Phobos

Color view of Phobos from Mars Reconnaissance Orbiter (Credit: NASA / JPL / U. Arizona)

The European Space Agency’s Mars Express Orbiter has been examining Mars since late 2003. It’s currently undertaking a series of 12 flybys of the larger of Mars’s two Moons – Phobos. ESA has posted a detailed schedule of the flybys and the experiments conducted for each. They’re also hosting a blog to follow the events. The closest approach of 50 km will occur on March 3^rd.

Phobos is an irregularly shaped (non-spheroidal) body only 27 km across at its longest point. Based on spectral and density data, Phobos and Deimos (Mars’s other moon) seem to have very primitive compositions similar to carbonaceous chondrite meteorites. Asteroids matching that composition compose most of the asteroid belt, and it is suspected that Phobos and Deimos may be captured asteroids.

Either Phobos or Deimos is a possible target for the Flexible Path option raised by the Augustine Commission (PDF, see section 3.5). This alternative would place humans in orbit around Mars and/or on the surface of a Martian moon. From there they could sample Phobos or Deimos directly and teleoperate rovers on the Martian surface.  (Teleoperation would be much more efficient than driving rovers from more than 170 million kilometers away). One of the biggest energy expenses and engineering obstacles in manned exploration is getting back off of whatever body you land on – assuming you want to come back – and the larger the body’s gravity, the harder it is. That’s why visiting a small Martian moon is attractive – you could even have a craft return samples from the Martian surface to astronauts in orbit, since getting a small robotic craft off of the surface avoids the added weight and safety constraints that come with human passengers.

Kaidun meteorite (image from the Vernadsky Institute)

It would be cool to sample Phobos directly, but it’s possible that we already have an indirect sample in the form of the Kaidun meteorite, which fell in Yemen in 1980. It is suspected to be a piece of Phobos that was ejected from the moon’s surface by an impact. (See an Astrobiology Magazine story here and an abstract on it here.) This is one of my favorite meteorites (though I’ve only seen pictures and read papers) because it contains pieces of alkaline igneous rock – a subclass of magmatic rocks that is one of my research interests as well as a geeky fixation. Alkaline rocks are rare on Earth but almost non-existent in meteorites except for two 3-4 mm clasts in Kaidun and in one other meteorite.