Planetary Systems

A Little Telescope Goes a Long Way

PASADENA, CA (Feb. 9, 2010) – NASA astronomers have successfully demonstrated that a David of a telescope can tackle Goliath-size questions in the quest to study Earth-like planets around other stars. Their work, reported today in the journal Nature, provides a new tool for ground-based observatories, promising to accelerate by years the search for prebiotic, or life-related, molecules on planets orbiting stars beyond our solar system.

FIGURE CAPTION – This artist concept shows the planetary system called HD 189733, located 63 light-years away in the constellation Vulpecula. Image credit: NASA/JPL-Caltech

The scientists reported on a new technique used with a relatively small Earth-based telescope to identify an organic molecule in the atmosphere of a Jupiter-size planet nearly 63 light-years away. The measurement revealed details of the exoplanet's atmospheric composition and conditions, an unprecedented achievement from an Earth-based observatory.

The surprising new finding comes from a venerable 30-year-old, 3-meter-diameter (10-foot) telescope that ranks 40th among ground-based telescopes - NASA's Infrared Telescope Facility atop Mauna Kea, Hawaii.

The new technique promises to further speed the work of studying planet atmospheres by enabling studies from the ground that were previously possible only through a few very high-performance space telescopes. "Given favorable observing conditions, this work suggests we may be able to detect organic molecules in the atmospheres of terrestrial planets with existing instruments," said lead author Mark Swain, an astronomer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. This can allow fast and economical advances in focused studies of exoplanet atmospheres, accelerating our understanding of the growing stable of exoplanets.

"The fact that we have used a relatively small, ground-based telescope is exciting because it implies that the largest telescopes on the ground, using this technique, may be able to characterize terrestrial exoplanet targets," Swain said.

Currently, more than 400 exoplanets are known. Most are gaseous like Jupiter, but some "super-Earths" are thought to be large terrestrial, or rocky, worlds. A true Earth-like planet, with the same size as our planet and distance from its star, has yet to be discovered. NASA's Kepler mission is searching from space now, and is expected to find several of these earthly worlds by the end of its three-and-a-half-year prime mission.

On Aug. 11, 2007, Swain and his team turned the infrared telescope to the hot, Jupiter-size planet HD 189733b in the constellation Vulpecula. Every 2.2 days, the planet orbits a K-type main sequence star slightly cooler and smaller than our sun. HD189733b had already yielded breakthrough advances in exoplanet science, including detections of water vapor, methane and carbon dioxide, using space telescopes. Using the new technique, the astronomers successfully detected carbon dioxide and methane in the atmosphere of HD 189733b with a spectrograph, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Their key work was development of a novel calibration method to remove systematic observation errors caused by the variability of Earth's atmosphere and instability due to the movement of the telescope system as it tracks its target.

"As a consequence of this work, we now have the exciting prospect that other suitably equipped yet relatively small ground-based telescopes should be capable of characterizing exoplanets," said John Rayner, the NASA Infrared Telescope Facility support scientist who built the SpeX spectrograph used for these measurements. "On some days we can't even see the sun with the telescope, and the fact that on other days we can now obtain a spectrum of an exoplanet 63 light-years away is astonishing."

In the course of their observations, the team found unexpected bright infrared emission from methane that stands out on the day side of HD189733b, indicating some kind of activity in the planet's atmosphere. Swain said this puzzling feature could be related to the effect of ultraviolet radiation from the planet's parent star hitting the planet's upper atmosphere, but more detailed study is needed. "This feature indicates the surprises that await us as we study exoplanet atmospheres," he added.

"An immediate goal for using this technique is to more fully characterize the atmosphere of this and other exoplanets, including detection of organic and possibly prebiotic molecules" like those that preceded the evolution of life on Earth, said Swain. "We're ready to undertake that task." Some early targets will be the super-Earths. Used in synergy with observations from NASA's Hubble, Spitzer and the future James Webb Space Telescope, the new technique "will give us an absolutely brilliant way to characterize super-Earths," Swain said.

Other authors are Pieter Deroo, Gautam Vasisht and Pin Chen of JPL; Caitlin A. Griffith of the University of Arizona, Tucson; Giovanna Tinetti of University College London; Ian J. Crossfield of UCLA; Azam Thatte of the Georgia Institute of Technology, Atlanta; Jeroen Bouwman, Cristina Afonso and Thomas Henning of Max-Planck Institute for Astronomy, Heidelberg, Germany; and Daniel Angerhausen of the German SOFIA Institute, Stuttgart, Germany.

The work was carried out with funding from NASA's Office of Space Science in Washington, D.C. The NASA Infrared Telescope Facility is managed by the University of Hawaii's Institute for Astronomy. JPL is managed by the California Institute of Technology for NASA.

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

In All the Universe, Just 10 Percent of Solar Systems Are Like Ours

WASHINGTON, DC (Jan. 5, 2010) – In their quest to find solar systems analogous to ours, astronomers have determined how common our solar system is.

They’ve concluded that about 15 percent of stars in the galaxy host systems of planets like our own, with several gas giant planets in the outer part of the solar system.

FIGURE CAPTION – The planets are shown in the correct order of distance from the Sun, the correct relative sizes, and the correct relative orbital distances. The sizes of the bodies are greatly exaggerated relative to the orbital distances. The faint rings of Jupiter, Uranus, and Neptune are not shown. Eris, Haumea, and Makemake do not appear in the illustration owing to their highly tilted orbits. The dwarf planet Ceres is not shown separately; it resides in the asteroid belt between Mars and Jupiter. (Credit: NASA)

“Now we know our place in the universe,” said Ohio State University astronomer Scott Gaudi. “Solar systems like our own are not rare, but we’re not in the majority, either.”

Gaudi reported the results of the new study on Tuesday, January 5 at the American Astronomical Society Meeting in Washington, DC, when he accepts the Helen B. Warner Prize for Astronomy.

The find comes from a worldwide collaboration headquartered at Ohio State called the Microlensing Follow-Up Network (MicroFUN), which searches the sky for extrasolar planets.

MicroFUN astronomers use a method called gravitational microlensing, which occurs when one star happens to cross in front of another as seen from Earth. The nearer star magnifies the light from the more distant star like a lens. If planets are orbiting the lens star, they boost the magnification briefly as they pass by.

This method is especially good at detecting giant planets in the outer reaches of solar systems -- planets analogous to our own Jupiter.

This latest MicroFUN result is the culmination of 10 years’ work -- and one sudden epiphany, explained Gaudi and Andrew Gould, professor of astronomy at Ohio State.

Ten years ago, Gaudi wrote his doctoral thesis on a method for calculating the likelihood that extrasolar planets exist. At the time, he concluded that less than 45 percent of stars could harbor a configuration similar to our own solar system.

Then, in December of 2009, Gould was examining a newly discovered planet with Cheongho Han of the Institute for Astrophysics at Chungbuk National University in Korea. The two were reviewing the range of properties among extrasolar planets discovered so far, when Gould saw a pattern.

“Basically, I realized that the answer was in Scott’s thesis from 10 years ago,” Gould said. “Using the last four years of MicroFUN data, we could add a few robust assumptions to his calculations, and we could now say how common planet systems are in our galaxy.”

The find boils down to a statistical analysis: in the last four years, the MicroFUN survey has discovered only one solar system like our own -- a system with two gas giants resembling Jupiter and Saturn, which astronomers discovered in 2006 and reported in the journal Science in 2008.

“We’ve only found this one system, and we should have found about six by now -- if every star had a solar system like Earth’s,” Gaudi said.

The slow rate of discovery makes sense if only a small number of systems -- around 15 percent -- are like ours, they determined.

“While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today,” Gaudi added.

As to the possibility of life as we know it existing elsewhere in the galaxy, scientists will now be able to make a rough guess based on how many solar systems are like our own.

Our solar system may be a minority, but Gould said that the outcome of the study is actually positive.

“With billions of stars out there, even narrowing the odds to 15 percent leaves a few hundred million systems that might be like ours,” he said.

This research was partly funded by the National Science Foundation.

Contact: Scott Gaudi, (614) 292-1914; Gaudi.1@osu.edu
Andrew Gould, (614) 292-1892; Gould.34@osu.edu
Written by Pam Frost Gorder, (614) 292-9475; Gorder.1@osu.edu

NASA's Kepler Space Telescope Discovers Five Exoplanets

PASADENA, CA (Jan. 4, 2010) – NASA's Kepler space telescope, designed to find Earth-size planets in the habitable zone of sun-like stars, has discovered its first five new exoplanets, or planets beyond our solar system.

Kepler's high sensitivity to both small and large planets enabled the discovery of the exoplanets, named Kepler 4b, 5b, 6b, 7b and 8b. The discoveries were announced Monday, Jan. 4, by members of the Kepler science team during a news briefing at the American Astronomical Society meeting in Washington.

