In the most unusual to me case of data randomly showing something unexpected, analysis of ultraviolet data from ESA’s Rosetta mission’s 2014-2016 encounter with Comet 67P/Churyumov-Gerasimenko shows evidence of the comet having aurorae. According to Southwest Research Institute’s Jim Burch: Charged particles from the Sun streaming towards the comet in the solar wind interact with the gas surrounding the comet’s icy, dusty nucleus and create the auroras. 

Researcher Joel Parker goes on to state: Initially, we thought the ultraviolet emissions at comet 67P were phenomena known as ‘dayglow,’ a process caused by solar photons interacting with cometary gas. We were amazed to discover that the UV emissions are aurora, driven not by photons, but by electrons in the solar wind that break apart water and other molecules in the coma and have been accelerated in the comet’s nearby environment. The resulting excited atoms make this distinctive light.

This new work appears in Nature Astronomy and was led by Marina Galand.

More Information

SwRI press release 

NASA JPL press release 

University of Bern press release 

“Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko,” M. Galand et al., 2020 Sep. 21, Nature Astronomy