moons of giant planets, Pluto cannot be heated by gravitational interactions with a much larger planetary body. Some other process must be generating the mountainous landscape.

“This may cause us to rethink what powers geological activity on many other icy worlds,” says GGI deputy team leader John Spencer of the Southwest Research Institute in Boulder, Colo.

The mountains are probably composed of Pluto’s water-ice “bedrock.”

Although methane and nitrogen ice covers much of the surface of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice, created the peaks. “At Pluto’s temperatures, water-ice behaves more like rock,” said deputy GGI lead Bill McKinnon of Washington University, St. Louis.

The close-up image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the craft was 47,800 miles (77,000 kilometers) from the surface of the planet. The image easily resolves structures smaller than a mile across.

Story Source:

The above post is reprinted from materials provided by NASA. Note: Materials may be edited for content and length.

{  http://nationalufocenter.com/ }

In a contract signed with the Breakthrough Prize Foundation, significant funding — approximately $2 million per year for 10 years — will go to the GBT to participate in this exhilarating journey of discovery.

“Beginning early next year, approximately 20 percent of the annual observing time on the GBT will be dedicated to searching a staggering number of stars and galaxies for signs of intelligent life via radio signals,” said Tony Beasley, director of the National Radio Astronomy Observatory, which operates the GBT and other world-class radio astronomy facilities. “We are delighted to play such a vital role in hopefully answering one of the most compelling questions in all of science and philosophy: are we alone in the Universe?”

In addition to the GBT, the Parkes Telescope in Australia will also be involved in this endeavor.

Breakthrough Listen will be the biggest scientific search ever undertaken for signs of intelligent life beyond Earth. It will be 50 times more sensitive and cover 10 times more of the sky than previous searches. In tandem with this radio search, the Automated Planet Finder Telescope at Lick Observatory in California will undertake the world’s deepest and broadest search for optical laser transmissions, a tantalizing complementary approach to searching the cosmos for extraterrestrial intelligence.

The $100 million Breakthrough Listen initiative was announced today at the Royal Society in London.

The program will include a survey of the one million closest stars to Earth. It will scan the center of our Galaxy and the entire galactic plane. Beyond the Milky Way, it will search for messages from the 100 closest galaxies. If a civilization based around one of the 1,000 nearest stars transmits to us with the power of common aircraft radar, the GBT and the Parkes Telescope could detect it.

The program will generate vast amounts of data; all of which will be open to the public. This will likely constitute the largest amount of scientific data ever made publicly available. The Breakthrough Listen team will use and develop the most powerful software for sifting and searching this flood of data. All software will be open source. Both the software and the hardware used in the Breakthrough Listen project will be compatible with other telescopes around the world, so that they could join the search for intelligent life. As well as using the Breakthrough Listen software, scientists and members of the public will be able to add to it, developing their own applications to analyze the data.

Breakthrough Listen will also be joining and supporting SETI@home, the University of California, Berkeley ground-breaking distributed computing platform, with 9 million volunteers around the world donating their spare computing power to search astronomical data for signs of life. Collectively, they constitute one of the largest supercomputers in the world.

The 100-meter Green Bank Telescope is the world’s largest fully steerable radio telescope. Its location in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone protects the incredibly sensitive telescope from unwanted radio interference, enabling it to perform unique observations.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Story Source:

The above post is reprinted from materials provided by National Radio Astronomy Observatory. Note: Materials may be edited for content and length.

{ http://nationalufocenter.com/ }

The mountains likely formed no more than 100 million years ago — mere youngsters relative to the 4.56-billion-year age of the solar system — and may still be in the process of building, says Geology, Geophysics and Imaging (GGI) team leader Jeff Moore of NASA’s Ames Research Center in Moffett Field, California.. That suggests the close-up region, which covers less than one percent of Pluto’s surface, may still be geologically active today.

Moore and his colleagues base the youthful age estimate on the lack of craters in this scene. Like the rest of Pluto, this region would presumably have been pummeled by space debris for billions of years and would have once been heavily cratered — unless recent activity had given the region a facelift, erasing those pockmarks.

