Category: Extrasolar Planets

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Persistence has paid off for astronomer Paul Kalas. After eight years and taking repeated photographs with the Hubble Space Telescope of a nearby star, he finally has what he and many astronomers have been striving for: the first visible-light snapshot of a planet outside our solar system. This coincides with the announcement of the first time astronomers have taken pictures of another multi-planet solar system, using the Gemini and Keck Telescopes. Kalas has been studying the star Fomalhaut, located about 25 light years from Earth, for several years. He knew the planet was there, because its perturbations were evident in the ring of gas and dust surrounding the star. The planet is probably close to the mass of Jupiter, and it orbits Fomalhaut at a distance about four times that between Neptune and the sun. Formally known as Fomalhaut b, the planet could have a ring system about the dimension of Jupiter’s early rings, before the dust and debris coalesced into the four Galilean moons. Learn more in the video below…

The planet’s existence was suspected in 2005, when images Kalas took with the Hubble Space Telescope’s Advanced Camera for Surveys showed a sharply defined inner edge to the dust belt around Fomalhaut, in the southern constellation Piscus Austrinus. The sharp edge and off-center belt suggested to Kalas that a planet in an elliptical orbit around the star was shaping the inner edge of the belt, much like Saturn’s moons groom the edges of its rings.

“The gravity of Fomalhaut b is the key reason that the vast dust belt surrounding Fomalhaut is cleanly sculpted into a ring and offset from the star,” Kalas said. “We predicted this in 2005, and now we have the direct proof.”

Check out this video from ESA about the discovery:

“It will be hard to argue that a Jupiter-mass object orbiting an A star like Fomalhaut is anything other than a planet,” said coauthor James R. Graham, professor of astronomy at UC Berkeley. “That doesn’t mean it’s exactly what we expected when we went hunting for planets in this system.”

“Every planet has a chaotic zone, which is basically a swath of space that encloses the planet’s orbit and from which the planet ejects all particles,” said Eugene Chiang, a UC Berkeley associate professor of astronomy and of earth and planetary science, and first author of the ApJ paper. “This zone increases with the mass of the planet, so, given the size of the chaotic zone around Fomalhaut b, we can estimate that its likely mass is in the vicinity of one Jupiter mass.”

Kalas now has two photographs of the planet, taken in 2004 and 2006, which show that its movement over a 21-month period exactly fits what would be expected from a planet orbiting Fomalhaut every 872 years at a distance of 119 astronomical units, or 11 billion miles. One astronomical unit (AU) is the average distance between the Earth and the sun, or 93 million miles.

“I nearly had a heart attack at the end of May when I confirmed that Fomalhaut b orbits its parent star,” Kalas said. “It’s a profound and overwhelming experience to lay eyes on a planet never before seen.”

Sources: EurekAlert, ESA’s Space Telescope site

Here’s what we’ve all been waiting for: for the first time, astronomers have taken pictures of a multi-planet solar system, much like ours, orbiting another star. This coincides with announcement of the first visible light image of an extrasolar planet taken by the Hubble Space Telescope. This new solar system orbits a dusty young star named HR8799, which is 140 light years away and about 1.5 times the size of our sun. Three planets, roughly 10, 10 and 7 times the mass of Jupiter, orbit the star. The size of the planets decreases with distance from the parent star, much like the giant planets do in our system. And there may be more planets out there, but scientists say they just haven’t seen them yet.

“We’ve been trying to image planets for eight years with no luck and now we have pictures of three planets at once,” said Bruce Macintosh, an astrophysicist from Lawrence Livermore National Laboratory.

Using high-contrast, near-infrared adaptive optics observations with the Keck and Gemini telescopes, the team of researchers were able to see three orbiting planetary companions to HR8799.

Astronomers have known for a decade through indirect techniques that the sun was not the only star with orbiting planets.

“But we finally have an actual image of an entire system,” Macintosh said. “This is a milestone in the search and characterization of planetary systems around stars.”

The planets are 24, 37 and 67 times the Earth-sun separation from the host star. The furthest planet in the new system orbits just inside a disk of dusty debris, similar to that produced by the comets of the Kuiper belt of our solar system (just beyond the orbit of Neptune at 30 times Earth-sun distance).

“HR8799’s dust disk stands out as one of the most massive in orbit around any star within 300 light years of Earth” said UCLA’s Ben Zuckerman.

