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Unlocking the frozen secrets of comet Wild 2
December 20, 2006Washington, D.C. - Eleven months ago, NASA's Stardust mission touched down in the Utah desert with the first solid comet samples ever retrieved from space. Since then, nearly 200 scientists from around the globe have studied the minuscule grains, looking for clues to the physical and chemical history of our solar system. Although years of work remain to fully decipher the secrets of comet Wild 2, researchers are sure that it contains some of the most primitive and exotic chemical structures ever studied in a laboratory.
Preliminary results appear in a special section of the December 15 issue of Science. Overall, research efforts have focused on answering "big-picture" questions regarding the nature of the comet samples that were returned, including determining mineral structures, chemical composition, and the chemistry of the organic, or carbon-containing, compounds they carry. Carnegie researchers made key contributions to the latter effort. Out of seven papers in total, four involved Carnegie scientists from the Geophysical Laboratory (GL) and the Department of Terrestrial Magnetism (DTM).
"Carnegie enjoys a unique concentration of instrumentation and expertise to be able to engage in cutting-edge questions such as those posed by the Stardust mission," said GL's Andrew Steele.
Scientists have believed that comets formed long ago in the cool outer reaches of the solar system and thus largely consist of material that formed at cold temperatures and escaped alteration in the blast furnace of the inner solar nebula-the cloud of hot gases that condensed to form the Sun and terrestrial planets some 4.5 billion years ago.
According to the record contained in the Stardust grains, it appears that this hypothesis is about 90% right. Evidence from the ratios of certain isotopes-variants of atoms that have the same chemical properties, yet differ in weight-suggest that as much as 10% of the comet's material formed in the hot inner solar nebula and was transported to the cold outer reaches where the comet came together as the Sun formed. Chief among these tell-tale isotopes are those of oxygen, for which the ratios resemble those seen in meteorites known to have formed in the inner solar system.
Yet, isotopic measurements of hydrogen and nitrogen made at DTM and elsewhere tell a different picture. "The presence of excesses of heavier isotopes-deuterium and nitrogen 15, to be specific-is a strong indication that some of the comet dust was around before the Sun formed," said DTM's Larry Nittler. "It's really quite striking."
The structures of the comet's organic molecules tell a similar tale. "This comet's organic material is really quite unusual compared to other extraterrestrial sources we have studied, such as meteorites and interstellar dust particles," said GL's George Cody. "Yet there are some important similarities that tell that us we are not dealing with matter that is totally foreign to our solar system."
The samples contain very few of the stable ringed, or aromatic, carbon structures that are common on Earth and in meteorites. Instead, they have many fragile carbon structures that would most likely not have survived the harsh conditions in the solar nebula. These molecules also contain considerably more oxygen and nitrogen than even the most primordial examples retrieved from meteorites and exist in forms that are new to meteorite studies.
"These forms of carbon don't look like what we find in meteorites, which is something like compacted soot from your chimney. The carbon compounds from this comet are a much more complicated mix of compounds," commented GL's Marc Fries. "It will be an exciting challenge to explain how these compounds formed and wound up in the comet."
"This leads us to our next big question," Cody remarked. "How could such fragile material have survived capture at 6 km/sec collision velocity?"
"At this point, every question we answer raises several more questions," Nittler said. "But that is precisely what makes exploration so exciting and makes sample return so important. We now have the samples to study for many years to come."
The Carnegie Institution of Washington
Scientists have believed that comets formed long ago in the cool outer reaches of the solar system and thus largely consist of material that formed at cold temperatures and escaped alteration in the blast furnace of the inner solar nebula-the cloud of hot gases that condensed to form the Sun and terrestrial planets some 4.5 billion years ago.
According to the record contained in the Stardust grains, it appears that this hypothesis is about 90% right. Evidence from the ratios of certain isotopes-variants of atoms that have the same chemical properties, yet differ in weight-suggest that as much as 10% of the comet's material formed in the hot inner solar nebula and was transported to the cold outer reaches where the comet came together as the Sun formed. Chief among these tell-tale isotopes are those of oxygen, for which the ratios resemble those seen in meteorites known to have formed in the inner solar system.
