Kepler discovers smallest "habitable zone" planets

Fig : The diagram compares the planets of the inner solar system to Kepler-62, a five-planet system about 1,200 light-years from Earth in the constellation Lyra. The five planets of Kepler-62 orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the Sun and only one-fifth as bright. At 7 billion years old, the star is somewhat older than the Sun. The green areas mark each star's habitable zone. (NASA Ames/JPL-Caltech)

By NASA Headquarters, Washington, D.C., NASA's Ames Research Center in Moffett Field, California 

Published: April 19, 2013

NASA’s Kepler mission has discovered two new planetary systems that include three super-Earth-sized planets in the “habitable zone,” the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water.

The Kepler-62 system has five planets: 62b, 62c, 62d, 62e, and 62f. The Kepler-69 system has two planets: 69b and 69c. Kepler-62e, 62f, and 69c are the super-Earth-sized planets.

Two of the newly discovered planets orbit a star smaller and cooler than the Sun. Kepler-62f is only 40 percent larger than Earth, making it the exoplanet closest to the size of our planet known in the habitable zone of another star. Kepler-62f is likely to have a rocky composition. Kepler-62e orbits on the inner edge of the habitable zone and is roughly 60 percent larger than Earth.

The third planet, Kepler-69c, is 70 percent larger than Earth and orbits in the habitable zone of a star similar to our Sun. Astronomers are uncertain about the composition of Kepler-69c, but its orbit of 242 days around a Sun-like star resembles that of our neighboring planet Venus.

Scientists do not know whether life could exist on the newfound planets, but their discovery signals that astronomers are another step closer to finding a world similar to Earth around a star like our Sun.


“The Kepler spacecraft has certainly turned out to be a rock star of science,” said John Grunsfeld, associate administrator of the Science Mission Directorate at NASA Headquarters in Washington, D.C. “The discovery of these rocky planets in the habitable zone brings us a bit closer to finding a place like home. It is only a matter of time before we know if the galaxy is home to a multitude of planets like Earth, or if we are a rarity.”

The Kepler space telescope, which simultaneously and continuously measures the brightness of more than 150,000 stars, is NASA’s first mission capable of detecting Earth-sized planets around stars like our Sun.

Orbiting its star every 122 days, Kepler-62e was the first of these habitable zone planets identified. Kepler-62f, with an orbital period of 267 days, was later found by Eric Agol, associate professor of astronomy at the University of Washington.

The scientists have measure the size of Kepler-62f is now measured, but they have yet to determine its mass and composition. Based on previous studies of rocky exoplanets similar in size, however, astronomers are able to estimate its mass by association.

“The detection and confirmation of planets is an enormously collaborative effort of talent and resources, and requires expertise from across the scientific community to produce these tremendous results,” said William Borucki, Kepler science principal investigator at NASA’s Ames Research Center at Moffett Field, California. “Kepler has brought a resurgence of astronomical discoveries, and we are making excellent progress toward determining if planets like ours are the exception or the rule.”

The two habitable zone worlds orbiting Kepler-62 have three companions in orbits closer to their star, two larger than the size of Earth and one about the size of Mars. Kepler-62b, Kepler-62c, and Kepler-62d orbit every five, 12, and 18 days, respectively, making them very hot and inhospitable for life as we know it.

The five planets of the Kepler-62 system orbit a star classified as a K2 dwarf, measuring just two-thirds the size of the Sun and only one-fifth as bright. At 7 billion years old, the star is somewhat older than the Sun. It is about 1,200 light-years from Earth in the constellation Lyra.

A companion to Kepler-69c, known as Kepler-69b, is more than twice the size of Earth and whizzes around its star every 13 days. The Kepler-69 planets’ host star belongs to the same class as our Sun, called G-type. It is 93 percent the size of the Sun and 80 percent as luminous; it's located approximately 2,700 light-years from Earth in the constellation Cygnus.

“We only know of one star that hosts a planet with life — the Sun. Finding a planet in the habitable zone around a star like our Sun is a significant milestone toward finding truly Earth-like planets,” said Thomas Barclay, Kepler scientist at the Bay Area Environmental Research Institute in Sonoma, California, and lead author of the Kepler-69 system discovery.

When a planet candidate transits, or passes in front of, the star from the spacecraft’s vantage point, a percentage of light from the star is blocked. The resulting dip in the brightness of the starlight reveals the transiting planet’s size relative to its star. Using the transit method, Kepler has detected 2,740 candidates. Using various analysis techniques, ground telescopes and other space assets, astronomers have confirmed 122 as planets.

Early in the mission, the Kepler telescope primarily found large gas giants in very close orbits of their stars. Known as “hot Jupiters,” these worlds are easier to detect due to their size and very short orbital periods. Earth would take three years to accomplish the three transits required to be accepted as a planet candidate. As Kepler continues to observe, transit signals of habitable zone planets the size of Earth orbiting stars like the Sun will begin to emerge.

 

Next Door Earth Like Planets

This artist’s conception shows a hypothetical habitable planet with two moons orbiting a red dwarf star. Astronomers have found that 6 percent of all red dwarf stars have an Earth-sized planet in the habitable zone, which is warm enough for liquid water on the planet’s surface. Since red dwarf stars are so common, then statistically the closest Earth-like planet should be only 13 light-years away. // David A. Aguilar (CfA)

By Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts

Published: February 6, 2013
 
Using publicly available data from NASA’s Kepler space telescope, astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA) in Cambridge, Massachusetts, have found that 6 percent of red dwarf stars have habitable Earth-sized planets. Since red dwarfs are the most common stars in our galaxy, the closest Earth-like planet could be just 13 light-years away.

“We thought we would have to search vast distances to find an Earth-like planet. Now, we realize another Earth is probably in our own backyard waiting to be spotted,” said Courtney Dressing from CfA.

Red dwarf stars are smaller, cooler, and fainter than our Sun. An average red dwarf is only one-third as large and one-thousandth as bright as the Sun. From Earth, no red dwarf is visible to the naked eye.

Despite their dimness, these stars are good places to look for Earth-like planets. Red dwarfs make up three out of every four stars in our galaxy for a total of at least 75 billion. The signal of a transiting planet is larger since the star itself is smaller, so an Earth-sized world blocks more of the star’s disk. And since a planet has to orbit a cool star closer in order to be in the habitable zone, it’s more likely to transit from our point of view.

Dressing culled the Kepler catalog of 158,000 target stars to identify all the red dwarfs. She then reanalyzed those stars to calculate more accurate sizes and temperatures. She found that almost all of those stars were smaller and cooler than previously thought.

Since the size of a transiting planet is determined relative to the star size, based on how much of the star’s disk the planet covers, shrinking the star shrinks the planet. And a cooler star will have a tighter habitable zone.

Dressing identified 95 planetary candidates orbiting red dwarf stars. This implied that at least 60 percent of such stars have planets smaller than Neptune. However, most weren’t quite the right size or temperature to be considered truly Earth-like. Three planetary candidates were both warm and approximately Earth-sized. Statistically, this means that 6 percent of all red dwarf stars should have an Earth-like planet.

“We now know the rate of occurrence of habitable planets around the most common stars in our galaxy,” said David Charbonneau from CfA. “That rate implies that it will be significantly easier to search for life beyond the solar system than we previously thought.”

Locating nearby Earth-like worlds may require a dedicated small space telescope or a large network of ground-based telescopes. Follow-up studies with instruments like the Giant Magellan Telescope and James Webb Space Telescope could tell scientists whether any warm, transiting planets have an atmosphere and further probe its chemistry.

Such a world would be different from our own. Orbiting so close to its star, the planet would probably be tidally locked. However, that doesn’t prohibit life since a reasonably thick atmosphere or deep ocean could transport heat around the planet. And while young red dwarf stars emit strong flares of ultraviolet light, an atmosphere could protect life on the planet’s surface. In fact, such stresses could help life evolve. “You don’t need an Earth clone to have life,” said Dressing.

