Phobos, the larger of the two moons of Mars has many unknowns. For instance, what formed the grooves that run across its surface?
Image: ESA/DLR/FU Berlin (G. Neukum)
Mars has been nothing but bad luck for the Russians. They have launched 20 probes to the planet since 1960, and all either failed or suffered from severe technical problems. But soon—as early as this October—Russia will attempt to reverse its fortunes with one of the most ambitious unmanned space missions ever.
Instead of aiming straight for Mars, the Russians are going after Phobos, the larger of its two little satellites and one of the oddest objects around. Their probe, called Fobos-Grunt (“Phobos soil” in Russian), will not only land on Phobos but also scoop up some samples of the surface and send them to Earth. Understanding Phobos could tell us a lot about the early history of the solar system. “It may give us clues to the formation of Earth’s moon and the moons of the other planets, and the role played by asteroid impacts in shaping the terrestrial [rocky] planets,” says Alexander Zakharov of the Moscow-based Space Research Institute and chief scientist for Fobos-Grunt. Even more important, this mission could lay the groundwork for an innovative strategy for exploring—and even colonizing—Mars itself.
Phobos is very different from our moon. It is a potato-shaped rock measuring only 12 miles by 17 miles, nearly as dark as coal, and dominated by a six-mile-wide crater called Stickney, evidence of a collision that nearly shattered the puny satellite. Phobos circles just 3,721 miles above the Martian surface (Earth’s moon averages a distance of 239,000 miles) and completes an orbit in 7 hours and 39 minutes, making a Phobos “month” on Mars less than one-third of a Martian day. In fact, Phobos circles so close to Mars that tidal forces are slowly causing its orbit to decay. Within the next few tens of millions of years it will crash into the planet; we are catching it at the tail end of its 4.5-billion-year life.
The same proximity to Mars that will one day doom Phobos makes it an extremely attractive staging post for human explorers. One side of Phobos always faces Mars, and on that “hemisphere” the planet dominates the sky. This makes Phobos a good place for monitoring most of the Martian surface. Moreover, any manned outpost on Phobos would be well shielded from space radiation—protected on one side by Mars and on the other by the satellite’s own bulk. From Phobos humans could explore the planet’s surface remotely using robots, eliminating the agonizing 10- to 20-minute delay that the operators of NASA’s Mars rovers currently have to endure. Phobos would also be a natural staging area for manned excursions to Mars.
Hebes Chasma, a Martian valley where water once flowed, could
be studied in detail from Phobos. Phobos's soil may also contain debris
blasted off Mars by ancient impacts
Image: ESA/DLR/FU Berlin (G. Neukum)
Before we start drawing up plans for outposts on Phobos, though, we need a much better grasp of what kind of place it is. Right now scientists do not even know exactly what Phobos is made of. It appears similar to a group of asteroids known as carbonaceous chondrites. These primitive objects contain amino acids, the building blocks of life, and appear to be nearly unchanged fragments of the material from which the solar system formed. Scientists have speculated that a rain of carbonaceous chondrites may have seeded early Earth with the raw material for biology here. Phobos’s distinctive composition has led some scientists to suspect that it (along with Deimos, Mars’s other miniature satellite) might be a captured asteroid. But that is far from a foregone conclusion.