“This is one of the youngest surfaces we’ve ever seen in the solar system,” says Moore.

Unlike the icy moons of giant planets, Pluto cannot be heated by gravitational interactions with a much larger planetary body. Some other process must be generating the mountainous landscape.

“This may cause us to rethink what powers geological activity on many other icy worlds,” says GGI deputy team leader John Spencer of the Southwest Research Institute in Boulder, Colo.

The mountains are probably composed of Pluto’s water-ice “bedrock.”

Although methane and nitrogen ice covers much of the surface of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice, created the peaks. “At Pluto’s temperatures, water-ice behaves more like rock,” said deputy GGI lead Bill McKinnon of Washington University, St. Louis.

The close-up image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the craft was 47,800 miles (77,000 kilometers) from the surface of the planet. The image easily resolves structures smaller than a mile across.

Story Source:

The above post is reprinted from materials provided by NASA. Note: Materials may be edited for content and length.

{ http://nationalufocenter.com/ }

The mountains likely formed no more than 100 million years ago — mere youngsters relative to the 4.56-billion-year age of the solar system — and may still be in the process of building, says Geology, Geophysics and Imaging (GGI) team leader Jeff Moore of NASA’s Ames Research Center in Moffett Field, California.. That suggests the close-up region, which covers less than one percent of Pluto’s surface, may still be geologically active today.

Moore and his colleagues base the youthful age estimate on the lack of craters in this scene. Like the rest of Pluto, this region would presumably have been pummeled by space debris for billions of years and would have once been heavily cratered — unless recent activity had given the region a facelift, erasing those pockmarks.

“This is one of the youngest surfaces we’ve ever seen in the solar system,” says Moore.

Unlike the icy moons of giant planets, Pluto cannot be heated by gravitational interactions with a much larger planetary body. Some other process must be generating the mountainous landscape.

“This may cause us to rethink what powers geological activity on many other icy worlds,” says GGI deputy team leader John Spencer of the Southwest Research Institute in Boulder, Colo.

The mountains are probably composed of Pluto’s water-ice “bedrock.”

Although methane and nitrogen ice covers much of the surface of Pluto, these materials are not strong enough to build the mountains. Instead, a stiffer material, most likely water-ice, created the peaks. “At Pluto’s temperatures, water-ice behaves more like rock,” said deputy GGI lead Bill McKinnon of Washington University, St. Louis.

The close-up image was taken about 1.5 hours before New Horizons closest approach to Pluto, when the craft was 47,800 miles (77,000 kilometers) from the surface of the planet. The image easily resolves structures smaller than a mile across.

Story Source:

The above post is reprinted from materials provided by NASA.
Note: Materials may be edited for content and length.

{ http://nationalufocenter.com/ }

For decades, astronomers have wondered whether the solar system’s circular orbits might be a rarity in our universe. Now a new analysis suggests that such orbital regularity is instead the norm, at least for systems with planets as small as Earth.

In a paper published in the Astrophysical Journal, researchers from MIT and Aarhus University in Denmark report that 74 exoplanets, located hundreds of light-years away, orbit their respective stars in circular patterns, much like the planets of our solar system.

These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.

“Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere,” says Vincent Van Eylen, a visiting graduate student in MIT’s Department of Physics. “Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm.”

Ultimately, Van Eylen says that’s good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)

“If eccentric orbits are common for habitable planets, that would be quite a worry for life, because they would have such a large range of climate properties,” Van Eylen says. “But what we find is, probably we don’t have to worry too much because circular cases are fairly common.”

Star-crossed numbers

In the past, researchers have calculated the orbital eccentricities of large, “gas giant” exoplanets using radial velocity — a technique that measures a star’s movement. As a planet orbits a star, its gravitational force will tug on the star, causing it to move in a pattern that reflects the planet’s orbit. However, the technique is most successful for larger planets, as they exert enough gravitational pull to influence their stars.

Researchers commonly find smaller planets by using a transit-detecting method, in which they study the light given off by a star, in search of dips in starlight that signify when a planet crosses, or “transits,” in front of that star, momentarily diminishing its light. Ordinarily, this method only illuminates a planet’s existence, not its orbit. But Van Eylen and his colleague Simon Albrecht, of Aarhus University, devised a way to glean orbital information from stellar transit data.