Since red dwarf stars live much longer than Sun-like stars, this discovery raises the interesting possibility that life on such a planet would be much older and more evolved than life on Earth. “We might find an Earth that’s 10 billion years old,” said Charbonneau.

The three habitable-zone planetary candidates identified in this study are Kepler Object of Interest (KOI) 1422.02, which is 90 percent the size of Earth in a 20-day orbit; KOI 2626.01, 1.4 times the size of Earth in a 38-day orbit; and KOI 854.01, 1.7 times the size of Earth in a 56-day orbit. All three are located about 300 to 600 light-years away and orbit stars with temperatures between 5700° and 5900° Fahrenheit (3100° and 3300° Celsius). For comparison, our Sun’s surface is 10000° F (5500° C).

New Secrets of Super-Earths

Fig : A diagram comparing Earth, at left, to a cross-section of a super-Earth on the right. The super-Earth has a relatively small rocky core, an atmosphere of methane, water, and hydrogen, and an extended hydrogen envelope. // Credit: H. Lammer

By Royal Astronomical Society, United Kingdom


Published: February 4, 2013

In the past two decades, astronomers have found hundreds of planets in orbit around other stars. One type of these so-called “exoplanets” is the super-Earths that are thought to have a high proportion of rock but at the same time are significantly bigger than our world. Now, a new study led by Helmut Lammer of the Space Research Institute (IWF) of the Austrian Academy of Sciences suggests that these planets are actually surrounded by extended hydrogen-rich envelopes and that they are unlikely to ever become Earth-like. Rather than being super-Earths, these worlds are more like mini-Neptunes.

Super-Earths follow a different evolutionary track from the planets found in our solar system, but the question is whether they can evolve to become rocky bodies like the terrestrial planets Mercury, Venus, Earth, and Mars. To try to answer this, Lammer and his team looked at the impact of radiation on the upper atmospheres of super-Earths orbiting the stars Kepler-11, Gliese 1214, and 55 Cancri.

These planets are each a few times more massive and slightly larger than Earth and orbit close to their respective stars. The way in which the mass of planets scales with their sizes suggests that they have solid cores surrounded by hydrogen or hydrogen-rich atmospheres, probably captured from the clouds of gas and dust — nebulae — from which the planets formed.

The new model suggests that the short wavelength of extreme ultraviolet light — much bluer than the blue light we see with our eyes — of the host stars heats up the gaseous envelopes of these worlds so that they expand to several times the radius of each planet, and gas escapes from them fairly quickly. Nonetheless, most of the atmosphere remains in place over the whole lifetime of the stars that they orbit.

“Our results indicate that although material in the atmosphere of these planets escapes at a high rate, unlike lower-mass Earth-like planets, many of these super-Earths may not get rid of their nebula-captured hydrogen-rich atmospheres,” said Lammer.

Rather than becoming more like Earth, the super-Earths may more closely resemble Neptune, which together with Uranus is a smaller “gas giant” in our solar system. If the scientists’ results are right, then super-Earths farther out from their stars in the “habitable zone,” where the temperature would allow liquid water to exist, would hold on to their atmospheres even more effectively. If that happens, they would be much less likely to be habitable.
 

Kepler's First Planet Inside Habitable (Outside Solar System)

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission. NASA/Ames/JPL-Caltech

By NASA Headquarters, Washington, D.C.

Published: December 5, 2011

NASA’s Kepler mission has confirmed its first planet in the “habitable zone,” the region where liquid water could exist on a planet’s surface. Kepler also has discovered more than 1,000 new planet candidates, nearly doubling its previously known count. Ten of these candidates are near Earth’s size and orbit in the habitable zone of their host star. Candidates require follow-up observations to verify they are actual planets.

The newly confirmed planet, Kepler-22b, is the smallest yet found to orbit in the middle of the habitable zone of a star similar to our Sun. The planet is about 2.4 times the radius of Earth. Scientists don’t yet know if Kepler-22b has a predominantly rocky, gaseous, or liquid composition, but its discovery is a step closer to finding Earth-like planets.

Previous research hinted at the existence of near-Earth-sized planets in habitable zones, but clear confirmation proved elusive. Two other small planets orbiting stars smaller and cooler than our Sun recently were confirmed on the edges of the habitable zone, with orbits more closely resembling those of Venus and Mars.

“This is a major milestone on the road to finding Earth’s twin,” said Douglas Hudgins from NASA Headquarters in Washington, D.C. “Kepler’s results continue to demonstrate the importance of NASA’s science missions, which aim to answer some of the biggest questions about our place in the universe.”

Kepler discovers planets and planet candidates by measuring dips in the brightness of more than 150,000 stars to search for planets that cross in front, or “transit,” the stars. Kepler requires at least three transits to verify a signal as a planet.

“Fortune smiled upon us with the detection of this planet,” said William Borucki from NASA Ames Research Center at Moffett Field, California. “The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season.”

The Kepler science team uses ground-based telescopes and the Spitzer Space Telescope to review observations on planet candidates the spacecraft finds. The star field that Kepler observes in the constellations Cygnus and Lyra are only visible from ground-based observatories in spring through early fall. The data from these other observations help determine which candidates can be validated as planets.

Kepler-22b is located 600 light-years away. While the planet is larger than Earth, its orbit of 290 days around a Sun-like star resembles that of our world. The planet’s host star belongs to the same class as our Sun, called G-type, although it is slightly smaller and cooler.

Of the 54 habitable zone planet candidates reported in February 2011, Kepler-22b is the first to be confirmed.

The Kepler team is hosting its inaugural science conference at Ames December 5–9, announcing 1,094 new planet candidate discoveries. Since the last catalog was released in February, the number of planet candidates identified by Kepler has increased by 89 percent, and now totals 2,326. Of these, 207 are approximately Earth-sized, 680 are super-Earth-sized, 1,181 are Neptune-sized, 203 are Jupiter-sized, and 55 are larger than Jupiter.

The findings, based on observations conducted May 2009 to September 2010, show a dramatic increase in the numbers of smaller-sized planet candidates.


Kepler observed many large planets in small orbits early in its mission, which were reflected in the February data release. Having had more time to observe three transits of planets with longer orbital periods, the new data suggest that planets one to four times the size of Earth may be abundant in the galaxy.

The number of Earth-sized and super-Earth-sized candidates has increased by more than 200 and 140 percent since February, respectively.

There are 48 planet candidates in their stars’ habitable zones. While this is a decrease from the 54 reported in February, the Kepler team has applied a stricter definition of what constitutes a habitable zone in the new catalog to account for the warming effect of atmospheres, which would move the zone away from the star out to longer orbital periods.

“The tremendous growth in the number of Earth-size candidates tells us that we’re honing in on the planets that Kepler was designed to detect: those that are not only Earth-size, but also are potentially habitable,” said Natalie Batalha from San Jose State University in California. “The more data we collect, the keener our eye for finding the smallest planets out at longer orbital periods.”

New evidence about the existence of a magnetosphere around WASP-12b

Artists impression of the WASP-12 system. ESA/C. Carreau
By Royal Astronomical Society, United Kingdom
Published: April 18, 2011

Jupiter-like worlds around other stars push shock waves ahead of them, according to a team of United Kingdom astronomers. Just as Earth’s magnetic “bowshock” protects us from the high-energy solar wind, these planetary shocks protect their atmospheres from their star’s damaging emissions.

In 2008, observations of the star WASP-12 detected a periodic dip in light as a large planet — cataloged as WASP-12b — passed in front of its host star. Planet hunting with transit instruments like SuperWASP allows astronomers to obtain a wealth of information about exoplanetary systems including their composition and size.

WASP-12b turns out to be one of the largest exoplanets found to date, and it completes each orbit around its parent star in just 26 hours. The planet is more than 155,000 miles (250,000 kilometers) across. With its atmosphere swollen by the intense heat it receives from the star, it makes it a “hot Jupiter.”

