Phobos (moon)

Asaph Hall

Phobos ( Mars also I), from Greek Φόβος for " fear " is Deimos before the larger of the two natural satellites of Mars. It is named after Phobos, son and companion of the Greek war god Ares (Latin Mars).

Phobos was in 1877 along with Deimos by the American astronomer Asaph Hall at the U.S. Naval Observatory in Washington, DC discovered.

Properties

With a large semi-major axis of only 9378 kilometers, Phobos less than 6000 km flexing of the surface of Mars away around the planet and needed for a round only 7 hours, 39 minutes and 12 seconds. Its orbital period is thus much smaller than the period of rotation of Mars. With his sense of circulation rechtläufigen he overhauled as the surface of Mars and going there - unlike the other celestial bodies - in the west and set in the east. The sunrises or sunsets take place in an interval of 11 hours 6 minutes and 18 seconds, so that they take place twice a day, sometimes three times. The apparent size ( based on the diameter ) of Phobos at the culmination of the Mars equator is about half of our full Moon. The apparent brightness of the Vollphobos reached on Mars equator like to -8.9, or about one -twentieth of the full moon brightness. Due to the close proximity to Mars, it comes with every round of Phobos at a solar eclipse and lunar eclipse. However, the eclipses are not total, as the apparent diameter of the sun with about 20 minutes of arc is significantly larger than that of Phobos (see also: Phobosdurchgang from Mars ).

The orbital plane of Phobos is inclined only 1.08 ° from the equatorial plane of its planet. In contrast to the Deimos orbit of Phobos is within the critical for the tidal forces Roche limit of Mars and approaches the planet more and more. The distance can be reduced to 1.8 meters in a century, so that the satellite would crash in about 50 million years ago. However, it is believed that he is falling apart by the increasingly strong tidal forces before and form a ring around the planet, as the rings around Saturn.

Phobos has as Earth's Moon synchronous rotation, that is, he turns the Mars always the same side to. The Trabant is a very small irregularly shaped body that can be modeled approximately as a triaxial ellipsoid with axes of 27, 22 and 19 kilometers. The longest axis of the Martian moon showing through the synchronous rotation always to the planet. It has a mean density of 1.887 g / cm ³ (which is substantially less than that of the Mars ) and a volume of 5680 cubic kilometers on. It is coated with a layer of dust, called regolith, as he also found on our moon.

The composition is unclear, the most likely seems carbonaceous material, covered with approximately one meter of regolith ( composition similar to the regolith of the Moon consisting of silicon, oxygen, and iron). In addition, it may contain small amounts of water or methane. He leaves a trail of evaporating volatile elements behind them; most likely water.

Surface

The largest and most conspicuous crater Stickney on Phobos is called, after the birth name of Chloe Angeline Stickney Hall (1830-1892), the wife of the discoverer of Phobos. She encouraged her husband in search of the Mars moons, when the latter was about to give up. The crater measures about 10 km in diameter. The responsible must be felling - similar to the crater Herschel on Mimas - have almost tore the small moon.

Further, named after well-known astronomer craters on Phobos are:

  • D' Arrest - after Heinrich Louis d'Arrest,
  • Hall - by Asaph Hall,
  • Roche - by Édouard Albert Roche,
  • Sharpless - by Bevan Sharpless (1904-1950),
  • Todd - by David Todd (1845-1912),
  • Wendell - by Oliver Wendell ( 1845-1912 ).

Furthermore, Phobos has a named after Johannes Kepler (1571-1630) ridge called Kepler Dorsum ( Latin for " Kepler - back ").

A small, yet striking surface feature, the Phobos monolith looming sharply from its surroundings and is located near the Stickney crater.

Genesis

Its genesis is unclear. Because of its irregular shape was - as in the case of Deimos - widely believed that he is a captured asteroid of Mars that would have occurred in the outer asteroid belt. There are strong indications that Phobos is a so-called Rubble Pile, a debris body, held together only by gravity.

Two independent evaluations of measurements of the ESA's Mars Express and NASA 's Mars Global Surveyor in 2010, is now also contemplated that Phobos could have arisen due to a collision: crustal material was prepared by an asteroid impact on Mars in its orbit thrown where it is agglomerated. The material is also very porous and less dense than an asteroid. Also, it is discussed whether Phobos is the remnant of an older, destroyed moon.

Research

Due to its close proximity to Mars Phobos is in the telescope difficult to detect because it is literally outshined by Mars. Its angular separation is during an average opposition of Mars only a maximum of 16 seconds of arc of the planet's surface, but the planet is over 13 size classes, ie, more than 200,000 times brighter than its moon. He was only discovered in 1877 by Hall.

The Soviet probes Phobos 1 and 2 should land on the moon and " bounce around " with a clever mechanism on the moon. Shortly before being lost of the two probes were able to detect these gas eruptions on Phobos. Where this result is unknown; possibly it was water vapor.

On November 8, 2011 Russia launched the Phobos -Grunt mission, which was to collect soil samples on Phobos and bring back to Earth. China participated in this mission with its own Mars probe Yinghuo -1. The ignition of the engine, which was to bring the probe from Earth orbit to Mars course, failed, however. On 15 January 2012, the probe entered the Earth's atmosphere and burned up over the eastern Pacific. In addition, the two- probe mission of the Canadian Prime Space Agency and NASA mission Asaph are planned.

Close-ups of Phobos created in 1971 by Mariner 9, 1977 by Viking 1, 1988 by Fobos 2 and 1998 and 2003 by Mars Global Surveyor.

For the 1980 fallen meteorite Kaidun Phobos has been proposed as a possible origin of the body. If this is the case, Phobos would mainly consist of a material corresponding to the carbonaceous chondrites CR.

Cultural History

The existence of two small and so close to mars moons was purely fictitious mentioned in 1727 by Jonathan Swift, in the third part of Gulliver's Travels - Lemuel Gulliver - long before their discovery by Asaph Hall. The book tells the laputanischen astronomers would " know two smaller stars, or satellites, which run around Mars; this is the innermost from the center of the planet exactly three of its diameters away the outermost five; former completes its orbit in the period of ten, the latter in twenty-one and a half hours. "

This story ran in 1750 in Voltaire's novel Micromégas in which a giant from the star Sirius visited our solar system.

Remarkably, this anticipation is not only because of the similarity in relation to the track sizes and orbital periods, but also because all other hitherto known moons ( Earth's Moon, the Galilean moons of Jupiter and Saturn 's moon Titan ) have much longer orbital periods and make it difficult in as a template question come.

The American electronic musician Larry Fast dedicated to both the Martian moons Phobos and Deimos in 1978 appeared on his album Cords composition Phobos And Deimos Go To Mars.

Phobos and Deimos are scenes of the famous computer game Doom in 1993. Early as 1986 appeared the text adventure Leather Goddesses of Phobos.

1997 Phobos was the title of an album by the band Voivod. In interviews, said Michel Langevin, drummer of the band, that the moon is a perfect metaphor for the fear of their own demise due to the fact that he would fall into a few million years because of its orbit to Mars.

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