NASA - Kepler Mission
Extrasolar Planets Encyclopedia
Geoff Marcy's Web page on New Planets
Michel Mayor's Web page on New Planets
Very Large Telescope Homepage
Hubble Space Telescope
JPL Exoplanets Site
JPL New Worlds Atlas
Spitzer View of Fomalhaut's Dust Disc
Eddington Mission: Transits of Extrasolar
Berkeley - Astronomers at the University of California, Berkeley, have discovered the nearest and youngest star with a visible disk of dust that may be a nursery for planets.
The dim red dwarf star is a mere 33 light years away, close enough that the Hubble Space Telescope or ground-based telescopes with adaptive optics to sharpen the image should be able to see whether the dust disk contains clumps of matter that might turn into planets.
"Circumstellar disks are signposts for planet formation, and this is the nearest and youngest star where we directly observe light reflected from the dust produced by extrasolar comets and asteroids - i.e., the objects that could possibly form planets by accretion," said Paul Kalas, assistant research astronomer at UC Berkeley and lead author of a paper reporting the discovery.
"We're waiting for the summer and fall observing season to go back to the telescopes and study the properties of the disk in greater detail. But we expect everyone else to do the same thing - there will be lots of follow-up."
A paper announcing the discovery will be published online in Science Express this week, and will appear in the printed edition of the journal in March. Coauthors with Kalas are Brenda C. Matthews, a post-doctoral researcher with UC Berkeley's Radio Astronomy Laboratory, and astronomer Michael C. Liu of the University of Hawaii. Kalas also is affiliated with the Center for Adaptive Optics at UC Santa Cruz.
The young M-type star, AU Microscopium (AU Mic), is about half the mass of the sun but only about 12 million years old, compared to the 4.6 billion year age of the sun. The team of astronomers found the star while searching for dust disks around stars emitting more than expected amounts of infrared radiation, indicative of a warm, glowing dust cloud.
The image of AU Mic, obtained last October with the University of Hawaii's 2.2-meter telescope atop Mauna Kea, shows an edge-on disk of dust stretching about 210 astronomical units from the central star - - about seven times farther from the star than Neptune is from the sun. One astronomical unit, or AU, is the average distance from the Earth to the sun, about 93 million miles.
"When we see scattered infrared light around a star, the inference is that this is caused by dust grains replenished by comets and asteroid collisions," Kalas said. Because 85 percent of all stars are M-type red dwarfs, the star provides clues to how the majority of planetary systems form and evolve.
Other nearby stars, such as Gliese 876 at 16 light years and epsilon-Eridani at 10 light years, wobble, providing indirect evidence for planets. But images of debris disks around stars are rare. AU Mic is the closest dust disk directly imaged since the discovery 20 years ago of a dust disk around beta-Pictoris, a star about 2.5 times the mass of the sun and 65 light years away. Though the two stars are in opposite regions of the sky, they appear to have been formed at the same time and to be traveling together through the galaxy, Kalas said.
"These sister stars probably formed together in the same region of space in a moving group containing about 20 stars," Kalas said. This represents an unprecedented opportunity to study stars formed under the same conditions, but of masses slightly larger and slightly smaller than the sun.
"Theorists are excited, too, at the opportunity to understand how planetary systems evolve differently around high-mass stars like beta-Pictoris and low-mass stars like AU Mic," he said.
The pictures of AU Mic were obtained by blocking glare from the star with a coronagraph like that used to view the sun's outer atmosphere, or corona. The eclipsing disk on the University of Hawaii's 2.2-meter telescope blocked view of everything around the star out to about 50 AU. At this distance in our solar system, only the Kuiper Belt of asteroids and the more distant Oort cloud, the source of comets, would be visible.
Kalas said that sharper images from the ground or space should show structures as close as 5 AU, which means a Jupiter-like planet or lump in the dusty disk would be visible, if present.
"With the adaptive optics on the Lick 120-inch telescope or the Keck 10-meter telescopes, or with the Hubble Space Telescope, we can improve the sharpness by 10 to 100 times," Kalas said.
In a companion paper accepted for publication in The Astrophysical Journal, the Berkeley-Hawaii team reports indirect evidence for a relatively dust-free hole within about 17 AU of the star. This would be slightly inside the orbit of Uranus in our own solar system.
"Potential evidence for the existence of planets comes from the infrared spectrum, where we notice an absence of warm dust grains," he said. "That means that grains are depleted within about 17 AU radius from the star. One mechanism to clear out the dust disk within 17 AU radius is by planet-grain encounters, where the planet removes the grains from the system."
"The dust missing from the inner regions of AU Mic is the telltale sign of an orbiting planet. The planet sweeps away any dust in the inner regions, keeping the dust in the outer region at bay," said Liu.
Aside from further observations with the 2.2-meter telescope in Hawaii, Kalas and his colleagues plan to use the Spitzer Space Telescope, an infrared observatory launched last August by the National Aeronautics and Space Administration (NASA), to conduct a more sensitive search for gas.
The research was supported by the NASA Origins Program and the National Science Foundation's Center for Adaptive Optics.