"These observations contribute to our understanding of how planetary systems form and evolve from the gas and dust disks that give rise to both the stars and their planets," said William Borucki of NASA's Ames Research Center in Moffett Field, Calif. Borucki is the mission's science principal investigator. "The discoveries also show that our science instrument is working well. Indications are that Kepler will meet all its science goals."

Known as "hot Jupiters" because of their high masses and extreme temperatures, the new exoplanets range in size from similar to Neptune to larger than Jupiter. They have orbits ranging from 3.3 to 4.9 days. Estimated temperatures of the planets range from 2,200 to 3,000 degrees Fahrenheit, hotter than molten lava and much too hot for life as we know it. All five of the exoplanets orbit stars hotter and larger than Earth's sun.

"It's gratifying to see the first Kepler discoveries rolling off the assembly line," said Jon Morse, director of the Astrophysics Division at NASA Headquarters in Washington. "We expected Jupiter-size planets in short orbits to be the first planets Kepler could detect. It's only a matter of time before more Kepler observations lead to smaller planets with longer-period orbits, coming closer and closer to the discovery of the first Earth analog."

Launched on March 6, 2009, from Cape Canaveral Air Force Station in Florida, the Kepler mission continuously and simultaneously observes more than 150,000 stars. Kepler's science instrument, or photometer, already has measured hundreds of possible planet signatures that are being analyzed.

While many of these signatures are likely to be something other than a planet, such as small stars orbiting larger stars, ground-based observatories have confirmed the existence of the five exoplanets. The discoveries are based on approximately six weeks' worth of data collected since science operations began on May 12, 2009.

Kepler looks for the signatures of planets by measuring dips in the brightness of stars. When planets cross in front of, or transit, their stars as seen from Earth, they periodically block the starlight. The size of the planet can be derived from the size of the dip. The temperature can be estimated from the characteristics of the star it orbits and the planet's orbital period.

Kepler will continue science operations until at least November 2012. It will search for planets as small as Earth, including those that orbit stars in a warm, habitable zone where liquid water could exist on the surface of the planet. Since transits of planets in the habitable zone of solar-like stars occur about once a year and require three transits for verification, it is expected to take at least three years to locate and verify an Earth-size planet.

According to Borucki, Kepler's continuous and long-duration search should greatly improve scientists' ability to determine the distributions of planet size and orbital period in the future. "Today's discoveries are a significant contribution to that goal," Borucki said. "The Kepler observations will tell us whether there are many stars with planets that could harbor life, or whether we might be alone in our galaxy."

Kepler is NASA's 10th Discovery mission. NASA Ames is responsible for the ground system development, mission operations and science data analysis. NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., was responsible for developing the Kepler flight system. Ball and the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder are supporting mission operations. The California Institute of Technology in Pasadena manages JPL for NASA.

Ground observations necessary to confirm the discoveries were conducted with ground-based telescopes: the Keck I in Hawaii; Hobby-Ebberly and Harlan J. Smith 2.7m in Texas; Hale and Shane in California; WIYN, MMT and Tillinghast in Arizona; and Nordic Optical in the Canary Islands, Spain. For more information about the Kepler mission, visit http://www.nasa.gov/kepler .

Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

J.D. Harrington 202-358-5241

Headquarters, Washington

j.d.harrington@nasa.gov

Avatar's Moon Pandora Could Be Real

CAMBRIDGE, MA (Dec. 18, 2009) – In the new blockbuster Avatar, humans visit the habitable - and inhabited - alien moon called Pandora. Life-bearing moons like Pandora or the Star Wars forest moon of Endor are a staple of science fiction. With NASA's Kepler mission showing the potential to detect Earth-sized objects, habitable moons may soon become science fact. If we find them nearby, a new paper by Smithsonian astronomer Lisa Kaltenegger shows that the James Webb Space Telescope (JWST) will be able to study their atmospheres and detect key gases like carbon dioxide, oxygen, and water vapor.

FIGURE CAPTION – This artist's conception shows a hypothetical gas giant planet with an Earth-like moon similar to the moon Pandora in the movie Avatar. New research shows that, if we find such an "exomoon" in the habitable zone of a nearby star, the James Webb Space Telescope will be able to study its atmosphere and detect key gases like carbon dioxide, oxygen, and water. The key is to find a planet that transits its star, and then find a moon orbiting that planet more than one stellar radius away, so that the moon can be studied independently of the planet. Moreover, an alien moon orbiting the gas giant planet of a red dwarf star may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths. Credit: David A. Aguilar, CfA

"If Pandora existed, we potentially could detect it and study its atmosphere in the next decade," said Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics (CfA).

So far, planet searches have spotted hundreds of Jupiter-sized objects in a range of orbits. Gas giants, while easier to detect, could not serve as homes for life as we know it. However, scientists have speculated whether a rocky moon orbiting a gas giant could be life-friendly, if that planet orbited within the star's habitable zone (the region warm enough for liquid water to exist).

"All of the gas giant planets in our solar system have rocky and icy moons," said Kaltenegger. "That raises the possibility that alien Jupiters will also have moons. Some of those may be Earth-sized and able to hold onto an atmosphere."

Kepler looks for planets that cross in front of their host stars, which creates a mini-eclipse and dims the star by a small but detectable amount. Such a transit lasts only hours and requires exact alignment of star and planet along our line of sight. Kepler will examine thousands of stars to find a few with transiting worlds.

Once they have found an alien Jupiter, astronomers can look for orbiting moons, or exomoons. A moon's gravity would tug on the planet and either speed or slow its transit, depending on whether the moon leads or trails the planet. The resulting transit duration variations would indicate the moon's existence.

Once a moon is found, the next obvious question would be: Does it have an atmosphere? If it does, those gases will absorb a fraction of the star's light during the transit, leaving a tiny, telltale fingerprint to the atmosphere's composition.

The signal is strongest for large worlds with hot, puffy atmospheres, but an Earth-sized moon could be studied if conditions are just right. For example, the separation of moon and planet needs to be large enough that we could catch just the moon in transit, while its planet is off to one side of the star.

Kaltenegger calculated what conditions are best for examining the atmospheres of alien moons. She found that alpha Centauri A, the system featured in Avatar, would be an excellent target.

"Alpha Centauri A is a bright, nearby star very similar to our Sun, so it gives us a strong signal" Kaltenegger explained. "You would only need a handful of transits to find water, oxygen, carbon dioxide, and methane on an Earth-like moon such as Pandora."

"If the Avatar movie is right in its vision, we could characterize that moon with JWST in the near future," she added.

While alpha Centauri A offers tantalizing possibilities, small, dim, red dwarf stars are better targets in the hunt for habitable planets or moons. The habitable zone for a red dwarf is closer to the star, which increases the probability of a transit.

Astronomers have debated whether tidal locking could be a problem for red dwarfs. A planet close enough to be in the habitable zone would also be close enough for the star's gravity to slow it until one side always faces the star. (The same process keeps one side of the Moon always facing Earth.) One side of the planet then would be baked in constant sunlight, while the other side would freeze in constant darkness.

An exomoon in the habitable zone wouldn't face this dilemma. The moon would be tidally locked to its planet, not to the star, and therefore would have regular day-night cycles just like Earth. Its atmosphere would moderate temperatures, and plant life would have a source of energy moon-wide.

"Alien moons orbiting gas giant planets may be more likely to be habitable than tidally locked Earth-sized planets or super-Earths," said Kaltenegger. "We should certainly keep them in mind as we work toward the ultimate goal of finding alien life."

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.

For more information, contact:

Lisa Kaltenegger
617-495-7158
617-838-2808
lkaltene@cfa.harvard.edu

David A. Aguilar
Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
daguilar@cfa.harvard.edu

Christine Pulliam
Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
617-495-7463
cpulliam@cfa.harvard.edu

First Direct Observation of a Planet-like Object Orbiting a Star Similar to the Sun.

PRINCETON, NJ (Dec. 3, 2009) – An international team of scientists that includes an astronomer from Princeton University has made the first direct observation of a planet-like object orbiting a star similar to the sun.

The finding marks the first discovery made with the world's newest planet-hunting instrument on the Hawaii-based Subaru Telescope and is the first fruit of a novel research collaboration announced by the University in January.

The object, known as GJ 758 B, could be either a large planet or a "failed star," also known as a brown dwarf. The faint companion to the sun-like star GJ 758 is estimated to be 10 to 40 times as massive as Jupiter and is a "near neighbor" in our Milky Way galaxy, hovering a mere 300 trillion miles from Earth.

"It's a groundbreaking find because one of the current goals of astronomy is to directly detect planet-like objects around stars like our sun," said Michael McElwain, a postdoctoral research fellow in Princeton's Department of Astrophysical Sciences who was part of the team that made the discovery. "It is also an important verification that the system -- the telescope and its instruments -- is working well."

