The Martian oceans may yet prove to be a mirage. Scientists analyzing the Martian data may have had a case of mistaken hematite identity:

Although the NASA rover Opportunity has found other evidence that the plain was likely to have been a shallow sea, it has yet to find a single flake of the grey hematite.

“It’s not panned out so far in the images we’re seeing,” said U.S. geochemist Professor Donald Burt of Arizona State University.

Opportunity may be finding the same old red hematite that gives the planet its nickname, eats away at our cars here on Earth and doesn’t require nearly as much water to form.

I’m still more interested in the methane, myself.