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Not to be confused with the Greek god Phobos, or Phoebus, an epithet of the Greek god Apollo.

Phobos

False color image of Phobos from the Mars Reconnaissance Orbiter with Stickney crater on the right
Discovery
Discovered by	Asaph Hall
Discovery date	18 August 1877
Designations
Designation	Mars I
Pronunciation	[1] or [2]
Named after	Φόβος
Adjectives	Phobian[3] [4]
Orbital characteristics
Epoch J2000
Periapsis	9234.42 km[5]
Apoapsis	9517.58 km[5]
Semi-major axis	9376 km[5] (2.76 Mars radii/1.472 Earth radii)
Eccentricity	0.0151[5]
Orbital period (sidereal)	0.31891023 d (7 h 39 m 12 sec)
Average orbital speed	2.138 km/s[5]
Inclination	1.093° (to Mars’s equator) 0.046° (to local Laplace plane) 26.04° (to the ecliptic)
Satellite of	Mars
Physical characteristics
Dimensions	27 × 22 × 18 km[5]
Mean radius	11.2667 km (1.76941 mEarths)
Surface area	1548.3 km2[5] (3.03545 µEarths)
Volume	5783.61 km3 (5.33933 nEarths)
Mass	1.0659×1016 kg[5] (1.78477 nEarths)
Mean density	1.876 g/cm3[5]
Surface gravity	0.0057 m/s2[5] (581.4 µ g)
Escape velocity	11.39 m/s (41 km/h)[5]
Synodic rotation period	Synchronous
Equatorial rotation velocity	11.0 km/h (6.8 mph) (at longest axis)
Axial tilt	0°
Albedo	0.071±0.012[6]
Temperature	≈ 233 K
Apparent magnitude	11.8[7]

Phobos (; systematic designation: Mars I) is the innermost and larger of the two natural satellites of Mars,^[8] the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. It is named after Phobos, the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos.

Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi).^[5] Phobos orbits 6,000 km (3,700 mi) from the Martian surface, closer to its primary body than any other known planetary moon. It is so close that it orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day.

Phobos is one of the least reflective bodies in the Solar System, with an albedo of just 0.071. Surface temperatures range from about −4 °C (25 °F) on the sunlit side to −112 °C (−170 °F) on the shadowed side.^[9] The defining surface feature is the large impact crater, Stickney, which takes up a substantial proportion of the moon’s surface. The surface is also home to many grooves, with there being numerous theories as to how these grooves were formed.

Images and models indicate that Phobos may be a rubble pile held together by a thin crust that is being torn apart by tidal interactions.^[10] Phobos gets closer to Mars by about 2 cm per year, and it is predicted that within 30 to 50 million years it will either collide with the planet or break up into a planetary ring.^[9]

Discovery[edit]

Phobos was discovered by astronomer Asaph Hall on 18 August 1877 at the United States Naval Observatory in Washington, D.C., at about 09:14 Greenwich Mean Time. (Contemporary sources, using the pre-1925 astronomical convention that began the day at noon,^[11] give the time of discovery as 17 August at 16:06 Washington mean time, meaning 18 August 04:06 in the modern convention.)^[12][13][14] Hall had discovered Deimos, Mars’s other moon, a few days earlier on 12 August 1877 at about 07:48 UTC. The names, originally spelled Phobus and Deimus respectively, were suggested by Henry Madan (1838–1901), science master at Eton College, based on Greek mythology, in which Phobos is a companion to the god, Ares.^[15][16]

Shklovsky’s «Hollow Phobos» hypothesis[edit]

In the late 1950s and 1960s, the unusual orbital characteristics of Phobos led to speculations that it might be hollow.^[17] Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular acceleration of Phobos’s orbital motion, suggested a «thin sheet metal» structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin.^[18] Shklovsky based his analysis on estimates of the upper Martian atmosphere’s density, and deduced that for the weak braking effect to be able to account for the secular acceleration, Phobos had to be very light—one calculation yielded a hollow iron sphere 16 kilometers (9.9 mi) across but less than 6 cm thick.^[18][19] In a February 1960 letter to the journal Astronautics,^[20] Fred Singer, then science advisor to U.S. President Dwight D. Eisenhower, said of Shklovsky’s theory:

If the satellite is indeed spiraling inward as deduced from astronomical observation, then there is little alternative to the hypothesis that it is hollow and therefore Martian made. The big ‘if’ lies in the astronomical observations; they may well be in error. Since they are based on several independent sets of measurements taken decades apart by different observers with different instruments, systematic errors may have influenced them.^[20]

Subsequently, the systematic data errors that Singer predicted were found to exist, and the claim was called into doubt,^[21] and accurate measurements of the orbit available by 1969 showed that the discrepancy did not exist.^[22] Singer’s critique was justified when earlier studies were discovered to have used an overestimated value of 5 cm/yr for the rate of altitude loss, which was later revised to 1.8 cm/yr.^[23] The secular acceleration is now attributed to tidal effects, which create drag on the moon and therefore cause it spiral inward.^[24]

