University Communications
Washington University in St. Louis

Media Assistance:
Tony Fitzpatrick, Senior Science Editor
(314) 935-5272

Subject Matter Experts:
Bruce Fegley, (314) 935-4852
Laura Schaefer, Laboratory assistant, (314) 935-6310

Sept. 7, 2005

Field guide for confirming new earth-like planets described

'Light breaks where no sun shines'

By Tony Fitzpatrick

Astronomers looking for earth-like planets in other solar systems --
exoplanets -- now have a new field guide thanks to earth and planetary
scientists at Washington University in St. Louis.

Bruce Fegley, Ph.D., Washington University professor of earth and
planetary sciences in Arts & Sciences, and Laura Schaefer, laboratory
assistant, have used thermochemical equilibrium calculations to model
the chemistry of silicate vapor and steam-rich atmospheres formed when
earth-like planets are undergoing accretion. During the accretion
process, with surface temperatures of several thousands degrees Kelvin
(K), a magma ocean forms and vaporizes.

"What you have are elements that are typically found in rocks in a vapor
atmosphere," said Schaefer. "At temperatures above 3,080 K, silicon
monoxide gas is the major species in the atmosphere. At temperatures
under 3,080 K, sodium gas is the major species. These are the indicators
of an earth-like planet forming."

At such red-hot temperatures during the latter stages of the exoplanets'
formation, the signal should be distinct, said Fegley.

"It should be easily detectable because this silicon monoxide gas is
easily observable," with different types of telescopes at infrared and
radio wavelengths, Fegley said.

Schaefer presented the results at the annual meeting of the Division of
Planetary Sciences of the American Astronomical Society, held Sept. 4-9
in Cambridge, England. The NASA Astrobiology Institute and Origins
Program supported the work.

Forming a maser

Steve Charnley, a colleague at NASA AMES, suggested that some of the
light emitted by SiO gas during the accretion process could form a maser
-- Microwave Amplification by Stimulation Emission of Radiation. Whereas
a laser is comprised of photons in the ultraviolet or visible light
spectrum, masers are energy packets in the microwave image.

Schaefer explains: "What you basically have is a clump of silicon
monoxide gas, and some of it is excited into a state higher than ground
level. You have some radiation coming in and it knocks against these
silicon monoxide molecules and they drop down to a lower state.

"By doing that, it also emits another photon, so then you essentially
have a propagating light. You end up with this really very high
intensity illumination coming out of this gas."

According to Schaefer, the light from newly forming exoplanets should be
possible to see.

"There are natural lasers in the solar system," she said. "We see them
in the atmospheres of Mars and Venus, and also in some cometary
atmospheres."

In recent months, astronomers have reported earth-like planets with six
to seven times the mass of our earth. While they resemble a terrestrial
planet like earth, there has not yet been a foolproof method of
detection. The spectra of silicon monoxide and sodium gas would be the
indication of a magma ocean on the astronomical object, and thus an
indication a planet is forming, said Fegley.

The calculations that Fegley and Schaefer used also apply to our own
earth. The researchers found that during later, cooler stages of
accretion (below 1,500 K), the major gases in the steam-rich atmosphere
are water, hydrogen, carbon dioxide, carbon and nitrogen, with the
carbon converting to methane as the steam atmosphere cools.

Related Links:

* Laura Schaefer's Web site
http://solarsystem.wustl.edu/laura_schaefer.htm
* Planetary Chemistry Laboratory
http://solarsystem.wustl.edu/