Using NASA's Chandra X-ray Observatory, scientists have detected X-rays from a low mass brown dwarf in a multiple star system, which is as young as 12 million years old. This discovery is an important piece in an increasingly complex picture of how brown dwarfs -- and perhaps the very massive planets around other stars -- evolve.
Chandra's observations of the brown dwarf, known as TWA 5B, clearly resolve it from a pair of Sun-like stars known as TWA 5A. The system is about 180 light years from the Sun and a member of a group of about a dozen young stars in the southern constellation Hydra. The brown dwarf orbits the binary stars at a distance about 2.75 times that of Pluto. This is the first time that a brown dwarf this close to its parent star(s) has beenresolved in X-rays.
"Our Chandra data show that the X-rays originate from the brown dwarf's coronal plasma which is some 3 million degrees Celsius," said Yohko Tsuboi of Chuo University in Tokyo and lead author of the April 10th issue of Astrophysical Journal Letters paper describing these results. "The brown dwarf is sufficiently far from the primary stars that the reflection of X-rays is unimportant, so the X-rays must come the brown dwarf itself."
TWA 5B is estimated to be only between 15 and 40 times the mass of Jupiter, making it one of the least massive brown dwarfs known. Its mass is rather near the currently accepted boundary (about 12 Jupiter masses) between planets and brown dwarfs. Therefore, these results may also have implications for very massive planets, including those that have been discovered as extrasolar planets in recent years.
"This brown dwarf is as bright as the Sun today in X-ray light, while it is fifty times less massive than the Sun," said Tsuboi. "This observation, thus, raises the possibility that even massive planets might emit X-rays by themselves during their youth!"
This research on TWA 5B also provides a link between an active X-ray state in young brown dwarfs (about 1 million years old) and a later, quieter period of brown dwarfs when they reach ages of 500 million to a billion years.
Brown dwarfs are often referred to as "failed stars," as they are believed to be under the mass limit (about 80 Jupiter masses) needed to spark the nuclear fusion of hydrogen to helium, which characterizes traditional stars. Scientists hope to better understand the evolution of magnetic activity in brown dwarfs through the X-ray behavior.
Chandra observed TWA 5B for about three hours on April 15, 2001, with its Advanced CCD Imaging Spectrometer (ACIS). Along with Chandra's mirrors, ACIS can achieve the angular resolution of a half arc second.
"This brown dwarf is about 200 times dimmer than the primary and located just two arcseconds away," said Gordon Garmire of Penn State University who led the ACIS team. "It's quite an achievement that Chandra was able to resolve it."
Other members of the research team included Yoshitomo Maeda (Institute of Space and Astronautical Science, Kanagawa, Japan), Eric Feigelson, Gordon Garmire, George Chartas, and Koji Mori (Penn State University), and Steve Prado (Jet Propulsion Laboratory).
Vanderbilt University press release, December 14, 2002
NOTE: A multimedia version of this story, including an animation and additional background, is available on Exploration, Vanderbilt's online research magazine, at http://exploration.vanderbilt.edu.
Classical T Tauri stars - those less than 3 million years old - are invariably accompanied by a thick disk of dust and gas, which is often called a protoplanetary disk because it is a breeding ground for planet formation. Most older T Tauri stars show no signs of encircling disks. Because they are not old enough for planets to form, astronomers have concluded that most of these stars must loose their disk material before planetary systems can develop.
Weintraub and Bary are pursuing an alternative theory. They propose that most older T Tauri stars haven't lost their disks at all: The disk material has simply changed into a form that is nearly invisible to Earth-based telescopes. They published a key observation supporting their hypothesis in the September 1 issue of the Astrophysical Journal Letter and the article was highlighted by the editors of Science magazine as particularly noteworthy. The two researchers currently are preparing to publish additional evidence in support of their hypothesis. The dense disks of dust and gas surrounding classical T Tauri stars are easily visible because dust glows brightly in the infrared region of the spectrum. Although infrared light is invisible to the naked eye, it is readily detectable with specially equipped telescopes. The second group of T Tauri stars that are somewhat older - between three to six billion years - and show no evidence of disks have been labeled as "naked" or "weak line" T Tauri stars.
Because there is no visible evidence that naked T Tauri stars possess protoplanetary disks. So astronomers have concluded that the material must have been absorbed by the star or blown out into interplanetary space or pulled away by the gravitational attraction of a nearby star in the first few million years. According to current theories, it takes about 10 million years to form a Jupiter-type planet and even longer to form a planet like Earth. If the models are correct and if most Sun-like stars loose their protoplanetary disks in the T Tauri stage, then very few stars like the Sun are likely to possess planetary systems.
This picture doesn't sit well with Weintraub, however. "Approaching it from a planetary evolution point of view, I have not been comfortable with some of the underlying assumptions," he says.
Current models do not take the evolution of protoplanetary disks into account. Over time, the disk material should begin agglomerating into solid objects called planetesimals. As the planetesimals grow, an increasing amount of the mass in the disk becomes trapped inside these solid objects where it cannot emit light directly into space. The constituents of the disk that astronomers knew how to detect - small grains of dust and carbon monoxide molecules - should quickly disappear during the first steps of planet building.
"Rather than the disk material dissipating," says Bary, "It may simply become invisible to our instruments." So Weintraub and Bary began searching for ways to determine if such "invisible protoplanetary disks" actually exist.