They first reasoned that if they knew the mass and radius of a planet’s star, they could calculate how long a planet would take to orbit that star, if its orbit were circular. The mass and radius of a star determines its gravitational pull, which in turn influences how fast a planet travels around the star.

By calculating a planet’s orbital velocity in a circular orbit, they could then estimate a transit’s duration — how long a planet would take to cross in front of a star. If the calculated transit matched an actual transit, the researchers reasoned that the planet’s orbit must be circular. If the transit were longer or shorter, the orbit must be more elongated, or eccentric.

Not so eccentric

To obtain actual transit data, the team looked through data collected over the past four years by NASA’s Kepler telescope — a space observatory that surveys a slice of the sky in search of habitable planets. The telescope has monitored the brightness of over 145,000 stars, only a fraction of which have been characterized in any detail.

The team chose to concentrate on 28 stars for which mass and radius have previously been measured, using asteroseismology — a technique that measures stellar pulsations, which reflect a star’s mass and radius.

These 28 stars host multiplanet systems — 74 exoplanets in all. The researchers obtained Kepler data for each exoplanet, looking not only for the occurrence of transits, but also their duration. Given the mass and radius of the host stars, the team calculated each planet’s transit duration if its orbit were circular, then compared the estimated transit durations with actual transit durations from Kepler data.

Across the board, Van Eylen and Albrecht found the calculated and actual transit durations matched, suggesting that all 74 exoplanets maintain circular, not eccentric, orbits.

“We found that most of them matched pretty closely, which means they’re pretty close to being circular,” Van Eylen says. “We are very certain that if very high eccentricities were common, we would’ve seen that, which we don’t.”

Van Eylen says the orbital results for these smaller planets may eventually help to explain why larger planets have more extreme orbits.

“We want to understand why some exoplanets have extremely eccentric orbits, while in other cases, such as the solar system, planets orbit mostly circularly,” Van Eylen says. “This is one of the first times we’ve reliably measured the eccentricities of small planets, and it’s exciting to see they are different from the giant planets, but similar to the solar system.”

Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu. Note: Materials may be edited for content and length.

Journal Reference:

1. F. Mullally, Jeffrey L. Coughlin, Susan E. Thompson, Jason Rowe, Christopher Burke, David W. Latham, Natalie M. Batalha, Stephen T. Bryson, Jessie Christiansen, Christopher E. Henze, Aviv Ofir, Billy Quarles, Avi Shporer, Vincent Van Eylen, Christa Van Laerhoven, Yash Shah, Angie Wolfgang, W. J. Chaplin, Ji-Wei Xie, Rachel Akeson, Vic Argabright, Eric Bachtell, Thomas Barclay, William J. Borucki, Douglas A. Caldwell, Jennifer R. Campbell, Joseph H. Catanzarite, William D. Cochran, Riley M. Duren, Scott W. Fleming, Dorothy Fraquelli, Forrest R. Girouard, Michael R. Haas, Krzysztof G. Hełminiak, Steve B. Howell, Daniel Huber, Kipp Larson, Thomas N. Gautier III, Jon M. Jenkins, Jie Li, Jack J. Lissauer, Scot McArthur, Chris Miller, Robert L. Morris, Anima Patil-Sabale, Peter Plavchan, Dustin Putnam, Elisa V. Quintana, Solange Ramirez, V. Silva Aguirre, Shawn Seader, Jeffrey C. Smith, Jason H. Steffen, Chris Stewart, Jeremy Stober, Martin Still, Peter Tenenbaum, John Troeltzsch, Joseph D. Twicken, Khadeejah A. Zamudio. PLANETARY CANDIDATES OBSERVED BYKEPLER. VI. PLANET SAMPLE FROM Q1–Q16 (47 MONTHS). The Astrophysical Journal Supplement Series, 2015; 217 (2): 31 DOI: 10.1088/0067-0049/217/2/31

{ http://nationalufocenter.com/ }

In a paper published in the journal Icarus, the researchers use state-of-the-art computer models to simulate the dynamics of comet impacts on the lunar soil. The simulations suggest that such impacts can account for many of the features in the mysterious swirls.

