Observations of nitrogen in the Earth's atmosphere by a NASA spacecraft 17 million miles away are giving astronomers fresh clues on how that gas might reveal itself on faraway planets, thus aiding in the search for life.
Finding and measuring nitrogen in the atmosphere of an exoplanet -- one outside our solar system -- can be crucial to determining if that world might be habitable.
Edward Schwieterman, astronomy doctoral student at the University of Washington (UW) and astronomy professor Victoria Meadows show that a future large telescope could detect this unusual signature in the atmospheres of terrestrial, or rocky planets, given the right instrumentation.
The researchers used 3D planet-modelling data from the UW-based Virtual Planetary Laboratory to simulate how the signature of nitrogen molecule collisions might appear in the Earth's atmosphere.
They compared this simulated data to real observations of Earth by NASA's unmanned Deep Impact Flyby spacecraft, launched in 2005.
By comparing the data, the authors were able to confirm the signatures of nitrogen collisions in our own atmosphere, and that they would be visible to a distant observer.
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"Studying Earth as an exoplanet is so important that we were able to validate that nitrogen produces an impact on the spectrum of our own planet as seen by a distant spacecraft. This tells us it's something worth looking for elsewhere," Schwieterman noted.
The detection of nitrogen will help astronomers characterise the atmospheres of potentially habitable planets and determine the likelihood of oxygen production by non-living processes.
"One of the interesting results from our study is that, basically, if there's enough nitrogen to detect at all, you have confirmed that the surface pressure is sufficient for liquid water, for a very wide range of surface temperatures," Schwieterman said.
Nitrogen can provide clues to surface pressure.
If nitrogen is found to be abundant in a planet's atmosphere, that world almost certainly has the right pressure to keep liquid water stable on its surface.
Liquid water is one of the pre-requisites for life.
Should life truly exist on an exoplanet, detecting nitrogen as well as oxygen could help astronomers verify the oxygen's biological origin by ruling out certain ways oxygen can be produced abiotically, or through means other than life, the authors noted in a paper published in the Astrophysical Journal.