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New method to study the atmospheric pressure of exoplanets for signs of life

Jenny Winder, News Writer
Mar 6, 2014, 8:00 UTC

Sen—Astronomers at the University of Washington (UW) have developed a new method of gauging the atmospheric pressure of exoplanets, by looking for a certain type of molecule. Scientists may one day be able to use this technique to detect the telltale chemical signs of life in the atmosphere of an alien world.

Understanding atmospheric pressure is key to knowing if conditions at the surface of a terrestrial, or rocky, exoplanet might allow liquid water, thus giving life a chance.

The method, devised by Amit Misra, a UW astronomy doctoral student, and co-authors, involves computer simulations of the chemistry of Earth's own atmosphere that isolate so called "dimer molecules" - pairs of molecules, consisting of two structurally similar monomers, that tend to form at high pressures and densities in a planet's atmosphere. There are many types of dimer molecules but this research focused only on those of oxygen.

Dimer molecules absorb light in a distinctive pattern, and the rate at which they form is sensitive to the pressure, or density, in the planet's atmosphere. The researchers ran simulations testing the spectrum of light in various wavelengths.

"So the idea is that if we were able to do this for another planet, we could look for this characteristic pattern of absorption from dimer molecules to identify them," Misra said in a statement. The presence of such molecules, he said, likely means the planet has at least one-quarter to one-third the pressure of Earth's atmosphere.

The James Webb Space Telescope, scheduled for launch in 2018, may enable astronomers to use this method on distant exoplanets. With such powerful telescopes astronomers might detect dimer molecules in actual exoplanet atmospheres, leading to a clear understanding of the planet's atmosphere.

The team realized along the way that oxygen dimer molecules are often more detectable in an atmosphere than other markers of oxygen. That is important from a biological standpoint and may play a part in the greatest astronomical quest of all, the ongoing search for life in the cosmos.

Misra explained "It's tied to photosynthesis, and we have pretty good evidence that it's hard to get a lot of oxygen in an atmosphere unless you have algae or plants that are producing it at a regular rate.

"So if we find a good target planet, and you could detect these dimer molecules — which might be possible within the next 10 to 15 years — that would not only tell you something about pressure, but actually tell you that there's life on that planet."

Misra is first author of the paper published in the February issue of the journal Astrobiology.