A pair of meteorites discovered in Antarctica last year has geologists here atwitter, mostly because they just don’t know where the thing came from. “It’s a weirdo,” says Yang Liu, of the University of Tennessee at Knoxville. “There’s nothing like it.”

Three different consortia got rights to analyse wee bits of the rocks and are comparing their results. It’s very old — about 4.5 billion years. Based on that age, and its oxygen isotope composition, both the Earth and Mars are ruled out as sources. It probably didn’t come from the Moon, because it has too much sodium in it.

Liu says it could have come from an especially big asteroid, maybe even a former planet — but it had to be big enough to have heat for melting rocks below a crust. An alternative theory — one that has people most excited — is that the rock came from Venus. If so, it would be the first Venusian meteorite — and the first sample at all from that planet.

In the 1970s, the Soviet Venera probes touched down on Venus’ surface and found basaltic material, like flows from a volcano. This particular meteorite has too much silica to be a basalt, but recent studies have shown that magma compositions on Venus could be more varied than previously thought.