Phobos (moon)
| Phobos | |
|---|---|
|
|
| Phobos in Color from Mars Reconnaissance Orbiter (2008) | |
| Provisional or systematic name | Mars I |
| Central body | Mars |
| Properties of the orbit | |
| Major semi-axis | 9378 km |
| Periapsis | 9236 km |
| Apoapsis | 9519 km |
| eccentricity | 0.0151 |
| Orbit inclination | 1.075 ° |
| Orbital time | 0.3189 d |
| Mean orbital velocity | 2.139 km / s |
| Physical Properties | |
| Albedo | 0.07 |
| Apparent brightness | 11.3-14.8 mag |
| Dimensions | (26.8 × 22.4 × 18.4) km |
| Dimensions | 1.072 x 10 16 kg |
| surface | approx. 6350 km 2 |
| Medium density | 1.887 g / cm 3 |
| Sidereal rotation | 7.65384 h |
| Axis inclination | 0 ° |
| Acceleration of gravity on the surface | 4–8 · 10 −3 m / s 2 |
| Escape speed | 10.3-12.2 m / s |
| Surface temperature | 163-268 K |
| discovery | |
| Explorer | |
| Date of discovery | 17th August 1877 |
| Remarks | Simply bound rotation. |
Phobos , from ancient Greek φόβος for " fear ", spoken [ foː.bɔs ], is one of the two moons of the planet Mars . Together with the even smaller Deimos , it was discovered by the American astronomer Asaph Hall at the US Naval Observatory in 1877 . It was named after Phobos , the son and companion of the Greek god of war Ares ( lat. Mars ).
properties
With a large orbit half-axis of only 9378 kilometers, Phobos moves less than 6000 km from the surface of Mars around the planet and needs only 7 hours, 39 minutes and 12 seconds for one orbit. Its orbital period is thus much smaller than the period of Mars' rotation. With its right-hand rotation it overtakes the surface of Mars and there - unlike the other celestial bodies - rises in the west and sets in the east. The rises and sets take place in an interval of 11 hours 6 minutes and 18 seconds, so that they take place twice, sometimes three times per Martian day. The orbital period is 3.958 times the size of Deimos and is close to a 1: 4 orbital resonance .
Like the Earth's moon, Phobos has a bound rotation , that is, it always turns the same side to Mars. The little satellite is a very irregularly shaped body that can be modeled approximately as a three-axis ellipsoid with axes of 27, 22 and 19 kilometers. The longest axis of the Martian moon always points to the planet due to the bound rotation.
The apparent brightness at the Martian equator reaches up to −8.9 mag, i.e. about a twentieth of the full moon brightness. Due to the close proximity to Mars, a lunar eclipse occurs with each orbit of the Phobos , as well as a passage of the Phobos in front of the sun at certain places on the surface of Mars, i.e. a (partial) solar eclipse . The solar eclipses are never total, because the apparent diameter of the sun is about 20 minutes of arc, significantly larger than that of Phobos.
The plane of the orbit of Phobos is only 1.08 ° inclined to the equatorial plane of his planet. In contrast to Deimos , the orbit of Phobos lies within the Roche limit of Mars, which is critical for tidal forces, and is getting closer and closer to the planet. The distance is reduced by 1.8 meters in a century, so that the Trabant would crash in about 50 million years. However, it is assumed that it will break apart before the ever-increasing tidal forces and form a ring around the planet, like the rings around Saturn .
Phobos has an average density of 1.887 g / cm³ (which is much lower than that of Mars) and a volume of 5680 cubic kilometers. Its composition is unclear, most likely carbonaceous material, covered with a layer of dust about a meter long regolith , which is similar to the regolith of the Earth's moon and consists of silicon, oxygen and iron. Phobos could also contain small amounts of water or methane. It traces a fine trail of volatile substance evaporating, most likely water.
A body in a near-surface orbit around Phobos would, assuming the moon hypothetically as approximately spherical for the calculation , need about 144 minutes to orbit and have an orbit speed of only 33 km / h. An astronaut who landed on Phobos could theoretically throw a tennis ball into orbit.
surface
The largest and most striking crater on Phobos is called Stickney , after the maiden name of Chloe Angeline Stickney Hall (1830-1892), the wife of the discoverer of Phobos. She encouraged her husband to search for the Martian moons when he was about to give up. The crater measures about nine kilometers in diameter. The responsible impact must - similar to the Herschel crater on Mimas - have almost torn the little moon apart.