The host star is known as a bright, blue A-type star. These types of stars are usually ignored in ground and space-based direct imaging surveys since they offer a less favorable contrast between a bright star and a faint planet. But they do have an advantage over our sun: Early in their life, they can retain heavy disks of planet-making material and therefore form more massive planets at wider separations that are easier to detect. In the recent study, the star also is young – less than 100 million years old – which means its planets are still glowing with heat from their formation.

“Seeing these planets directly – separating their light from the star – lets us study them as individuals, and use spectroscopy to study their properties, like temperature or composition,” Macintosh said.

During the past 10 years, various planet detection techniques have been used to find more than 200 exoplanets. But these methods all have limitations. Most infer the existence of a planet through its
influence on the star that it orbits, but don’t actually tell scientists anything about the planet other than its mass and orbit. Second, the techniques are all limited to small to moderate planet-star separation, usually less than about 5 astronomical units.

The planets themselves each appear very interesting.

“Detailed comparison with theoretical model atmospheres confirms that all three planets possess complex atmospheres with dusty clouds partially trapping and re-radiating the escaping heat” said Lowell Observatory astronomer Travis Barman.

Source: Gemini Observatory

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Back in 2000, astronomers discovered a Jupiter-sized planet orbiting the nearby star Epsilon Eridani. Since that star system is listed in some Star Trek lore as the location of the fabled planet Vulcan, astronomers joked they had found Spock’s homeworld. But enticing new discoveries of the Epsilon Eridani system implies it could be a younger twin to our own solar system. It has two rocky asteroid belts and an outer icy ring, making it a triple-ring system. The inner asteroid belt looks strikingly similar to the one in our solar system, while the outer asteroid belt holds 20 times more material. All of this material implies that unseen planets lie hidden, shaping the rings. But if another civilization possibly could have developed in this region, let’s hope they are more like Spock than Kirk’s evil twin….

Epsilon Eridani is the ninth closest star to the Sun. It is slightly smaller and cooler than our own Sun, and is located about 10.5 light-years from Earth in the constellation Eridanus. Epsilon Eridani is visible to the unaided eye, and is younger than the Sun, with an approximate age of 850 million years.

Astronomers say Epsilon Eridani and its planetary system show remarkable similarities to our solar system at a comparable age.

“Studying Epsilon Eridani is like having a time machine to look at our solar system when it was young,” said Smithsonian astronomer Massimo Marengo. Dana Backman from the SETI Institute agreed, saying, “This system probably looks a lot like ours did when life first took root on Earth.” The two astronomers’ paper will appear in the Jan. 10 issue of The Astrophysical Journal.

As the above image shows, the two systems are structured similarly, and both host asteroids (brown), comets (blue) and planets (white dots). Epsilon Eridani’s inner asteroid belt is located at about the same position as ours, approximately three astronomical units from its star (an astronomical unit is the distance between Earth and the sun.). The system’s second, denser belt lies at about the same place where Uranus orbits in our solar system, or 20 astronomical units from the star. Epsilon Eridani is thought to have planets orbiting near the rims of its two belts. The “Vulcan” –like home world was identified in 2000 via the radial velocity technique. The second planet orbiting near the rim of the outer asteroid belt at 20 astronomical units was inferred when Spitzer discovered the belt. A third planet might orbit in Epsilon Eridani at the inner edge of its outermost comet ring, which lies between 35 and 90 astronomical units. This planet was first hinted at in 1998 due to observed lumpiness in the comet ring.

When the Sun was 850 million years old, theorists calculate that our Kuiper Belt looked about the same as that of Epsilon Eridani. Since then, much of the Kuiper Belt material was swept away, some hurled out of the solar system and some sent plunging into the inner planets in an event called the Late Heavy Bombardment. (The Moon shows evidence of the Late Heavy Bombardment—giant craters that formed the lunar seas of lava called mare.) It is possible that Epsilon Eridani will undergo a similar dramatic clearing in the future.

“Epsilon Eridani looks a lot like the young solar system, so it’s conceivable that it will evolve similarly,” said Marengo.

The Spitzer data show gaps between each of the three rings surrounding Epsilon Eridani. Such gaps are best explained by the presence of planets that gravitationally mold the rings, just as the moons of Saturn constrain its rings.

“Planets are the easiest way to explain what we’re seeing,” stated Marengo.