“We think this makes a pretty strong case that the swirls represent remnants of cometary collisions,” said Peter Schultz, a planetary geoscientist at Brown University. Schultz co-wrote the paper with his former graduate student, Megan Bruck Syal, who is now a researcher at the Lawrence Livermore National Laboratory.

Lunar swirls have been the source of debate for years. The twisting, swirling streaks of bright soil stretch, in some cases, for thousands of miles across the lunar surface. Most are found on the unseen far side of the Moon, but one famous swirl called Reiner Gamma can be seen by telescope on the southwestern corner of the Moon’s near side. “It was my favorite object to look at when I was an amateur astronomer,” Schultz said.

At first glance, the swirls do not appear to be related to large impact craters or any other topography. “They simply look as if someone had finger-painted the surface,” Schultz said. “There has been an intense debate about what causes these features.”

In the 1970s, scientists discovered that many of the swirls were associated with anomalies of the Moon’s crustal magnetic field. That revelation led to one hypothesis for how the swirls may have formed. Rocks below the surface in those spots might contain remanent magnetism from early in the Moon’s history, when its magnetic field was much stronger than it is now. It had been proposed that those strong, locally trapped magnetic fields deflect the onslaught of the solar wind, which was thought to slowly darken the Moon’s surface. The swirls would remain brighter than the surrounding soil because of those magnetic shields.

But Schultz had a different idea for how the swirls may form — one that has its roots in watching the lunar modules land on the Moon during the Apollo program.

“You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,” Schultz said. “That was part of what got me started thinking comet impacts could cause the swirls.”

Comets carry their own gaseous atmosphere called a coma. Schultz thought that when small comets slam into the Moon’s surface — as they occasionally do — the coma may scour away loose soil from the surface, not unlike the gas from the lunar modules. That scouring may produce the bright swirls.

Schultz first published a paper outlining the idea in the journal Nature in 1980. That paper focused on how the scouring of the delicate upper layer of lunar soils could produce brightness consistent with the swirls. The structure of the grains in the upper layer (termed the “fairy castle structure” because of the way grains stick together) scatters sun’s rays, causing a dimmer and darker appearance. When this structure is stripped away, the remaining smoothed surface would be brighter than unaffected areas, especially when the sun’s rays strike it at certain angles. For Reiner Gamma on the lunar nearside, those areas appear brightest during the crescent Moon just before sunrise.

As computer simulations of impact dynamics have gotten better, Schultz and Bruck-Syal decided it might be time to take a second look at whether comet impacts could produce that kind of scouring. Their new simulations showed that the impact of a comet coma plus its icy core would indeed have the effect of blowing away the smallest grains that sit atop the lunar soil. The simulations showed that the scoured area would stretch for perhaps thousands of kilometers from the impact point, consistent with the swirling streaks that extend across the Moon’s surface. Eddies and vortices created by the gaseous impact would explain the swirls’ twisty, sinuous appearance.

The comet impact hypothesis could also explain the presence of magnetic anomalies near the swirls. The simulations showed that a comet impact would melt some of the tiny particles near the surface. When small, iron-rich particles are melted and then cooled, they record the presence of any magnetic field that may be present at the time. “Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,” Schultz said. “As the gas collides with the lunar surface, the cometary magnetic field becomes amplified and recorded in the small particles when they cool.”

Taken together, the results offer a more complete picture of how the swirls form, the researchers say.

“This is the first time anyone has looked at this using modern computational techniques,” Schultz said. “Everything we see in simulations of comet impacts is consistent with the swirls as we see them on the Moon. We think this process provides a consistent explanation, but may need new Moon missions to finally resolve the debate.”

Story Source:

The above story is based on materials provided by Brown University. Note: Materials may be edited for content and length.

