NASA to announce second major discovery on Mars

The last time NASA promised something like this involving Mars, the result was the revelation that the Opportunity rover's landing site had once been soaked with water, providing the first evidence gleaned from the surface for past liquid water on Mars.

A spokesperson for NASA told SPACE.com that the big announcement Tuesday would again involve a discovery by the Opportunity rover and not its twin, Spirit. The agency did not provide detail regarding the science involved, and the spokesperson would not elaborate.

The announcement will be made at NASA Headquarters in Washington, D.C. and carried live on NASA TV.