Interstellar comet just like ones from our solar system – astronomers

Scientists tracking 2I/Borisov say some formation processes may be common between stars

The first interstellar comet to be tracked by astronomers as it hurtles through the solar system is unremarkable in every way apart from where it comes from, researchers have said.

Scientists reached the conclusion after observing 2I/Borisov with two of the most powerful telescopes on Earth. They decided that it looked like any other comet except that it came from beyond the solar system and would soon leave for good.

The unusual body was spotted in August by a Crimean amateur astronomer, Gennady Borisov. It was swiftly identified as an outcast from another star system and may have been wandering the Milky Way for millions if not billions of years.

“This is the first comet known to science that arrived from outside the solar system, and it is completely similar to those we see inside the solar system,” said Michal Drahus, an astronomer at Jagiellonian University in Krakow, Poland.

The team, led by Piotr Guzik, gathered images of the comet after receiving an alert from a computer system that detects cosmic interlopers. Unlike comets and asteroids that formed in the solar system, the arrivals are on trajectories that do not swing around the sun.

Pictures from the William Herschel Telescope on La Palma, Spain, and the Gemini North telescope on Mauna Kea, Hawaii, revealed that 2I/Borisov has a coma – a billowing cloud of dust and gas that surrounds a comet’s nucleus – and a short, fat tail. Both are created when ices on the comet’s surface sublimate into gas and blast dust and vapour into space. Details are published in Nature Astronomy.

The observations confirmed that the reddish body is a comet with a nucleus about 2km wide. It is only the second interstellar body to be spotted in the solar system, after the apparently more rocky and cigar-shaped Oumuamua, which was tracked in 2017 as it barrelled out of the solar system at 196,000mph.

Comets are what is left over when a planetary system forms, and the similarity of 2I/Borisov to solar system comets suggests our own planetary system is not unusual in the Milky Way. “The first thing it tells us is that at least some other planetary systems around other stars are similar to ours,” said Guzik.

Scientists are unsure where 2I/Borisov comes from, but another Polish research team has tentatively traced its trajectory back to a star system with twin red dwarves called Kruger 60, 13 light years from Earth.

The new comet tore into the solar system several years ago from an angle of about 45 degrees north. In October 2015 it was as far away as Neptune, the outermost planet, and now it is between Mars and Jupiter. On 27 October it will cross the plane of Earth’s orbit.

The early detection means astronomers will be able to observe the 71,500mph comet as it makes its closest approach to the sun on 8 December, when the extra heat will make the comet more active and its tail longer.

Colin Snodgrass, an astronomer at Edinburgh University and a member of a team that has separate observations of 2I/Borisov coming out in Astrophysical Journal Letters, said: “This appears to be a completely unremarkable comet on a very remarkable orbit.”

“It’s very interesting that this interstellar comet looks like our own ones,” he added. “It implies that some of the formation processes we are trying to figure out with detailed observation of comets and asteroids, or space missions like Rosetta, are common between stars.”

A new mission being developed for the European Space Agency will send a robotic probe into space to intercept and study a passing comet. Geraint Jones, the head of planetary science at UCL Mullard Space Science Laboratory and the lead proposer of the Comet Interceptor mission, said the primary target would be a pristine, unaltered comet arriving fresh from the Oort cloud, a distant region of the solar system where comets reside.

“But we on the proposing team made it clear that if an interstellar object could be reached instead, it would clearly make an extremely compelling target,” he said. Launch is scheduled for 2028.


Ian Sample Science editor

The GuardianTramp

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