To the credit of those who think it might be an alien probe, its composition and shape are unique — The Guardian describes it as “dark, reddish, about 400 metres long by 40 meters wide… roughly the size and shape of a skyscraper.” Weirder still is that it appears to be made out of something carbon-based, rather than metal and ice, the materials more commonly associated with objects in interstellar transit.

It has also caught attention for speeding up when it passed the Sun, which Physics World says couldn’t have happened because of gravity.

Now, to be fair, even the Harvard scientists who speculated that the object might be a “fully operational probe sent intentionally to Earth’s vicinity by an alien civilization” have put forward other more Earth-bound theories. They also postulated that it could be the shard of an exploded planet, or just a common comet or asteroid with a few quirks. But those theories aren’t as exciting as the possibility of it being a “light sail,” designed to use radiation from stars for propulsion.

Unfortunately, we may never know, as the “probe” didn’t stick around for a taste of its own medicine. Really, it’s probably for the best. Anyone who’s ever seen a sci-fi movie knows alien species don’t travel across the universe to play Tiddlywinks.