The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm³.^[25] Current observations are consistent with Phobos being a rubble pile.^[25] In addition, images obtained by the Viking probes in the 1970s clearly showed a natural object, not an artificial one. Nevertheless, mapping by the Mars Express probe and subsequent volume calculations do suggest the presence of voids and indicate that it is not a solid chunk of rock but a porous body.^[26] The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty.^[27]

Physical characteristics[edit]

Phobos has dimensions of 27 km × 22 km × 18 km,^[5] and retains too little mass to be rounded under its own gravity. Phobos does not have an atmosphere due to its low mass and low gravity.^[29] It is one of the least reflective bodies in the Solar System, with an albedo of about 0.071.^[6] Infrared spectra show that it has carbon-rich material found in carbonaceous chondrites, and its composition shows similarities to that of Mars’ surface.^[30] Phobos’s density is too low to be solid rock, and it is known to have significant porosity.^[31][32][33] These results led to the suggestion that Phobos might contain a substantial reservoir of ice. Spectral observations indicate that the surface regolith layer lacks hydration,^[34][35] but ice below the regolith is not ruled out.^[36][37]

Unlike Deimos, Phobos is heavily cratered,^[38] with one of the craters near the equator having a central peak despite the moon’s small size.^[39] The most prominent of these is the crater Stickney, a large impact crater some 9 km (5.6 mi) in diameter, which takes up a substantial proportion of the moon’s surface area. As with Mimas’s crater Herschel, the impact that created Stickney must have nearly shattered Phobos.^[40]

Many grooves and streaks also cover the oddly shaped surface. The grooves are typically less than 30 meters (98 ft) deep, 100 to 200 meters (330 to 660 ft) wide, and up to 20 kilometers (12 mi) in length, and were originally assumed to have been the result of the same impact that created Stickney. Analysis of results from the Mars Express spacecraft, however, revealed that the grooves are not in fact radial to Stickney, but are centered on the leading apex of Phobos in its orbit (which is not far from Stickney). Researchers suspect that they have been excavated by material ejected into space by impacts on the surface of Mars. The grooves thus formed as crater chains, and all of them fade away as the trailing apex of Phobos is approached. They have been grouped into 12 or more families of varying age, presumably representing at least 12 Martian impact events.^[41] However, in November 2018, following further computational probability analysis, astronomers concluded that the many grooves on Phobos were caused by boulders, ejected from the asteroid impact that created Stickney crater. These boulders rolled in a predictable pattern on the surface of the moon.^[42][43]

Faint dust rings produced by Phobos and Deimos have long been predicted but attempts to observe these rings have, to date, failed.^[44] Recent images from Mars Global Surveyor indicate that Phobos is covered with a layer of fine-grained regolith at least 100 meters thick; it is hypothesized to have been created by impacts from other bodies, but it is not known how the material stuck to an object with almost no gravity.^[45]

The unique Kaidun meteorite that fell on a Soviet military base in Yemen in 1980 has been hypothesized to be a piece of Phobos, but this has been difficult to verify because little is known about the exact composition of Phobos.^[46][47]

A person who weighs 68 kilogram-force (150 pounds) on Earth would weigh about 40 gram-force (2 ounces) standing on the surface of Phobos.

Named geological features[edit]

Geological features on Phobos are named after astronomers who studied Phobos and people and places from Jonathan Swift’s Gulliver’s Travels.^[48]

Craters on Phobos[edit]

A number of craters have been named, and are listed in the following table.^[49]

