Astronomy Picture of the Day

Explanation: What is this unusual mound on Mars? NASA's Curiosity rover rolling across Mars has come across a group of these mounds that have been labelled Murray Buttes. Pictured is a recently assembled mosaic image of one of the last of the buttes passed by Curiosity on its way up Mt. Sharp -- but also one of the most visually spectacular. The 15-meter tall butte is topped with ancient water-deposited layers in relatively dense -- but now dried-out -- windblown sandstone. The rim of Gale crater is visible in the distance. Curiosity continues to accumulate clues about how Mars changed from a planet with areas wet and hospitable to microbial life to the dry, barren, rusted landscape seen today.