Journal Reference:

1. Megan Bruck Syala, Peter H. Schultzb. Cometary impact effects at the Moon: Implications for lunar swirl formation. Icarus, 2015; DOI: 10.1016/j.icarus.2015.05.005

{ http://nationalufocenter.com/ }

This quartet is composed of (from left to right) NGC 839, NGC 838, NGC 835, and NGC 833 — four of the seven galaxies that make up the entire group. They shine brightly with their glowing golden centres and wispy tails of gas,* set against a background dotted with much more distant galaxies.

Compact groups represent some of the densest concentrations of galaxies known in the Universe, making them perfect laboratories for studying weird and wonderful phenomena. Hickson Compact Groups in particular, as classified by astronomer Paul Hickson in the 1980s, are surprisingly numerous, and are thought to contain an unusually high number of galaxies with strange properties and behaviours.

HCG 16 is certainly no exception. The galaxies within it are bursting with dramatic knots of star formation and intensely bright central regions. Within this single group, astronomers have found two LINERs, one Seyfert 2 galaxy and three starburst galaxies.

These three types of galaxy are all quite different, and can each help us to explore something different about the cosmos. Starbursts are dynamic galaxies that produce new stars at much greater rates than their peers. LINERs (Low-Ionisation Nuclear Emission-line Regions) contain heated gas at their cores, which spew out radiation. In this image NGC 839 is a LINER-type and luminous infrared galaxy and its companion NGC 838 is a LINER-type galaxy with lots of starburst activity and no central black hole.

The remaining galaxies, NGC 835 and NGC 833, are both Seyfert 2 galaxies which have incredibly luminous cores when observed at other wavelengths than in the visible light, and are home to active supermassive black holes.

The X-ray emission emanating from the black hole within NGC 833 (far right) is so high that it suggests the galaxy has been stripped of gas and dust by past interactions with other galaxies. It is not alone in having a violent history — the morphology of NGC 839 (far left) is likely due to a galactic merger in the recent past, and long tails of glowing gas can be seen stretching away from the galaxies on the right of the image.

This new image uses observations from Hubble’s Wide Field Planetary Camera 2, combined with data from the ESO Multi-Mode Instrument installed on the European Southern Observatory’s New Technology Telescope in Chile. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestants Jean-Christophe Lambry and Marc Canale.

* A tidal tail is a thin, elongated region of stars and interstellar gas that extends into space from a galaxy. They are a result of the strong gravitational forces around interacting galaxies.

Story Source:

The above post is reprinted from materials provided by ESA/Hubble Information Centre. Note: Materials may be edited for content and length.

In a paper published in the journal Icarus, the researchers use state-of-the-art computer models to simulate the dynamics of comet impacts on the lunar soil. The simulations suggest that such impacts can account for many of the features in the mysterious swirls.

“We think this makes a pretty strong case that the swirls represent remnants of cometary collisions,” said Peter Schultz, a planetary geoscientist at Brown University. Schultz co-wrote the paper with his former graduate student, Megan Bruck Syal, who is now a researcher at the Lawrence Livermore National Laboratory.

Lunar swirls have been the source of debate for years. The twisting, swirling streaks of bright soil stretch, in some cases, for thousands of miles across the lunar surface. Most are found on the unseen far side of the Moon, but one famous swirl called Reiner Gamma can be seen by telescope on the southwestern corner of the Moon’s near side. “It was my favorite object to look at when I was an amateur astronomer,” Schultz said.

At first glance, the swirls do not appear to be related to large impact craters or any other topography. “They simply look as if someone had finger-painted the surface,” Schultz said. “There has been an intense debate about what causes these features.”

In the 1970s, scientists discovered that many of the swirls were associated with anomalies of the Moon’s crustal magnetic field. That revelation led to one hypothesis for how the swirls may have formed. Rocks below the surface in those spots might contain remanent magnetism from early in the Moon’s history, when its magnetic field was much stronger than it is now. It had been proposed that those strong, locally trapped magnetic fields deflect the onslaught of the solar wind, which was thought to slowly darken the Moon’s surface. The swirls would remain brighter than the surrounding soil because of those magnetic shields.

But Schultz had a different idea for how the swirls may form — one that has its roots in watching the lunar modules land on the Moon during the Apollo program.

