More evidence for water on Mars.

More evidence for water on Mars.  The Curiosity rover returned the images used to make the beautiful composite at right (high res version).  This rock would look right at home on Earth: it's the kind of rock formed in streambeds here.  Its presence on Mars strongly suggests that water once flowed freely there.  From the NASA/JPL image description:

Reddish dust coats much of the surface visible in this mosaic, but the patch of rock also offers some bare patches where sand and pebble grains can be seen. Pebbles here are mostly gray, with some white in them. Some grains are somewhat translucent, and some are shiny.

Researchers interpret the sand and pebbles in the rock as material that was deposited by flowing water, then later buried and cemented into rock. Curiosity's science team is studying the textures and composition of the conglomerate rock at Darwin to understand its relationship to streambed conglomerate rock found closer to Curiosity's landing site.

Note they used a 1909 penny for scale – there's got to be a story behind that!