Future studies may detect these currently unseen worlds, as well as any terrestrial planets that may orbit inside the innermost asteroid belt.

Source: Harvard Smithsonia CfA

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The current exoplanet count — the number of planets astronomers have found orbiting other stars –stands at 312. That’s a lot of planets. But not a single one of them can be classified as Earth-like. We just don’t have the ability to detect planets that small yet. But it might help if we knew exactly where to look. New research using supercomputer simulations of dusty disks around sun-like stars show that planets nearly as small as Mars can create patterns in the dust that future telescopes may be able to detect. The research points to a new avenue in the search for habitable planets. “It may be a while before we can directly image earth-like planets around other stars but, before then, we’ll be able to detect the ornate and beautiful rings they carve in interplanetary dust,” says Christopher Stark, the study’s lead researcher at the University of Maryland, College Park.

Working with Marc Kuchner at NASA’s Goddard Space Flight Center in Greenbelt, Md., Stark modeled how 25,000 dust particles responded to the presence of a single planet — ranging from the mass of Mars to five times Earth’s — orbiting a sun-like star. Using NASA’s Thunderhead supercomputer at Goddard, the scientists ran 120 different simulations that varied the size of the dust particles and the planet’s mass and orbital distance.

“Our models use ten times as many particles as previous simulations. This allows us to study the contrast and shapes of ring structures,” Kuchner adds. From this data, the researchers mapped the density, brightness, and heat signature resulting from each set of parameters.

“It isn’t widely appreciated that planetary systems — including our own — contain lots of dust,” Stark adds. “We’re going to put that dust to work for us.”

Much of the dust in our solar system forms inward of Jupiter’s orbit, as comets crumble near the sun and asteroids of all sizes collide. The dust reflects sunlight and sometimes can be seen as a wedge-shaped sky glow — called the zodiacal light — before sunrise or after sunset.

The computer models account for the dust’s response to gravity and other forces, including the star’s light. Starlight exerts a slight drag on small particles that makes them lose orbital energy and drift closer to the star.

“The particles spiral inward and then become temporarily trapped in resonances with the planet,” Kuchner explains. A resonance occurs whenever a particle’s orbital period is a small-number ratio — such as two-thirds or five-sixths — of the planet’s.

For example, if a dust particle makes three orbits around its star every time the planet completes one, the particle repeatedly will feel an extra gravitational tug at the same point in its orbit. For a time, this extra nudge can offset the drag force from starlight and the dust can settle into subtle ring-like structures.

“The particles spiral in toward the star, get trapped in one resonance, fall out of it, spiral in some more, become trapped in another resonance, and so on,” Kuchner says. Accounting for the complex interplay of forces on tens of thousands of particles required the mathematical horsepower of a supercomputer.

Some scientists note that the presence of large amounts of dust could present an obstacle to directly imaging earthlike planets. Future space missions — such as NASA’s James Webb Space Telescope, now under construction and scheduled for launch in 2013, and the proposed Terrestrial Planet Finder — will study nearby stars with dusty disks. The models created by Stark and Kuchner give astronomers a preview of dust structures that signal the presence of otherwise hidden worlds.

“Our catalog will help others infer a planet’s mass and orbital distance, as well as the dominant particle sizes in the rings,” Stark says.

Stark and Kuchner published their results in the October 10 issue of The Astrophysical Journal. Stark has made his atlas of exo-zodiacal dust simulations available online.

Source: Goddard Space Flight Center

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What astronomers had expected to be a run-of-the-mill protoplanetary disk turned out to be evidence of a much more intriguing story. While observing the sun-like star BD 20 307, a team of astronomers noticed a large disk of dust surrounding the star. Usually, this is evidence of planetary formation around younger stars. The 8 planets (and plutoids…) in our own solar system formed out of just such a disk. Disks like this aren’t generally found around older stars, though, and when the age of the star was calculated to be several billion years old, the source of the dust appears to come from a rare event: it is the resulting debris of two planets slamming into each other.

Using data from the Chandra X-ray Observatory, and taking the brightness using one of Tennessee State University’s automated telescopes in Arizona, the team first discovered BD 20 307 to in fact be part of a close binary pair. Not only that, but the system was much older than previously thought: several billions of years old, rather than a few hundred million. The system is 300 light-years away from Earth in the constellation Ares.

