6 | New Scientist | 12 October 2019
RUMOURS began to circulate in
early September that an object
from another solar system had
been spotted. Now its status as
only the second interstellar visitor
ever seen has been confirmed.
With this, the race is on to find
out as much about the comet
as we can. We know it would be
possible to send a spacecraft to
visit – and there is plenty more
excitement on the way.
The object, officially known as
2I/Borisov, was first spotted by
Gennady Borisov, an astronomer
from Crimea, using a homemade
0.65-metre telescope. At first,
its trajectory left some doubt as
to whether it really came from
outside the solar system.
“It wasn’t quite as obvious
as being hyperbolic as the first
one was, so there was some
caution,” says Robert Weryk atthe University of Hawaii at
Manoa, who discovered the
first interstellar object, the
asteroid ‘Oumuamua, in 2017.
Calculations from NASA’s solar
system dynamics group have now
confirmed that comet Borisov
is from outside the solar system.
Borisov himself has taken a back
seat since he found the object.
“The last four weeks have been
just crazy,” he says. “When the big
telescopes came in, I took a break.”
With the comet set to reach
its closest point to us – at twice
the Earth-sun distance – on
7 December, other astronomers
are gearing up for a major
observing campaign.Unlike ‘Oumuamua, comet
Borisov was spotted approaching
the solar system rather than
leaving it. This gives us more
time to study it – probably about
a year. Another difference is that
the comet appears to be spewing
dust and gas into space.
Astronomers led by Alan
Fitzsimmons at Queen’s
University Belfast, UK, looked at
the trail of gas using the William
Herschel Telescope on the Spanish
island of La Palma. This showed
that it contained cyanide gas
(arxiv.org/abs/1909.12144). We
see this in comets from our solar
system, suggesting that Borisov
may have been formed in a
similar way. This matters because
astronomers want to know moreabout whether our system is
relatively typical or unique.
Over 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’s balance of water
and carbon monoxide. “Usually 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,” says Emmanuël
Jehin at the University of Liège
in Belgium. He plans to use the
TRAPPIST telescopes in Chile and
Morocco to study whether that is
true of Borisov.
We should soon also know the
comet’s shape. ‘Oumuamua had
an unusual shape – like that of a
long, thin cigar – and was rapidly
tumbling end over end through
space. Several telescopes,
including the Hubble Space
Telescope, will be trained on
Borisov in the next few weeks
so we can work out its size and
deduce its shape by observing
how it reflects sunlight. Ourbest current estimate is that
it is between 700 metres and
3 kilometres wide.
Attempts have also been made
to work out where the comet came
from. By tracing back its trajectory,
Piotr Dybczyński at the Adam
Mickiewicz University in Poland
and his colleagues suggest that it
may have come from a pair of red
dwarfs called Kruger 60 that lie
13 light years from us, although
Dybczyński is far from certain
about it. “Probably we will never
know for sure,” he says. However,
measuring the isotopes of carbon
in the comet could tell us which
region of the galaxy it came from.Slingshot manoeuvre
Andreas Hein at the Initiative for
Interstellar Studies in the UK and
his colleagues looked at how a
spacecraft could be dispatched to
Borisov. We have already sent craft
to comets, so it isn’t unthinkable.
Getting to the object would
involve slingshotting a craft
around the sun and possibly
Jupiter. This can only be done
when the planets are aligned a
certain way. Hein found that the
optimal launch window would
have been July 2018. But he also
found that we could launch in
2030 and get to Borisov by 2045
using a large rocket such as NASA’s
upcoming Space Launch System
(arxiv.org/abs/1909.06348). “It’s
possible from a technical point
of view,” says Hein.
Michele Bannister at
Queen’s University Belfast says
astronomers are working to get
as much information as possible
before the comet waves goodbye.
“We have most of the major
facilities sorted out that will be
able to observe it,” she says.
We are about to get a better
glimpse into an alien solar system
than ever before. ❚News
SpaceNIKSZYMANEKWe can visit comet from alien star
As comet Borisov nears Earth, we are learning a lot about the second-ever
interstellar object seen – including how to travel to it, says Jonathan O’CallaghanThis composite image
shows Borisov streaking
towards us700
Best estimate of comet Borisov’s
minimum width, in metresThe William Herschel
Telescope has found that
comet Borisov emits cyanideGE
MI
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RV
AT
ORY/NSF
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