Hot Jupiters are similar to the planet Jupiter in our own solar system but located far closer to their host star — WASP-12b is 2.1 million miles (3.4 million km) away from WASP-12, which compares with the Earth-Sun distance of 93 million miles (150 million km). With such a small distance between them, violent interactions between the star and the planet can take place. As one of the largest hot Jupiters discovered to date, WASP-12b also gives a unique opportunity to observe the interactions between the planetary magnetic field and the host star’s magnetic field. The very presence of a magnetic field reveals that the planet must have a conducting, rotating interior.

There is now tantalizing new evidence from Hubble Space Telescope data that a magnetosphere exists around WASP-12b. Observations of the planet taken in ultraviolet wavelengths by a team, including scientists from the Open University, reveal that the start of the dip in the light from the star during the transit of the planet is earlier in ultraviolet than visible light. Originally, material flowing from the planet onto the star was thought to have caused it. A University of St. Andrews, Scotland, group have, however, determined that the planet plows into a supersonic headwind and pushes a shock ahead of it — just like the one around a supersonic jet aircraft.The astronomers carried out simulations of a planet and its bow shock transiting a star and by investigating various shock geometries, orientations, and densities have reproduced the dip in ultraviolet light observed in WASP-12b.

“The location of this bow shock provides us with an exciting new tool to measure the strength of planetary magnetic fields,” said Aline Vidotto from St. Andrews. “This is something that presently cannot be done in any other way.”

“Our models are able to reproduce the data from the Hubble Space Telescope for a range of wind speeds, implying that bow shocks could be far more commonplace than had been thought,” said Joe Llama from St. Andrews.

Bow shocks may also protect the atmospheres of hot Jupiters from their harsh environment. These planets are constantly bombarded with highly charged, energized particles from the wind from their parent stars, meaning that their atmosphere can be eroded. The presence of a magnetic field could greatly reduce the amount of stellar wind the planet is exposed to, effectively acting as a shield and helping the atmosphere survive.“Although our model predicts a bow shock similar to that of the Earth, we are not expecting any messages from WASP-12b as it is too hot to support life,” said Joe Llama. “But the first hints that extrasolar planets have magnetosphere is a big step forward in understanding and identifying the habitable zones where we ultimately hope to find signs of life”.

Astronomers can tune in to radio aurorae to find exoplanets

This image of Jupiter’s northern ultraviolet aurorae was obtained using the Advanced Camera for Surveys aboard the Hubble Space Telescope in February 2007. Scientists believe emissions from similar aurorae on exoplanets should be detectable by radio telescopes.

Photo by Boston University and NASA.
By Royal Astronomical Society, United Kingdom
Published: April 18, 2011

Detecting exoplanets that orbit at large distances from their stars remains a challenge for planet hunters. Now, scientists at the University of Leicester in the United Kingdom have shown that emissions from the radio aurorae of planets like Jupiter should be detectable by radio telescopes such as LOFAR, which will be completed later this year.“This is the first study to predict the radio emissions by exoplanetary systems similar to those we find at Jupiter or Saturn,” said Jonathan Nichols of the University of Leicester. “At both planets, we see radio waves associated with auroras generated by interactions with ionized gas escaping from the volcanic moons Io and Enceladus. Our study shows that we could detect emissions from radio auroras from Jupiter-like systems orbiting at distances as far out as Pluto.”

Of the hundreds of exoplanets that have been detected to date, less than 10 percent orbit at distances where the outer planets in our own solar system lie. Most exoplanets have been found by the transit method, which detects a dimming in light as a planet moves in front of a star, or by looking for a wobble as a star is tugged by the gravity of an orbiting planet. With both these techniques, it is easiest to detect planets close in to the star and moving very quickly.

“Jupiter and Saturn take 12 and 30 years respectively to orbit the Sun, so you would have to be incredibly lucky or look for a very long time to spot them by a transit or a wobble,” said Nichols.

Nichols examined how the radio emissions for Jupiter-like exoplanets would be affected by the rotation rate of the planet, the rate of plasma outflow from a moon, the orbital distance of the planet, and the ultraviolet (UV) brightness of the parent star.He found that, in many scenarios, exoplanets orbiting UV-bright stars between 1 and 50 astronomical units (AU; 1 AU is the average distance between Earth and the Sun) would generate enough radio power to be detectable from Earth. For the brightest stars and fastest-spinning planets, the emissions would be detectable from systems 150 light-years away from Earth.

“In our solar system, we have a stable system with outer gas giants and inner terrestrial planets, like Earth, where life has been able to evolve,” Nichols said. “Being able to detect Jupiter-like planets may help us find planetary systems like our own, with other planets that are capable of supporting life.”

New observations of the monster planet revolving Beta Pictoris

Multi-epoch observations of the β Pictoris b exoplanet. The planet was imaged in 2003 (left image) in the L' band (3.8 μm) in the plane of the circumstellar disk surrounding the star (not seen here). It was detected again October 2009 (middle) when it had moved to the other side of the star. The new observations made March 2010 at 2.18 μm are shown in the right panel. The planet has moved yet again relative to its position measured in 2009.

By Astronomy & Astrophysics, Paris, France
Published: March 4, 2011

Astronomy and Astrophysics is publishing new observations of the giant planet around Beta Pictoris. Discovered in 2009, this planet, called Beta Pictoris b, has now been detected again with the NaCo instrument on the Very Large Telescope (VLT). Astronomers find that the planet is moving around the star. They have also measured the mass and the effective temperature of Beta Pic b.

Astronomy & Astrophysics publishes new high angular resolution observations of the giant planet orbiting the star Beta Pictoris. Located 63.4 light-years from the Sun, Beta Pic is a young star about 12 million years old and 75 percent more massive than our Sun. Beta Pic is well-known for harboring an extended and structured circumstellar disk. It was actually the first star to have its disk directly imaged more than 25 years ago. In 2009, a giant planet was seen orbiting within the disk. With an orbital distance of 8 to 15 astronomical units (AU), Beta Pictoris b is the closest exoplanet to its star that has ever been imaged. This planet offers a new opportunity to study the planetary formation processes, in particular the interactions between the planets and their native disks.

An international team of astronomers observed the Beta Pic system using the VLT/NaCo instrument at 2.18 microns, previous observations having been made near 4 microns. They detected the planet again and compared these new observations with the previous ones. Combining all the data together shows that the planet is moving around the star, as expected from the previous data. Analyzing these new observations, the team was then able to measure the mass of the planet, around 7 to 11 times the mass of Jupiter, and its effective temperature, between 2000° and 3100° Fahrenheit (1100° and 1700° Celsius).

This new data already tell us something about the formation of the planet, especially because the system is young. The planet Beta Pic b is still warm, implying that it has retained most of the primordial heat acquired during its formation. If it has been formed in a similar way to the giant planets of our solar system, and its mass and temperature cannot be explained by some evolutionary models that hypothesize a total release of the energy acquired during the accretion of disk materials.

Forthcoming observations of Beta Pictoris b with NaCo and also with the next generation VLT instrument SPHERE should soon provide more details about its atmosphere and orbital properties and about the way this companion influences the surrounding disk material.

Kepler's newest discovery: A Rocky Exoplanet

Artist depiction of Kepler-10b
Photo by NASA

By NASA Headquarters, Washington, D.C. — Published: January 10, 2011

NASA’s Kepler mission has confirmed the discovery of its first rocky planet, named Kepler-10b. Measuring 1.4 times the size of Earth, it is the smallest planet ever discovered outside our solar system.

The discovery of this so-called exoplanet is based on more than 8 months of data collected by the spacecraft from May 2009 to early January 2010.

“All of Kepler’s best capabilities have converged to yield the first solid evidence of a rocky planet orbiting a star other than our Sun,” said Natalie Batalha, Kepler’s deputy science team lead at NASA’s Ames Research Center in Moffett Field, California, and primary author of a paper on the discovery accepted by The Astrophysical Journal. “The Kepler team made a commitment in 2010 about finding the telltale signatures of small planets in the data, and it’s beginning to pay off.”
Kepler’s ultra-precise photometer measures the tiny decrease in a star’s brightness that occurs when a planet crosses in front of it. The size of the planet can be derived from these periodic dips in brightness. The distance between the planet and the star is calculated by measuring the time between successive dips as the planet orbits the star.

