Phobos
Written by John Carl Villanueva
Phobos is one of two moons orbiting the planet Mars. It is larger than the other moon, Deimos, and has a smaller orbit. Phobos' distance from its primary, about 9,377 km, is the closest among all recorded planetary moons.
The orbit of Phobos is so small that it circles around Mars fast enough for an observer on the planet to see it to rise and set twice per day. Because of its nearness, and since it moves parallel to the equator, observers near the poles cannot see it above the horizon. This small orbit may also lead to the future demise of Phobos, which may spiral into Mars.
Images taken of Phobos show that this moon has an irregular shape. This is due to its small size. At its widest, Phobos only spans a length of 26.8 km across.That is, it doesn't have enough gravity (which is dependent on its mass) to pull itself into a spherical form.
Because of its highly irregular shape, acceleration due to gravity varies in different places on its surface by up to 210%. Thus, a 1-lb object at its point of lowest gravity would weigh more than twice as much at its point of highest gravity.
Phobos and Deimos were both discovered by Asaph Hall, Sr. The largest crater on Phobos, Stickney crater, is named after Hall's wife, Chloe Angeline Stickney Hall. Stickney also has a smaller, but prominent, crater inside it named Limtoc. You can see both craters in the lower-right side of the image above.
On its Phobos-Grunt mission that is scheduled for launch two years from now (2011), the Russians plan to take along with them little critters like bacteria, spores, insects, fungi, etc. The purpose is to find out how these organisms react when subjected to prolonged space flight. This may give scientists ideas as to how humans might react themselves. The Phobos-Grunt unmanned mission was formerly intended for launch this year (2009).
Phobos, like Mars, is believed to contain traces of water. Much of the speculation is based on the low density of the moon. One highly possible reason may be that it is porous, while another could be that it contains water ice.
Because of this possibility, some people even believe that this moon might also have been inhabited by Martians before. Hence, one of the main objectives of the Phobos-Grunt mission is to find water or traces of it.
An article in Universe Today talks about Russia's plan of sending life to Phobos. Another one talks about Mars Express' close up view of Phobos.
NASA has an article that talks about both Phobos and Deimos and their seemingly unorthodox names. There's another one that features the doomed moon of Mars.
Here are two episodes at Astronomy Cast that you might want to check out as well:
Decelerating Black Holes, Earth-Sun Tidal Lock, and the Crushing Gravity of Dark Matter
Gravity
Filed under: Astronomy
Related stories on Universe Today
- Mars' Moon Phobos
- Amazing Image of the Martian Moon Phobos
- Mars Surveyor Snaps Phobos
- How Many Moons Does Mars Have?
- Phobos Might Only Have 10 Million Years to Live