Images of the object were taken in May and August during early test runs of the new observation equipment. The team has members from Princeton, the University of Hawaii, the University of Toronto, the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and the National Astronomical Observatory of Japan (NAOJ) in Tokyo. The results were released online Nov. 18 in an electronic version of the Astrophysical Journal Letters.

"This challenging but beautiful detection of a very low mass companion to a sun-like star reminds us again how little we truly know about the census of gas giant planets and brown dwarfs around nearby stars," said Alan Boss, an astronomer at the Carnegie Institution for Science in Washington, D.C., who was not involved in the research. "Observations like this will enable theorists to begin to make sense of how this hitherto unseen population of bodies was able to form and evolve."

Brown dwarfs are stars that are not massive enough to sustain fusion reactions at their core, so they burn out and cool off as they age.

Aided by new varieties of viewing techniques, scientists started finding extrasolar planets (planets beyond the solar system) in 1992 and have located more than 400 planet-like objects so far. Most, however, have not been directly observed, but inferred from viewing the star around which the planet orbits. GJ 758 B is one of the first planet-like objects to be directly seen. Of the others that have been directly viewed, most have been on larger orbits than the distance between GJ 758 B and its star, or around stars with temperatures far above the average temperature of GJ 758 or our sun.

Scientists were able to spot the object even though it was hidden in the glare of the star it orbits by subtracting out that brighter light. To do this, they used the High Contrast Coronagraphic Imager with Adaptive Optics that has been attached to the Subaru Telescope. Also known as HiCIAO, it is part of a new generation of instruments specially made to detect faint objects near a bright star by masking its far more intense light. They also employed a technique known as angular differential imaging to capture the images.

"It's amazing how quickly this instrument has come online and burst into the forefront," said Marc Kuchner, an exoplanet scientist at the NASA Goddard Space Flight Center in Greenbelt, Md., who was not involved in the work. "I think this is just the beginning of what HiCIAO is going to do for the field." He added that the discovery also emphasizes that this new method of finding exoplanets -- direct detection -- is "really hitting its stride."

The planet-like object is currently at least 29 times as far from its star as the Earth is from the sun, approximately as far as Neptune is from the sun. However, further observations will be required to determine the actual size and shape of its orbit. At a temperature of only 600 F, the object is relatively "cold" for a body of its size. It is the coldest companion to a sun-like star ever recorded in an image.

The fact that such a large planet-like object appears to orbit at this location defies traditional thinking on planet formation. It is thought most larger planets are formed either closer to or farther from stars, but not in the location where GJ 758 is now. Discoveries such as this one could help theorists refine their ideas.

Telescope images also revealed a second companion to the star, which the scientists have called GJ 758 C. More observations, however, are needed to confirm whether it is nearby or just looks that way. "It looks very promising," said Christian Thalmann, one of the team's lead scientists. If it should turn out to be a second companion, he said, that would make both B and C more likely to be young planets rather than old brown dwarfs, since two brown dwarfs in such close proximity would not remain stable for such a long period of time.

Researchers from Princeton and NAOJ announced an agreement on Jan. 15 to collaborate over the next 10 years, using new equipment on the Subaru Telescope to peer into hidden corners of the nearby universe and ferret out secrets from its distant past. This research is a part of that collaboration. The HiCIAO team is led by Professor Motohide Tamura of NAOJ.

The partnership, called the NAOJ-Princeton Astrophysics Collaboration or N-PAC, provides for the exchange of scientific resources and supports a variety of long-term research projects in which the scientists from both Princeton and the Japanese astronomical community will participate on an equal basis. The collaboration builds on a decades-long tradition of scientific collaboration between Japanese and Princeton astronomers in a wide range of astronomical fields.

An important part of that partnership is the search for planets, previously hidden by the glare of stars. Finding these planets is a crucial step in answering the age-old question of the existence of extraterrestrial life.

The Subaru Telescope, whose name is the Japanese word for the Pleiades star cluster, is one of the largest telescopes in the world. The 8.2-meter optical infrared telescope is located on the summit of Mauna Kea, a dormant volcano in Hawaii. The isolated peak protrudes above most of the Earth's weather, making the site one of the best on the planet for astronomical observing. The telescope is owned and operated by NAOJ.

Exoplanet: Atmosphere

An "exoplanet" is an extra-solar planet, that is, a planet orbiting a star other than our own sun. Of the roughly 307 currently known extrasolar planets, about thirty of them transit their star (that is, their orbits take them in front of their star as seen from earth). Because an exoplanet is so faint as compared to its their respective sun, and usually also appear so close to it in the sky, its light is extremely difficult to measure. Astronomers trying to better understand all planets, including the earth, have, however, recently been able to measure useful limits to the reflected light of an exoplanet (see the SAO Science Weekly of 16 July 2008), and thereby to conclude, at least in this case, that its upper atmosphere probably does not contain clouds.

SAO astronomer Joe Hora, together with five of his colleagues, has used the Infrared Array Camera (IRAC) on the Spitzer Space Telescope to probe even further into the nature of the atmosphere of an exoplanet. The team studied the transiting exoplanet known as XO-1b as it passed behind its star in a series of so-called "secondary eclipses." IRAC's resolution is unable to spatially distinguish the planet from the star, but its detectors were able to detect the drop in total flux as the planet disappeared behind the star, and the increase when it emerged. Careful analysis at four infrared wavelengths revealed that the planet has noticeably more infrared emission than would be expected from a cloudless planet. The data are consistent with models in which the stratosphere of XO-1b contains absorbing gas or dust, and in which the atmosphere has a layer with warm vapor emitting in the infrared. The results not only improve our understanding of this particular exoplanet, they demonstrate the power of new infrared technology while helping us understand the nature of the atmospheres of planets far away.

32 New Exoplanets Found

ESO (Oct. 21, 2009) – Today, at an international ESO/CAUP exoplanet conference in Porto, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO's 3.6-metre telescope, reports on the incredible discovery of some 32 new exoplanets, cementing HARPS's position as the world’s foremost exoplanet hunter. This result also increases the number of known low-mass planets by an impressive 30%. Over the past five years HARPS has spotted more than 75 of the roughly 400 or so exoplanets now known.

FIGURE CAPTION –On 19 October 2009, the team who built the High Accuracy Radial Velocity Planet Searcher, better known as HARPS, the spectrograph for ESO’s 3.6-metre telescope, reported on the incredible discovery of some 32 new exoplanets, cementing HARPS’s position as the world’s foremost exoplanet hunter. One of these is surrounding the star Gliese 667 C, which belongs to a triple system. The 6 Earth-mass exoplanet circulates around its low-mass host star at a distance equal to only 1/20th of the Earth-Sun distance. The host star is a companion to two other low-mass stars, which are seen here in the distance.

"HARPS is a unique, extremely high precision instrument that is ideal for discovering alien worlds," says Stéphane Udry, who made the announcement. “We have now completed our initial five-year programme, which has succeeded well beyond our expectations.”

The latest batch of exoplanets announced today comprises no less than 32 new discoveries. Including these new results, data from HARPS have led to the discovery of more than 75 exoplanets in 30 different planetary systems. In particular, thanks to its amazing precision, the search for small planets, those with a mass of a few times that of the Earth — known as super-Earths and Neptune-like planets — has been given a dramatic boost. HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 20 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system.

In 1999, ESO launched a call for opportunities to build a high resolution, extremely precise spectrograph for the ESO 3.6-metre telescope at La Silla, Chile. Michel Mayor, from the Geneva Observatory, led a consortium to build HARPS, which was installed in 2003 and was soon able to measure the back-and-forward motions of stars by detecting small changes in a star’s radial velocity — as small as 3.5 km/hour, a steady walking pace. Such a precision is crucial for the discovery of exoplanets and the radial velocity method, which detects small changes in the radial velocity of a star as it wobbles slightly under the gentle gravitational pull from an (unseen) exoplanet, has been most prolific method in the search for exoplanets.

In return for building the instrument, the HARPS consortium was granted 100 observing nights per year during a five-year period to carry out one of the most ambitious systematic searches for exoplanets so far implemented worldwide by repeatedly measuring the radial velocities of hundreds of stars that may harbour planetary systems.

The programme soon proved very successful. Using HARPS, Mayor’s team discovered — among others — in 2004, the first super-Earth (around µ Ara; ESO 22/04); in 2006, the trio of Neptunes around HD 69830 (ESO 18/06); in 2007, Gliese 581d, the first super Earth in the habitable zone of a small star (ESO 22/07); and in 2009, the lightest exoplanet so far detected around a normal star, Gliese 581e (ESO 15/09). More recently, they found a potentially lava-covered world, with density similar to that of the Earth’s (ESO 33/09).

“These observations have given astronomers a great insight into the diversity of planetary systems and help us understand how they can form,” says team member Nuno Santos.

The HARPS consortium was very careful in their selection of targets, with several sub-programmes aimed at looking for planets around solar-like stars, low-mass dwarf stars, or stars with a lower metal content than the Sun. The number of exoplanets known around low-mass stars — so-called M dwarfs — has also dramatically increased, including a handful of super Earths and a few giant planets challenging planetary formation theory.

