SAN FRANCISCO -- Using spectral tools for infrared and submillimeter wave observations, astronomers are looking for the building blocks of life in all the right places: where there might be oxygen and where it is wet.

"We may now have the tools to find those elements that are the preconditions for life." says Martin Harwit, professor emeritus of astronomy at Cornell University in Ithaca, N.Y.

He will host a symposium, "Infrared Astronomy: In Search of the Molecules of Life," at the annual meeting of American Association for the Advancement of Science at the Hilton San Francisco today (Feb. 19, 9 a.m. to noon).

"In the past we were not able to see water vapor or molecular oxygen in the distant universe through our own atmosphere, because Earth's atmosphere blocks out those spectral features," says Harwit. Now with space-borne tools such as the Submillimeter Wave Astronomy Satellite (SWAS) and the Infrared Space Observatory (ISO), observations are being undertaken for the conditions from which life might evolve.

Harwit is a member of a team of astronomers planning the design of a space observatory that could search the heavens for habitable planets. That means examining regions of the cosmos where there is a very faint object that could be a planet near a very bright star. "We will need a widely spaced array of small telescopes operating in unison to separate out the planet's faint image," says Harwit. "Coupled to this will have to be a spectrometer to search the planet's atmosphere for molecules that could act as tracers for life." At the symposium, Gary Melnick, of the Harvard-Smithsonian Center for Astrophysics, will explain key SWAS findings, such as how interstellar space is substantially more parched than previously believed. Recently, Melnick and colleagues from Cornell reported they had found that water is 10,000 times less abundant in interstellar, molecular clouds. So scarce, in fact, that it is found in the ratio of only one part in a hundred million compared with hydrogen molecules, which are the most common component. Molecular oxygen is at least 100 times less abundant than had been predicted.

This paucity of molecular oxygen and water makes finding life-sustaining planets much more difficult, since both elements are considered essential constituents of the molecular clouds from which stars form. Astronomers think these elements might be locked in a primordial deep freeze. The molecular clouds are as cold as only 30 degrees above absolute zero -- or a frigid minus 240 degrees Celsius. Thus water might be frozen on the dust grains in the clouds, making detection hard for radio telescopes.

But with an array of spectral tools, astronomers can still be hot on this frosty trail. Martin Kessler, of the European Space Agency, Madrid, will discuss the key findings of ISO, which operated with near-perfection from 1995 to 1998. The astronomer will present the first clear evidence of interstellar water vapor, obtained by the far-infrared spectrometer aboard the observatory. ISO also has detected frozen carbon dioxide, carbon monoxide and methane dust in interstellar clouds.

Edwin A Bergin, of the Harvard-Smithsonian Center for Astrophysics, will re-evaluate the chemical composition of interstellar matter, in light of the new spectral findings. He will show how cosmic water vapor freezes on the surface of dust grains in the cold, dark expanse of molecular clouds. In this planetary nursery, water-ice-coated grains eventually coagulate to form pre-planetary rocks and comets, which ultimately could form the interiors and atmospheres of planets.

Thijs de Graauw, of the SRON Laboratory/Kapteyn Institute, The Netherlands, will report on the detection, by the short wavelength spectrometer aboard ISO, of water molecules in some unexpected places, such as Jupiter and Saturn. De Graauw also will explain how the mineral forsterite -- found in dust clouds around young stars and in comet Hale-Bopp in our own solar system -- could lead to understanding how elemental molecules and minerals form together in interstellar space and eventually appear here on Earth.