Kepler is the first NASA mission capable of finding Earth-sized planets in or near the habitable zone, the region in a planetary system where liquid water can exist on the planet’s surface. However, since it orbits once every 0.84 days, Kepler-10b is more than 20 times closer to its star than Mercury is to our Sun and not in the habitable zone.

Kepler-10 was the first star identified that could potentially harbor a small transiting planet, placing it at the top of the list for ground-based observations with the W.M. Keck Observatory 10-meter telescope in Hawaii. Scientists waiting for a signal to confirm Kepler-10b as a planet were not disappointed. Keck was able to measure tiny changes in the star’s spectrum, called Doppler shifts, caused by the telltale tug exerted by the orbiting planet on the star.

“The discovery of Kepler 10-b is a significant milestone in the search for planets similar to our own,” said Douglas Hudgins, Kepler program scientist at NASA Headquarters in Washington, D.C. “Although this planet is not in the habitable zone, the exciting find showcases the kinds of discoveries made possible by the mission and the promise of many more to come."

Knowledge of the planet is only as good as the knowledge of the star it orbits. Because Kepler-10 is one of the brighter stars being targeted by Kepler, scientists were able to detect high-frequency variations in the star’s brightness generated by stellar oscillations, or starquakes. This analysis allowed scientists to pin down Kepler-10b’s properties.

There is a clear signal in the data arising from light waves that travel within the interior of the star. Kepler Asteroseismic Science Consortium scientists use the information to better understand the star, just as earthquakes are used to learn about Earth’s interior structure. As a result of this analysis, Kepler-10 is one of the most well-characterized planet-hosting stars in the universe.The exoplanet’s star, Kepler-10, was the first one identified as capable of harboring a small transiting planet, placing the star at the top of the list for ground-based observations using the W.M. Keck Observatory 10-meter telescope in Hawaii. Kepler-10 is located 560 light-years from our solar system and is approximately the same size as our sun. The star is estimated to be 11.9 billion years old.

That’s good news for the team studying Kepler-10b. Accurate stellar properties yield accurate planet properties. In the case of Kepler-10b, the picture that emerges is of a rocky planet with a mass 4.6 times that of Earth and with an average density of 8.8 grams per cubic centimeter — similar to that of an iron dumbbell.

Determining 500th Exoplanet Will Be a Tricky Job

2MASS J044144 is a brown dwarf with a companion about 5-10 times the mass of Jupiter. It is not clear whether this companion object is a sub-brown dwarf or a planet.
Provided By: Space.com
Date: 14th November,2010

The number of planets that astronomers have discovered orbiting distant stars hovers right below 500. But confirming which remote flicker of light is the milestone alien world will be a tricky affair.At NASA's last count, astronomers had confirmed the discovery of 496 planets around alien suns. There are signs of dozens more, if not hundreds, but it will take time to weed out which of the detections are actual worlds and which are merely false alarms.Some astronomers now expect that official discovery of the 500th alien planet by January 2011.In the meantime, scientists lean on telescopes and space observatories, as well as a tried-and-true bag of tricks, for identifying and confirming planets beyond our own solar system.There are four primary techniques currently used to find exoplanets, each with its own pitfalls.The radial velocity method looks for repeated wobbles in a star's movements that are signs of a planet's gravitational pull yanking it back and forth.

However, if a planet has very little mass, it hardly exerts much of a pull — if an astronomer is trying to detect something like an Earth-size planet, the noise or static in the data can be mistaken for a planet. Overcoming this problem largely requires measuring the star over and over and over again, said astrobiologist Alan Boss at Carnegie Institution of Washington."That can take a lot of telescope time, which can be very, very expensive," said planetary scientist Sara Seager at the Massachusetts Institute of Technology. "One night of time at the Keck telescope can cost $50,000."The transit method looks for dips in a star's brightness whenever a planet crosses in front of it. The problem is that if the star under observation is in mutual orbit with another star, it's that other star that could lead to regular dips and surges in brightness.

Another technique, called the microlensing method, looks for distortions in light resulting from the pull of gravity. The gravitational field of a planet can have a measurable effect on light that passes by it.However, this occurs only when a star with a planet happens to line up with another star — a brief event that never happens again, "like two ships passing in the night," explained astronomer Geoffrey Marcy at the University of California at Berkeley.The difficulty in reproducing results can make microlensing hard to rely on, although there have been solid examples of microlensing that overcame any doubts.Astronomers also may directly image the light from an exoplanet. "The down side there is, how do you know if that candidate is a planet or a faint star?" Marcy said. "Faint stars look a lot like glowing planets."

What makes a planet?

There is no exoplanet list formally sanctioned by the International Astronomical Union, the body that assigns official designations to celestial bodies.Instead, there are only unofficial lists maintained by researchers in the field, such as astrobiologist Jean Schneider at the Paris-Meudon Observatory and astronomer Jason Wright of the University of California in Berkeley.There are also no hard and fast rules as to whether a candidate should be declared an exoplanet; each researcher and group has its own preferences, Schneider said. To get others to accept their results, scientists often wait until the probability that their results are false alarms falls below 1 percent or so.The standard way that the field confirms the report of a planet is through its acceptance by knowledgeable referees into a scientific journal. Still, as many as 50 to 100 exoplanets were revealed in talks, only to wait years before their appearance in a journal. The discoverers may simply have been too busy doing actual work to write up the papers, Schneider explained.

False alarms:
In addition, even after publication, a few exoplanets have been retracted as false alarms — "five to 10 since 1989," Schneider estimated."My research group publishes data on an exoplanet when the false alarm probability drops below 1 percent, which means about 1 percent will be wrong," Marcy said. "There's always a chance to be wrong, and as scientists we try to calculate what that probability is and present it openly." "There's always a chance there's a few errors in data to make something look like a planet," he added. "This can happen to anyone — just one of those things that happens when you're pushing a frontier, pushing instruments to their bitter limits. This kind of astronomy is hard work, and there are lots of ways to make a mistake. A number might slip through, but they're generally corrected in a year or two."

Another possible point of confusion is the fuzzy boundary that separates a planet from a "brown dwarf" — a large gaseous body, more than 13 times the mass of Jupiter, that failed to become a star. "Something 20 Jupiter masses and below is likely a planet, but there's ambiguity there," Schneider said.All these concerns might give the impression of a list of published exoplanet being a bit of a mess, but overall, Schneider contended, only 1 or 2 percent of these discoveries are unclear so far."The real acid test in the field is getting two methods to detect an object — for instance, a radial velocity signature plus a transit detection," Boss said. "There are about 100 of such absolutely, positively identified planets so far."

Exoplanet overdrive

In the end, "there is no real honor roll of planets, no real way to say which the 500th planet will be," Boss said.Still, while it has taken scientists roughly 15 years to confirm the detection of the nearly 500 planets known so far, the pace promises to grow rapidly.NASA's Kepler mission, a space observatory surveying a large sample of stars as it orbits the sun, revealed in June that it had detected more than 750 possible exoplanets using the transit method within its first 43 days of operation."Kepler is beating us all by a million miles," Marcy said.Many of the candidates Kepler discovered are now getting verified with radial velocity confirmations. "On Feb. 1, we'll announce all of them — a huge avalanche of exoplanet candidates," Marcy said."The days of having to have perfect exoplanets are going away," Seager noted. "We're going to publish so many planets that we're not going to be able to validate all of them. Instead, we'll have so many we can start studying them statistically in groups."Even without Kepler, there are roughly 100 exoplanet candidates that researchers are working hard to confirm, Marcy said."We could well hit 500 on Jean Schneider's list by January," Boss said.

