鈥極umuamua the 鈥渋nterstellar asteroid鈥� may not have been the first interstellar rock we鈥檝e ever seen. A meteor that burned up in Earth鈥檚 atmosphere in 2014 may have come from a distant planetary system 鈥� and if it did, it was probably from the area around the system鈥檚 star where life would be most likely to develop.
Every day, more than 100 tonnes of space dust and rocks hit Earth鈥檚 atmosphere, where most of it burns up before it hits the surface. 鈥淓arth is just sweeping up all of this material like the front of a car鈥檚 windshield as it goes around the sun,鈥� says Michele Bannister at Queen鈥檚 University Belfast. 鈥淭here鈥檚 this regular pitter patter.鈥�
Most of this material comes from bits of comets, asteroids, and even planets within our own solar system, but Amir Siraj and Avi Loeb at Harvard University claim to have found the signal of a meteor that came from somewhere else.
Advertisement
They combed through a catalogue of meteors spotted by a network of detectors owned by the US government. They were looking for objects that might not be gravitationally bound to the sun 鈥� meaning they鈥檝e probably been tossed here from somewhere else 鈥� based on their speeds and trajectories.
This is similar to how astronomers spotted 鈥極umuamua, our solar system鈥檚 first documented interstellar visitor, in 2017. It was far from Earth, but its trajectory made it clear that it could not have come from inside our solar system.
The researchers found a meteor that also seemed to be from somewhere else. It was about half a metre across and vapourised in our atmosphere in 2014. If we could take detailed measurements of the remnants of meteors like this as they burn up, we might be able to tell what they are made of to learn about other stellar systems.
The meteor hit the atmosphere at about 45 kilometres per second. For it to have been bound to the solar system, it would have to have been moving at no more than about 20 kilometres per second, Loeb says.
This is far from the first claim of an interstellar meteor, say Bannister and Peter Brown at Western University in Ontario, Canada. 鈥淭o date, pretty much all of them can be explained with measurement uncertainty,鈥� he says. 鈥淭o be able to say we found an interstellar meteor, you have to know your uncertainties very well, and I don鈥檛 think we can in this case.鈥� The government database does not provide precise measurement uncertainties.
If this meteor truly was interstellar, its speed and trajectory indicate it may have come from relatively close to another star in the Milky Way. If it was a dwarf star, this means that the rock could have once lived in the habitable zone, where it is neither too hot nor too cold for liquid water, which is necessary for life as we know it.
Loeb calculated that objects about this size should hit Earth about once a decade, while larger objects like 鈥極umuamua are rarer. This particular object was too small to carry life safely through interstellar space from its home star: if the radiation didn鈥檛 kill it, being vapourised in the atmosphere certainly would have.
But the larger, rarer objects could potentially spread life throughout the galaxy and even leave evidence in meteorites that make it to the ground. 鈥淚 think it鈥檚 like looking for a message in a bottle on the beach,鈥� says Loeb. 鈥淢ost of the time you see rocks, but once in a while you might find a bottle.鈥�
arxiv
