X is for . . .

I've been reading about Gliese 581 C, the smallest exoplanet yet discovered, a "Goldilocks" planet that's not too far, not too close, to its star, a red dwarf in the constellation Libra. Gliese 581C is 20.5 light years away and five times as massive as Earth.

“On the treasure map of the universe, one would be tempted to mark this planet with an X," said one scientist.

That seems very optimistic, but perhaps he is thinking "X for exoplanet." Or...of his own name?

"Xavier Delfosse!"