The Planet that will die soon

Picture: The camera which has found Planet WASP-18b

WASP-18b is an extrasolar planet that is notable for having an orbital period of less than one day. It has a mass equal to 10 Jupiter masses,just below the boundary line between planets and brown dwarfs, about 13 Jupiter masses. Due to tidal deceleration, it is expected to spiral towards and eventually merge with its host star, WASP-18, in less than a million years.The planet is approximately 1.9 million miles from its star, which is about 325 light years from Earth. It was discovered by Coel Hellier, a professor of astrophysics at Keele University in England.

Scientists at Keele and at the University of Maryland are working to understand whether the discovery of this planet so shortly before its expected demise (with less than 0.1% of its lifetime remaining) was fortuitous, or whether tidal dissipation by WASP-18 is actually much less efficient than astrophysicists typically assume.Observations made over the next decade should yield a measurement of the rate at which WASP-18b's orbit is decaying.

The closest example of a similar situation in our own solar system is Mars' moon, Phobos. Phobos orbits Mars at a distance of only about 5,600 miles, 40 times closer than our moon is to the Earth,and is expected to be destroyed in about eleven million years.

Huge new planet tells of game of planetary billiards

A team of scientists has found a new planet which orbits the wrong way around its host star. The planet, named WASP-17, and orbiting a star 1000 light years away, was found by the UK's WASP project in collaboration with Geneva Observatory. The discovery, which casts new light on how planetary systems form and evolve, is being announced today (12th August) in a paper submitted to Astrophysical Journal.

Since planets form out of the same swirling gas cloud that creates a star, they are expected to orbit in the same direction that the star spins. Graduate students David Anderson, of Keele University, and Amaury Triaud, of Geneva Observatory, were surprised to find that WASP-17 is orbiting the wrong way, making it the first planet known to have a ``retrograde'' orbit. The likely explanation is that WASP-17 was involved in a near collision with another planet early in its history.

WASP-17 appears to have been the victim of a game of planetary billiards, flung into its unusual orbit by a close encounter with a ``big brother'' planet. Professor Coel Hellier, of Keele University, remarks: "Shakespeare said that two planets could no more occupy the same orbit than two kings could rule England; WASP-17 shows that he was right.”

David Anderson added “Newly formed solar systems can be violent places. Our own moon is thought to have been created when a Mars-sized planet collided with the recently formed Earth and threw up a cloud of debris that turned into the moon. A near collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit.”

The first sign that WASP-17 was unusual was its large size. Though it is only half the mass of Jupiter it is bloated to nearly twice Jupiter's size, making it the largest planet known.

Astronomers have long wondered why some extra-solar planets are far bigger than expected, and WASP-17 points to the explanation. Scattered into a highly elliptical, retrograde orbit, it would have been subjected to intense tides. Tidal compression and stretching would have heated the gas-giant planet to its current, hugely bloated extent. "This planet is only as dense as expanded polystyrene, seventy times less dense than the planet we're standing on", notes Prof. Hellier.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council, which funded the research, said, “This is a fascinating new find and another triumph for the WASP team. Not only are they locating these far flung and mysterious planets but revealing more about how planetary systems, such as our own Solar System, formed and evolved. The WASP team has proved once again why this project is currently the World's most successful project searching for transiting exoplanets.”

WASP-17 is the 17th new exoplanet (planet outside our solar system) found by the Wide Area Search for Planets (WASP) consortium of UK universities. The WASP team detected the planet using an array of cameras that monitor hundreds of thousands of stars, searching for small dips in their light when a planet transits in front of them. Geneva Observatory then measured the mass of WASP-17, showing that it was the right mass to be a planet. The WASP-South camera array that led to the discovery of WASP-17 is hosted by the South African Astronomical Observatory.

Wednesday, August 12, 2009

COROT discovers smallest exoplanet yet, with a surface to walk on

One of the methods for detecting exoplanets is to look for the drop in brightness they cause when they pass in front of their parent star. Such a celestial alignment is known as a planetary transit.From Earth, both Mercury and Venus occasionally pass across the front of the Sun. When they do, they look like tiny black dots passing across the bright surface.Such transits block a tiny fraction of the light that COROT is able to detect.

Credits: CNES
3 February 2009

COROT has found the smallest terrestrial planet ever detected outside the Solar System. The amazing planet is less than twice the size of Earth and orbits a Sun-like star. Its temperature is so high that it is possibly covered in lava or water vapour.

About 330 exoplanets have been discovered so far, most of which are gas giants with characteristics similar to Jupiter and Neptune.

The new find, COROT-Exo-7b, is different: its diameter is less than twice that of Earth and it orbits its star once every 20 hours. It is located very close to its parent star, and has a high temperature, between 1000 and 1500°C. Astronomers detected the new planet as it transited its parent star, dimming the light from the star as it passed in front of it.

The density of the planet is still under investigation: it may be rocky like Earth and covered in liquid lava. It may also belong to a class of planets that are thought to be made up of water and rock in almost equal amounts. Given the high temperatures measured, the planet would be a very hot and humid place.

“Finding such a small planet was not a complete surprise”, said Daniel Rouan, researcher at the Observatoire de Paris Lesia, who coordinates the project with Alain Léger, from Institut d’Astrophysique Spatiale (Paris, France). “COROT-Exo-7b belongs to a class of objects whose existence had been predicted for some time. COROT was designed precisely in the hope of discovering some of these objects,” he added.

Very few exoplanets found so far have a mass comparable to Earth’s and the other terrestrial planets: Venus, Mars, and Mercury. This is because terrestrial planets are extremely difficult to detect. Most of the methods used so far are indirect and sensitive to the mass of the planet, while COROT can directly measure the size of its surface, which is an advantage. In addition, its location in space allows for longer periods of uninterrupted observation than from ground.This discovery is significant because recent measurements have indicated the existence of planets of small masses but their size remained undetermined until now.

The internal structure of COROT-exo-7b particularly puzzles scientists; they are unsure whether it is an ‘ocean planet’, a kind of planet whose existence has never been proved so far. In theory, such planets would initially be covered partially in ice and they would later drift towards their star, with the ice melting to cover it in liquid.

"This discovery is a very important step on the road to understanding the formation and evolution of our planet," said Malcolm Fridlund, ESA’s COROT Project Scientist. “For the first time, we have unambiguously detected a planet that is 'rocky' in the same sense as our own Earth. We now have to understand this object further to put it into context, and continue our search for smaller, more Earth-like objects with COROT," he added.

Transit Search Finds Super-Neptune

This artist's conception reveals the newly discovered Super-Neptune planet orbiting a star 120 light years away from Earth. Normally blue in color, its red hue is caused by the illumination from the nearby Red Dwarf star. Credit: David A. Aguilar (CfA)

Tuesday, January 20, 2009

Astronomers at the Harvard-Smithsonian Center for Astrophysics have discovered a planet somewhat larger and more massive than Neptune orbiting a star 120 light-years from Earth. While Neptune has a diameter 3.8 times that of Earth and a mass 17 times Earth's, the new world (named HAT-P-11b) is 4.7 times the size of Earth and has 25 Earth masses.

HAT-P-11b was discovered because it passes directly in front of (transits) its parent star, thereby blocking about 0.4 percent of the star's light. This periodic dimming was detected by a network of small, automated telescopes known as "HATNet," which is operated by the Center in Arizona and Hawaii. HAT-P-11b is the 11th extrasolar planet found by HATNet, and the smallest yet discovered by any of the several transit search projects underway around the world.

Transit detections are particularly useful because the amount of dimming tells the astronomers how big the planet must be. By combining transit data with measurements of the star's "wobble" (radial velocity) made by large telescopes like Keck, astronomers can determine the mass of the planet.

A number of Neptune-like planets have been found recently by radial velocity searches, but HAT-P-11b is only the second Neptune-like planet found to transit its star, thus permitting the precise determination of its mass and radius.

The newfound world orbits very close to its star, revolving once every 4.88 days. As a result, it is baked to a temperature of around 1100 degrees F. The star itself is about three-fourths the size of our Sun and somewhat cooler.

There are signs of a second planet in the HAT-P-11 system, but more radial velocity data are needed to confirm that and determine its properties.

