Interstellar meteorites may be even stranger than we thought. They seem to be stronger than meteorites produced in our own solar system, which hints that they could have formed in a supernova or some other extreme cosmic event.
These interloping rocks are swift 鈥� any meteorite travelling at a high speed compared to the sun may come from beyond our solar system, and its origin can be confirmed by calculating the direction it came from.
The first interstellar meteorite聽to be discovered struck Earth off the coast of Papua New Guinea in 2014. and at Harvard University identified it in 2019 while digging through meteorite data collected by the US government鈥檚 Center for Near-Earth Object Studies (CNEOS).
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This data is primarily used to track missiles, so the details are kept private by the government. The trajectory of the object, which Siraj and Loeb called IM1, was confirmed by government scientists as interstellar. Now, the researchers have found what appears to be a second interstellar meteorite, called IM2, which struck Earth off the coast of Portugal in 2017.
Using the CNEOS data, they calculated the strength of all 273 meteorites based on the altitude at which they broke up in the atmosphere. 鈥淲hen a meteor is travelling through the atmosphere, the deeper it gets 鈥� the closer it gets to the ground 鈥� the denser the air gets and the more likely the meteor is to break up,鈥� says Siraj.
It turned out that IM1 was by far the strongest meteorite on the list 鈥� so strong that we鈥檙e not entirely sure what it鈥檚 made of, says Siraj 鈥� and IM2 was the third strongest. The second strongest was very likely an iron meteorite, he says.
If the population of interstellar meteorites has the same distribution of strengths as local meteorites, the chances of randomly finding two interstellar objects this strong would be between one in 10,000 and one in a million, according to the team鈥檚 calculations. That hints that perhaps these objects didn鈥檛 originate from a planetary system, like those in our solar system.
With only two interstellar meteorites spotted so far, we can鈥檛 be sure about where they came from, but one suggestion is that they could聽have formed in supernovae. 鈥淲e know that supernovae produce these so-called 鈥榮upernova bullets鈥�, which are basically clumps of iron-rich material, and it鈥檚 possible that those clumps break up into smaller bits which could be objects like IM1 and IM2,鈥� says Siraj.
He and Loeb have proposed an expedition to search for fragments of IM1 on the sea floor, and anything they find could help explain why interstellar meteorites seem to be so strong.
The Astrophysical Journal Letters
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