They decided that their best bet was to search for evidence of molecular hydrogen, the main constituent of the protoplanetary disk, which should persist much longer than the dust grains and carbon monoxide. Unfortunately, molecular hydrogen is notoriously difficult to stimulate into emitting light: It must be heated to a fairly high temperature before it will give off infrared light.
The fact that T Tauri stars are also strong X-ray sources gave them an idea. Perhaps the X-rays coming from the star could act as an energy source capable of stimulating the molecular hydrogen. To produce enough light to be seen from earth, however, the molecular hydrogen could not b mixed with dust and had to be at an adequate density. Studying various theories of planet formation, they determined that the proper conditions should hold in a "flare region" near the outer edge of the protoplanetary disk.
The next step was to get observation time on a big telescope to put their out-of-the-mainstream theory to the test. After repeated rejections, they were finally allocated viewing time on the four-meter telescope at the National Optical Astronomical Observatory in Kitt Peak, Arizona. When they finally took control of the telescope and pointed it toward one of their prime targets - a naked, apparently diskless T Tauri star named DoAr21 - they found the faint signal for which they were searching.
"We found evidence for hydrogen molecules where no hydrogen molecules were thought to exist," says Weintraub. When Bary calculated the amount of hydrogen involved in producing this signal, however, he came up with about a billionth of the mass of the Sun, not even enough to make the Moon. As they argued in their Astrophysical Journal Letter article, they believe that they have detected only the proverbial tip of the iceberg, since most of the hydrogen gas will not radiate in the infrared. But the calculation raises the question of whether the molecular hydrogen that they detected is part of a complete protoplanetary disk or just its shadowy remains. Although they do not completely answer the question, additional observations that the two are readying for publication provides additional support for their contention that DoAr21 contains a sizeable but invisible disk.The new observations are the detection of the same molecular hydrogen emission line around three classical T Tauri stars with visible protoplanetary disks. The strength of the hydrogen emission lines in the three is comparable to that measured at DoAr21. In addition, they have calculated the ratio between the mass of hydrogen molecules that are producing the infrared emissions and the mass of the entire disk in the three systems. For all three they calculate that the ratio is about one in 100 million.
"If the ratio between the amount of hydrogen emitting in the infrared and the total amount of hydrogen in the disk is about the same in the two types of T Tauri stars, which is not an unreasonable assumption, this suggests the naked T Tauri star has a sizable but hard-to-detect disk," says Bary.
Weintraub and Bary admit that they have more work to do to in order to convince their colleagues to adopt their theory. They have been allocated time on a larger telescope, the eight-meter Gemini South in Chile and plan to survey 50 more naked T Tauri stars to see how many of them produce the same molecular hydrogen emissions. If a large number of them do, it will indicate that they have discovered a general mechanism involved in the planetary formation process. They also intend to search for a second, fainter hydrogen emission line. If they find it, it will provide additional insights into the excitation process.
Currently, the number of naked T Tauri stars that have been discovered is much greater than the number of known classical T Tauri stars. If Weintraub and Bary are proven right, however, and a significant percentage of the naked T Tauri stars develop planetary systems, it means that solar systems similar to our own are a common sight in the universe.
NASA Press Release, October 29, 2002
NASA awarded a contract to Ball Aerospace and Technology Corp.(BATC), Boulder, Colo. for development of the optics and detectors fora high-tech camera for the Kepler planet-finding spacecraft,scheduled for launch in 2007.
Eastman Kodak will provide the entire optical subsystem for the spacecraft. Kodak is providing a unique optical subsystem for Kepler. Nothing similar has ever been flown in space. The two-piece system enables an extremely wide field of view, allowing Kepler to continuously gaze at more than 100,000 stars at the same time.
The Kepler Mission differs from previous ways of looking for planets, which have led to the discovery of about 100 giant Jupiter-sized planets. Kepler will look for the "transit" signature that occurs each time a planet crosses the line-of-sight between a planet's parent star, the one it orbits, and the observer. During the orbital "transit," the planet blocks some of the light from its parent star resulting in periodic dimming. This periodic signature is used to detect the planet and to determine its size and orbit. Kepler will be able to determine if any Earth-sized planets make a transit across any of the stars.
"With its cutting-edge capability, Kepler may help us answer one of the most enduring questions humans have asked throughout history: 'are there other planets like Earth in the universe?'" said principal investigator William Borucki of NASA's Ames Research Center, Moffett Field, Calif., leader of the mission.
NASA - Kepler Mission
University of Rochester press release, October 23, 2002
A new extrasolar planet has been discovered using a new technique that will allow astronomers to detect planets no other current method can. Planets around other stars have been previously detected only by the effect they have on their parent star, limiting the observations to large, Jupiter-like planets and those in very tight orbits. The new method uses the patterns created in the dust surrounding a star to discern the presence of a planet that could be as small as Earth or in an orbit so wide that it would take hundreds of years to observe its effect on its star.
The research by Alice Quillen, assistant professor of physics and astronomy at the University of Rochester, and undergraduate student Stephen Thorndike, appears in the current issue of The Astrophysical Journal Letters.
"We're very excited because this will open up the possibility of finding planets that we'd probably never detect just looking at the parent star," says Quillen. "We can confirm the presence of certain planets in five years instead of the two centuries it would otherwise take."
