A Second Interstellar Visitor Has Arrived in Our Solar System. This Time, Astronomers Think They Know Where It Came From


When ‘Oumuamua passed through our solar system in 2017, no one could figure out where the object came from. However, astronomers believe they have figured out how Comet 2I/Borisov got here.


Astronomers have discovered an interstellar object flying through our solar system for the second period in history. But this time, scientists believe they know where it came from.


Gennady Borisov, an amateur astronomer working with his own telescope in Crimea, first spotted the interstellar comet. His discovery made the object the first discovered interstellar visitor since the oblong ‘Oumuamua flashed through our solar neighborhood in 2017. A team of Polish astronomers has calculated the path this new comet — known as Comet 2I/Borisov or (in early descriptions) as C/2019 Q4 — took to reach our sun’s gravity well in a publication. And that path leads back to Kruger 60, a binary red dwarf star system 13.15 light-years away.


Rewinding Comet Borisov’s path through space reveals that it passed just 5.7 light-years from the center of Kruger 60 1 million years ago, moving at just 2.13 miles per second (3.43 kilometers per second), according to the researchers.


In human terms, that’s quick – around the top speed of an X-43A Scramjet, one of the fastest aircraft ever built. However, an X-43A Scramjet cannot escape our solar system due to the sun’s gravity. And the researchers discovered that if the comet was moving so slowly at a distance of no more than 6 light-years from Kruger 60, it wasn’t merely passing by. They believed that it was most probably from a star system. At some point in the distant past, Comet Borisov lively orbited those stars the way comets in our system orbit ours.


Based on the data available thus far, Ye Quanzhi, an astronomer and comet expert at the University of Maryland who was not involved in this work, told Live Science that the evidence linking Comet 2I/Borisov to Kruger 60 is quite convincing.


“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-year distance between the new comet and Kruger appears to be greater than a “small gap” — over 357,000 times Earth’s distance from the sun — it is close enough to count as “small” for these types of calculations, he explains.


“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 may look like Jupiter snagging a falling comet, slingshotting it around in a brief, partial orbit, and then throwing it away into interstellar space.


“This ejection speed has a limit,” Ye said. “It can’t be infinite because planets have a certain mass,” and the mass of a planet determines how hard it can throw a comet into the void. “Jupiter is pretty massive,” he added, “but you can’t have a planet that’s 100 times more massive than Jupiter because then it would be a star.”


According to Ye, this mass threshold limits the speed at which comets can escape star systems. And, if their trajectory estimates are correct, the authors of this research demonstrated that Comet 2I/Borisov passed within the minimum speed and distance from Kruger 60 to suggest it originated there.


“Studying interstellar comets is exciting”, Ye said, because it offers a rare opportunity to study distant solar systems using the precise tools scientists employ when examining our own.


Astronomers can observe Comet 2I/Borisov through telescopes, which may reveal facts about the comet’s surface. They can figure out whether it behaves like comets in our own system (so far, it has) or does anything unusual, like ‘Oumuamua famously did. 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.


This research means that anything we learn about Comet Borisov could be a lesson about Kruger 60, a nearby star system where no exoplanets have been discovered. ‘Oumuamua, on the other hand, appears to have originated from the general direction of the bright star Vega, but astronomers at NASA’s Jet Propulsion Laboratory believe it came from a newly-forming star system (though they aren’t sure which one). If these findings are confirmed, Comet Borisov will be the first interstellar object to be tracked back to its home system.


However, the authors of the research were careful to warn out that these findings are not yet conclusive. Astronomers are still collecting more data about Comet 2I/path Borisov’s through space, and additional data may reveal that the original trajectory was wrong and that the comet came from somewhere else.


The paper tracing the comet’s origin has not yet been peer-reviewed, but it is available on the arXiv preprint server.

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