Ian
priscilla 1Moons of Mars
August 31st 2006 03:47
Mars has two tiny natural moons, Phobos and Deimos, which are thought to be captured asteroids.
Both satellites were discovered in 1877 by Asaph Hall, and are named after the characters Phobos (panic/fear) and Deimos (terror/dread) who, in Greek mythology, accompanied their father Ares, god of war, into battle. Ares was known as Mars to the Romans. Phobos is the largest with a diameter of 22.2 km with Deimos 12.6 km (The diameter of Mars is 227,936,637 km).
Both moons are tidally locked, always presenting the same face towards Mars. The graphic to the right shows the orbit of both moons to scale.
Searches have been conducted for additional satellites, but so far none have been found.
Since Phobos orbits Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. In about 50 million years Phobos will either impact the surface of Mars or more likely break up into a planetary ring. Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates. Therefore it rises in the west, moves comparatively rapidly across the sky (in 4 h 15 min or less) and sets in the east, approximately twice a day
Unlike Phobos, which orbits so fast that it actually rises in the west and sets in the east, Deimos rises in the east and sets in the west. Deimos is probably an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars. It is composed of carbon-rich rock and ice.
In part 3 chapter 3 (the "Voyage to Laputa") of Jonathan Swift's famous satire Gulliver's Travels, a fictional work written in 1726, the astronomers of Laputa are described as having discovered two satellites of Mars orbiting at distances of 3 and 5 Martian diameters, and periods of 10 and 21.5 hours, respectively. The actual orbital distances and periods of Phobos and Deimos are 1.4 and 3.5 Martian diameters, and 7.6 and 30.3 hours, respectively. This is regarded as a fascinating coincidence; no telescope in Swift's day would have been even remotely powerful enough to discover these satellites.
*The graphic showing the orbits of the moons is licensed under the Creative Commons Attribution ShareAlike License v. 2.5. It came from the Wikipedia page for Mars Moons.
**The photos of Phobos and Deimos are in the public domain as they were taken by NASA. They came from the Wikipedia pages for Phobos and Deimos.
***This article is licensed under the GNU Free Documentation Licence. It uses material from the Wikipedia articles Deimos (moon), Phobos (moon) and Mars' natural satellites.
Both satellites were discovered in 1877 by Asaph Hall, and are named after the characters Phobos (panic/fear) and Deimos (terror/dread) who, in Greek mythology, accompanied their father Ares, god of war, into battle. Ares was known as Mars to the Romans. Phobos is the largest with a diameter of 22.2 km with Deimos 12.6 km (The diameter of Mars is 227,936,637 km).
A simulated view of the orbits of Phobos and Deimos.
Searches have been conducted for additional satellites, but so far none have been found.
Since Phobos orbits Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. In about 50 million years Phobos will either impact the surface of Mars or more likely break up into a planetary ring. Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates. Therefore it rises in the west, moves comparatively rapidly across the sky (in 4 h 15 min or less) and sets in the east, approximately twice a day
A detailed image of Phobos, taken by Mars Global Surveyor on June 1, 2003.
Unlike Phobos, which orbits so fast that it actually rises in the west and sets in the east, Deimos rises in the east and sets in the west. Deimos is probably an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars. It is composed of carbon-rich rock and ice.
An image of Deimos taken by the Viking 1 orbiter.
In part 3 chapter 3 (the "Voyage to Laputa") of Jonathan Swift's famous satire Gulliver's Travels, a fictional work written in 1726, the astronomers of Laputa are described as having discovered two satellites of Mars orbiting at distances of 3 and 5 Martian diameters, and periods of 10 and 21.5 hours, respectively. The actual orbital distances and periods of Phobos and Deimos are 1.4 and 3.5 Martian diameters, and 7.6 and 30.3 hours, respectively. This is regarded as a fascinating coincidence; no telescope in Swift's day would have been even remotely powerful enough to discover these satellites.
*The graphic showing the orbits of the moons is licensed under the Creative Commons Attribution ShareAlike License v. 2.5. It came from the Wikipedia page for Mars Moons.
**The photos of Phobos and Deimos are in the public domain as they were taken by NASA. They came from the Wikipedia pages for Phobos and Deimos.
***This article is licensed under the GNU Free Documentation Licence. It uses material from the Wikipedia articles Deimos (moon), Phobos (moon) and Mars' natural satellites.
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