Apparently Curiosity has made an Earth-shaking discovery, but NASA is not announcing it because they want to verify the data, which is expected to take a few weeks. A few weeks! I can't stand the suspense!!
My guesses below:
Microscopic fossils
Evidence of wet soil below the surface
"The importance of a telescope is not how big it is, how well made it is.
It is how many people, less fortunate than you, got to look through it."
-- John Dobson.