The curiously large amount of dust orbiting BD 20 307 is 1 million times the amount of dust than is found in our own solar system, and orbits at a distance from the star that is similar to the orbits of Earth and Venus around our own Sun. The abundance of dust particles in this orbit – and around such a mature star – led scientists to the conclusion that it was created by the violent collision of two exoplanets.

Benjamin Zuckerman, UCLA professor of physics and astronomy and co-author of a paper on the discovery said, “It’s as if Earth and Venus collided with each other. Astronomers have never seen anything like this before. Apparently, major catastrophic collisions can take place in a fully mature planetary system.” Zuckerman and his team will report their findings in the December issue of the Astrophysical Journal.

Normally, warm disks of dust surround younger star systems, out of which larger and larger structures can form, eventually yielding planets. To find a disk of dust in around a star that is several billions of years old is odd, because the pressure of stellar radiation pushes out the lighter dust over time, and the larger chunks either form planets and asteroids, or break down in collisions and get blown away.

The collision between the planets took place within the past few hundred thousand years, though it is possible that it happened even more recently. Such a colossal collision raises the question of how the orbits of the two planets became destabilized, and whether such a collision could happen in our own solar system.

“The stability of planetary orbits in our own solar system has been considered for nearly two decades by astronomer Jacques Laskar in France and, more recently, by Konstantin Batygin and Greg Laughlin in the U.S.A. Their computer models predict planetary motions into the distant future and they find a small probability for collisions of Mercury with Earth or Venus sometime in the next billion years or more. The small probability of this happening may be related to the rarity of very dusty planetary systems like BD+20 307,” said paper co-author Gregory Henry, astronomer at Tennessee State University (TSU).

Source: EurekAlert

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Astronomers have unveiled what is likely the first picture of a planet around a normal star similar to the Sun. Using the Gemini North telescope on Mauna Kea in Hawaii, astronomers from the University of Toronto imaged the young star 1RXS J160929.1-210524, which lies about 500 light-years from Earth and a candidate companion of that star. They also obtained spectra to confirm the nature of the companion, which has a mass about eight times that of Jupiter, and lies roughly 330 times the Earth-Sun distance away from its star. For comparison, the most distant planet in our solar system, Neptune, orbits the Sun at only about 30 times the Earth-Sun distance. The parent star is similar in mass to the Sun, but is much younger. “This is the first time we have directly seen a planetary mass object in a likely orbit around a star like our Sun,” said David Lafrenière, lead author of a paper detailing the discovery. “If we confirm that this object is indeed gravitationally tied to the star, it will be a major step forward.”

Until now, the only planet-like bodies that have been directly imaged outside of the solar system are either free-floating in space (i.e. not found around a star), or orbit brown dwarfs, which are dim and make it easier to detect planetary-mass companions.

The existence of a planetary-mass companion so far from its parent star comes as a surprise, and poses a challenge to theoretical models of star and planet formation. “This discovery is yet another reminder of the truly remarkable diversity of worlds out there, and it’s a strong hint that nature may have more than one mechanism for producing planetary mass companions to normal stars,” said team member Ray Jayawardhana.

The team’s Gemini observations took advantage of adaptive optics technology to dramatically reduce distortions caused by turbulence in Earth’s atmosphere. The near-infrared images and spectra of the suspected planetary object indicate that it is too cool to be a star or even a more massive brown dwarf, and that it is young.

While it could be a chance alignment between the object and the young star, it will take up to two years to verify that the star and its likely planet are moving through space together. “Of course it would be premature to say that the object is definitely orbiting this star, but the evidence is extremely compelling. This will be a very intensely studied object for the next few years!” said Lafrenière.

Team member Marten van Kerkwijk described the group’s search method. “We targeted young stars so that any planetary mass object they hosted would not have had time to cool, and thus would still be relatively bright,” he said. “This is one reason we were able to see it at all.”

The Jupiter-sized body has an estimated temperature of about 1800 Kelvin (about 1500ºC), much hotter than our own Jupiter, which has a temperature of about 160 Kelvin (-110ºC), and its likely host is a young star of type K7 with an estimated mass of about 85% that of the Sun.

“This discovery certainly has us looking forward to what other surprises nature has in stock for us,” said Van Kerkwijk.

Read the team’s paper here.