Yet, isotopic measurements of hydrogen and nitrogen made at DTM and elsewhere tell a different picture. "The presence of excesses of heavier isotopes-deuterium and nitrogen 15, to be specific-is a strong indication that some of the comet dust was around before the Sun formed," said DTM's Larry Nittler. "It's really quite striking."
The structures of the comet's organic molecules tell a similar tale. "This comet's organic material is really quite unusual compared to other extraterrestrial sources we have studied, such as meteorites and interstellar dust particles," said GL's George Cody. "Yet there are some important similarities that tell that us we are not dealing with matter that is totally foreign to our solar system."
The samples contain very few of the stable ringed, or aromatic, carbon structures that are common on Earth and in meteorites. Instead, they have many fragile carbon structures that would most likely not have survived the harsh conditions in the solar nebula. These molecules also contain considerably more oxygen and nitrogen than even the most primordial examples retrieved from meteorites and exist in forms that are new to meteorite studies.
"These forms of carbon don't look like what we find in meteorites, which is something like compacted soot from your chimney. The carbon compounds from this comet are a much more complicated mix of compounds," commented GL's Marc Fries. "It will be an exciting challenge to explain how these compounds formed and wound up in the comet."
"This leads us to our next big question," Cody remarked. "How could such fragile material have survived capture at 6 km/sec collision velocity?"
"At this point, every question we answer raises several more questions," Nittler said. "But that is precisely what makes exploration so exciting and makes sample return so important. We now have the samples to study for many years to come."
The Carnegie Institution of Washington
Comet Current Events and Comet News RSSFollow Rosetta's final Earth boost
ESA's comet chaser Rosetta will swing by Earth for the last time on 13 November to pick up energy and begin the final leg of its 10-year journey to comet 67P/Churyumov-Gerasimenko. ESA's European Space Operations Centre will host a media briefing on that day.
'Ultra-primitive' particles found in comet dust
Dust samples collected by high-flying aircraft in the upper atmosphere have yielded an unexpectedly rich trove of relicts from the ancient cosmos, report scientists from the Carnegie Institution.
Cassini Helps Redraw Shape of Solar System
In a paper published Oct. 15 in Science, researchers from the Johns Hopkins Applied Physics Laboratory (APL) present a new view of the region of the sun's influence, or heliosphere, and the forces that shape it. Images from one of the Magnetospheric Imaging Instrument's sensors, the Ion and Neutral Camera (MIMI/INCA), on NASA's Cassini spacecraft suggest that the heliosphere may not have the comet-like shape predicted by existing models.
NASA Goddard visualization team previews lunar impact
At 7:30 a.m. EDT on October 9, a two-ton rocket body will slam into a crater near the moon's south pole. By studying the resulting plume of gas and dust, scientists hope this grand experiment will confirm the presence of ice in permanently shadowed craters at the lunar poles.
CU-Boulder space scientists set for final spacecraft flyby of Mercury
NASA's MESSENGER spacecraft, which is toting an $8.7 million University of Colorado at Boulder instrument, will make its third and final flyby of Mercury on Sept. 29 -- a clever gravity-assist maneuver that will steer it into orbit around the rocky planet beginning in March 2011.
Sea level stargazing: Astronomers make key sighting with Fla. telescope
This summer, University of Florida astronomers inaugurated the world's largest optical telescope on a nearly 8,000-foot mountaintop 3,480 miles away.
Deep Impact and Other Spacecraft Find Clear Evidence of Water on Moon
New data from the Deep Impact spacecraft and the Moon Mineralogy Mapper (M3), an instrument aboard India's recently ended Chandrayaan-1 spacecraft, provide, for the first time, clear evidence that water exists on the surface of the Moon.
Key process for space outpost proved on 'vomit comet' ride
Flying high over the Gulf of Mexico, researchers from NASA and Case Western Reserve University found a key to unlocking oxygen from the surface of the moon.
Twin Keck Telescopes Probe Dual Dust Disks
Astronomers using the twin 10-meter telescopes at the W. M. Keck Observatory in Hawaii have explored one of the most compact dust disks ever resolved around another star.
Lunar Reconnaissance Orbiter's LAMP shedding light on permanently shadowed regions of the Moon
NASA's Lunar Reconnaissance Orbiter (LRO), launched on June 18 of this year, has begun its extensive exploration of the lunar environment and will return more data about the Moon than any previous mission.
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