Exoplanet Atmospheres
March 5, 2014

Astronomers Search For Molecular Oxygen In Exoplanet Atmospheres

John P. Millis, Ph.D. for redOrbit.com - Your Universe Online

The holy grail of planetary astronomy is the search for a potentially habitable planet, or even better, one that is shown to already contain life. There are various parameters that are needed in order to ascertain the habitability of worlds, such as whether liquid water can be sustained on its surface.

Recent studies, however, have found that identifying some of these characteristics is rather difficult, and we may in fact not know as much as we once thought about exoplanetary atmospheres. But now a new study from the University of Washington is shedding some light on a new way to study planetary atmospheres, and perhaps one day root out life beyond Earth.

By looking for dimers – pairs of atoms that are bound together, such as two oxygen molecules – astronomers may be able to show evidence that a planetary atmosphere has a minimum density. In this case, molecular oxygen is an indication that the planet has an atmosphere that is at least one-quarter of the Earth’s atmospheric pressure, since below that value, it is improbable that the molecules would form.

The way that the scientists look for the presence of dimer oxygen is to do a spectral analysis on the planetary atmosphere, looking for specific patterns in the data. “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,” reports Amit Misra, a UW astronomy doctoral student who led the project.

Even more exciting is the prospect that such searches could yield even more important results. The specific use of dimer oxygen is also expected to be a telltale signature of life.

“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," Misra added. "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.”

The research was performed through the UW-based Virtual Planetary Laboratory and funded by NASA (Grant NNH05ZDA001C), as well as a grant from Advancing Science in America, Seattle chapter.

Results of this research are published in the February issue of the journal Astrobiology.