The new planet was discovered orbiting the star Epsilon Eridani about 10 light years from Earth. It is one of the lowest mass planets yet discovered around another star and has by far the longest, largest orbit of any yet discovered. Epsilon Eridani already has one discovered planet, the size of Jupiter (our solar system's largest planet) and orbiting around the star about every five years. By contrast, the new planet is roughly a tenth of Jupiter's mass and completes an orbit once every 280 years.
Traditional planet-detection methods cannot reveal the new planet, tentatively named "Epsilon Eridani C," because those methods watch for the effect a planet has on it's parent star, and low-mass planets or those in very large orbits do not dramatically effect their star. The method that has detected most of the 100+ extrasolar planets so far measures how much the parent star "wobbles" as the planet's gravity tugs on it throughout its orbit. A newer method watches for planets as they pass in front of a star and slightly dims its light.
Unlike current methods, Quillen's technique does not use direct light from the star, but rather light radiating from the dust surrounding it. Not all stars have large concentrations of dust, but those that do, like Epsilon Eridani, can display certain telltale patterns in their dust fields. These patterns can betray the existence of a planet.
Quillen started her research by running computer simulations of how a planet might sculpt the dust surrounding a star. Instead of using a simple, circular orbit like most planets in our own solar system follow, she decided to experiment with highly eccentric orbits- orbits where the planet sometimes swings very close to the star and then moves very far away. She found that for certain situations where the planet orbited the star three times for every two times the dust orbited, or five times for every three dust orbits, the dust would settle into definable clumps in a ring around the star. These clumps formed as the planet swung to its farthest point from the star and its gravity pulled the dust into the patterned clumps. After finding this pattern in her simulations, Quillen turned to the heavens to see if she could find a star surrounded with dust with these patterns. She found Epsilon Eridani.
"The fact that the dust around this star closely matches what we expected to see if a planet were present doesn't mean we know for sure that a planet is really there," says Quillen. "The images of Epsilon Eridani that we matched with our model are five years old. If Epsilon Eridani were re-observed then the clumps should have moved. The rate that they move will pin down the likely location of the planet."
Quillen plans to find more planets and work out new simulations to determine if patterns could emerge from other kinds of planetary orbits. She's hoping to find if a change in the light emitted from the dust fields could help signal the presence of a planet, as well as what other kinds of patterns might form from the dust, such as rings or swaths of orbiting dust-free zones. She's also planning to learn where the disk of dust comes from, if it comes from frequently colliding planetesimals as she expects. If she pins down how the dust forms, she may be able to estimate the number of planetesimals needed to create the dust.
Anglo-Australian Observatory press release, Sept 17, 2002
British astronomers, together with Australian and American colleagues, have used the 3.9m Anglo-Australian Telescope [AAT] in New South Wales, Australia to discover a new planet outside our Solar System - the 100th to be detected. The discovery, which is part of a search for solar systems that resemble our own, was announced on September 12. at a conference on "The origin of life" in Graz, Austria. This takes the total number of planets found outside our solar system to 100, and scientists are now seeing a pattern in the orbits, giving clues to how they form.
The new planet, which has a mass about that of Jupiter, circles its star Tau1 Gruis about every four years. Tau1 Gruis can be found in the constellation Grus (the crane) and is about 100 light years away from Earth. The planet is three times as far from its star as the Earth is from the Sun.
'Now our searches have become precise enough to find many planets in orbits like those in our Solar System, we are seeing clues which may help us understand how planets are formed.' said UK team leader Hugh Jones of Liverpool John Moores University. 'We are seeing a pattern for these planets to be of two types, those very close-in and another set with orbits further out. This Tau1 Gruis planet builds this second group. Why are there these two groups? We hope the theorists will be able to explain this.'
The long-term goal of this programme is the detection of true analogues to the Solar System. This discovery of a companion planet to the Tau1 Gruis star with a relatively long-period orbit and mass similar to that of Jupiter is a step toward this goal. The discovery of other such planets and planetary satellites within the next decade will help astronomers assess the Solar System's place in the galaxy and whether planetary systems like our own are common or rare.
'The Anglo-Australian Telescope is providing the most accurate planet-search observations in the Southern Hemisphere', said Dr Alan Penny, the other UK team member from the Rutherford Appleton Laboratory.
The researchers have found that as they probe for planets in larger orbits, the distribution of planets around stars is quite different from that of binary stars orbiting one another, where there is a smooth distribution of orbits. In contrast to the early discoveries of exoplanets, we now find that less than 1 in 5 exoplanets are to be found very close to their stars, a few orbiting with a period of 5 to 50 days but most giant planets are orbiting at large distances from their host stars. This supports the idea that they are formed at Jupiter-like distances from their host star. Dependent on the details of the early solar system, most giant planets probably spiral inwards towards their star until they reach a point where a lack of frictional forces stops their further migration.
To find evidence of planets, the astronomers use a high-precision technique developed by Paul Butler of the Carnegie Institute of Washington and Geoff Marcy of the University of California at Berkeley to measure how much a star "wobbles" in space as it is affected by a planet's gravity. As an unseen planet orbits a distant star, the gravitational pull causes the star to move back and forth in space. That wobble can be detected by the 'Doppler shifting' it causes in the star's light. The AAT team measure the Doppler shift of stars to an accuracy of 3 metres per second - bicycling speed. This very high precision allows the team to find planets.