Another team has located one other transiting super-Neptune, known as GJ436b, around a different star. It was discovered by a radial velocity search and later found to have transits.

"Having two such objects to compare helps astronomers to test theories of planetary structure and formation," said Harvard astronomer Gaspar Bakos, who led the discovery team.

HAT-P-11 is in the constellation Cygnus, which puts in it the field of view of NASA's upcoming Kepler spacecraft. Kepler will search for extrasolar planets using the same transit technique pioneered by ground-based telescopes. This mission potentially could detect the first Earth-like world orbiting a distant star. "In addition, however, we expect Kepler to measure the detailed properties of HAT-P-11 with the extraordinary precision possible only from space," said Robert Noyes, another member of the discovery team.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Scientists discover new planet

The mirror of the 9.2-meter Hobby-Eberly Telescope is visible through the open louvers in this twilight view. In daylight, the flagpoles on the right show the flags of the five HET partner institutions. McDonald Observatory, University of Texas, Austin

November 20, 2008

Provided by Penn State University, University Park

A team of astronomers from Penn State University and Nicolaus Copernicus University in Poland has discovered a new planet that is closely orbiting a red-giant star, HD 102272, which is much more evolved than our own Sun. The planet has a mass that is nearly 6 times that of Jupiter, the largest planet in our solar system. The team includes Alexander Wolszczan, the discoverer of the first planets ever found outside our solar system and an Evan Pugh professor of astronomy and astrophysics and the director of the Center for Exoplanets and Habitable Worlds at Penn State; and Andrzej Niedzielski, who leads his collaborators in Poland. The team suspects that a second planet may be orbiting HD 102272, as well. The findings, which will be published in a future issue of The Astrophysical Journal, shed light on the ways in which aging stars can influence nearby planets.

Scientists already know that stars expand as they age and that they eventually may gobble up adjacent planets. In fact, they expect the Sun will swallow Earth in about a billion years. But what scientists don't yet understand fully is how aging stars influence nearby planets before they are destroyed. The team's newly discovered planet is interesting because it is located closer to a red-giant star than any other known planet. From the distance of 0.6 astronomical units, which is less than the distance between Venus and the Sun, the steadily expanding giant appears in the planet's alien skies as a huge reddish disk that is more than 16 times larger than the face of Earth's Full Moon as it appears to us.

"When red-giant stars expand, they tend to eat up the nearby planets," said Wolszczan. "Although the planet we discovered conceivably could be closer to the star without being harmed by it, there appears to be a zone of avoidance around such stars. Our discovery pushes it back to about 0.6 astronomical units, which is the size of the new planet's orbit. It is important to find out why planets don't want to get any closer to stars, so one of our next steps is to try to figure out why this zone of avoidance exists and whether it occurs around all red-giant stars."

The team used the Hobby-Eberly Telescope of McDonald Observatory in southwestern Texas to make its discovery. Through the telescope, which is equipped with a precise spectrograph, the scientists observed a pattern of alternating shifts of spectral lines in the light coming from the star, which are located 1,200 light-years from Earth in the constellation Leo. These tiny alternating shifts represent the fingerprint of a star that is moving alternately toward and away from Earth as it wobbles in space responding to the gravitational pull of an orbiting planet. Because of the Doppler effect, the light from the star becomes bluer as it moves toward Earth and then redder as it recedes from it, which is reflected by the measured shifts of the spectral lines. The specific pattern of these shifts, which the research team observed, allowed the scientists to determine that one planet — and possibly two planets — orbit the star. If the second planet exists, the system would become the first multi-planet system discovered around a red-giant star.

Wolszczan said that he is particularly interested in applying to our own solar system the knowledge he gains about the effects of aging stars on planets orbiting other stars. "Our own Sun one day will become a red giant, and it is interesting to think about what will happen to the outer planets of our solar system as the Sun expands," he said. "For example, Europa, one of Jupiter's moons, is covered by ice, but if it were to exist closer to the Sun, it might become a warm ocean world that could possibly support life."

In 1992, Wolszczan became the first person to discover planets outside our solar system when he used the 1,000-foot Arecibo radio telescope to detect three planets orbiting a rapidly spinning neutron star. The discovery opened the door to the current intense era of planet hunting by suggesting that planet formation could be quite common throughout the universe and that planets can form around different types of stellar objects. The Penn State Center for Exoplanets and Habitable Worlds, which Wolszczan directs, fosters research in the field of extrasolar-planet studies in which the primary goals are to find planets where living organisms exist, or might exist, and to determine their rate of occurrence in the universe. The researchers received support from the Polish Ministry of Science and Higher Education, the NASA Astrobiology Program, the Foundation for Polish Science, and the Polish Academy of Sciences.

New detector design enhances exoplanet studies

When the planet WASP-10b crosses the disk of its star, WASP-10, the brightness of the star decreases, allowing scientists to measure the precise size of the planet. John Johnson

December 11, 2008

Provided by Institute for Astronomy, Honolulu

A team of astronomers led by John Johnson of the University of Hawaii's Institute for Astronomy (UH) has used a new technique to measure the precise size of a planet orbiting a distant star. The team used a camera so sensitive that it could detect the passage of a moth in front of a lit window from a distance of 1,000 miles.

The camera, mounted on UH's 2.2-meter telescope on Mauna Kea, measures the small decrease in brightness that occurs when a planet passes in front of its star along the line-of-sight from Earth. These "planet transits" allow researchers to measure the diameters of worlds outside our solar system.

"While we know of more than 330 planets orbiting other stars in our Milky Way galaxy, we can measure the physical sizes of only the few that line up just right to transit," said Johnson. The team studied a planet called WASP-10b, which was thought to have an unusually large diameter. They measured its diameter with higher precision than before, and they found it is one of the densest planets known, rather than one of the most bloated. The planet orbits the star WASP-10, which is about 300 light-years from Earth.

Institute for Astronomy (IfA) astronomer John Tonry designed the camera, known as Orthogonal Parallel Transfer Imaging Camera (OPTIC), and it was built at the IfA. It uses a new type of detector, an orthogonal transfer array, which is the same type used in the Pan-STARRS 1.4 Gigapixel Camera, the largest digital camera in the world. These detectors are similar to the CCDs (charge-coupled devices) commonly used in scientific and consumer digital cameras, but they are more stable and can collect more light, which leads to higher precision.

"This new detector design is going to change the way we study planets. It's the killer app for planet transits," said team member Joshua Winn of Massachusetts Institute of Technology (MIT). The precision of the camera is high enough to detect transits of much smaller planets than previously possible. It measures light to a precision of one part in 2,000. For the first time, scientists are approaching the precision needed to measure transits of Earth-size planets.

Bigger planets block more of the star's surface and cause a deeper brightness dip. The diameter of WASP-10b is only 6 percent larger than that of Jupiter, even though WASP-10b is three times more massive. Correspondingly, its density is about three times higher than Jupiter's. Because their interiors become partially degenerate, Jovian planets have a nearly constant radius across a wide range of masses.

The photometric precision is three to four times higher than that of typical CCDs and two to three times higher than the best CCDs, and comparable to the most recent results from the Hubble Space Telescope for stars of the same brightness.

Carbon dioxide found on extrasolar planet

Artist's concept of the star Fomalhaut and the Jupiter-type planet that the Hubble Space Telescope observed

December 9, 2008

Provided by STScI, Baltimore, Maryland

The Jupiter-sized planet, called HD 189733b, is too hot for life, but the Hubble observations are a demonstration that the basic chemistry for life can be measured on planets orbiting other stars. Organic compounds can also be by-products of life processes. Their detection on an earthlike planet may someday provide the first evidence of life beyond Earth.

Previous Hubble and the Spitzer Space Telescope observations of HD 189733b found water vapor. Earlier this year, Hubble astronomers reported that they found methane in the planet's atmosphere.

"This is exciting because Hubble is allowing us to see molecules that probe the conditions, chemistry, and composition of atmospheres on other planets," said team leader Mark Swain of NASA's Jet Propulsion Laboratory in Pasadena, California. "Thanks to Hubble we're entering an era where we are rapidly going to expand the number of molecules we know about on other planets."