Crater	Coordinates	Diameter (km)	Approval Year	Eponym	Ref	Annotated map
Clustril	60°N 91°W / 60°N 91°W	3.4	2006	Character in Lilliput who informed Flimnap that his wife had visited Gulliver privately in Jonathan Swift’s novel Gulliver’s Travels	WGPSN	SKYRESH FLIMNAP GRILDRIG RELDRESAL CLUSTRIL GULLIVER DRUNLO STICKNEY LIMTOC KEPLER DORSUM LAPUTA REGIO? LAGADO PLANITIA? SHKLOVSKY? WENDELL? Öpik
D’Arrest	39°S 179°W / 39°S 179°W	2.1	1973	Heinrich Louis d’Arrest; German/Danish astronomer (1822–1875)	WGPSN
Drunlo	36°30′N 92°00′W / 36.5°N 92°W	4.2	2006	Character in Lilliput who informed Flimnap that his wife had visited Gulliver privately in Gulliver’s Travels	WGPSN
Flimnap	60°N 10°E / 60°N 10°E	1.5	2006	Treasurer of Lilliput in Gulliver’s Travels	WGPSN
Grildrig	81°N 165°E / 81°N 165°E	2.6	2006	Name given to Gulliver by the farmer’s daughter Glumdalclitch in the giants’ country Brobdingnag in Gulliver’s Travels	WGPSN
Gulliver	62°N 163°W / 62°N 163°W	5.5	2006	Lemuel Gulliver; surgeon captain and voyager in Gulliver’s Travels	WGPSN
Hall	80°S 150°E / 80°S 150°E	5.4	1973	Asaph Hall; American astronomer discoverer of Phobos and Deimos (1829–1907)	WGPSN
Limtoc	11°S 54°W / 11°S 54°W	2	2006	General in Lilliput who prepared articles of impeachment against Gulliver in Gulliver’s Travels	WGPSN
Öpik	7°S 63°E / 7°S 63°E	2	2011	Ernst J. Öpik, Estonian astronomer (1893–1985)	WGPSN
Reldresal	41°N 39°W / 41°N 39°W	2.9	2006	Secretary for Private Affairs in Lilliput; Gulliver’s friend in Gulliver’s Travels	WGPSN
Roche	53°N 177°E / 53°N 177°E	2.3	1973	Édouard Roche; French astronomer (1820–1883)	WGPSN
Sharpless	27°30′S 154°00′W / 27.5°S 154°W	1.8	1973	Bevan Sharpless; American astronomer (1904–1950)	WGPSN
Shklovsky	24°N 112°E / 24°N 112°E	2	2011	Iosif Shklovsky, Soviet astronomer (1916–1985)	WGPSN
Skyresh	52°30′N 40°00′E / 52.5°N 40°E	1.5	2006	Skyresh Bolgolam; High Admiral of the Lilliput council who opposed Gulliver’s plea for freedom and accused him of being a traitor in Gulliver’s Travels	WGPSN
Stickney	1°N 49°W / 1°N 49°W	9	1973	Angeline Stickney (1830–1892); wife of American astronomer Asaph Hall (above)	WGPSN
Todd	9°S 153°W / 9°S 153°W	2.6	1973	David Peck Todd; American astronomer (1855–1939)	WGPSN
Wendell	1°S 132°W / 1°S 132°W	1.7	1973	Oliver Wendell; American astronomer (1845–1912)	WGPSN

Other named features[edit]

There is one named regio, Laputa Regio, and one named planitia, Lagado Planitia; both are named after places in Gulliver’s Travels (the fictional Laputa, a flying island, and Lagado, imaginary capital of the fictional nation Balnibarbi).^[50] The only named ridge on Phobos is Kepler Dorsum, named after the astronomer Johannes Kepler.^[51]

Orbital characteristics[edit]

The orbital motion of Phobos has been intensively studied, making it «the best studied natural satellite in the Solar System» in terms of orbits completed.^[52] Its close orbit around Mars produces some unusual effects. With an altitude of 5,989 km (3,721 mi), Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates.^[32] Therefore, from the point of view of an observer on the surface of Mars, 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 each Martian day (every 11 h 6 min). Because it is close to the surface and in an equatorial orbit, it cannot be seen above the horizon from latitudes greater than 70.4°. Its orbit is so low that its angular diameter, as seen by an observer on Mars, varies visibly with its position in the sky. Seen at the horizon, Phobos is about 0.14° wide; at zenith it is 0.20°, one-third as wide as the full Moon as seen from Earth. By comparison, the Sun has an apparent size of about 0.35° in the Martian sky. Phobos’s phases, inasmuch as they can be observed from Mars, take 0.3191 days (Phobos’s synodic period) to run their course, a mere 13 seconds longer than Phobos’s sidereal period.

Solar transits[edit]

An observer situated on the Martian surface, in a position to observe Phobos, would see regular transits of Phobos across the Sun. Several of these transits have been photographed by the Mars Rover Opportunity. During the transits, Phobos’s shadow is cast on the surface of Mars; an event which has been photographed by several spacecraft. Phobos is not large enough to cover the Sun’s disk, and so cannot cause a total eclipse.^[53]

Predicted destruction[edit]

Tidal deceleration is gradually decreasing the orbital radius of Phobos by approximately two meters every 100 years,^[10] and with decreasing orbital radius the likelihood of breakup due to tidal forces increases, estimated in approximately 30–50 million years,^[10][52] with one study’s estimate being about 43 million years.^[54]

Phobos’s grooves were long thought to be fractures caused by the impact that formed the Stickney crater. Other modelling suggested since the 1970s support the idea that the grooves are more like «stretch marks» that occur when Phobos gets deformed by tidal forces, but in 2015 when the tidal forces were calculated and used in a new model, the stresses were too weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded by a layer of powdery regolith about 100 m (330 ft) thick. Stress fractures calculated for this model line up with the grooves on Phobos. The model is supported with the discovery that some of the grooves are younger than others, implying that the process that produces the grooves is ongoing.^{[10][55][inconsistent]}