“By targeting M dwarfs and harnessing the precision of HARPS we have been able to search for exoplanets in the mass and temperature regime of super-Earths, some even close to or inside the habitable zone around the star,” says co-author Xavier Bonfils.

The team found three candidate exoplanets around stars that are metal-deficient. Such stars are thought to be less favourable for the formation of planets, which form in the metal-rich disc around the young star. However, planets up to several Jupiter masses have been found orbiting metal-deficient stars, setting an important constraint for planet formation models.

Although the first phase of the observing programme is now officially concluded, the team will pursue their effort with two ESO Large Programmes looking for super-Earths around solar-type stars and M dwarfs and some new announcements are already foreseen in the coming months, based on the last five years of measurements. There is no doubt that HARPS will continue to lead the field of exoplanet discoveries, especially pushing towards the detection of Earth-type planets.

More Information

This discovery was announced today at the ESO/CAUP conference “Towards Other Earths: perspectives and limitations in the ELT era", taking place in Porto, Portugal, on 19–23 October 2009. This conference discusses the new generation of instruments and telescopes that is now being conceived and built by different teams around the world to allow the discovery of other Earths, especially for the European Extremely Large Telescope (E-ELT). The new planets are simultaneously presented by Michel Mayor at the international symposium “Heirs of Galileo: Frontiers of Astronomy” in Madrid, Spain.

This research was presented in a series of eight papers submitted — or soon to be submitted — to the Astronomy and Astrophysics journal.

The team is composed of

Geneva Observatory: M. Mayor, S. Udry, D. Queloz, F. Pepe, C. Lovis, D. Ségransan, X. Bonfils
LAOG Grenoble: X. Delfosse, T. Forveille, X. Bonfils, C. Perrier
CAUP Porto: N.C. Santos
ESO: G. Lo Curto, D. Naef
University of Bern: W. Benz, C. Mordasini
IAP Paris: F. Bouchy, G. Hébrard
LAM Marseille: C. Moutou
Service d’aéronomie, Paris: J.-L. Bertaux

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Contacts

Stéphane Udry
Geneva University, Switzerland
Phone: +41 22 379 2467
E-mail: stephane.udry (at) unige.ch

Xavier Bonfils
Université Joseph Fourier - Grenoble 1 / CNRS,
Laboratoire d'Astrophysique de Grenoble (LAOG), France
Phone : +33 47 65 14 215
E-mail: xavier.bonfils (at) obs.ujf-grenoble.fr

Nuno Santos
Centro de Astrofisica da Universidade do Porto,
Portugal
Phone: +351 226 089 893
E-mail: Nuno.Santos (at) astro.up.pt

Astronomers do it Again: Find Organic Molecules Around Gas Planet

NASA-JPL (Oct. 19, 2009) – Peering far beyond our solar system, NASA researchers have detected the basic chemistry for life in a second hot gas planet, advancing astronomers toward the goal of being able to characterize planets where life could exist. The planet is not habitable but it has the same chemistry that, if found around a rocky planet in the future, could indicate the presence of life.

FIGURE CAPTION – The basic chemistry for life has been detected in a second hot gas planet, HD 209458b, depicted in this artist's concept.

"It's the second planet outside our solar system in which water, methane and carbon dioxide have been found, which are potentially important for biological processes in habitable planets," said researcher Mark Swain of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Detecting organic compounds in two exoplanets now raises the possibility that it will become commonplace to find planets with molecules that may be tied to life."

Swain and his co-investigators used data from two of NASA's orbiting Great Observatories, the Hubble Space Telescope and Spitzer Space Telescope, to study HD 209458b, a hot, gaseous giant planet bigger than Jupiter that orbits a sun-like star about 150 light years away in the constellation Pegasus. The new finding follows their breakthrough discovery in December 2008 of carbon dioxide around another hot, Jupiter-size planet, HD 189733b. Earlier Hubble and Spitzer observations of that planet had also revealed water vapor and methane.

The detections were made through spectroscopy, which splits light into its components to reveal the distinctive spectral signatures of different chemicals. Data from Hubble's near-infrared camera and multi-object spectrometer revealed the presence of the molecules, and data from Spitzer's photometer and infrared spectrometer measured their amounts.

"This demonstrates that we can detect the molecules that matter for life processes," said Swain. Astronomers can now begin comparing the two planetary atmospheres for differences and similarities. For example, the relative amounts of water and carbon dioxide in the two planets is similar, but HD 209458b shows a greater abundance of methane than HD 189733b. "The high methane abundance is telling us something," said Swain. "It could mean there was something special about the formation of this planet."

Other large, hot Jupiter-type planets can be characterized and compared using existing instruments, Swain said. This work will lay the groundwork for the type of analysis astronomers eventually will need to perform in shortlisting any promising rocky Earth-like planets where the signatures of organic chemicals might indicate the presence of life.

Rocky worlds are expected to be found by NASA's Kepler mission, which launched earlier this year, but astronomers believe we are a decade or so away from being able to detect any chemical signs of life on such a body.

If and when such Earth-like planets are found in the future, "the detection of organic compounds will not necessarily mean there's life on a planet, because there are other ways to generate such molecules," Swain said. "If we detect organic chemicals on a rocky, Earth-like planet, we will want to understand enough about the planet to rule out non-life processes that could have led to those chemicals being there."

"These objects are too far away to send probes to, so the only way we're ever going to learn anything about them is to point telescopes at them. Spectroscopy provides a powerful tool to determine their chemistry and dynamics."

You can follow the history of planet hunting from science fiction to science fact with NASA's PlanetQuest Historic Timeline at http://planetquest.jpl.nasa.gov/timeline/ .

This interactive web feature, developed by JPL, conveys the story of exoplanet exploration through a rich tapestry of words and images spanning thousands of years, beginning with the musings of ancient philosophers and continuing through the current era of space-based observations by NASA's Spitzer and Kepler missions. The timeline highlights milestones in culture, technology and science, and includes a planet counter that tracks the pace of exoplanet discoveries over time.

More information about exoplanets and NASA's planet-finding program is at http://planetquest.jpl.nasa.gov .

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency and is managed by NASA's Goddard Space Flight Center in Greenbelt, Md. The Space Telescope Science Institute, Baltimore, Md., conducts Hubble science operations. The institute is operated for NASA by the Association of Universities for research in Astronomy, Inc., Washington, D.C.

JPL manages the Spitzer Space Telescope mission for NASA. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Written by Mary Beth Murrill
Media contact: Whitney Clavin/Jet Propulsion Laboratory 818-354-4671

SIM PlanetQuest

SIM (Space Interferometry Mission), scheduled for launch within the next decade, will be the most powerful planet-hunting space telescope ever devised. Using two separated mirrors and combining their light with a technique known as interferometry, SIM PlanetQuest will able to detect planets as small as Earth. These are the kind of planets that scientists believe have the most potential to support life.

Although more than 160 planets have been discovered beyond our solar system since 1995, the "holy grail" - Earthlike planets located in the habitable zone - remains beyond the reach of current telescopes.

SIM PlanetQuest will perform the first census of nearby Earth-like planets by observing the "wobble" in each parent star's apparent motion as the planet orbits, to an accuracy of one millionth of an arcsecond. That's the thickness of a nickel, viewed at the distance of the moon!

A second planet search program, called the "broad survey," will probe roughly 2,000 stars to determine the prevalence of Neptune and larger mass planets in all stellar types in our part of the galaxy.

A third component of the mission's planet-finding program consists of a search for Jupiter-mass planets around young stars.

This survey will help scientists understand the process of solar system formation, including the occurrence of "hot Jupiters" - massive planets located very close to their parent stars.

The SIM PlanetQuest study of neighboring planetary systems will set the stage for future space telescopes, like Terrestrial Planet Finder, that will be able to directly image these distant worlds, and probe their atmospheres for the signatures of life.

Simulation suggests rocky exoplanet has bizarre atmosphere

Washington Univ., St. Louis (Oct. 1, 2009) – So accustomed are we to the sunshine, rain, fog and snow of our home planet that we find it next to impossible to imagine a different atmosphere and other forms of precipitation

FIGURE CAPTION – The exoplanet COROT-7b is close enough to its star that its "day-face" is hot enough to melt rock. Theoretical models suggest the planet has an atmosphere of the components of rock in gaseous form and lava or boiling oceans on its surface. Image by ESO/L. Calcada.

To be sure, Dr. Seuss came up with a green gluey substance called oobleck that fell from the skies and gummed up the Kingdom of Didd, but it had to be conjured up by wizards and was clearly a thing of magic.

Not so the atmosphere of COROT-7b, an exoplanet discovered last February by the COROT space telescope launched by the French and European space agencies.

