Satellite Analyzes Cosmic Gas Clouds; Finds Puzzling Concentrations of Water in Space
Contact: Elizabeth Luciano, luciano@journ.umass.edu
Astronomers from a half-dozen institutions, including the University of Massachusetts, are looking at the universe in a new light with NASA’s Submillimeter Wave Astronomy Satellite (SWAS). The satellite is used to study the conditions that lead to the birth of stars, a process previously hidden in clouds of dust and gas in space. UMass researchers Ronald Snell and Neal Erickson are members of the scientific team.
Since its Dec. 1998 launch, SWAS has detected water vapor widely throughout interstellar space. However, in the very coldest reaches that have temperatures just 30 degrees above absolute zero, astronomers have measured water vapor concentrations of only a few parts per billion. "That’s far less than predicted by most theories and presents a real puzzle to our understanding of the chemistry of interstellar clouds," said Snell, professor of astronomy and a member of the SWAS science team.
"Because of our belief that water is an essential ingredient for life, the search for its presence in interstellar gas clouds has always attracted particular attention and that’s why these results are intriguing," said Gary Melnick of the Harvard-Smithsonian Center for Astrophysics, the team leader. The team’s findings will be published Aug. 20 in a special SWAS-dedicated issue of the Astrophysical Journal Letters.
The new results are the product of 18 months of observations with SWAS, a compact radio observatory. Approximately 400 miles above Earth’s surface, the observatory orbits Earth every 97 minutes, and relays information to ground stations twice a day. SWAS "sees" into the dense clouds by searching for submillimeter-wavelength radiation — a band between radio and infrared waves on the electromagnetic spectrum. The submillimeter-wave detectors were built at Millitech Corp. (now Telaxis Communications), a University spin-off company that Erickson helped found. Submillimeter emissions cannot easily be studied from the ground, even at mountain-top or airborne astronomical observatories, because of interference from the large quantities of water and molecular oxygen in Earth’s atmosphere, Snell said.
In warmer regions of interstellar space, SWAS has found that water vapor is far more plentiful, scientists said. "Within gas clouds where new stars are born, the gas can be heated to temperatures of several thousand degrees Fahrenheit; here the water concentration seems to be as much as ten thousand times larger," said SWAS team member David Neufeld, professor of physics and astronomy at Johns Hopkins University. "We can think of these stellar nurseries as giant chemical factories that are producing water vapor at a tremendous rate. The large amounts of water vapor present in regions of star formation will help the interstellar gas to cool, perhaps eventually triggering the birth of a future generation of stars."
SWAS is also capable of detecting oxygen molecules in interstellar space, although the results of searching for oxygen molecules have so far been uniformly negative. "There’s a mysterious absence of molecular oxygen in interstellar space," said team member Paul Goldsmith, professor of astronomy at Cornell University and director of the National Astronomy and Ionosphere Center. "There must be no more than one oxygen molecule for every 10 million hydrogen molecules. Otherwise SWAS would have detected a signal from molecular oxygen. This means that most of the oxygen atoms in interstellar space remain hidden in some form that we have yet to detect."
In addition to observing distant clouds of interstellar gas, SWAS has detected water vapor closer to home in the atmospheres of Mars and the gas giants Jupiter and Saturn. "The water vapor we’ve detected in the gas giants is almost certainly the result of bombardment by small icy particles that come from interplanetary space and are rapidly vaporized once they hit the planetary atmosphere," said Ted Bergin of the Harvard- Smithsonian Center of Astrophysics. "The water molecules within these icy particles may well have originated as water vapor in the interstellar gas cloud that formed the solar system more than 4 * billion years ago."
SWAS also measured the amount and distribution of water vapor in the atmosphere of Mars, confirming the long-held belief that the relative humidity of the atmosphere was near 100 percent, said Mark Gurwell of the Harvard-Smithsonian Center for Astrophysics.
The Submillimeter Wave Astronomy Satellite is operated by NASA with support from the German government and the participation of the University of Massachusetts, the Harvard-Smithsonian Center for Astrophysics, Cornell University, the Johns Hopkins University, the University of Cologne, Ball Aerospace Corp., and Millitech Corp. (now Telaxis Communications).
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NOTE: A parallel release is being issued today by NASA and the Harvard- Smithsonian Center for Astrophysics. Ronald Snell may be reached at 413/545-1949 or snell@astro.umass.edu