“You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,” Schultz said. “That was part of what got me started thinking comet impacts could cause the swirls.”

Comets carry their own gaseous atmosphere called a coma. Schultz thought that when small comets slam into the Moon’s surface — as they occasionally do — the coma may scour away loose soil from the surface, not unlike the gas from the lunar modules. That scouring may produce the bright swirls.

Schultz first published a paper outlining the idea in the journal Nature in 1980. That paper focused on how the scouring of the delicate upper layer of lunar soils could produce brightness consistent with the swirls. The structure of the grains in the upper layer (termed the “fairy castle structure” because of the way grains stick together) scatters sun’s rays, causing a dimmer and darker appearance. When this structure is stripped away, the remaining smoothed surface would be brighter than unaffected areas, especially when the sun’s rays strike it at certain angles. For Reiner Gamma on the lunar nearside, those areas appear brightest during the crescent Moon just before sunrise.

As computer simulations of impact dynamics have gotten better, Schultz and Bruck-Syal decided it might be time to take a second look at whether comet impacts could produce that kind of scouring. Their new simulations showed that the impact of a comet coma plus its icy core would indeed have the effect of blowing away the smallest grains that sit atop the lunar soil. The simulations showed that the scoured area would stretch for perhaps thousands of kilometers from the impact point, consistent with the swirling streaks that extend across the Moon’s surface. Eddies and vortices created by the gaseous impact would explain the swirls’ twisty, sinuous appearance.

The comet impact hypothesis could also explain the presence of magnetic anomalies near the swirls. The simulations showed that a comet impact would melt some of the tiny particles near the surface. When small, iron-rich particles are melted and then cooled, they record the presence of any magnetic field that may be present at the time. “Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,” Schultz said. “As the gas collides with the lunar surface, the cometary magnetic field becomes amplified and recorded in the small particles when they cool.”

Taken together, the results offer a more complete picture of how the swirls form, the researchers say.

“This is the first time anyone has looked at this using modern computational techniques,” Schultz said. “Everything we see in simulations of comet impacts is consistent with the swirls as we see them on the Moon. We think this process provides a consistent explanation, but may need new Moon missions to finally resolve the debate.”

Story Source:

The above story is based on materials provided by Brown University. Note: Materials may be edited for content and length.

Journal Reference:

1. Megan Bruck Syala, Peter H. Schultzb. Cometary impact effects at the Moon: Implications for lunar swirl formation. Icarus, 2015; DOI: 10.1016/j.icarus.2015.05.005

{ http://nationalufocenter.com/ }

For decades, astronomers have wondered whether the solar system’s circular orbits might be a rarity in our universe. Now a new analysis suggests that such orbital regularity is instead the norm, at least for systems with planets as small as Earth.

In a paper published in the Astrophysical Journal, researchers from MIT and Aarhus University in Denmark report that 74 exoplanets, located hundreds of light-years away, orbit their respective stars in circular patterns, much like the planets of our solar system.

These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.

“Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere,” says Vincent Van Eylen, a visiting graduate student in MIT’s Department of Physics. “Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm.”

Ultimately, Van Eylen says that’s good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)

“If eccentric orbits are common for habitable planets, that would be quite a worry for life, because they would have such a large range of climate properties,” Van Eylen says. “But what we find is, probably we don’t have to worry too much because circular cases are fairly common.”

Star-crossed numbers

In the past, researchers have calculated the orbital eccentricities of large, “gas giant” exoplanets using radial velocity — a technique that measures a star’s movement. As a planet orbits a star, its gravitational force will tug on the star, causing it to move in a pattern that reflects the planet’s orbit. However, the technique is most successful for larger planets, as they exert enough gravitational pull to influence their stars.

Researchers commonly find smaller planets by using a transit-detecting method, in which they study the light given off by a star, in search of dips in starlight that signify when a planet crosses, or “transits,” in front of that star, momentarily diminishing its light. Ordinarily, this method only illuminates a planet’s existence, not its orbit. But Van Eylen and his colleague Simon Albrecht, of Aarhus University, devised a way to glean orbital information from stellar transit data.

