12 | New Scientist | 21 September 2019
The world demands
less carbon.The world demands
more energy.EXCITEMENT is building among
astronomers following the
sighting of an object that seems
to have come from outside our
solar system. If its origins are
confirmed, it will be only the
second interstellar object we
have detected. And unlike the
last, this one is heading our way.
The first interstellar object,
an asteroid called ‘Oumuamua,
was discovered in October 2017.
When we spotted it, it was already
on its way out of the solar system
and moving so fast that it was
difficult to study.
The new object is a comet,
spotted in images from the
Crimean AstrophysicalObservatory on 30 August. Its
trajectory seems to indicate that it
came from beyond our solar
system, from the direction of the
constellation Casseiopeia. It was
initially known only as gb00234,
but is now being called comet
Borisov, after the astronomer who
first spotted it, Gennady Borisov.
Other astronomers have now
taken more than 150 pictures of
the object to try to nail down its
path. “We had one like this in late
May and it turned out to be a
normal comet,” says Michele
Bannister at Queen’s University
Belfast, UK. We don’t have enough
data yet to know whether Borisov
came from outside our solarsystem, she says. “It’s a bit
under-baked as yet.”
Bill Gray, an independent
astronomy software developer,
has modelled the object’s path.
“It’s either a really bright
interstellar comet, or it’s gettingpushed around a lot by non-
gravitational forces,” he says.
It could be that material on the
comet is evaporating, creating a
propulsive force that has forced it
into a strange orbit. “Both are alittle hard to believe, and we’ll
probably have to wait for more
data,” says Gray.
If it is an interstellar comet,
Gray’s modelling suggests that
it is heading towards us at about
30 kilometres per second and will
pass Earth in December. When it
passes us, it should be about twice
as far from us as the sun is.
This comet was caught much
earlier in its journey through the
solar system than ‘Oumuamua,
which will make it easier to
observe. This could give us a
unique opportunity to study
a rock from around another
star and perhaps learn what
other solar systems are like. ❚News
“ It’s either a really bright
interstellar comet, or it’s
getting pushed around by
non-gravitational forces”AstronomyLeah CraneA second interstellar tourist?
Mysterious comet heading our way may come from another star