Given Phobos’s irregular shape and assuming that it is a pile of rubble (specifically a Mohr–Coulomb body), it will eventually break up due to tidal forces when it reaches approximately 2.1 Mars radii.^[56] When Phobos is broken up, it will form a planetary ring around Mars.^[57] This predicted ring may last from 1 million to 100 million years. The fraction of the mass of Phobos that will form the ring depends on the unknown internal structure of Phobos. Loose, weakly bound material will form the ring. Components of Phobos with strong cohesion will escape tidal breakup and will enter the Martian atmosphere.^[58]

Origin[edit]

The origin of the Martian moons is still controversial.^[59] Phobos and Deimos both have much in common with carbonaceous C-type asteroids, with spectra, albedo, and density very similar to those of C- or D-type asteroids.^[60] Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids.^[61][62] Both moons have very circular orbits which lie almost exactly in Mars’s equatorial plane, and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most probably by a combination of atmospheric drag and tidal forces,^[63] although it is not clear that sufficient time is available for this to occur for Deimos.^[59] Capture also requires dissipation of energy. The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric braking.^[59] Geoffrey A. Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces.^[62][64]

Phobos could be a second-generation Solar System object that coalesced in orbit after Mars formed, rather than forming concurrently out of the same birth cloud as Mars.^[65]

Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal.^[66] The high porosity of the interior of Phobos (based on the density of 1.88 g/cm³, voids are estimated to comprise 25 to 35 percent of Phobos’s volume) is inconsistent with an asteroidal origin.^[27] Observations of Phobos in the thermal infrared suggest a composition containing mainly phyllosilicates, which are well known from the surface of Mars. The spectra are distinct from those of all classes of chondrite meteorites, again pointing away from an asteroidal origin.^[67] Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit,^[68] similar to the prevailing theory for the origin of Earth’s moon.

Some areas of the surface have turned out to be reddish in color, while others are bluish. The hypothesis is that gravity pull from Mars makes the reddish regolith move over the surface, exposing relatively fresh, unweathered and bluish material from the moon, while the regolith covering it over time has been weathered due to exposure of solar radiation. Because the blue rock differs from known Martian rock, it could contradict the theory that the moon is formed from leftover planetary material after the impact of a large object.^[69]

Most recently, Amirhossein Bagheri (ETH Zurich), Amir Khan (ETH Zurich), Michael Efroimsky (US Naval Observatory) and their colleagues proposed a new hypothesis on the origin of the moons. By analyzing the seismic and orbital data from Mars InSight Mission and other missions, they proposed that the moons are born from disruption of a common parent body around 1 to 2.7 Billion years ago. The common progenitor of Phobos and Deimos was most probably hit by another object and shattered to form Phobos and Deimos.^[70]

Exploration[edit]

Launched missions[edit]

Phobos has been photographed in close-up by several spacecraft whose primary mission has been to photograph Mars. The first was Mariner 7 in 1969, followed by Mariner 9 in 1971, Viking 1 in 1977, Phobos 2 in 1989^[71] Mars Global Surveyor in 1998 and 2003, Mars Express in 2004, 2008, 2010^[72] and 2019, and Mars Reconnaissance Orbiter in 2007 and 2008. On 25 August 2005, the Spirit rover, with an excess of energy due to wind blowing dust off of its solar panels, took several short-exposure photographs of the night sky from the surface of Mars, and was able to successfully photograph both Phobos and Deimos.^[73]

The Soviet Union undertook the Phobos program with two probes, both launched successfully in July 1988. Phobos 1 was accidentally shut down by an erroneous command from ground control issued in September 1988 and lost while the craft was still en route. Phobos 2 arrived at the Mars system in January 1989 and, after transmitting a small amount of data and imagery but shortly before beginning its detailed examination of Phobos’s surface, the probe abruptly ceased transmission due either to failure of the onboard computer or of the radio transmitter, already operating on the backup power. Other Mars missions collected more data, but no dedicated sample return mission has been performed.^{[citation needed]}

The Russian Space Agency launched a sample return mission to Phobos in November 2011, called Fobos-Grunt. The return capsule also included a life science experiment of The Planetary Society, called Living Interplanetary Flight Experiment, or LIFE.^[74] A second contributor to this mission was the China National Space Administration, which supplied a surveying satellite called «Yinghuo-1», which would have been released in the orbit of Mars, and a soil-grinding and sieving system for the scientific payload of the Phobos lander.^[75][76] However, after achieving Earth orbit, the Fobos–Grunt probe failed to initiate subsequent burns that would have sent it to Mars. Attempts to recover the probe were unsuccessful and it crashed back to Earth in January 2012.^[77]

On 1 July 2020, the Mars orbiter of the Indian Space Research Organisation was able to capture photos of the body from 4,200 km away.^[78]

Missions considered[edit]

In 1997 and 1998, the Aladdin mission was selected as a finalist in the NASA Discovery Program. The plan was to visit both Phobos and Deimos, and launch projectiles at the satellites. The probe would collect the ejecta as it performed a slow flyby (~1 km/s).^[79] These samples would be returned to Earth for study three years later.^[80][81] The Principal Investigator was Dr. Carle Pieters of Brown University. The total mission cost, including launch vehicle and operations was $247.7 million.^[82] Ultimately, the mission chosen to fly was MESSENGER, a probe to Mercury.^[83]