The Anglo-Australian Planet Search Home Page
Exoplanets Home Page
The Extra-solar Planets Encyclopaedia
NSF Press Release 02-54, June 13, 2002
After 15 years of observation and a lot of patience, the world's premier planet-hunting team has found a planetary system that reminds them of our home solar system.
Geoffrey Marcy, astronomy professor at the University of California, Berkeley, and astronomer Paul Butler of the Carnegie Institution of Washington, DC, announced the discovery of a Jupiter-like planet orbiting a Sun-like star at nearly the same distance as the Jovian system orbits our sun.
"All other extrasolar planets discovered up to now orbit closer to the parent star, and most of them have had elongated, eccentric orbits. This new planet orbits as far from its star as our own Jupiter orbits the sun," said Marcy. The National Science Foundation (NSF) and NASA fund the planet-hunting team.
The star, 55 Cancri in the constellation Cancer, was already known to have one planet, announced by Butler and Marcy in 1996. That planet is a gas giant slightly smaller than the mass of Jupiter and whips around the star in 14.6 days at a distance only one-tenth that from Earth to the sun.
Using as a yardstick the 93-million mile Earth-sun distance, called an astronomical unit or AU, the newfound planet orbits at 5.5 AU, comparable to Jupiter's distance from our sun of 5.2 AU (about 512 million miles). Its slightly elongated orbit takes it around the star in about 13 years, comparable to Jupiter's orbital period of 11.86 years. It is 3.5 to 5 times the mass of Jupiter.
"We haven't yet found an exact solar system analog, which would have a circular orbit and a mass closer to that of Jupiter. But this shows we are getting close, we are at the point of finding planets at distances greater than 4 AU from the host star," said Butler.
"I think we will be finding more of them among the 1,200 stars we are now monitoring," he added.
The team shared its data with Greg Laughlin, assistant professor of astronomy and astrophysics at the University of California, Santa Cruz. His dynamical calculations show that an Earth-sized planet could survive in a stable orbit between the two gas giants. For the foreseeable future, existence of any such planet around 55 Cancri will remain speculative.
Marcy, Butler and their team also announced a total of 15 new planets today, including the smallest ever detected: a planet circling the star HD49674 in the constellation Auriga at a distance of .05 AU, one-twentieth the distance from Earth to the sun. Its mass is about 15 percent that of Jupiter and 40 times that of Earth. This brings the total number of known planets outside our solar system to 91.
Discovery of a second planet orbiting 55 Cancri culminates 15 years of observations with the 3-meter (118-inch) telescope at Lick Observatory, owned and operated by the University of California. The team also includes Debra Fischer, UC Berkeley; Steve Vogt, UC Santa Cruz; Greg Henry, Tennessee State University, Nashville; and Dimitri Pourbaix, the Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles.
Marcy and Butler used a technique that measures the slight Doppler shift in starlight caused by a wobble in the star's position, due to the gravitational tug of an orbiting planet. By observing over a period of years, they can infer a planet's approximate mass and orbital size and period.
The star 55 Cancri is 41 light years from Earth and is about 5 billion years old. Further data are needed to determine whether yet another planet is orbiting it, because the two known planets do not explain all the observed Doppler wobbling. One possible explanation is a Saturn-mass planet orbiting about .24 AU from the star.
For more information, see: http://exoplanets.org
An artist's concept and animation is at:
from a NASA Press Release, December 24
NASA selected two low-cost Discovery missions in December 2001. The missions are Dawn, slated for launch in 2006, which will orbit the two largest asteroids in our solar system, and Kepler, a spaceborne telescope, also scheduled for launch in 2006, which will search for Earth-like planets around stars beyond the solar system.
"Kepler and Dawn are exactly the kind of missions NASA should be launching, missions that tackle some of the most important questions in science yet do it for a very modest cost," said Dr. Edward Weiler, associate administrator for space science at NASA Headquarters in Washington. "It's an indicator of how far we've come in our capability to explore space when missions with such ambitious goals are proposed for the Discovery Program of lower-cost missions rather than as major projects costing ten times as much."
The Dawn mission will make a nine-year journey to orbit the two most massive asteroids known, Vesta and Ceres, two "baby planets" very different from each other yet both containing tantalizing clues about the formation of the solar system. Using the same set of instruments to observe these two bodies, both located in the main asteroid belt between Mars and Jupiter, Dawn will improve our understanding of how planets formed during the earliest epoch of the solar system.
Ceres has quite a primitive surface, water-bearing minerals, and possibly a very weak atmosphere and frost. Vesta is a dry body that has been resurfaced by basaltic lava flows, and may have an early magma ocean like Earth's Moon. Like the Moon, it has been hit many times by smaller space rocks, and these impacts have sent out meteorites at least five times in the last 50 million years.
The Dawn mission builds on the highly successful ion- propulsion technology pioneered by NASA's Deep Space 1 spacecraft. During its nine-year journey through the asteroid belt, Dawn will rendezvous with Vesta and Ceres, orbiting from as high as 800 kilometers (500 miles) to as low as 100 kilometers (about 62 miles) above the surface.