They first reasoned that if they knew the mass and radius of a planet’s star, they could calculate how long a planet would take to orbit that star, if its orbit were circular. The mass and radius of a star determines its gravitational pull, which in turn influences how fast a planet travels around the star.

By calculating a planet’s orbital velocity in a circular orbit, they could then estimate a transit’s duration — how long a planet would take to cross in front of a star. If the calculated transit matched an actual transit, the researchers reasoned that the planet’s orbit must be circular. If the transit were longer or shorter, the orbit must be more elongated, or eccentric.

Not so eccentric

To obtain actual transit data, the team looked through data collected over the past four years by NASA’s Kepler telescope — a space observatory that surveys a slice of the sky in search of habitable planets. The telescope has monitored the brightness of over 145,000 stars, only a fraction of which have been characterized in any detail.

The team chose to concentrate on 28 stars for which mass and radius have previously been measured, using asteroseismology — a technique that measures stellar pulsations, which reflect a star’s mass and radius.

These 28 stars host multiplanet systems — 74 exoplanets in all. The researchers obtained Kepler data for each exoplanet, looking not only for the occurrence of transits, but also their duration. Given the mass and radius of the host stars, the team calculated each planet’s transit duration if its orbit were circular, then compared the estimated transit durations with actual transit durations from Kepler data.

Across the board, Van Eylen and Albrecht found the calculated and actual transit durations matched, suggesting that all 74 exoplanets maintain circular, not eccentric, orbits.

“We found that most of them matched pretty closely, which means they’re pretty close to being circular,” Van Eylen says. “We are very certain that if very high eccentricities were common, we would’ve seen that, which we don’t.”

Van Eylen says the orbital results for these smaller planets may eventually help to explain why larger planets have more extreme orbits.

“We want to understand why some exoplanets have extremely eccentric orbits, while in other cases, such as the solar system, planets orbit mostly circularly,” Van Eylen says. “This is one of the first times we’ve reliably measured the eccentricities of small planets, and it’s exciting to see they are different from the giant planets, but similar to the solar system.”

Story Source:

The above story is based on materials provided by Massachusetts Institute of Technology. The original article was written by Jennifer Chu. Note: Materials may be edited for content and length.

Journal Reference:

1. F. Mullally, Jeffrey L. Coughlin, Susan E. Thompson, Jason Rowe, Christopher Burke, David W. Latham, Natalie M. Batalha, Stephen T. Bryson, Jessie Christiansen, Christopher E. Henze, Aviv Ofir, Billy Quarles, Avi Shporer, Vincent Van Eylen, Christa Van Laerhoven, Yash Shah, Angie Wolfgang, W. J. Chaplin, Ji-Wei Xie, Rachel Akeson, Vic Argabright, Eric Bachtell, Thomas Barclay, William J. Borucki, Douglas A. Caldwell, Jennifer R. Campbell, Joseph H. Catanzarite, William D. Cochran, Riley M. Duren, Scott W. Fleming, Dorothy Fraquelli, Forrest R. Girouard, Michael R. Haas, Krzysztof G. Hełminiak, Steve B. Howell, Daniel Huber, Kipp Larson, Thomas N. Gautier III, Jon M. Jenkins, Jie Li, Jack J. Lissauer, Scot McArthur, Chris Miller, Robert L. Morris, Anima Patil-Sabale, Peter Plavchan, Dustin Putnam, Elisa V. Quintana, Solange Ramirez, V. Silva Aguirre, Shawn Seader, Jeffrey C. Smith, Jason H. Steffen, Chris Stewart, Jeremy Stober, Martin Still, Peter Tenenbaum, John Troeltzsch, Joseph D. Twicken, Khadeejah A. Zamudio. PLANETARY CANDIDATES OBSERVED BYKEPLER. VI. PLANET SAMPLE FROM Q1–Q16 (47 MONTHS). The Astrophysical Journal Supplement Series, 2015; 217 (2): 31 DOI: 10.1088/0067-0049/217/2/31

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In a paper published in the journal Icarus, the researchers use state-of-the-art computer models to simulate the dynamics of comet impacts on the lunar soil. The simulations suggest that such impacts can account for many of the features in the mysterious swirls.

