Phobos image by Mars Express. Credit: ESA
Mars Express encountered Phobos last night, smoothly skimming past at just 67 km, the closest any manmade object has ever approached Mars’ enigmatic moon. The data collected could help unlock the origin of not just Phobos but other ‘second generation’ moons.
Something is not right about Phobos. It looks like a solid object but previous flybys have shown that it is not dense enough to be solid all the way through. Instead, it must be 25-35% porous. This has led planetary scientists to believe that it is little more than a ‘rubble pile’ circling Mars. Such a rubble pile would be composed of blocks both large and small resting together, with possibly large spaces between them where they do not fit easily together.(read more)