NASA Science Briefing: Comet Siding Spring at Mars

Where did the two natural satellites of Mars, Phobos and Deimos, come from? For a long time, their shape suggested that they were captured asteroids. However, the shape and course of their orbits contradict this hypothesis. Two independent and complementary studies now provide an answer: these satellites formed from the debris of a gigantic collision between Mars and a protoplanet one-third its size.

While Mars doesn’t have much in the way of Earth-like weather, it does evidently share one kind of weird meteorology: acid fog. Planetary scientist Shoshanna Cole has pieced together a compelling story about how acidic vapours may have eaten at the rocks in Gusev Crater on Mars using a variety of data gathered by instruments on the 2003 Mars Exploration Rover Spirit.

NASA’s new planet-hunting TESS observatory completed its first post-launch thruster firing Saturday, setting up for a big boost Wednesday that will send the spacecraft toward the moon for a flyby next month, the next maneuvers in a two-month process to reach the mission’s final science orbit in mid-June.