Focus on Phobos

Phobos floats in front of Mars’ horizon in January 2007

The European Space Agency’s Mars Express has begun a series of flybys of Mars’ largest – albeit still very small – moon, Phobos. Begun on February 16 (2010) Mars Express will perform closer and closer approaches until, on March 3, it will pass by at an altitude of only 31 miles, giving us the most detailed views ever of Mars’ curious little moon.

The origins of Phobos (and its even smaller sister, Deimos) are still under debate. Did they form with Mars as a planet? Are they captured asteroids, now trapped in orbit? Are they chunks left over from some other event? Hopefully the information gleaned from these upcoming visits will help answer that question…as well as provide some really cool detailed images of Phobos’ surface!

Phobos from the HiRISE camera. Image: HiRISE, MRO, LPL (U. Arizona), NASA

As a moon Phobos really is an oddity. Despite its small size – only 16 miles across at its widest – and irregular shape, it also orbits its parent planet at a very low altitude, only 5,840 miles (compare that to our own Moon’s 248,000 mile distance), and thus needs to travel at a very high speed in order to stay in orbit. It is actually orbiting Mars over three times faster than Mars rotates, and thus appears to rise in Mars’ western sky. And its orbit is so low that it can’t even be seen from the polar regions on Mars. Clearly something is unusual about where exactly Phobos came from.

Phobos is especially important these days as it will likely become the next target for human exploration missions, since establishing a base there would be much easier than executing an all-out Mars landing due to its low gravity and lack of atmosphere. From Phobos, studying Mars closely and eventually getting to its surface would be a simpler – and much safer – task. Not to mention the views one would get of the red planet from there!

Stay tuned to LITD for flyby photos as they come in…and read more on the Mars Express Phobos mission blog here.

Image: ESA/DLR/FU Berlin (G. Neukum)