One of the strangest things about interstellar visitor Oumuamua is that when it flew right by the sun, it didn't get a comet-like tail.
Scientists now believe that's because it's coated in a half-metre thick shield.
"Planetary scientists have long expected that the interstellar object population is dominated by ice-rich small bodies like comets, however, Oumuamua didn't exhibit any comet-like activity when it passed close to the sun," said Alan Fitzsimmons of Queen's University Belfast in the UK.
But although some have suggested Oumuamua could be a probe sent by an alien civilization, Prof Fitzsimons says the shielding is not of the electromagnetic variety we see on Star Trek and Star Wars.
"The surface is similar to small solar system bodies that are covered in carbon-rich ices, whose structure is modified by exposure to cosmic rays," he said in a release.
"They developed a model of the thermal properties of Oumuamua and determine that a half-metre thick mantle of organic-rich material could have protected a water-ice-rich comet-like interior from vaporising when the object was heated by the sun."
The asteroid was first spotted in October, coming from above the solar system - clearly not from this part of the galaxy.
Oumuamua's strange cigar-like shape, its odd trajectory and lack of tail raised suspicions it could be artificial in origin.
A team of astronomers led by Stephen Hawking are currently collecting data on it, with initial scans not finding any trace of electromagnetic signals - a sure sign ET just paid us a visit.
"We are most likely not to find anything, but it is worth checking steadily our fishing hook," said Ari Loeb, Harvard University astronomer.