Swain used Hubble's Near Infrared Camera and Multi-Object Spectrometer (NICMOS) to study infrared light emitted from the planet, which lies 63 light-years away. Gases in the planet's atmosphere absorb certain wavelengths of light from the planet's hot glowing interior. Swain identified not only carbon dioxide, but also carbon monoxide. The molecules leave their own unique spectral fingerprint on the radiation from the planet that reaches Earth. This is the first time a near-infrared emission spectrum has been obtained for an exoplanet.

"The carbon dioxide is the main focus of the excitement, because that is a molecule that under the right circumstances could have a connection to biological activity as it does on Earth," Swain said. "The very fact that we're able to detect it, and estimate its abundance, is significant for the long-term effort of characterizing planets both to find out what they're made of and to find out if they could be a possible host for life."

This type of observation is best done for planets with orbits tilted edge-on to Earth. They routinely pass in front of and then behind their parent stars, a phenomenon known as an eclipse. The planet HD 189733b passes behind its companion star once every 2.2 days. This allows an opportunity to subtract the light of the star alone (when the planet is blocked) from that of the star and planet together prior to eclipse, thus isolating the emission of the planet and making possible a chemical analysis of its day-side atmosphere.

Swain uses the eclipse of the planet behind the star to probe the planet's dayside, which contains the hottest portions of its atmosphere. "We're starting to find the molecules and to figure out how many there are to see the changes between the day side and the night side," Swain said.

This successful demonstration of looking at near-infrared light emitted from a planet is encouraging for astronomers planning to use NASA's James Webb Space Telescope when it is launched in 2013. These biomarkers are best seen at near-infrared wavelengths.

Astronomers look forward to using the Webb telescope to spectroscopically look for biomarkers on a terrestrial planet the size of Earth or a super-Earth several times our planet's mass. "The Webb telescope should be able to make much more sensitive measurements of these primary and secondary eclipse events," Swain said.

Swain next plans to search for molecules in the atmospheres of other exoplanets and try to increase the number of molecules detected in exoplanet atmospheres. He also plans to use molecules to study changes that may be present in exoplanet atmospheres to learn something about the weather on these distant worlds.

Possible Beta Pictoris planet imaged

This composite image represents the close environment of Beta Pictoris as seen in near infrared light. This faint environment is revealed after a careful subtraction of the brighter stellar halo. The outer part of the image shows the reflected light on the dust disk; the inner part is the innermost part of the system. The newly detected source is more than 1,000 times fainter than Beta Pictoris, aligned with the disk, at a projected distance of 8 times the Earth-Sun distance. ESO telescopes equipped with adaptive optics obtained both parts of the image. ESO/A.-M. Lagrange et al.

November,2008

Provided by the European Southern Observatory

A team of French astronomers has discovered an object located close to the star Beta Pictoris that appears to lie inside the star's disk. With an estimated distance from the star of only 8 times the Earth-Sun distance, this giant planet likely is responsible for the star's oddly shaped disk and could explain the previously observed infall of comets onto the star. It would then be the first image of a planet that is as close to its host star as Saturn is to the Sun.

Only 12 million years old, the "baby star" Beta Pictoris lies about 70 light-years away toward the constellation Pictor the Painter. The hot star is one of the best-known examples of stars surrounded by a dusty "debris" disk. Collisions between larger bodies like planetary embryos or asteroids give off the dust that makes up such disks. They are a bigger version of the zodiacal dust in our solar system.

Beta Pictoris' disk was the first to be imaged — as early as 1984 — and remains the best-studied system. Earlier observations showed a warp of the disk, a secondary inclined disk, and infalling comets onto the star.

"These are indirect, but telltale signs that strongly suggest the presence of a massive planet lying between 5 and 10 times the mean Earth-Sun distance from its host star," said team leader Anne-Marie Lagrange. "However, probing the very inner region of the disk, so close to the glowing star, is a most challenging task."

In 2003, the French team used the Nasmyth Adaptive Optics System Near-Infrared Imager and Spectrograph (NAOS-CONICA) instrument (or NaCo), mounted on one of the 8.2-meter Unit Telescopes of European Southern Observatory's Very Large Telescope (VLT), to study the immediate surroundings of Beta Pictoris.

Recently, a team member reanalyzed the data in a different way to seek the trace of a companion to the star. Infrared wavelengths are well-suited for such searches. "For this, the real challenge is to identify and subtract as accurately as possible the bright stellar halo," said Lagrange. "We were able to achieve this after a precise and drastic selection of the best images recorded during our observations."

The astronomers were able to discern a feeble, point-like glow well inside the star's halo. To eliminate the possibility that this was an artifact and not a real object, the team conducted a battery of tests. This independent analysis led to the same result. Moreover, other data sets discovered the companion, further supporting the team's conclusion: The companion is real.

"Our observations point to the presence of a giant planet, about 8 times as massive as Jupiter and with a projected distance from its star of about 8 times the Earth-Sun distance, which is about the distance of Saturn in our solar system," said Lagrange.

"We cannot yet rule out definitively, however, that the candidate companion could be a foreground or background object," said co-worker Gael Chauvin. "To eliminate this very small possibility, we will need to make new observations that confirm the nature of the diskovery."

The team also dug into the archives of the Hubble Space Telescope but couldn't see anything, "while most possible foreground or background objects would have been detected," said another team member, David Ehrenreich.

The fact that the candidate companion lies in the disk's plane also implies that it is bound to the star and its proto-planetary disk.

"Moreover, the candidate companion has exactly the mass and distance from its host star needed to explain all the disk's properties. This is clearly another nail in the coffin of the false alarm hypothesis," said Lagrange.

When confirmed, this candidate companion will be the closest planet from its star ever imaged. In particular, it will be located well inside the orbits of the outer planets of the solar system. Several other planetary candidates have been imaged, but they are all located farther away from their host star: If they were located in our solar system, they would lie close or beyond the orbit of the farthest planet, Neptune. The formation processes of these distant planets are likely to be quite different from those in Beta Pictoris.

"Direct imaging of extrasolar planets is necessary to test the various models of formation and evolution of planetary systems. But such observations are only beginning. Limited today to giant planets around young stars, they will in the future extend to the detection of cooler and older planets, with the forthcoming instruments on the VLT and on the next generation of optical telescopes," said team member Daniel Rouan.

Youngest forming planet discovered

The false color image is a map of the radio emission (at a wavelength of 1.3 cm) emitted from the region around the star HL Tau. The candidate protoplanet is marked b. The bar at top left (marked 50 AU) indicates 50 times the Earth-Sun distance on the same scale, or about the size of the orbit of Pluto. HL Tau is located in the center of the image. The star is surrounded by a dusty disc tilted to the line of sight; only the inner part is visible here but its extent is indicated by the white ellipse. The arrows show the direction of the jets of hot gas emitted as overspill from the star growth process. VLA/Pie Town antenna

April 2, 2008

Provided by the Royal Astronomical Society

Using radio observatories in the UK and US and computer simulations, a team of astronomers has identified the youngest forming planet yet seen. Team leader Jane Greaves of the University of St. Andrews will discuss this new protoplanet in her talk at the RAS National Astronomy Meeting in Belfast on Wednesday April 2.

Taking advantage of a rare opportunity to use the Very Large Array (VLA) of radio telescopes in the U.S. with the special addition of an extra telescope 50 kilometers away, the team studied the disk of gas and rocky particles around the star HL Tau. This star is thought to be less than 100,000 years old (by comparison the Sun is 4,600 million years old) and lies in the direction of the constellation of Taurus at a distance of 520 light-years. The disk around HL Tau is unusually massive and bright, which makes it an excellent place to search for signs of forming planets.

The VLA gives very sharp images of HL Tau and its surroundings. The team studied the system using radio emission at a wavelength of 1.3 cm, specifically chosen to search for the emission from super-large rocky particles about the size of pebbles. The presence of these pebbles is a clue that rocky material is beginning to clump together to form planets.

