COSMIC RELIEF by David Grinspoon
EVERYTHING WE THINK WE KNOW
about the universe beyond our solar sys-
tem has come from photons and a few
grains of interstellar dust. But that near-
complete material isolation is about to
end. Our system apparently buzzes with
objects from elsewhere in the galaxy. It’s
time to go out and meet one.
The existence of extraterrestrial
comets isn’t a surprise. We’ve known
for decades that, unless there’s some-
thing seriously wrong with our ideas
about planet formation, they must
exist. Building planets through gravi-
tational accretion is messy. Planet
assembly should be causing a constant
exodus of bodies loosed from the grip of
their home stars. If anything, it seemed
a little strange that we hadn’t seen
something hurtling in from elsewhere
in the galaxy.
That changed in late 2017 when we
detected the bizarre extrasolar object
‘Oumuamua whipping through our
solar system (S&T: Oct. 2018, p. 20).
We didn’t get a very good look, and
‘Oumuamua was just so weird — cigar-
thin and seemingly accelerating myste-
riously — that it didn’t necessarily call
out, “I’m a typical interstellar wanderer
and there are many just like me.”
Now a second one has turned up.
Found by Crimean amateur astrono-
mer Gennady Borisov on August 30th,
2I/Borisov is already sporting a bit of
a coma, so it seems much more likeMission
to an
Interstellar
Object
It’s time to visit a body from
another star system — without
leaving ours.a “typical” comet (see page 10). Two
objects detected in a short interval
implies many more.
Could we launch a mission to
intercept 2I/Borisov and do a close
fl yby or even grab a sample? There isn’t
time. These things come in and fl y off
fast, far too fast to be in permanent
orbit around the Sun. But there will be
more. The trick is to build and launch
a spacecraft — a small and very fast
spacecraft — that will be ready to spring
into action when we spy another such
interloper on a trajectory we can reach.This is not how we usually do things:
constructing a spacecraft when we
haven’t even found the target. But the
merits of the approach became clear
with the recent success of New Hori-
zons at 2014 MU 69 , also known as
Ultima Thule (S&T: July 2019, p. 10).
That was a fantastically rewarding
encounter with a body that we hadn’t
discovered at the time of launch.The European Space Agency’s
recently selected Comet Interceptor
mission has this philosophy. It will wait
in a stable orbit and then shoot off
toward a suitable long-period comet.
These are hard to catch, because once
detected they quickly fl y through the
inner solar system and back out into
the dark. Such an approach will be even
more crucial for interstellar comets,
which come in even faster.
It has to be done, though, and if one
of the national space agencies doesn’t
take it on, it’s a great opportunity for azillionaire philanthropist to make his-
tory with a theatrical and scientifi cally
rich exploration fi rst.
Just think: We can touch “other”
star stuff. What are we waiting for?■ Contributing Editor DAVID GRIN-
SPOON is coauthor, with Alan Stern, of
Chasing New Horizons: Inside the Epic
First Mission to Pluto.It’s a great opportunity for a zillionaire philanthropist to make
history with a theatrical and scientifically rich exploration first.LE
AHTISCIONE^ /S&T