According to models by scientists at Washington University in St. Louis, COROT-7b's atmosphere is made up of the ingredients of rocks and when "a front moves in," pebbles condense out of the air and rain into lakes of molten lava below.

The work, by Laura Schaefer, research assistant in the Planetary Chemistry Laboratory, and Bruce Fegley Jr., Ph.D., professor of earth and planetary sciences in Arts & Sciences, appears in the Oct. 1 issue of The Astrophysical Journal.

Astronomers have found nearly 400 extra-solar planets, or exoplanets, in the past 20 years. But because of the limitations of the indirect means by which they are discovered, most are Hot Jupiters, chubby gas giants orbiting close to their parent stars. (More than 1,300 Earths could be packed inside Jupiter, which has 300 times the mass of Earth.)

COROT-7b, on the other hand, is less than twice the size of Earth and only five times its mass.

It was the first planet found orbiting the star COROT-7, an orange dwarf in the constellation Monoceros, or the Unicorn. (This priority is designated by the letter b.)

Solid as a Rock

In August 2009 a consortium of European observatories led by the Swiss reported the discovery of COROT-7c, a second planet orbiting COROT-7.

Using the data from both planets, they were able to calculate that COROT-7b has an average density about the same as Earth's. This means it is almost certainly a rocky planet made up of silicate rocks like those in Earth's crust, says Fegley.

Not that anyone would call it Earth-like, much less hospitable to life. The planet and its star are separated by only 1.6 million miles, 23 times less than the distance between the parboiled planet Mercury and our Sun.

Because the planet is so close to the star, it is gravitationally locked to it in the same way the Moon is locked to Earth. One side of the planet always faces its star, just as one side of the Moon always faces Earth.

This star-facing side has a temperature of about 2600 degrees Kelvin (4220 degrees Fahrenheit). That's infernally hot—hot enough to vaporize rocks. The global average temperature of Earth's surface, in contrast, is only about 288 degrees Kelvin (59 degrees Fahrenheit).

The side in perpetual shadow, on the other hand, is positively chilly at 50 degrees Kelvin (-369 degrees Fahrenheit).

Perhaps because they were cooked off, COROT-7b's atmosphere has none of the volatile elements or compounds that make up Earth's atmosphere, such as water, nitrogen and carbon dioxide.

"The only atmosphere this object has is produced from vapor arising from hot molten silicates in a lava lake or lava ocean," Fegley says.

What might that atmosphere be like? To find out Schaefer and Fegley have used thermochemical equilibrium calculations to model COROT-7b's atmosphere.

The calculations, which reveal which mineral assemblages are stable under different conditions, were carried out with MAGMA, a computer program Fegley developed in 1986 with the late A. G. W. Cameron, a professor of astrophysics at Harvard University.

Schaefer and Fegley modified the MAGMA program in 2004 in order to study high-temperature volcanism on Io, Jupiter's innermost Galilean satellite. This modified version was used in their present work.

Raining Rocks

Because the scientists didn't know the exact composition of the planet, they ran the program with four different starting compositions. "We got essentially the same result in all four cases," says Fegley.

"Sodium, potassium, silicon monoxide and then oxygen — either atomic or molecular oxygen — make up most of the atmosphere." But there are also smaller amounts of the other elements found in silicate rock, such as magnesium, aluminum, calcium and iron.

Why is there oxygen on a dead planet, when it didn't show up in Earth's atmosphere until 2.4 billion years ago, when plants started to produce it?

"Oxygen is the most abundant element in rock," says Fegley, "so when you vaporize rock what you end up doing is producing a lot of oxygen."

The peculiar atmosphere has its own singular weather. "As you go higher the atmosphere gets cooler and eventually you get saturated with different types of 'rock' the way you get saturated with water in the atmosphere of Earth," explains Fegley. "But instead of a water cloud forming and then raining water droplets, you get a 'rock cloud' forming and it starts raining out little pebbles of different types of rock."

Even more strangely, the kind of rock condensing out of the cloud depends on the altitude. The atmosphere works the same way as fractionating columns, the tall knobby columns that make petrochemical plants recognizable from afar. In a fractionating column, crude oil is boiled and its components condense out on a series of trays, with the heaviest one (with the highest boiling point) sulking at the bottom, and the lightest (and most volatile) rising to the top.

Instead of condensing out hydrocarbons such as asphalt, petroleum jelly, kerosene and gasoline, the exoplanet's atmosphere condenses out minerals such as enstatite, corundum, spinel, and wollastonite. In both cases the fractions fall out in order of boiling point.

Elemental sodium and potassium, which have very low boiling points in comparison with rocks, do not rain out but would instead stay in the atmosphere, where they would form high gas clouds buffeted by the stellar wind from COROT-7.

These large clouds may be detectable by Earth-based telescopes. The sodium, for example, should glow in the orange part of the spectrum, like a giant but very faint sodium vapor streetlamp.

Observers have recently spotted sodium in the atmospheres of two other exoplanets.

The atmosphere of COROT-7b may not be breathable, but it is certainly amusing.

NASA's Spitzer Spots Clump of Swirling Planetary Material

NASA-JPL (Sep. 24, 2009) – Astronomers have witnessed odd behavior around a young star. Something, perhaps another star or a planet, appears to be pushing a clump of planet-forming material around. The observations, made with NASA's Spitzer Space Telescope, offer a rare look into the early stages of planet formation.

Planets form out of swirling disks of gas and dust. Spitzer observed infrared light coming from one such disk around a young star, called LRLL 31, over a period of five months. To the astronomers' surprise, the light varied in unexpected ways, and in as little time as one week. Planets take millions of years to form, so it's rare to see anything change on time scales we humans can perceive.

One possible explanation is that a close companion to the star -- either a star or a developing planet -- could be shoving planet-forming material together, causing its thickness to vary as it spins around the star.

"We don't know if planets have formed, or will form, but we are gaining a better understanding of the properties and dynamics of the fine dust that could either become, or indirectly shape, a planet," said James Muzerolle of the Space Telescope Science Institute, Baltimore, Md. Muzerolle is first author of a paper accepted for publication in the Astrophysical Journal Letters. "This is a unique, real-time glimpse into the lengthy process of building planets."

One theory of planet formation suggests that planets start out as dusty grains swirling around a star in a disk. They slowly bulk up in size, collecting more and more mass like sticky snow. As the planets get bigger and bigger, they carve out gaps in the dust, until a so-called transitional disk takes shape with a large doughnut-like hole at its center. Over time, this disk fades and a new type of disk emerges, made up of debris from collisions between planets, asteroids and comets. Ultimately, a more settled, mature solar system like our own forms.

Before Spitzer was launched in 2003, only a few transitional disks with gaps or holes were known. With Spitzer's improved infrared vision, dozens have now been found. The space telescope sensed the warm glow of the disks and indirectly mapped out their structures.

Muzerolle and his team set out to study a family of young stars, many with known transitional disks. The stars are about two to three million years old and about 1,000 light-years away, in the IC 348 star-forming region of the constellation Perseus. A few of the stars showed surprising hints of variations. The astronomers followed up on one, LRLL 31, studying the star over five months with all three of Spitzer's instruments.

The observations showed that light from the inner region of the star's disk changes every few weeks, and, in one instance, in only one week. "Transition disks are rare enough, so to see one with this type of variability is really exciting," said co-author Kevin Flaherty of the University of Arizona, Tucson.

Both the intensity and the wavelength of infrared light varied over time. For instance, when the amount of light seen at shorter wavelengths went up, the brightness at longer wavelengths went down, and vice versa.

Muzerolle and his team say that a companion to the star, circling in a gap in the system's disk, could explain the data. "A companion in the gap of an almost edge-on disk would periodically change the height of the inner disk rim as it circles around the star: a higher rim would emit more light at shorter wavelengths because it is larger and hot, but at the same time, the high rim would shadow the cool material of the outer disk, causing a decrease in the longer-wavelength light. A low rim would do the opposite. This is exactly what we observe in our data," said Elise Furlan, a co-author from NASA's Jet Propulsion Laboratory, Pasadena, Calif.

The companion would have to be close in order to move the material around so fast -- about one-tenth the distance between Earth and the sun.

The astronomers plan to follow up with ground-based telescopes to see if a companion is tugging on the star hard enough to be perceived. Spitzer will also observe the system again in its "warm" mission to see if the changes are periodic, as would be expected with an orbiting companion. Spitzer ran out of coolant in May of this year, and is now operating at a slightly warmer temperature with two infrared channels still functioning.

"For astronomers, watching anything in real-time is exciting," said Muzerolle. "It's like we're biologists getting to watch cells grow in a petri dish, only our specimen is light-years away."

Other authors are Zoltan Balog, Max Planck Institute for Astronomy, Germany; Paul S. Smith and George Rieke, University of Arizona; Lori Allen, National Optical Astronomy Observatory, Tucson; Nuria Calvet, University of Michigan, Ann Arbor; Paola D'Alessio, National Autonomous University of Mexico; S. Thomas Megeath, University of Toledo, Ohio; August Muench, Harvard-Smithsonian Center for Astrophysics, Cambridge; William H. Sherry, National Solar Observatory, Tucson.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer .

