Life on Venus (!)?
Extrasolar Planets Encyclopedia
SETI Institute Homepage
New planets found
NASA Origins Program
NASA's main astrobiology site
Astrobiology Web
Interview with Stanley Miller
Arecibo Message in a Crop Circle
Will We Be Contaminating the Planets and Comets?
Kepler mission
Carl Sagan Sites:
www.carlsagan.com
www.w-link.net-~subodeon/Sagan/Sagan/htm
www.projectvoyager.com/frame_nav.html
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.
Links:
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.
Links:
The Anglo-Australian Planet Search Home Page
Exoplanets Home Page
The Extra-solar Planets Encyclopaedia
NASA RELEASE: 02-150, August 2, 2002
In the latest study of a 4.5 billion-year-old Martian meteorite, researchers have presented new evidence confirming that 25 percent of the magnetic material in the meteorite was produced by ancient bacteria on Mars. These latest results were published in the journal Applied and Environmental Microbiology.
The researchers used six physical properties they refer to as the Magnetite Assay for Biogenicity (MAB) to compare all the magnetic material found in the ancient meteorite -- using the MAB as a biosignature. A biosignature is a physical and/or chemical marker of life that does not occur through random processes or human intervention.
"No non-biologic magnetite population, whether produced by nature or in the laboratory, has ever met the MAB criteria," said Kathie Thomas-Keprta, an astrobiologist at NASA's Johnson Space Center (JSC) in Houston and the lead researcher on the study. "This means that one-quarter of the magnetite crystals embedded in the carbonates in Martian meteorite ALH84001 require the intervention of biology to explain their presence."
Magnetotactic bacteria, which occur in aquatic habitats on Earth, arrange magnetite crystals in chains within their cells to make compasses, which help the bacteria locate sources of food and energy. Magnetite (Fe3O4) is produced inorganically on Earth, but the magnetite crystals produced by magnetotactic bacteria are very different -- they are chemically pure and defect-free, with distinct sizes and shapes.
Four of the MAB biosignature properties relate to the external physical structure of the magnetite crystals, while another refers to their internal structure and another to their chemical composition.
In their earlier studies, the researchers found that approximately one-quarter of the nanometer-sized magnetite crystals in ALH84001 had remarkable physical and chemical similarities to magnetite particles produced by a bacteria strain on Earth called MV-1. This is the first time, however, that any researcher has used the full MAB range of biosignature properties to compare the proposed bacteria- produced crystals in Mars meteorite ALH84001with the bacteria-produced crystals from Earth and with the other magnetites in the meteorite.
The comparison between the proposed bacteria-produced crystals in the meteorite and crystals known to be produced by Earth-bacteria MV-1 is striking and provides strong evidence that these crystals were made by bacteria on Mars.
The fact that Mars Global Surveyor data suggest that early Mars had a magnetic field is consistent with a reason why Mars would have magnetotactic bacteria. "Our best working hypothesis is that early Mars supported the evolution of bacteria that share several traits with magnetotactic bacteria on Earth, most notably the MV-1 group," said Simon Clemett, a coauthor of the paper at Johnson.
Mars has long been understood to provide the sources of light and chemical energy sufficient to support life, but in 2001 the Mars Global Surveyor spacecraft observed magnetized stripes in the crust of Mars, which showed that a strong magnetic field existed in the planet's early history, about the same time as the carbonate containing the unique magnetites in ALH84001 was formed.
In June, researchers using the Mars Odyssey spacecraft announced that they had found water ice under the surface of Mars. These attributes, coupled with a carbon dioxide-rich atmosphere, would have provided the necessary environment for the evolution of microbes similar to the fossils found in ALH84001.
"We believe this latest study proves that the magnetites in ALH84001 can be best explained as the products of multiple biogenic and inorganic processes that operated on early Mars," Thomas-Keprta said.
An international team of nine researchers collaborated on the three-year study. The team, led by Thomas-Keprta of Lockheed Martin at Johnson Space Center, was funded by the NASA Astrobiology Institute. Co-authors of the study are Clemett and Susan Wentworth of Lockheed Martin at JSC; Dennis Bazylinski of Iowa State University (funded by the National Science Foundation); Joseph Kirschvink of the California Institute of Technology in Pasadena; David McKay and Everett Gibson of JSC; Hojatollah Vali of McGill University in Canada; and Christopher Romanek of the Savannah River Ecology Laboratory.
