archiv~1.txt: SETI [ASTRO] Water, Water Everywhere
SETI [ASTRO] Water, Water Everywhere
Larry Klaes ( email@example.com )
Fri, 05 Mar 1999 08:18:47 -0500
>X-Authentication-Warning: brickbat12.mindspring.com: majordom set sender
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>Date: Fri, 5 Mar 1999 2:17:31 GMT
>From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>Subject: [ASTRO] Water, Water Everywhere
>Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>25 February 1999
>Water, Water Everywhere
>Radio telescope finds water is common in universe
>By Lee Simmons, Special to the Gazette
>The universe, it seems, is full of water. That's the message being beamed to
>Earth from a new space-based radio telescope.
>Launched into orbit on Dec. 5, 1998, the Submillimeter-Wave Astronomy
>Satellite (SWAS) is for the first time detecting vast amounts of water vapor
>hidden in the dark pockets of our galaxy.
>The findings confirm what astronomers suspected, but have been unable to
>prove from the ground.
>"It's very gratifying," says Gary Melnick of the Harvard-Smithsonian Center
>for Astrophysics (CfA), who heads the scientific team behind the effort.
>"After 20 years of guessing that nature might work this way, to finally get
>an instrument up into space, turn it on, point it toward these regions and
>see confirmation -- we're seeing water everywhere we look."
>SWAS is designed to probe the cold, dark interstellar clouds in our galaxy
>where new stars are formed. The data it is collecting will provide crucial
>information about the composition and structure of these interstellar clouds
>and will improve our understanding of the early stages of star formation.
>The results also offer exciting clues to the origin of the water in Earth's
>oceans and suggest that the presence of potentially life-sustaining water
>is not unique to our solar system.
>Submillimeter Astronomy in Space
>SWAS is the third scientific satellite produced by NASA's Small Explorer
>Program, which was established to build small, specialized spacecraft that
>are economical but scientifically powerful. The entire satellite weighs only
>625 pounds and is controlled by an onboard computer not much different
>from a souped-up desktop PC.
>The scientific instrument itself, however, is sophisticated. Observing
>radiation at submillimeter wavelengths, a frequency band between radio
>and infrared on the electromagnetic spectrum, is still a relatively new
>frontier in astronomy. It is in this band that very cold water and molecular
>oxygen radiate. A radio telescope must be built and calibrated to exacting
>tolerances to distinguish such tiny signals. No one had previously attempted
>to put such an instrument in space.
>After 10 years of planning, construction, and waiting, the team gathered
>in the flight control room at NASA's Goddard Space Flight Center, outside
>Washington, D.C., for the launch this past December. "We were all holding
>our breath," admits Melnick. "The kick of a rocket launch is quite a jolt.
>It's like building a fine piece of hardware and then hitting it with a
>sledgehammer." To everyone's relief, the deployment went without a hitch
>and the instrument survived the trauma unscathed.
>Every night, newly collected data is transmitted to the mission's Science
>Operations Center at the CfA on Concord Avenue, in Cambridge. There,
>astronomers analyze the data and select the next week's targets.
>Besides Melnick, the other participating scientists at the CfA are Matthew
>Ashby, Ted Bergin, John Chang, Alex Dalgarno, Giovanni Fazio, Steven
>Kleiner, Ren=E9 Plume, John Stauffer, Patrick Thaddeus, Volker Tolls, Zho=ng
>Wang, and Yun-Fei Zhang. The project team also includes astronomers from
>Cornell, Johns Hopkins, the University of Massachusetts, the University of
>Cologne, and NASA.
>Sifting the Stardust
>The dark areas of the night sky are not mere voids, as once believed, but
>rather contain enormous quantities of matter in atomic and molecular form.
>This interstellar medium is concentrated in vast, amorphous clouds of dust
>and gas -- the atomic rubble, presumably, from the explosions of earlier
>generations of stars. It is from this primordial material that new stars
>and planets are formed.
>These interstellar clouds are extremely tenuous: less dense than even the
>best vacuum that can be created on Earth. But a single cloud can span
>hundreds of trillions of miles and contain enough mass to create hundreds
>of thousands of stars like our sun.
>Because the gas in these star-forming regions is so cold (typically less
>than 400 degrees F), it produces no visible light. These immense objects
>are generally invisible to even the most powerful optical telescopes. They
>do, however, emit low-energy radiation that can be detected by radio
>Over the past several decades, radio and infrared observations have taught
>us a great deal about these stellar nurseries. The earliest stages of star
>formation, however, remain poorly understood. Something causes these
>diffuse, quiescent clouds to become gravitationally unstable and begin to
>collapse, often fragmenting into smaller pieces in the process. The
>dimensions of this collapse are mind-boggling: analogous to something
>the size of Pennsylvania being compressed to the size of a nickel.
>Compression on this scale generates tremendous heat. Unless this heat is
>removed, thermal pressure would eventually overwhelm the force of
>gravity, halting the process of star formation. Astronomers hypothesize
>that the presence of water, carbon monoxide, and molecular oxygen helps
>to cool the gas, permitting compression to continue.
>Until now, however, it has been impossible to observe water and molecular
>oxygen in the cold interstellar medium because its emission is absorbed by
>the Earth's atmosphere. Only by lifting the telescope above this obscuring
>canopy has SWAS made it possible to measure the abundance of these
>molecules in interstellar space for the first time.
>The Origins of Oceans
>Will the interstellar water observed by SWAS someday end up in oceans
>like those on our own blue planet? "Nobody knows for sure where oceans
>come from," Melnick says. "It's believed that some portion of the Earth's
>water was produced at a later stage in the evolution of our solar system.
>But the exact percentage is unknown."
>"It's also quite plausible," he continues, "that some of the gaseous water
>from the interstellar medium freezes onto dust grains that are carried
>along with the gas as clouds collapse. Those dust grains can stick to each
>other, and this might well be how comets are formed. Comets contain a
>lot of ice. The collision of a big dirty snowball like this with a young
>planet would certainly transport water."
>SWAS is expected to observe several hundred star-forming regions in our
>galaxy during its 2- to 3-year life. Melnick's goal is not so much to
>collect information about individual sources, but to observe a large enough
>sample of sources to be able to make broad statements about the nature
>and dynamics of the interstellar medium.
>"I come in every day and get excited by what we've learned the night before,
>but it's just adding another piece to the puzzle. Once we have enough pieces
>in place that we can stand back and say, 'Aha! That's the big picture --
>this is how nature works when it comes to interstellar chemistry,' that's
>when I'll be willing to send up a flare and declare this mission a roaring
>Melnick: Looking at the big picture. Photo by Kris Snibbe.