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.