Phobos

Phobos is the larger and innermost of the two natural satellites of Mars, the other being Deimos. It was discovered by American astronomer Asaph Hall on August 18, 1877, at the United States Naval Observatory in Washington, D.C. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite, and the personification of fear ("phobos" in Greek means "fear").

Physical Characteristics

Phobos is a small, irregularly shaped body with a mean radius of about 11.267 km. It is heavily cratered and has a surface that is covered with a layer of fine dust and loose rocks, known as regolith. The most prominent feature on Phobos is the large impact crater named Stickney, which is about 9 km in diameter, nearly half the diameter of the moon itself.

The surface of Phobos is characterized by a series of grooves and streaks, which are believed to be the result of impacts and the moon's weak gravitational field. The grooves are typically less than 30 meters deep and can be up to 200 meters wide.

Orbit and Rotation

Phobos orbits Mars at a very close distance, with a semimajor axis of only 9,376 km. It is so close to Mars that it orbits the planet faster than Mars rotates on its axis, completing an orbit in just 7 hours and 39 minutes. This rapid orbit means that Phobos rises in the west and sets in the east, unlike most other moons in the solar system.

Phobos is in a synchronous rotation with Mars, meaning it always shows the same face to the planet. This is similar to how Earth's moon is tidally locked to Earth.

Origin and Composition

The origin of Phobos is still a subject of scientific debate. One hypothesis suggests that Phobos is a captured asteroid, possibly a C-type asteroid, due to its similar composition and low density. Another hypothesis is that Phobos formed from debris ejected into orbit around Mars after a large impact event.

Phobos is composed primarily of carbonaceous chondrite material, similar to that found in C-type asteroids. Its surface is dark, with a low albedo of 0.071, indicating that it is covered with a layer of dust and regolith.

Future and Exploration

Phobos is gradually spiraling inward towards Mars due to tidal forces, and it is expected to either crash into the planet or break apart to form a ring in about 30 to 50 million years.

Several missions have been proposed to explore Phobos, including sample return missions. The Phobos-Grunt mission launched by Russia in 2011 was intended to return samples from Phobos, but it failed to leave Earth's orbit.

Also see

• Deimos (moon)
• Mars
• Asteroid
• Tidal locking
• Mars Reconnaissance Orbiter