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

2009-146

First Solid Evidence for a Rocky Exoplanet

ESO (Sep. 16, 2009) – The longest set of HARPS measurements ever made has firmly established the nature of the smallest and fastest-orbiting exoplanet known, CoRoT-7b, revealing its mass as five times that of Earth's. Combined with CoRoT-7b's known radius, which is less than twice that of our terrestrial home, this tells us that the exoplanet's density is quite similar to the Earth's, suggesting a solid, rocky world. The extensive dataset also reveals the presence of another so-called super-Earth in this alien solar system.

FIGURE CAPTION – The exoplanet Corot-7b is so close to its Sun-like host star that it must experience extreme conditions. This planet has a mass five times that of Earth’s and is in fact the closest known exoplanet to its host star, which also makes it the fastest — it orbits its star at a speed of more than 750 000 kilometres per hour. The probable temperature on its “day-face” is above 2000 degrees, but minus 200 degrees on its night face. Theoretical models suggest that the planet may have lava or boiling oceans on its surface. Our artist has provided an impression of how it may look like if it were covered by lava. The sister planet, Corot-7c, is seen in the distance.

"This is science at its thrilling and amazing best," says Didier Queloz, leader of the team that made the observations. "We did everything we could to learn what the object discovered by the CoRoT satellite looks like and we found a unique system."

In February 2009, the discovery by the CoRoT satellite [1] of a small exoplanet around a rather unremarkable star named TYC 4799-1733-1 was announced one year after its detection and after several months of painstaking measurements with many telescopes on the ground, including several from ESO. The star, now known as CoRoT-7, is located towards the constellation of Monoceros (the Unicorn) at a distance of about 500 light-years. Slightly smaller and cooler than our Sun, CoRoT-7 is also thought to be younger, with an age of about 1.5 billion years.

Every 20.4 hours, the planet eclipses a small fraction of the light of the star for a little over one hour by one part in 3000 [2]. This planet, designated CoRoT-7b, is only 2.5 million kilometres away from its host star, or 23 times closer than Mercury is to the Sun. It has a radius that is about 80% greater than the Earth's.

The initial set of measurements, however, could not provide the mass of the exoplanet. Such a result requires extremely precise measurements of the velocity of the star, which is pulled a tiny amount by the gravitational tug of the orbiting exoplanet. The problem with CoRoT-7b is that these tiny signals are blurred by stellar activity in the form of "starspots" (just like sunspots on our Sun), which are cooler regions on the surface of the star. Therefore, the main signal is linked to the rotation of the star, with makes one complete revolution in about 23 days.

To get an answer, astronomers had to call upon the best exoplanet-hunting device in the world, the High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph attached to the ESO 3.6-metre telescope at the La Silla Observatory in Chile.

"Even though HARPS is certainly unbeaten when it comes to detecting small exoplanets, the measurements of CoRoT-7b proved to be so demanding that we had to gather 70 hours of observations on the star," says co-author François Bouchy.

HARPS delivered, allowing the astronomers to tease out the 20.4-hour signal in the data. This figure led them to infer that CoRoT-7b has a mass of about five Earth masses, placing it in rare company as one of the lightest exoplanets yet found.

"Since the planet's orbit is aligned so that we see it crossing the face of its parent star — it is said to be transiting — we can actually measure, and not simply infer, the mass of the exoplanet, which is the smallest that has been precisely measured for an exoplanet [3]," says team member Claire Moutou. "Moreover, as we have both the radius and the mass, we can determine the density and get a better idea of the internal structure of this planet."

With a mass much closer to that of Earth than, for example, ice giant Neptune's 17 Earth masses, CoRoT-7b belongs to the category of "super-Earth" exoplanets. About a dozen of these bodies have been detected, though in the case of CoRoT-7b, this is the first time that the density has been measured for such a small exoplanet. The calculated density is close to Earth's, suggesting that the planet's composition is similarly rocky.

"CoRoT-7b resulted in a 'tour de force' of astronomical measurements. The superb light curves of the space telescope CoRoT gave us the best radius measurement, and HARPS the best mass measurement for an exoplanet. Both were needed to discover a rocky planet with the same density as the Earth," says co-author Artie Hatzes.

CoRoT-7b earns another distinction as the closest known exoplanet to its host star, which also makes it the fastest — it orbits its star at a speed of more than 750 000 kilometres per hour, more than seven times faster than the Earth's motion around the Sun. "In fact, CoRoT-7b is so close that the place may well look like Dante's Inferno, with a probable temperature on its 'day-face' above 2000 degrees and minus 200 degrees on its night face. Theoretical models suggest that the planet may have lava or boiling oceans on its surface. With such extreme conditions this planet is definitively not a place for life to develop," says Queloz.

As a further testament to HARPS' sublime precision, the astronomers found from their dataset that CoRoT-7 hosts another exoplanet slightly further away than CoRoT-7b. Designated CoRoT-7c, it circles its host star in 3 days and 17 hours and has a mass about eight times that of Earth, so it too is classified as a super-Earth. Unlike CoRoT-7b, this sister world does not pass in front of its star as seen from Earth, so astronomers cannot measure its radius and thus its density.

Given these findings, CoRoT-7 stands as the first star known to have a planetary system made of two short period super-Earths with one that transits its host.

Notes

[1] The CoRoT mission is a cooperation between France and its international partners: ESA, Austria, Belgium, Brazil, Germany and Spain.

[2] We see exactly the same effect in our Solar System when Mercury or Venus transits the solar disc, as Venus did on 8 June 2004 (ESO PR 03/04). In the past centuries such events were used to estimate the Sun-Earth distance, with extremely useful implications for astrophysics and celestial mechanics.

[3] Gliese 581e, also discovered with HARPS, has a minimum mass about twice the Earth's mass (see ESO 15/09), but the exact geometry of the orbit is undefined, making its real mass unknown. In the case of CoRoT-7b, as the planet is transiting, the geometry is well defined, allowing the astronomers to measure the mass of the planet precisely.

Let the Planet Hunt Begin

NASA-JPL (May 13, 2009) – NASA's Kepler spacecraft has begun its search for other Earth-like worlds. The mission, which launched from Cape Canaveral, Fla., on March 6, will spend the next three-and-a-half years staring at more than 100,000 stars for telltale signs of planets. Kepler has the unique ability to find planets as small as Earth that orbit sun-like stars at distances where temperatures are right for possible lakes and oceans.

"Now the fun begins," said William Borucki, Kepler science principal investigator at NASA's Ames Research Center, Moffett Field, Calif. "We are all really excited to start sorting through the data and discovering the planets."

Scientists and engineers have spent the last two months checking out and calibrating the Kepler spacecraft. Data have been collected to characterize the imaging performance as well as the noise level in the measurement electronics. The scientists have constructed the list of targets for the start of the planet search, and this information has been loaded onto the spacecraft.

"If Kepler got into a staring contest, it would win," said James Fanson, Kepler project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "The spacecraft is ready to stare intently at the same stars for several years so that it can precisely measure the slightest changes in their brightness caused by planets." Kepler will hunt for planets by looking for periodic dips in the brightness of stars -- events that occur when orbiting planets cross in front of their stars and partially block the light.

The mission's first finds are expected to be large, gas planets situated close to their stars. Such discoveries could be announced as early as next year.

Kepler is a NASA Discovery mission. NASA Ames Research Center, Moffett Field, Calif., is the home organization of the science principal investigator, and is responsible for the ground system development, mission operations and science data analysis. JPL manages the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colo., is responsible for developing the Kepler flight system and supporting mission operations.

For more information about the Kepler mission, visit: http://www.nasa.gov/kepler and http://www.kepler.nasa.gov .

Media contacts: Whitney Clavin 818-354-4673

Jet Propulsion Laboratory, Pasadena, Calif.

whitney.clavin@jpl.nasa.gov

Michael Mewhinney 650-604-3937

NASA's Ames Research Center, Moffett Field, Calif.

michael.s.mewhinney@nasa.gov

Hubble Finds Hidden Exoplanet

Summary (Apr 03, 2009): Using a novel image-processing technique, astronomers have discovered a new extrasolar planet by looking back through archived data from the Hubble Space Telescope. The new technique could help identify additional planets hidden in over a decade's worth of Hubble data currently available.

Hubble Finds Hidden Exoplanet in Archival Data

(Based on a Space Telescope Science Institute news release.)

A powerful, newly refined image-processing technique may allow astronomers to discover extrasolar planets that are possibly lurking in over a decade's worth of Hubble Space Telescope archival data.

