Phobos and Deimos – An Introduction of Mar’s Moons

Mars, the fourth planet from the sun, is commonly known as the Red Planet due to its rusty colored soil. It is the only rocky planet (rocky planets are those that from the inner solar system and are not made of up of gases) that has more than one moon. Asaph Hall discovered two moons on Mars in 1877 and they are called Phobos and Deimos. The names Phobos and Deimos have been given to Mars’ moons after the names of twin sons of Ares, the god of war in Greek mythology. Mars was the Roman counterpart of Ares.

Moons that have been discovered orbiting Mars are different from the one that we see on earth and are among the smallest known moons of the solar system. They are more like captured asteroids by the planet’s gravity.

Mars Phobos MoonPhobos

Phobos, meaning panic or fear, is the larger moon of Mars and orbits very close to the planet, i.e. at 6,000 km. This makes it the only moon in the Solar System that orbits so close to its planet. Phobos completes its orbit in around seven hours and completes three orbits in one Martian day. In its longest dimension, Phobos is only 27/22.7 km long.

Scientists have discovered that Phobos is gradually moving closer to its home planet, and every 100 years it moves around 1.8 m closer to Mars’ surface. Additionally,  researchers from University of California, Berkeley have found that the gravitational pull of Mars, which is pulling Phobos towards it, has been opening grooves, as wide as 328–656 feet and as long as 33–98 feet, on the moon’s surface. It is expected that Phobos will either collide with Mars or break up to form a ring around Mars in about 50 million years.

Neptune’s moon Triton is also told to be in similar situation.

Mars Moon Deimos Deimos

Deimos, meaning terror, is the smallest of Mars’ moons measuring only about 15/12.6 km across. However,  it orbits farther than the Phobos, i.e. at a distance of about 23,460 km. It takes about 30 hours for Deimos to complete each orbit. Deimos is also less irregular in shape than Phobos.

Both Phobos and Deimos are dark, reddish in color, cratered, lumpy, covered with dust and loose rocks, and elongated in shape rather than round. According to scientists, both the Mars’ moons seem to be captured asteroids or may be made up of carbon rich rock and ice.

Although scientists have not yet confirmed how Mars’ moons were formed, but some, like Julien Salmon from the Southwest Research Institute in Boulder, Colorado and his associate Robin Canup claim that they were formed when a larger object was broken as a result of a collision. Mars’ moons have at least one thing common to the earth’s moon, for sure, and that is they both always present the same face to the Mars.

Scientists have been thinking to use one of the Mars’ moons as the astronauts’ base to observe the planet and to launch robots to the surface of the Mars.    


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