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ASTRONOMERS DISCOVER HOT AND STEAMY INTERSTELLAR GAS SUGGESTING POSSIBLE
ORIGIN OF WATER IN THE SOLAR SYSTEM
A team of U.S. astronomers, including a member of the CfA, has discovered a large concentration of water vapor within a cloud of interstellar gas close to the Orion nebula, using a satellite launched and operated by the European Space Agency with the participation of NASA. The concentration of water vapor measured in Orion is twenty times larger than that measured previously in other interstellar gas clouds, and may provide an important clue to the origin of water in the solar system.
The discovery was reported in the April 20 issue of the Astrophysical Journal Letters by Martin Harwit, former director of the National Air and Space Museum and now at Cornell University, Michael Kaufman of NASA/Ames Research Center, David Neufeld of Johns Hopkins University, and Gary Melnick of the CfA.
The astronomers observed water vapor within the Orion Molecular Cloud, a giant interstellar gas cloud composed primarily of hydrogen molecules, using the European Space Agency's Infrared Space Observatory (ISO) satellite, which was launched in November 1995. The new observations were carried out in October 1997 with the Long Wavelength Spectrometer, one of four instruments on board ISO. Looking in the far-infrared region of the electromagnetic spectrum, the astronomers observed the characteristic signature of emission by water vapor.
"The Orion Molecular Cloud is a site of particularly active star formation within our galaxy," said Melnick. "Several thousand stars have been born in this region in the last million years--which is very recent from the cosmic perspective--and is ongoing. When stars are born, for reasons that aren't entirely understood, their birth is accompanied by a strong outward wind of gas and dust. When this outflowing material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water we observe is rapidly produced in this warm dense gas."
The concentration of water vapor measured by the U.S. team was roughly one part in 2000 by volume, some twenty times larger than that measured previously in other interstellar gas clouds.
"An enhanced concentration of water is precisely what we expected in this gas cloud," said Melnick. "We are looking at a region of interstellar space where shock waves have made the gas abnormally warm. For the past 25 years, astrophysicists have been predicting that whenever the temperature exceeds about 100 degrees Celsius, chemical reactions will convert most of the oxygen atoms in the interstellar gas into water. And that's exactly what we've observed in Orion." Melnick also noted that the strength of the water radiation detected from Orion was in perfect agreement with theoretical predictions published in the PhD thesis of team member Michael Kaufman, a former Johns Hopkins graduate student now at NASA's Ames Research Center.
Astronomers believe that shock waves may be a cause as well as the result of starbirth. "In the future, they may also trigger the formation of additional stars and planets as they compress the gas cloud that we observed, but only if surplus heat can be radiated away," said Harwit. "Even though the interstellar gas is composed primarily of hydrogen molecules, water vapor is a particularly efficient radiator at far-infrared wavelengths and plays a critical role in cooling the gas and facilitating the star formation process."
The high concentration of water measured in Orion may also have implications for the origin of water in the solar system. "The interstellar gas cloud that we observed in Orion seems to be a huge chemical factory, generating enough water molecules in a single day to fill the Earth's oceans sixty times over," said Neufeld.
"Eventually that water vapor will cool and freeze, turning into small solid particles of ice. Similar ice particles were presumably present within the gas cloud from which the solar system originally formed," Neufeld added. "Thus, it seems quite plausible that much of the water in the solar system was originally produced in a giant water vapor factory like the one we have observed in Orion."
[On May 16, with its onboard supply of liquid helium coolant expended, the ISO was switched off by ESA, thus ending some 31 months of operations and some 26,000 observations.]
NASA STARTS UP SIRTF;
WILL CARRY SAO INSTRUMENT
NASA Administrator Daniel S. Goldin has authorized the start of the design and development phase of the Space Infrared Telescope Facility (SIRTF), an advanced orbiting observatory that will continue and expand the research of its predecessors ISO and IRAS to give astronomers unprecedented views of cosmic phenomena invisible to other types of telescopes.
Managed by the Jet Propulsion Laboratory (JPL), SIRTF is now scheduled for launch in December 2001 on a Delta 7920-H rocket from Cape Canaveral. Among the three scientific experiments planned for SIRTF, one will be designed and built by SAO, with Giovanni Fazio as the principal investigator.
"The Space Infrared Telescope Facility will do for infrared astronomy what the Hubble Space Telescope has done in its unveiling of the visible universe, and it will do it faster, better and cheaper than its predecessors," said Dr. Wesley Huntress, NASA's associate administrator for space science. "By sensing the heat given off by objects in space, this new observatory will see behind the cosmic curtains of dust particles that obscure much of the visible universe. We will be able to study fetal stars, detect other solar systems and study the most ancient, distant galaxies at the edge of the universe."
