After President Obama's review of NASA's human space exploration policy, a group of independent scientists and experts got together and concluded that NASA will be about $3 billion per year short of putting astronauts back on the moon; their report suggests that it may be more feasible for NASA to send crews to Mars's moons and asteroids.
Because of Phobos's lack of mass, it has a weak gravitational field; this works to the astronauts' favor because it will be cheaper and easier to take off from there. A large percentage of the cost of missions to Mars is the rockets required to leave the surface. As a matter of fact, it may actually be cheaper to send missions to Phobos than to our own moon.
XKCD does a fine job of explaining Phobos's and Deimos's gravity wells (as well as most other bodies in our solar system) in this amazing illustration. Notice the insets on the left where he discusses Mars, then Phobos and Deimos.
Phobos is an ideal stopping point for many reasons; the primary reason is the ability to study Mars through telescopes and remote-controlled rovers. Also, once we're there, it gives us a hopping point when funding allows us to venture to the surface.
Origins of Phobos
Not only will it help us study Mars, but Phobos is a scientific mystery in itself. No one is really sure what Phobos is or where it came from. Some say it is a wayward asteroid that got captured in Mars's gravitational field.
Another theory is that Phobos and Deimos were formed from the same matter that formed Mars; the evidence for the moons' surprisingly regular and precise orbit. It is highly unlikely that one rogue asteroid, let alone two, could assume this precise of an orbit.
A third theory (and probably the most likely) is that a large impact threw chunks of Martian rock into orbit. Over time, these chunks adhered to each other to form these two small moons. If this is the case, there may be large caverns within Phobos that can be used to house and protect humans that are stationed there.
(Read the essay on NASA's site entitled Under the Moons of Mars.)
Missions to Phobos
To solve this daunting problem, the Russians are planning a collector mission in late 2011 to gather rocks from Phobos and bring them back to Earth for study. Also, the collector is likely to pick up pieces of recent Martian soil that has been thrown into the moon's path by asteroid collisions with the surface.
If NASA begins planning a mission to Phobos, one of the areas it will likely target is the monolith, which is a large slab of rock that sticks out of the surface, 90 meters into space. It kind of reminds me of the monolith in 2001: A Space Odyssey. The report claims that NASA could be there within five years of getting approval, which sounds like an ambitious timeline. Also, as the interviewees of the New Scientist article mention, it would be tough to go all the way to Phobos and not continue to the Martian surface.
What do you think about a mission to Phobos? Weigh in with your comments in this discussion.