In 2007, the European aerospace subsidiary EADS Astrium was reported to have been developing a mission to Phobos as a technology demonstrator. Astrium was involved in developing a European Space Agency plan for a sample return mission to Mars, as part of the ESA’s Aurora programme, and sending a mission to Phobos with its low gravity was seen as a good opportunity for testing and proving the technologies required for an eventual sample return mission to Mars. The mission was envisioned to start in 2016, was to last for three years. The company planned to use a «mothership», which would be propelled by an ion engine, releasing a lander to the surface of Phobos. The lander would perform some tests and experiments, gather samples in a capsule, then return to the mothership and head back to Earth where the samples would be jettisoned for recovery on the surface.^[84]

Proposed missions[edit]

In 2007, the Canadian Space Agency funded a study by Optech and the Mars Institute for an uncrewed mission to Phobos known as Phobos Reconnaissance and International Mars Exploration (PRIME). A proposed landing site for the PRIME spacecraft is at the «Phobos monolith», a prominent object near Stickney crater.^[85][86][87] The PRIME mission would be composed of an orbiter and lander, and each would carry 4 instruments designed to study various aspects of Phobos’s geology.^[88]

In 2008, NASA Glenn Research Center began studying a Phobos and Deimos sample return mission that would use solar electric propulsion. The study gave rise to the «Hall» mission concept, a New Frontiers-class mission under further study as of 2010.^[89]

Another concept of a sample return mission from Phobos and Deimos is OSIRIS-REx II, which would use heritage technology from the first OSIRIS-REx mission.^[90]

As of January 2013, a new Phobos Surveyor mission is currently under development by a collaboration of Stanford University, NASA’s Jet Propulsion Laboratory, and the Massachusetts Institute of Technology.^[91] The mission is currently in the testing phases, and the team at Stanford plans to launch the mission between 2023 and 2033.^[91]

In March 2014, a Discovery class mission was proposed to place an orbiter in Mars orbit by 2021 to study Phobos and Deimos through a series of close flybys. The mission is called Phobos And Deimos & Mars Environment (PADME).^[92][93][94] Two other Phobos missions that were proposed for the Discovery 13 selection included a mission called Merlin, which would flyby Deimos but actually orbit and land on Phobos, and another one is Pandora which would orbit both Deimos and Phobos.^[95]

The Japanese Aerospace Exploration Agency (JAXA) unveiled on 9 June 2015 the Martian Moons Exploration (MMX), a sample return mission targeting Phobos.^[96] MMX will land and collect samples from Phobos multiple times, along with conducting Deimos flyby observations and monitoring Mars’s climate. By using a corer sampling mechanism, the spacecraft aims to retrieve a minimum 10 g amount of samples.^[97] NASA, ESA, DLR, and CNES^[98] are also participating in the project, and will provide scientific instruments.^[99][100] The U.S. will contribute the Neutron and Gamma-Ray
Spectrometer (NGRS), and France the Near IR Spectrometer (NIRS4/MacrOmega).^[97][101] Although the mission has been selected for implementation^[102][103] and is now beyond proposal stage, formal project approval by JAXA has been postponed following the Hitomi mishap.^[104] Development and testing of key components, including the sampler, is currently ongoing.^[105] As of 2017, MMX is scheduled to be launched in 2024, and will return to Earth five years later.^[97]

Russia plans to repeat Fobos-Grunt mission in the late 2020s, and the European Space Agency is assessing a sample-return mission for 2024 called Phootprint.^[106][107]

Human missions[edit]

Phobos has been proposed as an early target for a human mission to Mars. The teleoperation of robotic scouts on Mars by humans on Phobos could be conducted without significant time delay, and planetary protection concerns in early Mars exploration might be addressed by such an approach.^[108]

Phobos has been proposed as an early target for a crewed mission to Mars because a landing on Phobos would be considerably less difficult and expensive than a landing on the surface of Mars itself. A lander bound for Mars would need to be capable of atmospheric entry and subsequent return to orbit without any support facilities, or would require the creation of support facilities in-situ. A lander instead bound for Phobos could be based on equipment designed for lunar and asteroid landings.^[109] Furthermore, due to Phobos’s very weak gravity, the delta-v required to land on Phobos and return is only 80% of that required for a trip to and from the surface of the Moon.^[110]

It has been proposed that the sands of Phobos could serve as a valuable material for aerobraking during a Mars landing. A relatively small amount of chemical fuel brought from Earth could be used to lift a large amount of sand from the surface of Phobos to a transfer orbit. This sand could be released in front of a spacecraft during the descent maneuver causing a densification of the atmosphere just in front of the spacecraft.^[111][112]

While human exploration of Phobos could serve as a catalyst for the human exploration of Mars, it could be scientifically valuable in its own right.^[113]

