Phobos Facts

Phobos Facts
Phobos is the larger of Mars' two moons, the other being Deimos. It was discovered by American astronomer Asaph Hall, Sr. at the United States Naval Observatory in Washington D.C. on August 18, 1877. These two asteroid-size moons are two of the smallest moons in the Solar System. They appear to be composed of material similar to Type I or II carbonaceous chondrites which is the material that makes up asteroids and dwarf planets. Phobos is small, but seven times larger than Deimos. It orbits Mars at 3,700 miles (6,000 kilometers) from its surface. It is so close that it orbits Mars faster than Mars rotates and revolves around the Red Planet three times a day. It crosses the sky in about four hours. From the surface of Mars, it appears to rise in the west and set in the east.
Interesting Phobos Facts:
Hall named this moon after the Greek god, Phobos, a son of Ares (Mars) and Aphrodite (Venus), and the brother of Deimos. The name Phobos means fear or panic.
The origin of Mars' moons is controversial. Some scientists believe that they came from the asteroid belt, with Jupiter's gravity long ago nudging them into orbit around Mars. Others believed the moons may have formed as satellites around Mars, created by dust and rock that was drawn together by gravity. Another hypothesis is that Mars may have had an existing moon that may have collided with the red planet and created dust and rubble which drew together to form Phobos and Deimos.
Phobos is dark gray in color. It is one of the darkest and least reflective objects in the Solar System. It has an irregular, non-spherical shape.
Temperatures vary on Phobos. During the day, the highs on the sunlit side of the planet can reach minus 4 degrees Celsius (25 degrees Fahrenheit) and at night it can be as cold as minus 112 degrees Celsius (170 degrees Fahrenheit).
The large impact crater that dominates Phobos, Stickney, stretches nearly 6 miles (9.5 km) and covers most of its surface. The crater is so large that it likely came close to shattering the small moon. Hall named the crater after his dedicated wife, Chloe Angeline Stickney.
Every one hundred years, Phobos gets closer to Mars by about 2 meters and is predicted that within 30 to 50 million years it will either break up into a planetary ring or collide with its parent planet.
Phobos appears that it may be a rubble pile that is held together by a thin crust. There are long grooves on the surface that some believe to be early signs of the moon breaking apart due to tidal stresses caused by Mars' gravity. Others believe that the grooves could be remnants of the impact that caused the crater Stickney and that the grooves suggest loose material slid down inside the crater walls over time.
This moon does not have an atmosphere due to its low mass. It retains too little mass to be rounded under its own gravity.
On December 3, 1980, the Kaidun meteorite fell on a Soviet military base in Yemen. The single stone weighed about 4.4 pounds (2 kilograms) and was recovered from a small impact pit. In March 2004, it was suggested to be a piece of Phobos due to the existence of two extremely rare alkaline-rich clasts that were found in the meteorite.

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