The mission will determine these pre-planets' physical attributes, such as shape, size, mass, craters and internal structure, and study more complex properties such as composition, density and magnetism.
Led by principal investigator Dr. Christopher T. Russell of the University of California, Los Angeles, the project is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Orbital Sciences Corporation, Dulles, Va., will develop the spacecraft.
"With its cutting-edge capability, Kepler may help us answer one of the most enduring questions humans have asked throughout history: are there others like us in the universe?" said principal investigator William Borucki of NASA's Ames research Center, Moffett Field, Calif., leader of the second selected mission.
The Kepler Mission differs from previous ways of looking for planets which have led to the discovery of about 80 Jupiter- sized planets around 300 times more massive than Earth. Kepler will look for the 'transit' signature of planets that occurs each time a planet crosses the line-of-sight between the planet's parent star the planet is orbiting and the observer. When this happens, the planet blocks some of the light from its star, resulting in a periodic dimming. This periodic signature is used to detect the planet and to determine its size and orbit. Kepler will continuously fix its gaze at a region of space containing 100,000 stars and will be able to determine if Earth-sized planets make a transit across any of the stars.
The industrial partner for mission hardware development is Ball Aerospace & Technologies Corp., Boulder, Colo. Kepler's selection involves a delayed start of development of up to one year due to funding constraints in the Discovery program.
NASA selected these missions from 26 proposals made in early 2001. The missions must stay within the Discovery Program's development-cost cap of about $299 million.
The Discovery Program emphasizes lower-cost, highly focused scientific missions. The past Discovery missions are NEAR Shoemaker, Mars Pathfinder and Lunar Prospector, all of which successfully completed their missions. Stardust and Genesis are in space; both have begun collecting science data, although Stardust has not yet arrived at its target comet. CONTOUR is scheduled to launch next summer, Deep Impact in January 2004 and MESSENGER in March 2004. ASPERA-3 and NetLander are Discovery Missions-of-Opportunity under development.
Information about Dawn and images are available at:
Details about the Kepler Mission are available at:
http://www.kepler.arc.nasa.gov Kepler images are available at:
STScI Press Release, December 1
Astronomers using NASA's Hubble Space Telescope have made the first direct detection and chemical analysis of the atmosphere of a planet outside our solar system. Their unique observations demonstrate it is possible with Hubble and other telescopes to measure the chemical makeup of extrasolar planets' atmospheres and potentially to search for chemical markers of life beyond Earth.
The planet orbits a yellow, Sun-like star called HD 209458, a seventh-magnitude star (visible in an amateur telescope) that lies 150 light-years away in the autumn constellation Pegasus. Its atmospheric composition was probed when the planet passed in front of its parent star, allowing astronomers for the first time ever to see light from the star filtered through the planet's atmosphere.
Lead investigator David Charbonneau of the California Institute of Technology, Pasadena, and the Harvard- Smithsonian Center for Astrophysics, Cambridge, Mass.; Timothy Brown of the National Center for Atmospheric Research, Boulder, Colo.; and colleagues used Hubble's spectrometer (the Space Telescope Imaging Spectrograph, or STIS) to detect the presence of sodium in the planet's atmosphere.
"This opens up an exciting new phase of extrasolar planet exploration, where we can begin to compare and contrast the atmospheres of planets around other stars," says Charbonneau. The astronomers actually saw less sodium than predicted for the Jupiter-class planet, leading to one interpretation that high-altitude clouds in the alien atmosphere may have blocked some of the light. The team's findings are to be published in the Astrophysical Journal.
The Hubble observation was not tuned to look for gases expected in a life-sustaining atmosphere (which is improbable for a planet as hot as the one observed). Nevertheless, this unique observing technique opens a new phase in the exploration of exoplanets, or extrasolar planets, say astronomers. Such observations could potentially provide the first direct evidence for life beyond Earth by measuring unusual abundances of atmospheric gases caused by the presence of living organisms.
The planet was discovered in 1999 through its slight gravitational tug on the star. The planet was estimated to be 70 percent the mass of the giant planet Jupiter, or 220 times more massive than Earth. Subsequently, astronomers discovered that the tilt of the planet's orbit makes it pass in front of the star -- relative to our line-of-sight from Earth -- making it unique among all the approximately 80 extrasolar planets discovered to date. As the planet passes in front of the star, it causes the star to dim very slightly for the duration of the transit. Transit observations by Hubble and ground-based telescopes confirmed that the planet is primarily gaseous, rather than liquid or solid, meaning that the planet is a gas giant, like Jupiter and Saturn.
The planet is an ideal target for repeat observations because it transits the star every 3.5 days -- which is the extremely short time it takes the planet to whirl around the star at a distance of merely four million miles from the star's surface. This close proximity heats the planet's atmosphere to a torrid 2,000 degrees Fahrenheit (1,100 degrees Celsius).
Observations of four separate transits were made by Hubble in search of direct evidence of an atmosphere. During each transit a small fraction of the star's light on its way to Earth passed though the planet's atmosphere. When the color of the light was analyzed by STIS, the telltale "fingerprint" of sodium was detected. Though the star also has sodium in its outer layers, STIS precisely measured the added influence of sodium in the planet's atmosphere.