Phobos as a space elevator for Mars[edit]

Phobos is synchronously orbiting Mars, where the same face stays facing the planet at 6,000 km (3,700 mi) above the Martian surface. A space elevator could extend down from Phobos to Mars 6,000 km, about 28 kilometers from the surface, and just out of the atmosphere of Mars. A similar space elevator cable could extend out 6,000 km the opposite direction that would counterbalance Phobos. In total the space elevator would extend out over 12,000 km which would be below areostationary orbit of Mars (17,032 km). A rocket launch would still be needed to get the rocket and cargo to the beginning of the space elevator 28 km above the surface. The surface of Mars is rotating at 0.25 km/s at the equator and the bottom of the space elevator would be rotating around Mars at 0.77 km/s, so only 0.52 km/s of delta-v would be needed to get to the space elevator. Phobos orbits at 2.15 km/s and the outermost part of the space elevator would rotate around Mars at 3.52 km/s.^[114]

See also[edit]

• List of natural satellites
• List of missions to the moons of Mars
• Phobos and Deimos in fiction
• Phobos monolith
• Transit of Phobos from Mars

References[edit]

External links[edit]

• Phobos Profile at NASA’s Solar System Exploration site
• HiRISE Phobos
• USGS Phobos nomenclature
• Asaph Hall and the Moons of Mars
• Flight around Phobos (movie)
• Animation of Phobos
• Scale of Phobos [1] [2]
• Mars Express view of Phobos
• Phobos cartography (MIIGAiK Extraterrestrial Laboratory)

Not to be confused with the Greek god Phobos, or Phoebus, an epithet of the Greek god Apollo.

Phobos

False color image of Phobos from the Mars Reconnaissance Orbiter with Stickney crater on the right
Discovery
Discovered by	Asaph Hall
Discovery date	18 August 1877
Designations
Designation	Mars I
Pronunciation	[1] or [2]
Named after	Φόβος
Adjectives	Phobian[3] [4]
Orbital characteristics
Epoch J2000
Periapsis	9234.42 km[5]
Apoapsis	9517.58 km[5]
Semi-major axis	9376 km[5] (2.76 Mars radii/1.472 Earth radii)
Eccentricity	0.0151[5]
Orbital period (sidereal)	0.31891023 d (7 h 39 m 12 sec)
Average orbital speed	2.138 km/s[5]
Inclination	1.093° (to Mars’s equator) 0.046° (to local Laplace plane) 26.04° (to the ecliptic)
Satellite of	Mars
Physical characteristics
Dimensions	27 × 22 × 18 km[5]
Mean radius	11.2667 km (1.76941 mEarths)
Surface area	1548.3 km2[5] (3.03545 µEarths)
Volume	5783.61 km3 (5.33933 nEarths)
Mass	1.0659×1016 kg[5] (1.78477 nEarths)
Mean density	1.876 g/cm3[5]
Surface gravity	0.0057 m/s2[5] (581.4 µ g)
Escape velocity	11.39 m/s (41 km/h)[5]
Synodic rotation period	Synchronous
Equatorial rotation velocity	11.0 km/h (6.8 mph) (at longest axis)
Axial tilt	0°
Albedo	0.071±0.012[6]
Temperature	≈ 233 K
Apparent magnitude	11.8[7]

Phobos (; systematic designation: Mars I) is the innermost and larger of the two natural satellites of Mars,^[8] the other being Deimos. The two moons were discovered in 1877 by American astronomer Asaph Hall. It is named after Phobos, the Greek god of fear and panic, who is the son of Ares (Mars) and twin brother of Deimos.

Phobos is a small, irregularly shaped object with a mean radius of 11 km (7 mi).^[5] Phobos orbits 6,000 km (3,700 mi) from the Martian surface, closer to its primary body than any other known planetary moon. It is so close that it orbits Mars much faster than Mars rotates, and completes an orbit in just 7 hours and 39 minutes. As a result, from the surface of Mars it appears to rise in the west, move across the sky in 4 hours and 15 minutes or less, and set in the east, twice each Martian day.

Phobos is one of the least reflective bodies in the Solar System, with an albedo of just 0.071. Surface temperatures range from about −4 °C (25 °F) on the sunlit side to −112 °C (−170 °F) on the shadowed side.^[9] The defining surface feature is the large impact crater, Stickney, which takes up a substantial proportion of the moon’s surface. The surface is also home to many grooves, with there being numerous theories as to how these grooves were formed.