Other craters on Phobos named after well-known astronomers are:
- D'Arrest - after Heinrich Louis d'Arrest ,
- Hall - after Asaph Hall ,
- Öpik - after Ernst Öpik ,
- Roche - after Édouard Albert Roche ,
- Sharpless - after Bevan Sharpless (1904–1950),
- Shklovsky - after Iossif Schklowski ,
- Todd - after David Todd (1845-1912),
- Wendell - after Oliver Wendell (1845-1912).
Phobos also has a mountain ridge named after Johannes Kepler (1571-1630) called Kepler Dorsum (Latin for “Kepler back”). Other craters and other formations are named after characters and locations from the novel Gulliver's Travels by Jonathan Swift .
On the surface of Phobos there are conspicuous, often parallel grooves, most of which emanate from the Stickney crater. According to an interpretation from 2015, they are comparable to " stretch marks " on human skin and are caused by the strong tidal forces to which the moon is exposed. According to computer simulations published in November 2018, however, these are traces of the debris hurled during the formation of Stickney, which rolled over the moon and in some cases made it all the way around the moon.
A small but noticeable surface feature is the so-called Phobos monolith , which stands out sharply from its surroundings and is located near the Stickney crater.
History of origin
Its history is unclear. Because of its irregular shape, as in the case of Deimos , it was widely believed to be a Mars-captured asteroid that was formed in the outer asteroid belt . There are many indications that Phobos is a so-called rubble pile , a piece of debris that is only held together by gravity.
Two independent evaluations of measurements by ESA's Mars Express and NASA's Mars Global Surveyor in 2010 now also consider that Phobos could have been formed as a result of a collision: Crustal material was orbited by an asteroid impact on Mars hurled where it agglomerated. The material is also very porous and less dense than an asteroid. It is also discussed whether Phobos is the remnant of an older, destroyed moon.
exploration
Phobos was discovered by Asaph Hall on August 17th, 1877 - six days after the smaller, but more remote Deimos. Due to its close proximity to Mars, Phobos is difficult to see in the telescope because it is literally outshone by Mars. During an average opposition of Mars, its angular distance is only a maximum of 16 arc seconds from the planet's surface, but the planet is over 13 size classes, that is, more than 200,000 times brighter than its moon.
The first close-ups of Phobos were taken in 1971 by Mariner 9 and in 1977 by Viking 1 . For the meteorite Kaidun , which fell to earth in 1980 , Phobos was suggested as a possible origin. Should that be the case, Phobos would consist mainly of a material corresponding to the carbonaceous CR chondrites .
The Soviet probes Fobos 1 and 2 were to land on the satellite in 1988/1989; in Fobos 2, a “jumper” with a sophisticated mechanism was supposed to “hop around” on the moon. However, both probes were lost before reaching their destination. However, Fobos was able to detect 2 gas eruptions on Phobos. Where these come from is unknown; maybe it was water vapor. After Fobos 2, the Mars Global Surveyor probe provided further close-up images of Phobos in 2003 .
On November 8, 2011, Russia started the Fobos-Grunt mission , which was supposed to collect soil samples on Phobos and bring them to earth. China participated in this mission with its own Yinghuo-1 Mars probe . However, the ignition of the engine that was supposed to bring the probe from Earth orbit to Mars course failed. On January 15, 2012, the probe entered the earth's atmosphere and burned up over the Eastern Pacific.
Cultural history
The early assumption that Mars has two moons goes back to Johannes Kepler , who postulated it in 1610 after the discovery of the four Galilean moons because he was convinced of harmonious relationships in the solar system . The existence of two small moons so close to Mars was purely fictitiously described by Jonathan Swift in the third part of Gulliver's Travels - Lemuel Gulliver - in 1727 - long before their discovery by Asaph Hall. He also goes into Kepler's third law , which shows the relationship between orbit sizes and cycle times. The book tells that Laputian astronomers “know of two smaller stars or satellites orbiting Mars; of which the innermost is exactly three and the outermost five of its diameters from the center of the planet; the former completes its cycle in ten, the latter in twenty-one and a half hours ”. This story was incorporated into Voltaire's novel Micromégas in 1750 , in which a giant from Sirius visits the solar system. This anticipation is remarkable not only because of the similarity in terms of orbital sizes and orbital times, but also because almost all of the moons known at the time - the Earth's moon , the four Galilean moons of Jupiter and the five largest moons of Saturn - have significantly longer orbital times and are therefore difficult to use as a template come into question. The Martian moons sought had to be much smaller and orbit their planets much closer.
