A scientist has suggested an object that passed by Earth recently may be an alien spaceship suffering catastrophic engine failure.
1I/2017 U1 was first spotted in October as it hurtled into our region of space at a breakneck pace - 8.7km a second. Coming from directly above the solar system, astronomers immediately realised it wasn't from around these parts - and dubbed it Oumuamua, which in Hawaiian means "a messenger from afar arriving first".
After swinging around the sun, Oumuamua is now leaving just as quickly as it arrived - but a team of scientists led by famed cosmologist Stephen Hawking are going to test if it's emitting electromagnetic signals.
Breakthrough Listen will on Thursday (NZ time) scan Oumuamua for 10 hours, able to detect signals as weak as those given off by a cell phone.
"Just because their propulsion is broken doesn't mean that their radio transmitters would be broken," Penn State University associate professor Jason Wright wrote in a blog.
Oumuamua is currently about twice the distance between the Earth and the sun away. It sounds far, but it's still about 70 times closer than Voyager, which is beyond Neptune but still in touch with NASA.
Dr Wright says Oumuamua's shape and tumbling motion suggests it could be a failed probe sent across the galaxy to colonise far-flung systems like ours.
"Growth can be achieved via Von Neumann probes: self-replicating spacecraft that go to a system, make lots more of themselves, and then go to more systems," he wrote on his blog.
"You might expect some fraction to eventually go derelict (space is a harsh environment, and an optimal design will likely have a nonzero failure rate). Such derelict craft would, if they are not traveling so fast that they escape the galaxy, eventually… end up drifting around like any other interstellar comet or asteroid.
"In fact, since they (presumably) no longer have attitude control, one would expect that they would eventually begin to tumble, and if they are very rigid, that tumbling might distinguish them from ordinary interstellar asteroids."
Oumuamua is indeed tumbling chaotically, and it's been suggested its elongated cigar shape would be ideal for travelling large distances through space - minimising friction from interstellar dust. Virtually all asteroids observed in the solar system are round.
Oumuamua also appears to be made from an incredibly sturdy substance - perhaps metal.
Most objects flung from their stars during formation are icy because they're found at the edges, far from their stars. Oumuamua not only didn't form an icy tail as it approached the sun, scientists say its extreme tumbling would have pulled apart an asteroid made of any ordinary rock.
"While a natural origin is more likely, there is currently no consensus on what that origin might have been, and Breakthrough Listen is well positioned to explore the possibility that Oumuamua could be an artefact," Breakthrough Listen said in its announcement.