The team, including Robert Noyes of the Harvard-Smithsonian Center for Astrophysics and Ronald Gilliland of the Space Telescope Science Institute in Baltimore, plans to look at HD 209458 again with Hubble in other colors of the star's spectrum to see which are filtered by the planet's atmosphere. They hope eventually to detect methane, water vapor, potassium and other chemicals in the planet's atmosphere. Once other transiting giants are found in the next few years, the team expects to characterize chemical differences among the atmospheres of these planets.
See images and animations at
additional press release from the science governmental organization, PPARC, in the UK, October 15
An international team of astronomers has discovered eight new extrasolar planets, bringing to nearly 80 the number of planets found orbiting nearby stars. The latest discoveries, supported by the National Science Foundation (NSF) and NASA, uncovered more evidence of what the astronomers are calling a new class of planets. These planets have circular orbits similar to the orbits of planets in our solar system.
At least two of the recently detected planets have approximately circular orbits. This characteristic is shared by two planets (one of them the size of Jupiter) previously detected by the same team around 47 Ursae Majoris, a star in the Big Dipper constellation, and one around the star Epsilon Reticulum. The majority of the extrasolar planets found to date are in an elongated, or "eccentric," orbit.
The further a planet lies from its star, the longer it takes to complete an orbit and the longer astronomers have to observe to detect it.
"As our search continues, we're finding planets in larger and larger orbits," said Steve Vogt of the Lick Observatory, University of California at Santa Cruz. "Most of the planetary systems we've found have looked like very distant relatives of the solar system - no family likeness at all. Now we're starting to see something like second cousins.
"In a few years' time we could be finding brothers and sisters."
"This result is very exciting," said Anne Kinney, director of NASA's Astronomy and Physics Division. "To understand the formation and evolution of planets and planetary systems we need a large sample of planets to study. This result, added to others in the recent past, marks the beginning of an avalanche of data which will help to provide the answers."
The recently detected planets range in mass from 0.8 to 10 times the mass of Jupiter, the largest planet in our solar system. They orbit their stars at distances ranging from about 0.07 AU (astronomical unit, or the distance from the Sun to Earth), to three AU.
The astronomers--from the United States, Australia, Belgium and the United Kingdom--are searching the nearest 1,200 stars for planets similar to those in our solar system, particularly Jupiter-like gas giants. Their findings will help astronomers assess the solar system's place in the galaxy and whether planetary systems like our own are common or rare.
For most of their discoveries, the astronomers have used the Keck 10-meter telescope on Mauna Kea, Hawaii; the Lick 3-meter in Santa Cruz, California; and the 3.9-meter Anglo-Australian Telescope in New South Wales, Australia. To find evidence of planets, the astronomers use a high-precision technique developed by Paul Butler of the Carnegie Institution of Washington and and Geoff Marcy of the University of California at Berkeley to measure how much a star "wobbles" in space as it is affected by a planet's gravity.
The team also receives support from the UK and Australian governments.
Additional press release from the science governmental organization, PPARC, in the UK:
PLANETS DISCOVERED WITH SOLAR SYSTEM-LIKE ORBITS
Images of an impression of the possible scene from a moon orbiting the extra-solar planet in orbit around the star HD 23079 and a graphic visualising the relative orbital locations of the three new extra-solar planets are available from the PPARC website www.pparc.ac.uk or from Mark.Wells@pparc.ac.uk
Eight new planets have been discovered circling nearby stars, so-called extra-solar planets, and three of these are Jupiter-sized planets travelling in circular orbits similar to that of Earth and Mars in our own Solar System. The majority of extra-solar planets found previously, some 66, have eccentric orbits. These new findings strengthen the likelihood of finding an extra-solar 'sibling' to planet Earth in the future.
The discovery was made by a team of British astronomers using the 3.9m Anglo-Australian Telescope [AAT] in New South Wales, Australia, in partnership with colleagues from the US and Belgium. Two other telescopes were used in the collaborative research programme including the 10m Keck telescope in Hawaii, and the 3m Lick telescope in California to search the nearest 1,200 stars for planets.
'Most of the planets we have found so far have looked like extremely distant relatives to any planet in our own solar system - very little likeness at all. But these latest discoveries are almost like second cousins and in the future we could find Earth's brothers and sisters, a real planet sibling,' said Prof. Ian Halliday, Chief Executive of the Particle Physics and Astronomy Research Council, the UK's strategic science investment agency which funded the British element of the research programme.
The three planets found with Solar System-like orbits are circling the star HD23079 [discovered by the Anglo-Australian Planet Search team] and HD4208 [discovered by the Keck Planet Search team]. These planets constitute a new class of giant planets with orbits similar to that of Earth and
Mars in the Solar System. The reason why astronomers are only just beginning to find such planets is that they lie far from their parent stars and take longer to orbit, requiring more precise measurements over a longer observing period.
' The Anglo-Australian Telescope is providing the most accurate planet-search observations in the Southern hemisphere', said Dr Alan Penny, a UK team member from the Rutherford Appleton Laboratory.
