Astronomers See Aurorae Around A Comet For The First Time

Boulders getting caught moving across the surface of Comet 67P/Churyumov-Gerasimenko’s surface, ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA 

Northern and southern lights are not exclusive to our planet. Light shows from charged particles are seen on other celestial bodies of the solar system too, although often in other wavelengths of light. Now, astronomers have discovered that even comets can experience aurorae.

An international team of researchers used data from the European Space Agency’s Rosetta mission of Comet 67P/Churyumov-Gerasimenko. As reported in Nature Astronomy, the team discovered that the comet has an ultraviolet glow created by charged particles coming from the Sun.

"Initially, we thought the ultraviolet emissions at comet 67P were phenomena known as 'dayglow,' a process caused by solar photons interacting with cometary gas," co-author Dr Joel Parker, from Southwest Research Institute, in a statement. "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 image shows the key stages of the mechanism by which this aurora is produced. ESA/ATG medialab

Aurorae on Earth and on planets like Jupiter are a result of the magnetic fields. On Mars, instead, they occur without a magnetic field and are produced from the Sun's protons hitting the tenuous atmosphere of the Red Planet.

Comet 67P doesn't have an atmosphere but it does have a coma – a fuzzy, gassy envelope produced by the release of gas trapped in the icy nucleus of the comet. When electrons from the solar wind hit this gas, they produce aurorae.

Detecting these light shows wasn’t easy and the team had to combine every single instrument from Rosetta to study them. The lights are not like the ones we can see at higher latitudes on Earth.

"The glow surrounding 67P/C-G is one of a kind. By digging into data from numerous instruments on Rosetta and linking them together, we’ve discovered that this glow is auroral in nature: it’s caused by a mix of processes, some seen at Jupiter's moons Ganymede and Europa and others at Earth and Mars," lead author of the new study Professor Marina Galand, from the Department of Physics at Imperial, said in a statement.

Rosetta ended its mission just over three years ago when the spacecraft was crash-landed on the comet.

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