On Aug. 18, 1877, American astronomer Asaph Hall discovered the largest and innermost of Mars’ two natural satellites, Phobos. Phobos was named after the Greek God of fear, who was also the son of Ares (Mars).
There have been quite a few hypotheses put forward regarding Phobos’ origin. One theory is that Mars was once surrounded by objects similar to Phobos and Deimos (the smaller and outer moon). These objects could have been ejected into orbit by a collision with a large planetestimal.
Phobos orbits closer to a major planetary object than any other satellite in the solar system. It is relatively small by having only 17 miles in length. It is located 3,726 miles (6,000 km) above the center of Mars and rises the west, moves across the sky in a little more than four hours and sets in the east.
The moon maintains a rotational and orbital period of 7.66 hours.
One of the most fascinating aspects of Phobos is that it appears to be a type-D asteroid or a C-type rock and consists of carbonaceous chondrite material. Even astronomers were convinced for a short period of time that Phobos was an asteroid that was affected by the gravitational pull of Mars. However, it still remains to be a moon due to overwhelming evidence.
It has no atmosphere. Phobos’ climate is compared to a night in Antarctica – possibly even worse. The highest temperatures on Phobos have been recorded to be 25 degrees Fahrenheit (-4 degrees Celsius) and its lower temperatures have been measured at -170 degrees Fahrenheit (-112 degrees Celsius).
Phobos consists of a lot of craters. In fact, astronomers who have studied Phobos have given some of the craters names from “Gulliver’s Travels.” Craters Clustril, Gulliver, Limtoc, Skyresh and others are characters from the historic story.
Mostly due to its orbital period and reduction of tidal interactions, scientists expect that Phobos will either impact Mars or it will break up in the next 10 million years.
The Mars moon has been photographed extensively since 1971. Russia launched two probes, Phobos 1 and Phobos 2, but one was lost en route while the other failed to provide significant data.
The Russian Space Agency sent a sample return mission, Fobos-Grunt, to Phobos last year. In 2007, the European Space Agency began to construct a project with a projected launch date for 2016.
Scientists argue that human exploration of Phobos could be the starting point for human exploration of Mars.