Extrasolar Planets 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

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.