This is an image from the computer simulation of HL Tau and its surrounding disk. In the model the dense clump (seen here at top right) forms with a mass of about 8 times that of Jupiter at a distance from the star about 75 times that from the Earth to the Sun. Ken Rice/Royal Observatory Edinburgh

In the UK, scientists used the MERLIN array of radio telescopes centered on Jodrell Bank in Cheshire, to study the same system at longer wavelengths. This allowed the astronomers to confirm that the emission is from rocks and not from other sources such as hot gas. Jodrell Bank scientists Anita Richards and Tom Muxlow analyzed the data.The big surprise was that, as well as detecting super-large dust in the disk around HL Tau, an extra bright clump was seen in the image. It confirms tentative nebulosity reported a few years earlier at around the same position, by a team lead by Jack Welch of the Berkeley-Illinois-Maryland Array. The new image shows the same system in much greater detail.

Greaves comments, "We see a distinct orbiting ball of gas and dust, which is exactly how a very young protoplanet should look. In the future, we would expect this to condense out into a gas giant planet like a massive version of Jupiter. The protoplanet is about 14 times as massive as Jupiter and is about twice as far from HL Tau as Neptune is from our Sun."

Richards adds, "The new object, designated HL Tau b, is the youngest planetary object ever seen and is just 1 percent as old as the young planet found in orbit around the star TW Hydrae that made the news last year. HL Tau b gives a unique view of how planets take shape, because the VLA image also shows the parent disk material from which it formed."

Team member Ken Rice of the University of Edinburgh ran a computer simulation to find out how such a massive protoplanet could form. His animation shows a very similar body condensing out of a disk with similar properties to that actually observed around HL Tau. The planet forms because of gravitational instability in the disk, which is about half as massive as the star itself. This allows small regions to separate out and cool down into self-contained structures. This instability mechanism has been controversial, but the simulated and real data are such a good match that it seems the mechanism really does operate in nature.

Rice comments, "The simulations were as realistic as we could make them and we were delighted that the results compare so well with the observations."

One intriguing property is that XZ Tau, another young star in the same region, may have passed near HL Tau about 1,600 years ago. Although not required for planet formation, it is possible that this flyby tweaked the disk and helped it become unstable. This would be a very recent event in astronomical terms. Whether the proto-planet formed in only the last few hundred years, or sometime in the 100,000 years since the birth of HL Tau, the images provide a unique view of planet formation in action, and the first picture of a protoplanet still embedded in its birth material.

Extra-solar planet found

The planetary system of star HD 74156 is represented at the left, with the three elongated orbits of planets B, C, and D encircling the star. Rory Barnes

January 23, 2008

Provided by the University of Arizona

Astronomers have successfully predicted the existence of an unknown planet, the first since Neptune was predicted in the 1840s. This planet, however, is outside our own solar system, circling a star a little more than 200 light-years from Earth.

The University of Arizona's Rory Barnes and his associates predicted the unknown planet from their theoretical study of the orbits of two planets known to orbit star HD 74156.

Barnes and his colleagues studied the orbits of several planetary systems and found that planets' orbits tend to be packed as closely together as possible without gravity destabilizing their orbits. They reasoned that this tight packing resulted from universal processes of planetary formation.

But the two planets, named "B" and "C", orbiting the star HD 74156 had a big gap between them. They concluded that if their "Packed Planetary Systems" hypothesis was correct, then there must be another planet between planets B and C, and it must be in a particular orbit.

"When I realized that six out of seven multiplanet systems appeared 'packed,'" Barnes says, "I naturally expected there must be another planet in the HD 74156 system so that it, too, would be packed."

Jacob Bean and his colleagues from the University of Texas observed the planetary system carefully and confirmed that a new planet was located where Barnes had predicted. The new planet is named, by convention, HD 74156 D.Steven Soter, astronomer with the American Museum of Natural History in New York, has been following the discoveries of "extra-solar" planets, or planets orbiting other stars beyond our solar system. Soter notes that this team is the first to successfully predict the existence of an unknown planet since Neptune was predicted more than 160 years ago. Mid-19th century astronomers John Couch Adams in England and Urbain-Jean-Joseph Le Verrier in France independently calculated the position of Neptune based on irregularities in the motion of Uranus.

"As well as providing a way to predict planet discoveries, the Packed Planetary Systems hypothesis reveals something fundamental about the formation of planets," Barnes says. "The process by which planets grow from the clouds of dust and gas around young stars must be very efficient. Wherever there is room for a planet to form, it does."

The Packed Planetary Systems hypothesis also predicts that gaps between known planets in other systems are probably occupied by other, still undiscovered planets. Barnes notes that shortly after the discovery of HD 74156 D, a different team of astronomers found a planet orbiting the star 55 Cancri, again in an orbit that Barnes and Raymond predicted.

Barnes and colleagues also have predicted a specific planet orbiting a third system, HD 38529. So far, no planet has been discovered there. However, the scientists say they expect future observations may confirm another successful prediction by the Packed Planetary Systems hypothesis.

Two unusual older stars giving birth to a second wave of planets

In this image, the star BP Piscium is shown in the center in the constellation Pisces. The green and red streaks are jets of gas shot from the star. M. Perrin, UCLA/J. Graham, UC Berkeley

January 16, 2008

Provided by UCLA

Hundreds of millions, or even billions, of years after planets would have initially formed around two unusual stars, a second wave of planetesimal and planet formation appears to be taking place, UCLA astronomers and colleagues believe.

"This is a new class of stars, ones that display conditions now ripe for formation of a second generation of planets, long, long after the stars themselves formed," says UCLA astronomy graduate student Carl Melis, who reported the findings today at the American Astronomical Society meeting in Austin, Texas.

"If we took a rocket to one of these stars and discovered there were two totally distinct ages for their planets and more minor bodies like asteroids, that would blow scientists' minds away," says Benjamin Zuckerman, UCLA professor of physics and astronomy and co-author of the research, which has not yet been published. "We're seeing stars with characteristics that have never been seen before."

The stars, which Melis says possess "amazing" properties for their age, are known as BP Piscium, in the constellation Pisces, and TYCHO 4144 329 2, in the constellation Ursa Major.

These two stars have many characteristics of very young stars, Melis says, including rapid accretion of gas, extended orbiting disks of dust and gas, a large infrared excess emission and, in the case of BP Piscium, jets of gas that are being shot into space. Planetesimals, like comets and asteroids, along with planets, form from the gas and dust particles that orbit young stars; planetesimals are small masses of rock or ice that merge to form larger bodies.

"With all these characteristics that match so closely with young stars, we would expect that our two stars would also be young," Melis says. "As we gathered more data, however, things just did not add up."

For example, because stars burn lithium as they get older, young stars should have large quantities of lithium. The astronomers found, however, that the spectroscopic signature of lithium in BP Piscium is seven times weaker than expected for a young star of its mass.

"There is no known way to account for this small amount of lithium if BP Piscium is a young star," Melis says. "Rather, lithium has been heavily processed, as appropriate for old stars. Other spectral measurements also indicate it is a much older star."

As seen from Earth, some 75 percent of BP Piscium's radiant energy is being converted by the dust particles into infrared light, and about 12 percent of TYCHO 4144 329 2's. These are unusually high amounts, which Melis described as "spectacular" in comparison to other stars that are known to be not young.

TYCHO 4144 329 2 orbits a companion star that has a mass similar to that of our Sun; a second generation of planets is not forming around this companion, which appears to be an ordinary old star in all respects. By studying this companion star, the astronomers have deduced that TYCHO 4144 329 2 is just 200 light-years from Earth, very close by astronomical standards. They do not know precise age of TYCHO 4144 329 2, or BP Piscium's age or distance from Earth.

The astronomers are continuing to study these stars with a variety of ground-based telescopes and with space-based observatories, including NASA's Hubble Space Telescope and Chandra X-ray Observatory, and they are searching for additional similar stars.