Once Martian sand grains hop, they don’t stop. That’s the conclusion of a new study that finds sand can move on Mars without much windy encouragement. Mars’ sandy surface has clearly been shaped by wind. Its characteristic dunes and ripples are the kind formed by sand particles taking short wind-borne hops, a process called saltation. But atmospheric simulations and landers’ direct measurements... 

Santorini Panorama This panorama shows the vista from which NASA’s Mars Exploration Rover Opportunity spent five weeks in November and December 2008 while the sun was nearly directly in between Mars and Earth. Opportunity is approaching the fifth anniversary of its landing on Mars, continuing a surface mission that was initially scheduled to last three months. The rover landed on Jan. 24, 2004. Opportunity... 

Mercury was once seen as a cold, dead little world, spinning around the sun unchanged for the past 4 billion years. No longer: Observations from the Messenger spacecraft say it’s anything but. NASA’s orbiter is sending back evidence of massive volcanism, strange impact craters and magnetic tornadoes that funnel plasma directly from the sun to the planet’s surface. “It’s definitely not this...