Arthur C. Clarke's utopian narrative Hide-and-Seek (German:, Hide And Seek ') from the collection expedition to Earth ( Exiled in the future ) plays on and around Phobos.
The American electronic musician Larry Fast dedicated the composition Phobos and Deimos Go to Mars , published in 1978 on his album Cords , to the two Martian moons Phobos and Deimos .
Phobos and Deimos are the settings of the famous computer game Doom from 1993, and Unreal Tournament (UT99) also contains a card called "Phobos Moon". The text adventure Leather Goddesses of Phobos was published as early as 1986 .
In 1997 Phobos was the title of an album by the band Voivod . In interviews, Michel Langevin, the band's drummer, said that due to the fact that in a few million years it will fall on Mars because of its orbit, the moon is a perfect metaphor for fear of its own doom.
Web links
- Wiener Zeitung : Christian Pinter: The Sons of the God of War ( Memento from April 19, 2005 in the Internet Archive )
- Phobos: Doomed Moon of Mars - Astronomy Picture of the Day of December 3, 2006 (English).
- Phobos: Doomed Moon of Mars - Astronomy Picture of the Day from November 25, 2018 (English).
- DLR: Mars Express photographs Phobos from the shortest possible distance July 30, 2008
- DLR: New findings about the Martian moon Phobos October 16, 2008
- DLR: Images of the southern hemisphere in high resolution January 21, 2011
- DLR: New Mars Express images of the Martian moons Phobos and Deimos March 1, 2018
- Search NASA images
- ESA recordings - Mars Express mission
- NASA - Curiosity recording, Phobos pulls over Deimos over 2013 on YouTube
- Video: The Martian moons Phobos and Deimos . German Aerospace Center 2013, made available by the Technical Information Library (TIB), doi : 10.5446 / 12734 .
Individual evidence
- ↑ a b NASA Mars Fact Sheet , vestibules, orbital speed, surface and brightness calculated from it.
- ↑ a b Determination of mass by deflecting Mars Express (2008)
- ↑ a b New findings about the Martian moon Phobos (DLR; October 16, 2008)
- ↑ Stuart Clark: Cheap flights to Phobos. New Scientist , January 30, 2010, p. 29
- ↑ The Martian moon Phobos , accessed July 7, 2016
- ↑ Manfred Holl: Asaph Hall (1829-1907)
- ↑ a b Phobos in the Gazetteer of Planetary Nomenclature of the IAU (WGPSN) / USGS
- ↑ astropage.eu: The Martian moon Phobos is slowly falling apart - Astropage.eu / Wissenschaftsnachrichten. In: astropage.eu. Retrieved January 25, 2016 .
- ↑ Kenneth R. Ramsley, James W. Head: Origin of Phobos grooves: Testing the Stickney Crater ejecta model. Planetary and Space Science, November 2018, doi: 10.1016 / j.pss.2018.11.004
- ↑ scinexx .de: Phobos: Riddle of the trenches solved? 22nd November 2018
- ↑ Explosive Origin - The Martian Moon Phobos September 22, 2010, accessed on July 7, 2016
- ↑ How Mars came to its moons July 4, 2016, accessed July 7, 2016
- ↑ Planet and Satellite Names and Discoverers in the IAU's Gazetteer of Planetary Nomenclature (WGPSN) / USGS
- ↑ Calculated from the distances to the surface of Mars according to the information in the data tables of the article Mars (Planet) and this article.
- ↑ Mars probe trapped in Earth orbit at Raumfahrer.net, last accessed on November 10, 2011
- ↑ ESA: The five discoveries of the Martian moons.
- ↑ Uwe Topper: The riddle of the two Martian moons. (PDF)
- ↑ Dirk Lorenzen: The Martian moons of Laputa.
- ↑ Wolf-Rüdiger Mühlmann: The Power of the Machine , Interview with Michel Langevin, Rock Hard No. 124, 1997