“We think this makes a pretty strong case that the swirls represent remnants of cometary collisions,” said Peter Schultz, a planetary geoscientist at Brown University. Schultz co-wrote the paper with his former graduate student, Megan Bruck Syal, who is now a researcher at the Lawrence Livermore National Laboratory.

Lunar swirls have been the source of debate for years. The twisting, swirling streaks of bright soil stretch, in some cases, for thousands of miles across the lunar surface. Most are found on the unseen far side of the Moon, but one famous swirl called Reiner Gamma can be seen by telescope on the southwestern corner of the Moon’s near side. “It was my favorite object to look at when I was an amateur astronomer,” Schultz said.

At first glance, the swirls do not appear to be related to large impact craters or any other topography. “They simply look as if someone had finger-painted the surface,” Schultz said. “There has been an intense debate about what causes these features.”

In the 1970s, scientists discovered that many of the swirls were associated with anomalies of the Moon’s crustal magnetic field. That revelation led to one hypothesis for how the swirls may have formed. Rocks below the surface in those spots might contain remanent magnetism from early in the Moon’s history, when its magnetic field was much stronger than it is now. It had been proposed that those strong, locally trapped magnetic fields deflect the onslaught of the solar wind, which was thought to slowly darken the Moon’s surface. The swirls would remain brighter than the surrounding soil because of those magnetic shields.

But Schultz had a different idea for how the swirls may form — one that has its roots in watching the lunar modules land on the Moon during the Apollo program.

“You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,” Schultz said. “That was part of what got me started thinking comet impacts could cause the swirls.”

Comets carry their own gaseous atmosphere called a coma. Schultz thought that when small comets slam into the Moon’s surface — as they occasionally do — the coma may scour away loose soil from the surface, not unlike the gas from the lunar modules. That scouring may produce the bright swirls.

Schultz first published a paper outlining the idea in the journal Nature in 1980. That paper focused on how the scouring of the delicate upper layer of lunar soils could produce brightness consistent with the swirls. The structure of the grains in the upper layer (termed the “fairy castle structure” because of the way grains stick together) scatters sun’s rays, causing a dimmer and darker appearance. When this structure is stripped away, the remaining smoothed surface would be brighter than unaffected areas, especially when the sun’s rays strike it at certain angles. For Reiner Gamma on the lunar nearside, those areas appear brightest during the crescent Moon just before sunrise.

As computer simulations of impact dynamics have gotten better, Schultz and Bruck-Syal decided it might be time to take a second look at whether comet impacts could produce that kind of scouring. Their new simulations showed that the impact of a comet coma plus its icy core would indeed have the effect of blowing away the smallest grains that sit atop the lunar soil. The simulations showed that the scoured area would stretch for perhaps thousands of kilometers from the impact point, consistent with the swirling streaks that extend across the Moon’s surface. Eddies and vortices created by the gaseous impact would explain the swirls’ twisty, sinuous appearance.

The comet impact hypothesis could also explain the presence of magnetic anomalies near the swirls. The simulations showed that a comet impact would melt some of the tiny particles near the surface. When small, iron-rich particles are melted and then cooled, they record the presence of any magnetic field that may be present at the time. “Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,” Schultz said. “As the gas collides with the lunar surface, the cometary magnetic field becomes amplified and recorded in the small particles when they cool.”

Taken together, the results offer a more complete picture of how the swirls form, the researchers say.

“This is the first time anyone has looked at this using modern computational techniques,” Schultz said. “Everything we see in simulations of comet impacts is consistent with the swirls as we see them on the Moon. We think this process provides a consistent explanation, but may need new Moon missions to finally resolve the debate.”

Story Source:

The above story is based on materials provided by Brown University. Note: Materials may be edited for content and length.

Journal Reference:

1. Megan Bruck Syala, Peter H. Schultzb. Cometary impact effects at the Moon: Implications for lunar swirl formation. Icarus, 2015; DOI: 10.1016/j.icarus.2015.05.005

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