Images and models indicate that Phobos may be a rubble pile held together by a thin crust that is being torn apart by tidal interactions.^[10] Phobos gets closer to Mars by about 2 cm per year, and it is predicted that within 30 to 50 million years it will either collide with the planet or break up into a planetary ring.^[9]

Discovery[edit]

Phobos was discovered by astronomer Asaph Hall on 18 August 1877 at the United States Naval Observatory in Washington, D.C., at about 09:14 Greenwich Mean Time. (Contemporary sources, using the pre-1925 astronomical convention that began the day at noon,^[11] give the time of discovery as 17 August at 16:06 Washington mean time, meaning 18 August 04:06 in the modern convention.)^[12][13][14] Hall had discovered Deimos, Mars’s other moon, a few days earlier on 12 August 1877 at about 07:48 UTC. The names, originally spelled Phobus and Deimus respectively, were suggested by Henry Madan (1838–1901), science master at Eton College, based on Greek mythology, in which Phobos is a companion to the god, Ares.^[15][16]

Shklovsky’s «Hollow Phobos» hypothesis[edit]

In the late 1950s and 1960s, the unusual orbital characteristics of Phobos led to speculations that it might be hollow.^[17] Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky, studying the secular acceleration of Phobos’s orbital motion, suggested a «thin sheet metal» structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin.^[18] Shklovsky based his analysis on estimates of the upper Martian atmosphere’s density, and deduced that for the weak braking effect to be able to account for the secular acceleration, Phobos had to be very light—one calculation yielded a hollow iron sphere 16 kilometers (9.9 mi) across but less than 6 cm thick.^[18][19] In a February 1960 letter to the journal Astronautics,^[20] Fred Singer, then science advisor to U.S. President Dwight D. Eisenhower, said of Shklovsky’s theory:

If the satellite is indeed spiraling inward as deduced from astronomical observation, then there is little alternative to the hypothesis that it is hollow and therefore Martian made. The big ‘if’ lies in the astronomical observations; they may well be in error. Since they are based on several independent sets of measurements taken decades apart by different observers with different instruments, systematic errors may have influenced them.^[20]

Subsequently, the systematic data errors that Singer predicted were found to exist, and the claim was called into doubt,^[21] and accurate measurements of the orbit available by 1969 showed that the discrepancy did not exist.^[22] Singer’s critique was justified when earlier studies were discovered to have used an overestimated value of 5 cm/yr for the rate of altitude loss, which was later revised to 1.8 cm/yr.^[23] The secular acceleration is now attributed to tidal effects, which create drag on the moon and therefore cause it spiral inward.^[24]

The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm³.^[25] Current observations are consistent with Phobos being a rubble pile.^[25] In addition, images obtained by the Viking probes in the 1970s clearly showed a natural object, not an artificial one. Nevertheless, mapping by the Mars Express probe and subsequent volume calculations do suggest the presence of voids and indicate that it is not a solid chunk of rock but a porous body.^[26] The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty.^[27]

Physical characteristics[edit]

Phobos has dimensions of 27 km × 22 km × 18 km,^[5] and retains too little mass to be rounded under its own gravity. Phobos does not have an atmosphere due to its low mass and low gravity.^[29] It is one of the least reflective bodies in the Solar System, with an albedo of about 0.071.^[6] Infrared spectra show that it has carbon-rich material found in carbonaceous chondrites, and its composition shows similarities to that of Mars’ surface.^[30] Phobos’s density is too low to be solid rock, and it is known to have significant porosity.^[31][32][33] These results led to the suggestion that Phobos might contain a substantial reservoir of ice. Spectral observations indicate that the surface regolith layer lacks hydration,^[34][35] but ice below the regolith is not ruled out.^[36][37]

Unlike Deimos, Phobos is heavily cratered,^[38] with one of the craters near the equator having a central peak despite the moon’s small size.^[39] The most prominent of these is the crater Stickney, a large impact crater some 9 km (5.6 mi) in diameter, which takes up a substantial proportion of the moon’s surface area. As with Mimas’s crater Herschel, the impact that created Stickney must have nearly shattered Phobos.^[40]

Many grooves and streaks also cover the oddly shaped surface. The grooves are typically less than 30 meters (98 ft) deep, 100 to 200 meters (330 to 660 ft) wide, and up to 20 kilometers (12 mi) in length, and were originally assumed to have been the result of the same impact that created Stickney. Analysis of results from the Mars Express spacecraft, however, revealed that the grooves are not in fact radial to Stickney, but are centered on the leading apex of Phobos in its orbit (which is not far from Stickney). Researchers suspect that they have been excavated by material ejected into space by impacts on the surface of Mars. The grooves thus formed as crater chains, and all of them fade away as the trailing apex of Phobos is approached. They have been grouped into 12 or more families of varying age, presumably representing at least 12 Martian impact events.^[41] However, in November 2018, following further computational probability analysis, astronomers concluded that the many grooves on Phobos were caused by boulders, ejected from the asteroid impact that created Stickney crater. These boulders rolled in a predictable pattern on the surface of the moon.^[42][43]

Faint dust rings produced by Phobos and Deimos have long been predicted but attempts to observe these rings have, to date, failed.^[44] Recent images from Mars Global Surveyor indicate that Phobos is covered with a layer of fine-grained regolith at least 100 meters thick; it is hypothesized to have been created by impacts from other bodies, but it is not known how the material stuck to an object with almost no gravity.^[45]

The unique Kaidun meteorite that fell on a Soviet military base in Yemen in 1980 has been hypothesized to be a piece of Phobos, but this has been difficult to verify because little is known about the exact composition of Phobos.^[46][47]

A person who weighs 68 kilogram-force (150 pounds) on Earth would weigh about 40 gram-force (2 ounces) standing on the surface of Phobos.

