Phobos and Deimos: Human Exploration of the Two Moons of

The Lunar and Planetary Institute and other sponsors are holding a conference on The Exploration of Phobos and Deimos, the moons of Mars. Phobos (fear) and Deimos (panic) were named after the horses that pulled the chariot of the Greek war god Ares. Scientists are planning to evaluate what humans could accomplish on Phobos and Deimos, and how might they use these moons to explore Mars.

Some believe it would be relatively easy to visit the moons since they could be visited “along the way” to the red planet. It is believed that Phobos and Deimos are captured asteroids, so the visit would give explorers the chance to study asteroids up close.

Phobos—the larger of the two moons (image above)—is an irregularly-shaped “potato”, about 13.5 kilometers long. It orbits less than 10,000 km from the surface of Mars, which is closer to a major planet than any other moon in our solar system. Phobos completes it’s orbit in just seven hours and 39 minutes—much faster than the planet’s own rotational period. As a result, Phobos appears on the Martian surface to rise in the west and set in the east. Phobos is so close to that will eventually—after millions of years—crash into the planet.

The idea of utilizing the moons in order to study is not a new idea. Pascal Lee, the chairman of the Institute and the principal investigator of NASA’s Haughton-Project has been saying for years that Phobos in particular is interesting for it’s own sake, but also as a key component for future human exploration of itself. Because one side always faces Mars, he has said that the Martian moon is “valuable real estate” for setting up a monitoring system.

“So here’s a strategic location for you…that’s where you will have the best view from Phobos, the best opportunity to monitor Mars.”

Phobos’s small size and irregular surface results in some unusual properties. It would be easy for people to put objects (or themselves) into orbit around the moon, for example. “The gravity on Phobos is so weak that if you were to throw a baseball at a reasonable speed, it would come back to you in about an hour, having gone all the way around Phobos, as long as it didn’t hit any part of Phobos,” he said. In addition, there are places on the surface where the gravity vector goes against the slope, because the center of shape of the moon is not coincident with the center of mass. “There are places on Phobos where you might actually fall uphill,” said Lee.

To date, the most significant effort to explore Phobos was the Soviet Union’s Phobos 1 and 2 missions of the late 1980s. Both missions ended in failure before arriving at the moon. However, space technology has come a long way in the last two decades. It is anticipated that the conference will reveal a clearer definition of the place Phobos and Deimos should hold in future planetary exploration, both robotic and manned.

Posted by Rebecca Sato

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