Moon of mars.
Discovery of phobos
In the early 17th century, German astronomer Johannes Kepler proposed that Mars might host two moons, given that it lay between the Earth and Jupiter, which were known to have one and four satellites. No evidence of such moons could be found. Although most people thought that Mars had no moons, American astronomer Asaph Hall performed a methodical study from the U.S. Naval Observatory in Washington, D.C., searching closer to the planet than previous surveys.
After searching without success, a frustrated Hall was about to give up, but his wife, Angelina, urged him to continue. The next night, Aug. 12, 1877, he discovered the moon that would later be known as Deimos. Six days later, he found Phobos as well. The two moons lay so close to the planet that they were hidden by the glare of Mars. Asteroid-size, they are also two of the smallest moons in the solar system, with the larger Phobos 7.24 times as massive as its companion, deimos
In Greek mythology, Phobos was one of the sons of the god of war Ares (Mars to the Romans). The twin sons attended their father in battle. Phobos means fear (as in phobia), while (especially in the sense of fleeing after a defeat), according to NASA.
examination of Phobos and its companion revealed more than their odd, non-spherical shapes. The two moons are dark gray in color, and heavily cratered. The moons are some of the darkest, least reflective objects in the solar system.
After observing the pair, scientists concluded that they were made of material similar to Type I or II carbonaceous chondrites, the material that makes up asteroids and dwarf planets. The composition and odd shape led some scientists to conclude that Phobos and Deimos came from the asteroid belt, with Jupiter's gravity long ago nudging them into orbit around Mars.
However, scientists aren't certain that the aestiroid belt is the source of the moons' birth. Both have a nearly circular orbit unusual for captured objects. The thin atmosphere of Mars would have a hard time providing the necessary braking to settle the pair into their present-day orbits. Similarly, the moons are not as dense as objects in the asteroid belt.
Instead, the moons may have formed as satellites around Mars, with dust and rock drawn together by gravity.
A more violent birth may have occurred by collision. A large impactor smashing into the red planet could have sent pieces flying into the air, where gravity may have drawn them together. An existing moon might also have been destroyed, creating the rubble that later formed Phobos and Deimos.
A recently combines the last two possibilities. According to researchers, a collision once scattered debris into a ring around Mars. As Phobos approaches the red planet, it will be torn into a ring again, scientists predict.
"Solving the riddle of how Mars' moons came to be will help us better understand how planets formed around our sun and, in turn, around other stars," Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate (SMD), said in a statement.
Traveling only 3,700 miles (6,000 kilometers) above the Martian surface, Phobos flies around the Red Planet three times a day. Crossing the sky in about four hours, the moon appears to rise in the west and set in the east.
Many science fiction films feature large moons dominating alien skies, but despite its proximity to its planet, Phobos is only a third as wide as the full moon seen from Earth. On the other hand, Mars dominates the horizon of Phobos, taking up a fourth of the sky.
Doomed
But Phobos won't zip around Mars forever. The doomed moon is spiraling inward at a rate of 1.8 centimeters (seven-tenths of an inch) per year, or 1.8 meters (about 6 feet) each century. Within 50 million years, the moon will either collide with its parent planet or be torn into rubble and scattered as a ring around Mars.
The unusual characteristics of Phobos, including its decaying orbit, led some scientists in the 1950s and 1960s to conclude that it was artificial. One prominent proponent was the science adviser to President Dwight D. Eisenhower. Further examination revealed that the moon bears stronger resemblance to a rubble pile than an artificial satellite, and images sent back from orbiting craft show that it formed in nature
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