Phobos is one of Mars’ two moons, the other being Deimos. It is the larger and closer of the two, with several distinctive characteristics. Phobos is a small, irregularly shaped moon of Mars with a heavily cratered surface and prominent grooves. Its proximity to Mars and rapid orbital period makes it an intriguing object for study, and its eventual fate is expected to be a collision with Mars or disintegration into a ring. Phobos continues to be a key target for future exploration to better understand its composition and origin.

1. 1. Physical Characteristics

• • • Diameter: Phobos has a diameter of about 22.2 km (13.8 miles), making it relatively small compared to Earth’s Moon.
    • Mass: Its mass is approximately 1.0659 x 10^16 kg.
    • Shape: Phobos is not spherical but rather irregularly shaped, resembling a potato or a lumpy, elongated object.

 

1. 2. Orbit

• • • Orbit around Mars: Phobos orbits Mars at an average distance of about 9,377 km (5,827 miles), which is closer than any other moon in the Solar System to its parent planet.
    • Orbital Period: It has an extremely short orbital period of about 7 hours and 39 minutes, meaning it completes a full orbit around Mars in less than a Martian day. This is shorter than Mars’ rotation period, so Phobos rises in the west and sets in the east on Mars.
    • Tidal Forces: Phobos is gradually spiralling inward toward Mars due to tidal forces, and it is predicted that it will either crash into Mars or break apart to form a ring around the planet in about 50 million years.

 

1. 3. Surface Features

• • • Cratering: Phobos’ surface is heavily cratered, with the largest crater being Stickney Crater, which is about 9 km (5.6 miles) in diameter. Stickney Crater is prominent because it covers much of the moon’s surface.
    • Grooves: The surface also features long, linear grooves or ridges that appear to radiate from Stickney Crater and cover the moon’s surface. These grooves may have been formed by tectonic stresses or impacts.

 

1. 4. Composition

Phobos is composed of carbonaceous chondrite materials, which are rich in carbon and like some types of asteroids. Its surface is thought to be made of a mixture of rock and metal, with a dark, reddish colour.

 

1. 5. Exploration

• • • Spacecraft Observations: Phobos has been observed by several spacecraft, including NASA’s Mariner 9, Viking 1, Viking 2, and Mars Reconnaissance Orbiter. These missions have provided detailed images and data about Phobos’ surface and orbit.
    • Phobos Missions: The Phobos-Grunt mission was a Russian mission launched in 2011 intended to land on Phobos and return samples to Earth. However, the mission failed to leave Earth orbit. Other planned missions, such as those proposed by the Japanese space agency JAXA and ESA, aim to explore Phobos in more detail.

 

1. 6. Scientific Significance

Phobos is of interest to scientists because it could offer insights into the early Solar System and the formation of Mars’ moons. Its proximity to Mars and its irregular shape makes it an intriguing target for study.

 

1. 7. Interesting Facts

• • • Orbital Decay: Phobos is gradually getting closer to Mars due to tidal forces. It is predicted that it will eventually collide with Mars or break apart.
    • Rapid Orbit: Phobos’ rapid orbit around Mars means that it completes more than three orbits in a single Martian day, making it a fast-moving object in the Martian sky.