The William Herschel Telescope WHT, Roque de los Muchachos Observatory, La Palma, Canary Islands, Spain.

Researchers have used the William Herschel Telescope in the Canary Islands to study a comet hailing from beyond the reaches of the Solar System. Credit: Javier Larrea/Alamy

Astronomy and astrophysics

The comet that came in from interstellar space

The short-tailed 2I/Borisov is only the second known visitor to the Solar System from another star system.

The second object known to have crossed the boundary into the Solar System is a comet that looks surprisingly like those that orbit the Sun.

Amateur astronomer Gennady Borisov discovered the comet on 30 August. Subsequent observations showed that it came not from the Solar System’s outer reaches — as other comets do — but from deep space. Named 2I/Borisov, it is only the second interstellar object ever found in the Solar System.

A team led by Piotr Guzik at Jagiellonian University in Kraków, Poland, used telescopes in the Canary Islands and Hawaii to study the visitor. It is reddish in colour, with a fuzzy tail extending from its 2-kilometre-wide nucleus. It looks much more like an ordinary comet than the first interstellar object did. (That object, known as ‘Oumuamua, puzzled scientists with its rocky, asteroid-like appearance when it was detected in 2017.)

Astronomers will continue to study 2I/Borisov as it makes its closest approach to the Sun on 8 December and then zooms back out of the Solar System.