BY RAFI LETZTER
FOR the second time ever, astronomers have detected an interstellar object plunging through our solar system. But this time, researchers think they know where it came from.
Gennady Borisov, an amateur astronomer working with his own telescope in Crimea, first spotted the interstellar comet on Aug. 30. His find made the object the first interstellar visitor discovered since oblong ‘Oumuamua flashed through our solar neighborhood back in 2017. Now, in a new paper, a team of Polish researchers has calculated the path this new comet — known as Comet 2I/Borisov or (in early descriptions) as C/2019 Q4 — took to arrive in our sun’s gravity well. And that path leads back to a binary red dwarf star system 13.15 light-years away, known as Kruger 60.
When you rewind Comet Borisov’s path through space, you’ll find that 1 million years ago, the object passed just 5.7 lightyears from the center of Kruger 60, moving just 2.13 miles per second (3.43 kilometers per second), the researchers wrote.
That’s fast in human terms —— about the top speed of an X-43A Scramjet, one of the fastest aircraft ever built. But an X-43A Scramjet can’t overcome the sun’s gravity to escape our solar system. And the researchers found that if the comet were really moving that slowly at a distance of no more than 6 lightyears from Kruger 60, it probably wasn’t just passing by. That’s probably the star system it came from, they said. At some point in the distant past, Comet Borisov lively orbited those stars the way comets in our system orbit ours.
Ye Quanzhi, an astronomer and comet expert at the University of Maryland who wasn’t involved in this paper, told Live Science that the evidence pinning Comet 2I/Borisov to Kruger 60 is pretty convincing based on the data available so far.
“If you have an interstellar comet and you want to know where it came from, then you want to check two things,” he said. “First, has this comet had a small pass distance from a planetary system? Because if it’s coming from there, then its trajectory must intersect with the location of that system.” Though the 5.7 light-years between the new comet and Kruger may seem bigger than a “small gap” — nearly 357,000 times Earth’s distance from the sun — it’s close enough to count as “small” for these sorts of calculations, he said. “Second,” Ye added, “usually comets are ejected from a planetary system due to gravitational interactions with major planets in that system.”
In our solar system, that might look like