David Lafreniere of the University of Toronto, Ontario, Canada, has successfully demonstrated this new strategy for planet hunting by identifying an exoplanet that went undetected in Hubble images taken in 1998 with its Near Infrared Camera and Multi-Object Spectrometer (NICMOS). In addition to illustrating the power of new data-processing techniques, this finding underscores the value of the Hubble data archive, on which those new techniques can be used.

The planet, estimated to be at least seven times Jupiter 's mass, was originally discovered in images taken with the Keck and Gemini North telescopes in 2007 and 2008. It is the outermost of three massive planets known to orbit the dusty young star HR 8799, which is 130 light-years away. NICMOS could not see the other two planets because its coronagraphic spot -- a device which blots out the glare of the star - also interferes with observing the two inner planets.

"We've shown that NICMOS is more powerful than previously thought for imaging planets," says Lafreniere. "Our new image-processing technique efficiently subtracts the glare from a star that spills over the coronagraph's edge, allowing us to see planets that are one-tenth the brightness of what could be detected before with Hubble." Lafreniere adapted an image reconstruction technique that was first developed for ground-based observatories.

This is a Hubble Space Telescope NICMOS (Near Infrared Camera and Multi-Object Spectrometer) coronagraphic image of a planet orbiting the star HR 8799, located 130 light-years away. The coronagraph has been used to block the light from the bright star (black circle) allowing the search for the dim glow of the planet HR 8799b.
Credit: NASA, ESA, and D. Lafrenière (University of Toronto, Canada)

Using the new technique, he recovered the planet in NICMOS observations taken 10 years before the Keck/Gemini discovery. The Hubble picture not only provides important confirmation of the planet's existence, it provides a longer baseline for demonstrating that the object is in an orbit about the star. "To get a good determination of the orbit we have to wait a very long time because the planet is moving so slowly (it has a 400-year period)," says Lafreniere. "The 10-year-old Hubble data take us that much closer to having a precise measure of the orbit."

NICMOS's view provided new insights into the physical characteristics of the planet, too. This was possible because NICMOS works at near-infrared wavelengths that are severely blocked by Earth's atmosphere due to absorption by water vapor.

"The planet seems to be only partially cloud covered and we could be detecting the absorption of water vapor in the atmosphere," says Travis Barman of Lowell Observatory, Flagstaff, Ariz. "The infrared light measured from the Hubble data is consistent with a spectrum showing a broad water absorption feature (at 1.4-1.49 microns), but the level of absorption seen is lower than it would be if the photosphere were completely devoid of dust. Dust clouds can smooth out many of the spectral features that would otherwise be there - including water absorption bands," Barman says. "Measuring the water absorption properties will tell us a great deal about the temperatures and pressures in the atmospheres, in addition to the cloud coverage. If we can accurately measure the water absorption features for the outermost planet around HR 8799, we will learn a great deal about their atmospheric properties. Hubble, situated well above the Earth's atmosphere, is excellently located for such a study."

"During the past 10 years Hubble has been used to look at over 200 stars with coronagraphy, looking for planets and disks. We plan to go back and look at all of those archived images and see if anything can be detected that has gone undetected until now," says Christian Marois of the Herzberg Institute of Astrophysics, Victoria, Canada. "We'll need a baseline of a few years for most objects to detect Keplerian motion and hence confirm their status as planets. The hardest part is to find them in the first place."

The Hubble Space Telescope was launched in 1990 and has since been an invaluable tool for studying exosolar planets and dusty debris disks around distant stars.
Credit: Hubble

If his team sees a companion object to a star in more than one NICMOS picture, and it appears to have moved along an orbit, follow-up observations will be made with ground-based telescopes. If they see something once but its brightness and separation from the star would be reasonable for a planet, they will also do follow-up observations with ground-based telescopes.

Taking the image of an exoplanet is not an easy task. Planets can be billions of times fainter than the star around which they orbit and are typically located at separations smaller than 1/2000th the angular size of the full moon from their star. The planet recovered in the NICMOS data is about 100,000 times fainter than the star when viewed in the near-infrared.

"Even when using the best telescopes available, with the best resolution, the light from the bright star spills out in the area where the much fainter planets are located, making them impossible to see. It is essential to subtract out this bright glare of stellar light from the image to see faint dots, i.e., planets, that could be hidden underneath," says Rene Doyon of the University of Montreal.

The stability of how light is scattered in the NICMOS camera, called the point spread function (PSF), is key for using Hubble images to recover planets. This technique works by taking images of different stars and combining them to create a PSF of a star that closely resembles the star that is being studied for planets. This requires a reasonably steady PSF because images of different stars are taken on different days. Atmospheric conditions would vary from day-to-day for ground-based telescopes, but not for a space telescope that enjoys unprecedented image stability over repeated visits to a target.

Preview Image

An artistic illustration of the giant planet HR 8799b. Credit: NASA, ESA, and G. Bacon (STScI)

Kepler Mission

Importance of Planet Detection

The "Kepler Mission: A search for Habitable Planets" is NASA's first mission capable of finding Earth-size and smaller planets around other stars.

The centuries-old quest for other worlds like our Earth has been rejuvenated by the intense excitement and popular interest surrounding the discovery of giant planets like Jupiter orbiting stars beyond our solar system. With the exception of the pulsar planets, all of the extrasolar planets detected so far are gas giants, approximately 150 as of 2005. The challenge now is to find terrestrial planets (habitable planets like Earth), which are 30 to 600 times less massive than Jupiter.

The Kepler Mission, a NASA Discovery mission, is specifically designed to survey our region of the Milky Way galaxy to detect and characterize hundreds of Earth-size and smaller planets in or near the habitable zone. The habitable zone encompasses the distances from a star where liquid water can exist on a planet's surface.

Results from this mission will allow us to place our solar system within the continuum of planetary systems in the Galaxy.

Scientific Objective

The Extended Solar Neighborhood. The figure shows what we believe to be the local structure of our Galaxy, the Milky Way. The stars sampled are similar to the immediate solar neighborhood. Young stellar clusters, ionized hydrogen (HII) regions and the neutral hydrogen (HI) distribution define the arms of the Galaxy.

The scientific objective of the Kepler Mission is to explore the structure and diversity of planetary systems. This is achieved by surveying a large sample of stars to:

Determine the percentage of terrestrial and larger planets there are in or near the habitable zone of a wide variety of stars;
Determine the distribution of sizes and shapes of the orbits of these planets;
Estimate how many planets there are in multiple-star systems;
Determine the variety of orbit sizes and planet reflectivities, sizes, masses and densities of short-period giant planets;
Identify additional members of each discovered planetary system using other techniques; and
Determine the properties of those stars that harbor planetary systems.

The Kepler Mission also supports the objectives of future NASA Origins theme missions Space Interferometry Mission (SIM) and Terrestrial Planet Finder (TPF),

By identifying the common stellar characteristics of host stars for future planet searches,
By defining the volume of space needed for the search and
By allowing SIM to target systems already known to have terrestrial planets.

The Transit Method of Detecting Extrasolar Planets

When a planet crosses in front of its star as viewed by an observer, the event is call a transit. Transits by terrestrial planets produce a small change in a star's brightness of about 1/10,000 (100 parts per million, ppm), lasting for 2 to 16 hours. This change must be absolutely periodic if it is caused by a planet. In addition, all transits produced by the same planet must be of the same change in brightness and last the same amount of time, thus providing a highly repeatable signal and robust detection method.

Once detected, the planet's orbital size can be calculated from the period (how long it takes the planet to orbit once around the star) and the mass of the star using Kepler's Third Law of planetary motion. The size of the planet is found from the depth of the transit (how much the brightness of the star drops) and the size of the star. From the orbital size and the temperature of the star, the planet's characteristic temperature can be calculated. From this the question of whether or not the planet is habitable (not necessarily inhabited) can be answered.

Design

For a planet to transit, as seen from our solar system, the orbit must be lined up edgewise to us. The probability for an orbit to be properly aligned is equal to the diameter of the star divided by the diameter of the orbit. This is 0.5% for a planet in an Earth-like orbit about a solar-like star. (For the giant planets discovered in four-day orbits, the alignment probability is more like 10%.) In order to detect many planets one can not just look at a few stars for transits or even a few hundred. One must look at thousands of stars, even if Earth-like planets are common. If they are rare, then one needs to look at many thousands to find even a few. Kepler looks at 100,000 stars so that if Earths are rare, a null or near null result would still be significant. If Earth-size planets are common then Kepler should detect hundreds of them.

Considering that we want to find planets in the habitable zone, the time between transits is about one year. To reliably detect a sequence one needs four transits. Hence, the mission duration needs to be at least three and one half years.

The Kepler instrument is a specially designed 0.95-meter diameter telescope called a photometer or light meter. It has a very large field of view for an astronomical telescope —105 square degrees— or about the area of both your hands held at arm's length, in order to observe the necessary large number of stars. It stares at the same star field for the entire mission and continuously and simultaneously monitors the brightnesses of more than 100,000 stars for the life of the mission—3.5 years.

