We already know that here on Earth auroras are formed when electrically charged particles from the Sun hit the upper atmosphere creating colorful flashes in shades of green, white and red. But it is not the only place where we have seen auroras. In other parts of the solar system, such as Jupiter and some of its moons, as well as Saturn, Uranus, Neptune and even Mars, they also have their own version of the auroras (which although its atmosphere is extremely thin, its weak magnetic field is capable of housing them).
Now we have discovered that even comets can experience auroras.
An international team of researchers used data from the European Space Agency’s Rosetta mission of Comet 67P / Chury, discovering that the comet has an ultraviolet glow created by charged particles from the Sun. As it gets close enough to the Sun, the ice trapped in it comet sublimates, causing this cosmic spectacle.
“Initially, we thought that the ultraviolet emissions from Comet 67P were phenomena known as ‘daytime glow’, a process caused by solar photons interacting with cometary gas,” explains Joel Parker of the Southwest Research Institute in the journal Nature Astronomy. “We were surprised to find that UV emissions are auroras, driven not by photons, but by electrons in the solar wind that break up water and other molecules in the coma and have been accelerated in the nearby environment of the comet. The resulting excited atoms produce this distinctive light. “
But if it has no atmosphere, how is the aurora formed?
Comet 67P has no atmosphere, but it does eat, a fuzzy, gaseous envelope produced by the release of gas trapped in the comet’s icy nucleus. When electrons from the solar wind hit this gas, they produce auroras. However, because the comet does not have its own magnetic field, the aurora itself is quite diffuse , in contrast to the contained auroras generated by the excitation of the solar wind on Earth and Mars, for example. Be that as it may, this finding could offer new clues to understanding how auroras are generated throughout the solar system.
Referencia: M. Galand et al. Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko. Nat Astron, published online September 21, 2020; doi: 10.1038/s41550-020-1171-7
