Scientists have discovered that comets have their very own Northern Lights, with data from Southwest Research Institute (SwRI)-led instruments aboard ESA’s Rosetta spacecraft helping to reveal auroral emissions in the far ultraviolet surrounding a comet.
Down here on Earth, auroras form when charged particles from our Sun follow Earth’s magnetic field lines up to the north and south poles.
It is there where solar particles hit atoms and molecules in our planet’s atmosphere, resulting in ‘shimmering curtains of colourful light in high-latitude skies’.
Similar phenomena have previously been noted at a variety of planets and moons within our solar system, as well as around a distant star.
Now SwRI’s instruments – that include the Alice far-ultraviolet (FUV) spectrograph and the Ion and Electron Sensor (IES) – have helped to detect auroras at comet 67P/Churyumov-Gerasimenko (67P/C-G).
SwRI Vice President Dr. Jim Burch, who leads the IES, said:
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. The IES instrument detected the electrons that caused the aurora.
The envelope of gas surrounding 67P/C-G – known as the ‘coma’ – reportedly becomes ‘excited’ by the solar particles and ends up glowing in ultraviolet light. This interaction was first detected by the FUV instrument.
SwRI’s Dr. Joel Parker, who leads the Alice spectrograph, said:
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.
Rosetta has provided a wealth of data for scientists, giving them more information as to how exactly the Sun and solar wind interact with comets. As well as being behind the discovery of these cometary auroras, Rosetta has also been behind a number of other firsts.
The first craft to orbit the nucleus of a comet, Rosetta was also the first to fly beside a comet as it travelled into the inner part of our Solar System, and was also the first to send a lander to the surface of a comet.
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