A University of Maryland-led team of scientists has mapped the gas emissions of Comet 67P Churyumov-Gerasimenko up close for the first time. Using Rosetta’s Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) camera, the team studied some of the surprising processes taking place near the comet.

“It’s very tricky, as you can imagine, but we finally got it working and we’re presenting the first results of it at the DPS meeting in Washington DC this week,” study author Dennis Bodewits from the University of Maryland told IFLScience.

In particular, the team looked at the light from oxygen atoms, and cyanide and hydroxyl molecules, just above the surface of the comet. In most comets, these are the product of water and hydrogen cyanide molecules broken down by ultraviolet radiation from the Sun. In 67P, emission levels for all three were much higher than expected, by a factor of several hundred.  

Using their observations, the team had two explanations. One is that there is another source producing the atoms and molecules observed, perhaps CO₂ or the recently discovered oxygen molecules. Alternatively, there could be another unknown chemical process responsible for the excess emission. Now, the answer seems to be that the solar wind is destroying molecules in the coma 1,000 times faster than thought, producing the higher emission levels. This is possible because 67P produces so little gas that this radiation can penetrate deep into the cloud of gas close to the surface.

In the coma (atmosphere) of the comet, water is broken down into molecular hydrogen and an oxygen atom, which remains in an excited state and emits a photon, which can be tracked to identify the location of water. Hydrogen cyanide, meanwhile, is broken down into hydrogen and cyanide. The cyanide gas signature was surprising, because Earth-based observations suggest that cyanide escapes to thousands of kilometers from the comet and then reflects sunlight, known as fluoresence. This research, however, suggests it breaks down much closer to the surface, owing to the newly identified process.

As Rosetta’s orbit is lowered, the team will have more opportunities to study the gas emissions taking place on the surface and in the coma.