When ‘Oumuamua passed through our solar system in 2017, no one knew where it came from. Astronomers, on the other hand, think they know how Comet 2I/Borisov got here.
Astronomers have found an object from outside our solar
system flying through it for the second time in history. But scientists think
they know where it came from this time.
The interstellar comet was first seen by Gennady Borisov, an
amateur astronomer in Crimea who was using his own telescope to look at the
sky. When he found it, the object was the first interstellar visitor found
since 2017, when the long ‘Oumuamua flashed by our solar neighborhood. In a
publication, a group of Polish astronomers figured out how this new comet,
called Comet 2I/Borisov or (in earlier descriptions) C/2019 Q4, got to our
sun’s gravity well. And that path goes back to Kruger 60, which is a system of
two red dwarf stars 13.15 light-years away.
Researchers found that Comet Borisov passed just 5.7
light-years from the center of Kruger 60 1 million years ago. This means that
it was moving at just 2.13 miles per second (3.43 kilometers per second).
In human terms, that’s fast—about as fast as an X-43A
Scramjet can go, which is one of the fastest planes ever made. But because of
the sun’s gravity, an X-43A Scramjet can’t leave our solar system. And the
scientists found that if the comet was moving so slowly and was no more than 6
light-years away from Kruger 60, it wasn’t just passing through. They thought
it most likely came from a star system. Comet Borisov used to go around those
stars in the same way that comets in our system go around ours.
Ye Quanzhi, an astronomer and comet expert at the University
of Maryland who was not part of this project, told Live Science that the
evidence linking Comet 2I/Borisov to Kruger 60 is very strong based on what we
know so far.
“IF YOU HAVE A COMET FROM ANOTHER STAR SYSTEM AND WANT TO FIND OUT WHERE IT CAME FROM, YOU NEED TO CHECK TWO THINGS,” HE SAID. “FIRST OF ALL, HAS THIS COMET BEEN CLOSE TO A PLANETARY SYSTEM? BECAUSE IF IT’S COMING FROM THERE, ITS PATH MUST PASS THROUGH WHERE THAT SYSTEM IS.”
Even though the 5.7 light-year gap between the new comet and
Kruger seems bigger than a “small gap” (it is more than 357,000 times the
distance between Earth and the sun), it is close enough to be considered
“small” for these kinds of calculations, he says.
“SECOND,” YE CONTINUED, “COMETS ARE USUALLY THROWN OUT OF A PLANETARY SYSTEM WHEN THEIR GRAVITY INTERACTS WITH THAT SYSTEM’S MAJOR PLANETS.”
In our solar system, that might look like Jupiter catching a
falling comet, sending it on a short, partial orbit, and then tossing it into
space between the stars.
“THIS SPEED OF EJECTION CAN ONLY GO SO FAST,” YE SAID. “IT CAN’T BE INFINITE BECAUSE PLANETS HAVE A CERTAIN MASS,” AND HOW HARD A PLANET CAN THROW A COMET INTO THE VOID DEPENDS ON HOW MUCH MASS IT HAS. HE ALSO SAID, “JUPITER IS PRETTY BIG, BUT YOU CAN’T HAVE A PLANET 100 TIMES BIGGER THAN JUPITER BECAUSE THEN IT WOULD BE A STAR.”
Ye says that this mass threshold limits how fast comets can
move through the space between stars. And, if their estimates of the comet’s
path are right, the authors of this study showed that Comet 2I/Borisov passed
close enough to Kruger 60 in terms of speed and distance to suggest that it
came from there.
YE SAID, “STUDYING INTERSTELLAR COMETS IS EXCITING BECAUSE IT GIVES US A RARE CHANCE TO STUDY OTHER SOLAR SYSTEMS WITH THE SAME TOOLS WE USE TO STUDY OUR OWN.”
Astronomers can look at Comet 2I/Borisov through telescopes,
which may give them information about the surface of the comet. They can find
out if it acts like comets in our solar system do (so far, it has) or if it
does anything strange like ‘Oumuamua. That’s a whole area of study that’s
normally not possible with distant solar systems, where small objects only
appear — if at all — as faint, discolored shadows on their suns.
Because of this research, anything we find out about Comet
Borisov could teach us something about Kruger 60, a nearby star system where no
exoplanets have been found yet. ‘ Oumuamua, on the other hand, seems to have
come from the general direction of the bright star Vega, but astronomers at
NASA’s Jet Propulsion Laboratory think it came from a new star system, though
they don’t know which one. If these results are true, Comet Borisov will be the
first object from another star system that has been tracked back to its home
system.
But the people who did the research were careful to say that
these results are not yet proof. Astronomers are still gathering information
about Comet 2I/path Borisov’s path through space. More information may show
that the original trajectory was wrong and that the comet came from somewhere
else.