A huge object passing by Earth could be an alien spacecraft, scientists have said.
The bizarre cigar-shaped entity was previously thought to be an interstellar asteroid which had come from another part of the galaxy.
But evidence has been mounting which has led experts to suggest it could actually be a sign of intelligent life.
The object is hundreds of metres in length but only one tenth as wide which is highly unusual for a typical space rock, scientists have said.
It is also speeding through space at 196,000 mph, suggesting it is not gravitationally bound to the sun.
The mysterious body, which has been dubbed “Oumuamua”, was spotted by astronomers from the University of Hawaii in October as it passed the Earth at around 85 times further than the moon.
It is the first object discovered in the solar system that appears to have originated from another part of the galaxy.
Researchers involved in Seti - the Search for Extra-Terrestrial Intelligence – are preparing to turn a powerful dish telescope towards the object.
A statement from the $100 million (£75 million) Seti project Breakthrough Listen, launched by Russian digital tech mogul Yuri Milner in 2015, said: "Researchers working on long-distance space transportation have previously suggested that a cigar or needle shape is the most likely architecture for an interstellar spacecraft, since this would minimise friction and damage from interstellar gas and dust.
"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 artifact."
The team is using the Green Bank radio telescope in West Virginia, US, to study Oumuamua, which is named after the Hawaiian term for "scout" or "messenger".
From 8pm UK time on Wednesday, December 13, the giant dish - the largest fully steerable radio telescope in the world - will "listen" to the object across four radio frequency bands spanning one to 12 gigahertz.
The object is currently about two astronomical units (AU) from Earth, or twice the distance between the Earth and sun.
Breakthrough Listen aims to survey a million nearby stars and 100 nearby galaxies looking for alien signals.
Since the 1960s there have been more than 98 Seti projects around the world, none of which have turned up any convincing evidence of extra-terrestrial civilisations.
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