For a more technical discussion of this latest publication please visit the following Web site:
http://ares.jsc.nasa.gov/astrobiology/biomarkers/recentnews.html
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:
http://www.jpl.nasa.gov/images/newplanets
SETI Institute Press Release, March 27, 2002
Mountain View, CA -- A team of scientists including SETI Institute and NASA researchers today announced the successful creation of amino acids, chemicals essential to life, in a laboratory simulation of conditions found in deep space.
At NASA's Ames Research Center, Moffett Field, CA, the team reproduced the freezing conditions that exist in the gigantic interstellar clouds of dust, gas, and ice that are the birthplaces of new stars and planetary systems.
In their experiment, NASA scientists simulated space-like conditions by freezing mixtures of common molecules found in interstellar clouds then exposed them to ultraviolet radiation. When analyzed, the resulting material contained glycine, alanine, and serine, amino acids that play central roles in all living organisms on Earth. The team reported its results in the March 28 issue of the journal Nature.
"We had previously shown that the chemistry that occurs under these conditions makes a number of different types of organic compounds of biological interest," said Dr. Max Bernstein, first author and chemist at the Center for the Study of Life in the Universe at the SETI Institute and NASA Ames, "but because of their critical role in life on Earth, we really wanted to see if amino acids were in the mix."
"A variety of amino acids have previously been detected in certain kinds of primitive meteorites," noted Dr. George Cooper of Ames. "Their presence in meteorites proves that amino acids are, in fact, made in space. However, it has generally been thought that they were produced in the solar system within asteroids, the sources of most meteorites. Our latest work suggests that at least some of the amino acids found in meteorites may predate our solar system."
"Indeed," noted Dr. Scott Sandford of Ames, "these findings are particularly intriguing because the amino acids found in meteorites do show some signatures that suggest an interstellar connection. This connection, combined with our finding that amino acids can be made in interstellar clouds suggests that the Earth may have been seeded with amino acids from space in its earliest days."
"The infall of these materials on the early Earth may have facilitated the origin of life on our planet," said Dr. Jason Dworkin of the SETI Institute and Ames. "Furthermore, since new stars and planets are formed within the same clouds in which new amino acids are being created, this probably increases the odds that life has evolved elsewhere."
"It now seems possible that at least some of the amino acids found in meteorites predate the formation of our solar system and were in fact synthesized in interstellar space. If they were incorporated into meteorites, it's natural to ask if they would have been incorporated into comets as well. Since recent work [Amino acid survival in large cometary impacts (E. Pierazzo and C.F. Chyba). 1999. Meteoritics and Planetary Science 32, 909-918.] suggests that some amino acids should survive cometary impacts with Earth, there may be a direct link between prebiotic organic molecules on early Earth and interstellar space," says Dr. Christopher Chyba, a recent MacArthur Award winner who holds the Carl Sagan Chair and heads the Center for the Study of Life in the Universe (LITU) at the SETI Institute.
Previously, members of this team had demonstrated that irradiation of interstellar ice analogs results in the production of other compounds that are also of potential biological interest. These include a class of compounds called amphiphiles that can self-organize to form membranes and a class of compounds called quinones, aromatic ketones that play important roles in the metabolisms of living organisms on the modern Earth. "Taken in combination, these results suggest that interstellar chemistry may have played a significant part in supplying the Earth with some of the organic materials needed to get life started," Sandford concluded.
The mission of the SETI Institute is to explore, understand and explain the origin, nature, prevalence and distribution of life in the universe.
More detailed information about these findings can be found
at:
More information about the SETI Institute can be found at www.seti.org
Information about the Center for the Study of Life in the
Universe can be found at
http://www.seti.org/science/litu/Welcome.html
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:
http://www-ssc.igpp.ucla.edu/dawn/
Details about the Kepler Mission are available at:
http://www.kepler.arc.nasa.gov
Kepler images are available at:
http://www.kepler.arc.nasa.gov/downloading.html
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
http://oposite.stsci.edu/pubinfo/pr/2001/38