Observing the intruder from interstellar space
Astronomers at the University of Edinburgh’s Institute for Astronomy are currently studying an unusual comet. Known as 2I/Borisov, this comet is only the second one in history to be shown to have come from beyond our Solar System, following the discovery two years ago of 1I/‘Oumuamua.
While the first Interstellar Object (ISO) had very strange properties - it was small and had a very elongated shape, and showed almost no evidence of comet-like activity - Borisov appears more like the comets of our own Solar System. It shows a clear coma and tail, and this has allowed astronomers to measure its composition, through spectroscopic investigation of the unique signatures of gasses in the coma.
Edinburgh astronomers Cyrielle Opitom and Colin Snodgrass have been studying the comet using the UK’s telescopes in the Canary Islands (the Isaac Newton and William Herschel telescopes), and are now training the European Southern Observatory’s ‘Very Large Telescope’ (one of the most powerful in the world) on the comet as it moves into Southern hemisphere skies.
Results so far indicate that, despite its origin in the planetary system around a distant star, comet Borisov has a composition quite similar to our own Solar System’s comets. It appears to be closest in composition to a class of comets known as ‘carbon chain depleted’, which make up around a third of Solar System comets, and tend to come from the Kuiper Belt of icy bodies at the edge of the planetary region (the region where Pluto is found), rather than the much more distant Oort cloud at the very edge of the Sun’s influence, which is the source of long period comets.