This month, as part of the 2015 Mission to the Solar System, we’ve been visiting the planet Mars. How could we not spend at least one post talking about Mars’s two moons, Phobos and Deimos?
Someday, humanity will colonize Mars. When we do, these two moons should provide some interesting stargazing opportunities.
Phobos, as observed from the surface of Mars, may not be quite as large as Earth’s Moon as observed from the surface of Earth, but it’s still a large, easy to spot object. Now imagine watching this large object racing through the sky, rising and setting two or sometimes three times per day (I mean per sol). That’s what Martian colonists will get to see.
Meanwhile, Deimos only rises and sets once per day. That seems a bit more normal, expect for Martian stargazers, Phobos and Deimos will seem to be moving in opposite directions. This is because Deimos lags slightly behind Mars’s rotation, making it appear to be moving backwards compared to Phobos.
Deimos is also slowly drifting away from Mars.
Eventually, Deimos will break free of Mars’s gravity and escape into a new orbit around the Sun.
Phobos, on the other hand, is getting gradually closer to Mars. At some point, tens of millions of years from now, it’s expected to crash into the planet’s surface.
Lastly, both Phobos and Deimos look suspiciously like asteroids. On that note, our month-long tour of Mars comes to an end. The 2015 Mission to the Solar System will continue in July as we enter the asteroid belt (a region that went into an uproar after two of its asteroids mysteriously went missing).
P.S.: There’s another possible fate for Phobos: rather than crashing to the surface of Mars, it might be shredded by tidal forces. If so, the fragments could end up forming a faint planetary ring around Mars, which would be pretty cool.