Following the discovery of only the second interstellar object ever seen in our solar system, astronomers are racing to find out as much about it as possible. We are starting to get some intriguing results, with plenty more excitement on the way.聽We also know that it would be possible to send a spacecraft to the comet 鈥� although we may have to wait a while.
The object, officially known as 2I/Borisov, was spotted by Gennady Borisov, an astronomer from Crimea, in late August using a homemade 0.65-metre telescope. There was initially some doubt as to whether it really came from outside our solar system. 鈥淚t wasn鈥檛 quite as obvious as being hyperbolic as the first one was, so there was some caution,鈥� says Robert Weryk at the University of Hawaii at Manoa, who discovered the first interstellar object,聽鈥極umuamua, in 2017. But calculations from NASA鈥檚 solar system dynamics group have . This confirms Borisov is the second interstellar object to be observed.
Borisov himself has taken a back seat since he found the object. 鈥淭he last four weeks have been just crazy,鈥� he says. 鈥淲hen the big telescopes came in, I took a break.鈥� But with the comet set to reach its closest point to us 鈥� at twice the Earth-sun distance 鈥� on 7 December, other astronomers are gearing up for an observing campaign.
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Comet Borisov is different to 鈥極umuamua in that it was spotted approaching the solar system rather than leaving it. This gives us more time to study it 鈥� probably about a year. The comet also appears to be spewing dust and gas into space, whereas its predecessor didn鈥檛.
In September, astronomers led by Alan Fitzsimmons at Queen鈥檚 University Belfast, UK, looked at the trail of gas using the William Herschel Telescope on the Spanish island of La Palma. This showed it contained We see this in comets in our own planetary system,聽suggesting that Borisov may have been formed in a similar way. This matters because astronomers want to know more about whether our solar system is relatively typical or unique.
In the coming weeks, the comet should continue melting as it nears the sun, releasing more of its inner substances for us to observe. One important question we should be able to answer is about the comet鈥檚 balance of water and carbon monoxide. 鈥淯sually in typical comets of the solar system, there is about 75 per cent water, nearly 20 per cent carbon monoxide and the rest is mostly carbon dioxide,鈥� says Emmanu毛l Jehin at the University of Li猫ge in Belgium. He plans to use the TRAPPIST telescopes in Chile and Morocco to study whether that is true of Borisov.
Closer, but no cigar?
We should soon also know the comet鈥檚 shape. 鈥極umuamua had a very unusual shape 鈥� like that of a long, thin cigar 鈥� and was rapidly tumbling end over end through space. Several telescopes, including the Hubble Space Telescope, will be trained on Borisov in the coming weeks to see its size and deduce its shape by observing how it reflects sunlight. Our best current estimate is that it is between 700 metres and 3 kilometres wide.
Some attempts have even been made to work out . Piotr Dybczy艅ski at the Adam Mickiewicz University in Poland and his colleagues attempted to trace back the comet鈥檚 trajectory. It may have come from a pair of red dwarfs called Kruger 60 that lie 13 light years from us, but he is far from certain about it. 鈥淧robably we will never know for sure,鈥� he says. However, measuring the isotopes of carbon in the comet could tell us which region of the galaxy it came from, says Jehin.
Andreas Hein at the Initiative for Interstellar Studies in the UK and his colleagues also of sending a spacecraft to Borisov. We have already sent craft to asteroids聽and comets, so it isn鈥檛 an impossible proposition. Getting to the object would involve slingshotting a craft around the sun and possibly Jupiter. This can鈥檛 be done at any time though, because of the way the planets align. Hein found that the optimal launch time would have been July 2018. But he also found we could launch a probe in 2030 and get to Borisov by 2045聽using a large rocket such as NASA鈥檚 upcoming Space Launch System. 鈥淚t鈥檚 possible from a technical point of view,鈥� says Hein.
Michele Bannister at Queen鈥檚 University Belfast says astronomers are working to get as much information as possible from the comet before it waves goodbye. 鈥淲e have most of the major facilities sorted out that will be able to observe it,鈥� she says. With the comet鈥檚 peak activity in December, we are about to get a better glimpse into an alien solar system than ever before.
