Martian Jelly-Rock: Raked-Up by the Rover or -Left by Other Exploring Species?

[mythociate]

Apparently the Mars-rover Opportunity has discovered a special rock that resembles a jelly-doughnut.

When I heard about it, NASA-people had indicated that the rock was made of a substance unknown anywhere else in the universe---a substance not thought to be of Martian origin. They may have found out more about it, but I'm still waiting for the Sydney Morning Herald-page to open (which it just did ... and reminded me that the jelly-rock hadn't been there on Opportunity's first picture of the area).

Though one of their scientists imagines it was just something the rover kicked-up (and most NASA-scientists concur), I think it could be a couple different things:

• My wild imagination naturally thought it was something left there by an alien-species of explorers 'like us' (except such creatures as produce rock-like 'leavings')
• More rationally, I guessed it might be a fragment of meteor fallen to Mars from long ago.
• Some scientists think it is a rock from Mars which had been buried & unexposed to Martian surface-conditions---sort of a 'Martian magma-stone.'

What do You think it is?