SIRTF, whose design and development is cost-capped at $458 million, will be one of astronomy's most advanced telescopes. It is also the fourth and final element in NASA's family of complementary spaceborne "Great Observatories" that includes the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Advanced X-ray Astrophysics Facility. The project also represents a bridge to NASA's new Origins Program, which seeks to answer fundamental questions about the birth and evolution of the universe. SIRTF will lay the groundwork for many investigations fundamental to the Origins Program, such as studies of the birth and evolution of galaxies, their stars, and searches for planets that orbit some of those stars.
OLD MMT COMES DOWN, NEW MMT
GOES UP--IN PRINCIPLE
THE LAST MILE--Pushed from behind by a heavy loader, the semi-tractor-trailer carrying the "dummy" 6.5-meter replacement mirror for the MMT crawls up the last several hundred yards of heated and scored asphalt to the summit of Mt. Hopkins. (Craig Foltz photo)
On April 8 and 9, staff of the Multiple Mirror Telescope Observatory and Sierrita Mining and Ranching (SMR) transported a 9450-kilogram dummy mirror from the Whipple Observatory Base Camp in Amado, Arizona, to the top of Mount Hopkins. The surrogate mirror, packed inside the same box that will be used to transport the real 6.5-meter-diameter primary mirror, rode aboard a customized transporter trailer towed behind one of SMR's semi-tractors. A large loader, equipped with a wooden pusher bar, backed up the tractor-trailer combination on the steepest parts of the narrow, twisting, and largely unpaved 20-km-long road.
Inclinometers measured any tipping of the load during the practice run up the mountain. The largest excursions from level were well within specifications. In addition, other instruments measured the motion of the dummy mirror with respect to the transport box's frame. An initial review of the data indicated that the typical motion was about 1 mm, or roughly equivalent to 0.1 g of acceleration. All of this must have been reassuring to SAO's Bill Omann, who rode shotgun on the trailer bed beside the box for the entire trip.
BOXED IN--On the summit, with empty MMT building behind it, the "dummy" mirror sits in the specially built box and mount which will carry the real thing to the mountain later this summer. (Craig Foltz photo)
The test was deemed an unqualified success by SAO's J.T. Williams, who was responsible for planning and coordination of the practice run and who walked up much of the road ahead of the transport rig. The average speed for the trip up the mountain was 5 kph. The box came back down at nearly twice that speed.
A sampler of images of that move, along with short descriptions, is available here.
About two weeks earlier, on March 25, the old MMT's optics support structure was removed from the MMT building in two pieces. These were placed on semi-tractor trailers and hauled down the mountain to their resting place in the FLWO Basecamp storage yard.
In spite of winds gusting to nearly 96 kph, the operation went without a hitch! The 175-ton hydro crane and operators were provided by Marco Crane and Rigging Co., with expert truck drivers, again from Sierrita Mining and Ranching, and FLWO and MMTO staff support coordinated by Williams.
THE GOODBYE LOOK--The Optical Support Systems of the "old MMT" was removed from the telescope building in late March, essentially marking the end of the instrument's long reign as an astronomical radical. (Craig Foltz photo)
With the six mirrors removed earlier [the final observations had been made March 2], the instrument's observing chamber is now essentially empty, ready for the insertion of the new primary and secondary mirrors and optical support systems later this summer. The transition from old to new MMT looks more and more a reality daily.
The reality--and sadness--that an era has ended was dramatically brought home to current and past staff at special two-day "Last Light Celebration" February 14-15, organized by MMT pioneers Nat Carleton of SAO and Bill Hoffmann of the University of Arizona's Steward Observatory.
The gathering attracted several score "early timers" who played major roles in the conception, construction, testing, and early operations of this revolutionary instrument. In addition to a tour of the MMT on Saturday to watch near-final observations and to partake of a "mountain meal," the festivities included a seminar on Sunday in Tucson to review the scientific--and technical--legacy of the MMT. Among the guest speakers were: Fred Whipple, a "founding father" of the MMT concept; John Schaefer, the president of the UofA at the time of the MMT dedication; Jacques Beckers, the first MMT director; Frank Low, whose innovative work on the MMT's active optics would be adopted throughout the industry; Jill Bechtold, one of scores of astronomers who benefited from the MMT; and, Roger Angel, the creator of the spin-casting technique that made the 6.5-meter-diameter lightweight replacement mirror possible.