The diameter of the telescope needs to be large enough to reduce the noise from photon counting statistics, so that it can measure the small change in brightness of an Earth-like transit. The design of the entire system is such that the combine differential photometric precision over a 6.5 hour integration is less than 20 ppm (one-sigma) for a 12^th magnitude solar-like star including an assumed stellar variability of 10 ppm. This is a conservative, worse-case assumption of a grazing transit. A central transit of the Earth crossing the Sun lasts 13 hours. And about 75% of the stars older than 1 Gyr are less variable then the Sun on the time scale of a transit.

The photometer must be spacebased to obtain the photometric precision needed to reliably see an Earth-like transit and to avoid interruptions caused by day-night cycles, seasonal cycles and atmospheric perturbations, such as, extinction associated with ground-based observing.

Extending the mission beyond three and one half years provides for:

Improving the signal to noise by combining more transits to permit detection of smaller planets
Finding planets in orbits with larger periods
Finding planets around stars that are noisier either due to being fainter or having more variability

Expected Results

Based on the mission described above, including conservative assumptions about detection criteria, stellar variability, taking into account only orbits with 4 transits in 3.5 years, etc., and assuming that planets are common around other stars like our Sun, then we expect to detect:

From transits of terrestrial planets in one year orbits

About 50 planets if most are the same size as Earth (R~1.0 R_e) and none larger,
About 185 planets if most have a size of R~1.3 R_e,
About 640 planets if most have a size of R~2.2 R_e,
About 12% with two or more planets per system.

These numbers come out substantially higher, when one takes into consideration all orbits from a few days to more than one year.

From modulation of the reflected light from giant inner planets

About 870 planets with periods less than one week.

From transits of giant planets

About 135 inner-orbit planet detections,
Densities for 35 inner-orbit planets, and
About 30 outer-orbit planet detections.

Detection of the short-period giant planets should occur within the first several months of the mission.

The sample size of stars for this mission is large enough to capture the richness of the unexpected. Should no detection be made, a null result would still be very significant.

Kepler spacecraft and photometer.

Mission Characteristics

Continuously point at a single star field in Cygnus-Lyra region except during Ka-band downlink.
Roll the spacecraft 90 degrees about the line-of-sight every 3 months to maintain the sun on the solar arrays and the radiator pointed to deep space.
Monitor 100,000 main-sequence stars for planets.
Mission lifetime of 3.5 years extendible to at least 6 years.
D2925-10L (Delta II) launch into an Earth-trailing heliocentric orbit.
Scientific Operations Center and Project management (operations) at Ames Research Center.
Project management (development) at Jet Propulsion Laboratory.
Flight segment design and fabrication at Ball Aerospace & Technologies Corp.
Mission Operations Center at Laboratory for Atmospheric and Space Physics (LASP)—University of Colorado.
Data Management Center at Space Telescope Science Institute.
Deep Space Network for telemetry.
Routine contact:
X-band contact twice a week for commanding, health and status.
Ka-band contact once a month for science data downlink.

External Links

Kepler Education Projects - Kepler Mission, NASA.
Kepler Mission Homepage - Kepler Mission, NASA.
"Johannes Kepler: His Life, His Laws and Times" - Kepler Mission, NASA.
"International Year of Astronomy and Johannes Kepler" - Kepler Mission, NASA.
StarDate Radio Programs - The Kepler Mission EPO at SETI Institute works closely with the McDonald Observatory at the University of Texas, Austin, to coordinate a series of StarDate radio programs in both English and Spanish featuring Kepler and the search for extrasolar terrestrial planets.

Preview Image

"Kepler with distant solar system." "The Extended Solar Neighborhood." The figure shows what we believe to be the local structure of our Galaxy, the Milky Way. The stars sampled are similar to the immediate solar neighborhood. Young stellar clusters, ionized hydrogen (HII) regions and the neutral hydrogen (HI) distribution define the arms of the Galaxy. (Source: NASA-Kepler Mission.)

Disclaimer: This article is taken wholly from, or contains information that was originally published by, NASA. Topic editors and authors for the Encyclopedia of the Cosmos may have edited its content or added new information. The use of information from NASA should not be construed as support for, or endorsement by, that organization for any new information added by EoC personnel, or for any editing of the original content.
Original content retrieved from ""http://kepler.nasa.gov/""

Citation

Haisch, Bernard, Ph.D. (Contributing Author); National Aeronautics and Space Administration (Content source); BJoakim Lindblom (Topic Editor). 2008. "Kepler Mission." In: Encyclopedia of the Cosmos. Eds. Bernard Haisch and Joakim F. Lindblom (Redwood City, CA: Digital Universe Foundation). [First published April 3, 2008].
<http://www.cosmosportal.org/articles/view/135823/>

Detecting Extrasolar Planets

The first detection of extrasolar planets was announced in 1995 by two competing groups. One was headed by Geoff Marcy, then at San Francisco State University, the other by Michel Mayor at the Geneva Observatory. The same technique was used by both: measuring the back and forth motion of a star due to the “teeter-totter” like reaction induced by the orbiting of a massive planet. In the case of our own solar system, this motion would be predominantly due to Jupiter. Since the Sun outweighs Jupiter by more than a factor of 1000, the Sun’s back and forth motion is tiny: about the speed of a good runner. It is amazing that this can be precisely measured. To date well over 200 planets have been discovered using this technique, and in a few recent cases, as precision keeps improving, even multiple planets around a star can be extracted from the data.

Scale diagram of planet/star ratio for the WASP Planets. (Credit: SuperWASP project)

As powerful as this technique is, there are unavoidable limitations. We cannot measure the sizes and masses of planets accurately (because we do not know how tilted to our line-of-sight the orbits are). The technique is intrinsically biased toward the most massive planets in close orbits. That’s why so many of the planets are much more massive than Jupiter yet orbit their stars at distances closer than Mercury in our solar system.

A complementary technique is now showing its worth: planet transits. If we are lucky enough to be almost directly in the plane of the orbit of a planet, we can spot the transit of that planet against its sun. This happens here too. Venus transits the Sun as viewed from the Earth every now and then. On other stars we cannot image the planet as it crosses a stellar disk, but it is possible to measure changes in brightness with such precision that dips in the brightness of a star can be used to infer that a planet is crossing. This allows the actual size of the planet to be inferred from the dip in the star’s light (assuming we can infer the radius of the star from its spectral type).

Given that we need to rely on chance alignments of the orbital planes and transits that briefly happen every few months or years for those lucky alignments, you would not think that this looks too promising. It requires monitoring hundreds of thousands of stars all at once to stand a chance of catching one of those rare events.

Amazingly this can be done, and this technique has now resulted in 46 planet detections from ground-based observatories. The latest announcement comes from astronomers at the University of California, Santa Barbara, who have found ten new planets in a project called SuperWASP, for Wide Area Search for Planets. Planets found range from half the size of Jupiter to eight times as large.

This technique is being taken into space. The NASA Kepler Mission, scheduled for launch in February 2009, is designed to find planets 30 to 600 times less massive than Jupiter. As NASA states: To detect an Earth-size planet, the photometer must be able to sense a drop in brightness of only 1/100 of a percent. This is akin to sensing the drop in brightness of a car’s headlight when a fruitfly moves in front of it!

The Kepler Mission, a NASA Discovery mission, is specifically designed to find Earth-like planets in the habitable zone, which encompasses the distances from a star where liquid water can exist on a planet’s surface. It is amazing how quickly we are obtaining actual observations zeroing in on that most profound of questions: Are there other civilizations out there in the Universe?

Press Release from University of California, Santa Barbara.

NASA Kepler Mission home page.

Planetary Systems

A Little Telescope Goes a Long Way

In All the Universe, Just 10 Percent of Solar Systems Are Like Ours

NASA's Kepler Space Telescope Discovers Five Exoplanets

Avatar's Moon Pandora Could Be Real

First Direct Observation of a Planet-like Object Orbiting a Star Similar to the Sun.

Exoplanet: Atmosphere

32 New Exoplanets Found

More Information

Links

Contacts

Astronomers do it Again: Find Organic Molecules Around Gas Planet

SIM PlanetQuest

Simulation suggests rocky exoplanet has bizarre atmosphere

NASA's Spitzer Spots Clump of Swirling Planetary Material

First Solid Evidence for a Rocky Exoplanet

Notes

Let the Planet Hunt Begin

Hubble Finds Hidden Exoplanet

Hubble Finds Hidden Exoplanet in Archival Data

Related Articles

Preview Image

Kepler Mission

Importance of Planet Detection

Scientific Objective

The Transit Method of Detecting Extrasolar Planets

Design

Expected Results

From transits of terrestrial planets in one year orbits

From modulation of the reflected light from giant inner planets

From transits of giant planets

Mission Characteristics

External Links

Preview Image

Detecting Extrasolar Planets