Source: Gemini Observatory

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You gotta love this about science; someone is always checking your work. Early this year a new exoplanet discovery was announced: TW Hydrae b, a huge planet about ten times as massive as Jupiter. Astronomers thought the planet was in a super-tight orbit around its host star (TW Hydrae), circling in only 3.56 days at a distance of about 6 million kilometers, which is about 4 percent of the distance from the Sun to the Earth. However, another group of astronomers decided to analyze some new optical and infrared data to confirm the radial velocity signal of the planet. Something didn’t seem right, so they ran a few more tests and computer models and determined what they were seeing wasn’t a planet. It was a big sunspot. “Our model shows that a cold spot covering 7% of the stellar surface and located at a latitude of 54 deg can reproduce the reported RV variations,” the astronomers reported in their paper. The rest of the astronomical world must agree with the new determination, as TW Hydrae b has now been dropped from the Planet Quest New Worlds Atlas (a fun site to peruse.) But nature doesn’t like a void, — and astronomers have been working hard in the planet-search department, — so, three new extra solar planets have been discovered and added to the atlas, for a current planet count of 309.

GJ 832 b is about half the size mass of Jupiter and orbits 3.4 AU from its tiny host star. The star is a yellow, sun-like G star, about 16 light years from Earth. It was found with the Anglo-Australian Telescope. Astronomers say it has the largest angular distance from its star among radial velocity detected exoplanets, which makes it a potentially interesting target for future direct detection.

HD 205739 b was also just announced:. This exoplanet is 1.37 times the size mass of Jupiter, and orbits about .9 AU from its star, a blue to white star, which is 1.22x the size of the sun, and 294 light years from Earth. It has an eccentric orbit, and astronomers believe there may be an additional planet in this system, because of how the planet orbits.

Another planet found by the same astronomical team is HD 154672 b. This is a biggie, at about five times the size mass of Jupiter, but only about .6 AU distant from its star, which is just about sun-size, and about 213 light years from Earth. The planet has an orbital period of 163.9 days.

These last two planets were found using the N2K Doppler planet search program with the Magellan telescopes.

Sources: arXiv (here, here and here) and Twitter, PlanetQuest

Using a new technique with a near-infrared spectrograph attached to ESO’s Very Large Telescope, astronomers have been able to study planet-forming discs around young Sun-like stars in unsurpassed detail, clearly revealing the motion and distribution of the gas in the inner parts of the disc. Astronomers used a technique known as ‘spectro-astrometric imaging’ to give them a window into the inner regions of the discs where Earth-like planets may be forming. They were able not only to measure distances as small as one-tenth the Earth-Sun distance, but also measure the velocity of the gas at the same time. “This is like going 4.6 billion years back in time to watch how the planets of our own Solar System formed,” says Klaus Pontoppidan from Caltech, who led the research.

Pontoppidan and colleagues have analyzed three young analogues of our Sun that are each surrounded by a disc of gas and dust from which planets could form. These three discs are just a few million years old and were known to have gaps or holes in them, indicating regions where the dust has been cleared and the possible presence of young planets. However, each of the discs are very different from each other and likely will result in very different planetary systems. “Nature certainly does not like to repeat herself,” said Pontoppidan.

For one of the stars, SR 21, a massive giant planet orbiting at less than 3.5 times the distance between the Earth and the Sun has created a gap in the disc, while for the second star, HD 135344B, a possible planet could be orbiting at 10 to 20 times the Earth-Sun distance. Observations of the disc surrounding the third star, TW Hydrae, may indicate the presence of one or two planets.

The new results not only confirm that gas is present in the gaps in the dust, but also enable astronomers to measure how the gas is distributed in the disc and how the disc is oriented. In regions where the dust appears to have been cleared out, molecular gas is still highly abundant. This can either mean that the dust has clumped together to form planetary embryos, or that a planet has already formed and is in the process of clearing the gas in the disc.

CRIRES, the near-infrared spectrograph attached to ESO’s Very Large Telescope, is fed from the telescope through an adaptive optics module which corrects for the blurring effect of the atmosphere and so makes it possible to have a very narrow slit with a high spectral dispersion: the slit width is 0.2 arcsecond and the spectral resolution is 100 000. Using spectro-astrometry, an ultimate spatial resolution of better than 1 milli-arcsecond is achieved.

“The particular configuration of the instrument and the use of adaptive optics allow astronomers to carry out observations with this technique in a very user-friendly way: as a consequence, spectro-astrometric imaging with CRIRES can now be routinely performed,” says team member Alain Smette, from ESO.

Source: ESO Press Release