The 8 new planets range in mass from 0.8 to 10 times the mass of Jupiter, the largest planet in the Solar System. These planets have orbital periods between 6 days and 6 years. They orbit their stars at distances ranging from about 0.07 to 3.5 times the Earth-Sun distance. The Keck Planet Search found 5 of the new objects and the Anglo-Australian Planet Search found 3.
"These discoveries strengthen the statistics we are accumulating for such planets", said UK team leader Dr Hugh Jones of Liverpool John Moores University," and we are now starting to see, if not twins, then second cousins".
The long-term goal of this programme is the detection of Solar System-analogs, Jupiter-like planets in Jupiter-like orbits. The discovery of such planets within the next decade will help astronomers assess the Solar System's place in the galaxy and whether planetary systems like our own are common or rare.
To find evidence of planets, the astronomers use a high-precision technique developed by Paul Butler of the Carnegie Institute of Washington and Geoff Marcy of the University of California at Berkeley to measure how much a star "wobbles" in space as it is affected by a planet's gravity. As an unseen planet orbits a distant star the gravitational pull causes the star to move back and forth in space. That wobble can be detected by the 'doppler shifting' it causes in the star's light. Some planet-hunting groups can pick up the Doppler shift in light from a star moving at 10 metres/sec - the speed of a world-class sprinter. But the search technique used by the team is three times as precise making it sensitive to the effects of smaller planets.
The first extrasolar planet ever discovered was found by a Swiss team in 1995. With the new planets announced today a total 74 extra-solar planets have now been discovered.
The team are supported by the UK Particle Physics and Astronomy Research Council, the Australian government, the US National Science Foundation and NASA.
The members of the Anglo-Australian Planet Search team are:
from the UK: Dr Hugh R. A. Jones (Liverpool John Moores University),Dr AlanJ. Penny (Rutherford Appleton Laboratory); from Australia: Dr Chris G. Tinney (Anglo-Australian Observatory), Dr Brad Carter (University of Southern Queensland); from the US: Dr R. Paul Butler (Carnegie Institution of Washington), Dr Geoffrey W. Marcy [University of California Berkeley and San Francisco State University), Dr Chris McCarthy (Carnegie Institution of Washington).
The members of the Keck Planet Search team are:
from the UK: Mr Kevin Apps (University of Sussex); from the US: Dr Steven S. Vogt (UCO/Lick Observatory), Dr R. Paul Butler (Carnegie Institution of Washington), Dr Geoffrey W. Marcy (University of California Berkeley and San Francisco State University), Dr Debra A. Fischer (University of California, Berkeley), Gregory Laughlin (University of California, Berkeley).
especially Figure 3. The article is Hubble Space Telescope Time-Series Photometry of the Transiting Planet of HD 2094581 by Timothy M. Brown, David Charbonneau, Ronald L. Gilliland, Robert W. Noyes, and Adam Burrows.
NSF Press Release, 8/15/01
Image available at:
A team of astronomers has found a Jupiter-size planet in a circular orbit around a faint nearby star, raising intriguing prospects of finding a solar system with characteristics similar to our own.
The planet is the second found to orbit the star 47 Ursae Majoris in the Big Dipper, also known as Ursa Major or the Big Bear. The new planet is at least three-fourths the mass of Jupiter and orbits the star at a distance that, in our solar system, would place it beyond Mars but within the orbit of Jupiter.
"Astronomers have detected evidence of more than 70 extrasolar planets," said Morris Aizenman, a senior science advisor at the National Science Foundation (NSF). "Each discovery brings us closer to determining whether other planetary systems have features like those of our own."
"For the first time we have detected two planets in nearly circular orbits around the same star," said team member Debra Fischer of the University of California at Berkeley. "Most of the 70 planets people have found to date are in bizarre solar systems, with short periods and eccentric orbits close to the star. As our sensitivity improves we are finally seeing planets with longer orbital period, planetary systems that look more like our solar system."
The planet-search team, which is supported by NSF and NASA, has been instrumental in finding a majority of the extrasolar planets. Besides Fischer, the team includes Geoffrey Marcy, also of Berkeley; Paul Butler of the Carnegie Institution of Washington; Steve Vogt of the University of California at Santa Cruz; and Gregory Laughlin of NASA's Ames Research Center. Their report on the new planet has been submitted to Astrophysical Journal.
A few years ago, Marcy and Butler discovered a planet more than twice the mass of Jupiter in a circular orbit around the same star. The star is one of 100 that the scientists have targeted since 1987 in their search for evidence of extrasolar planets. They use the 3-meter and 0.6-meter telescopes at the University of California's Lick Observatory to measure Doppler shifted light reaching the earth from stars. Regular changes in the Doppler shift, they believe, signal the presence of a planet periodically pulling the star toward or away from Earth.
Fischer was able to see the periodic wobble from the second planet, smaller and farther from the star than the first, because of improved instrumentation that can measure motions as small as three meters per second.
The star is a yellow star similar to the sun, probably about seven billion years old and located about 51 light years from Earth.
"Every new planetary system reveals some new quirk that we didn't expect. We've found planets in small orbits and wacky eccentric orbits," said Marcy. "With 47 Ursae Majoris, it's heartwarming to find a planetary system that finally reminds us of our solar system."
For a list of extrasolar planets, see: www.exoplanets.org