Named geological features[edit]

Geological features on Phobos are named after astronomers who studied Phobos and people and places from Jonathan Swift’s Gulliver’s Travels.^[48]

Craters on Phobos[edit]

A number of craters have been named, and are listed in the following table.^[49]

Crater	Coordinates	Diameter (km)	Approval Year	Eponym	Ref	Annotated map
Clustril	60°N 91°W / 60°N 91°W	3.4	2006	Character in Lilliput who informed Flimnap that his wife had visited Gulliver privately in Jonathan Swift’s novel Gulliver’s Travels	WGPSN	SKYRESH FLIMNAP GRILDRIG RELDRESAL CLUSTRIL GULLIVER DRUNLO STICKNEY LIMTOC KEPLER DORSUM LAPUTA REGIO? LAGADO PLANITIA? SHKLOVSKY? WENDELL? Öpik
D’Arrest	39°S 179°W / 39°S 179°W	2.1	1973	Heinrich Louis d’Arrest; German/Danish astronomer (1822–1875)	WGPSN
Drunlo	36°30′N 92°00′W / 36.5°N 92°W	4.2	2006	Character in Lilliput who informed Flimnap that his wife had visited Gulliver privately in Gulliver’s Travels	WGPSN
Flimnap	60°N 10°E / 60°N 10°E	1.5	2006	Treasurer of Lilliput in Gulliver’s Travels	WGPSN
Grildrig	81°N 165°E / 81°N 165°E	2.6	2006	Name given to Gulliver by the farmer’s daughter Glumdalclitch in the giants’ country Brobdingnag in Gulliver’s Travels	WGPSN
Gulliver	62°N 163°W / 62°N 163°W	5.5	2006	Lemuel Gulliver; surgeon captain and voyager in Gulliver’s Travels	WGPSN
Hall	80°S 150°E / 80°S 150°E	5.4	1973	Asaph Hall; American astronomer discoverer of Phobos and Deimos (1829–1907)	WGPSN
Limtoc	11°S 54°W / 11°S 54°W	2	2006	General in Lilliput who prepared articles of impeachment against Gulliver in Gulliver’s Travels	WGPSN
Öpik	7°S 63°E / 7°S 63°E	2	2011	Ernst J. Öpik, Estonian astronomer (1893–1985)	WGPSN
Reldresal	41°N 39°W / 41°N 39°W	2.9	2006	Secretary for Private Affairs in Lilliput; Gulliver’s friend in Gulliver’s Travels	WGPSN
Roche	53°N 177°E / 53°N 177°E	2.3	1973	Édouard Roche; French astronomer (1820–1883)	WGPSN
Sharpless	27°30′S 154°00′W / 27.5°S 154°W	1.8	1973	Bevan Sharpless; American astronomer (1904–1950)	WGPSN
Shklovsky	24°N 112°E / 24°N 112°E	2	2011	Iosif Shklovsky, Soviet astronomer (1916–1985)	WGPSN
Skyresh	52°30′N 40°00′E / 52.5°N 40°E	1.5	2006	Skyresh Bolgolam; High Admiral of the Lilliput council who opposed Gulliver’s plea for freedom and accused him of being a traitor in Gulliver’s Travels	WGPSN
Stickney	1°N 49°W / 1°N 49°W	9	1973	Angeline Stickney (1830–1892); wife of American astronomer Asaph Hall (above)	WGPSN
Todd	9°S 153°W / 9°S 153°W	2.6	1973	David Peck Todd; American astronomer (1855–1939)	WGPSN
Wendell	1°S 132°W / 1°S 132°W	1.7	1973	Oliver Wendell; American astronomer (1845–1912)	WGPSN

Other named features[edit]

There is one named regio, Laputa Regio, and one named planitia, Lagado Planitia; both are named after places in Gulliver’s Travels (the fictional Laputa, a flying island, and Lagado, imaginary capital of the fictional nation Balnibarbi).^[50] The only named ridge on Phobos is Kepler Dorsum, named after the astronomer Johannes Kepler.^[51]

Orbital characteristics[edit]

The orbital motion of Phobos has been intensively studied, making it «the best studied natural satellite in the Solar System» in terms of orbits completed.^[52] Its close orbit around Mars produces some unusual effects. With an altitude of 5,989 km (3,721 mi), Phobos orbits Mars below the synchronous orbit radius, meaning that it moves around Mars faster than Mars itself rotates.^[32] Therefore, from the point of view of an observer on the surface of Mars, 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 each Martian day (every 11 h 6 min). Because it is close to the surface and in an equatorial orbit, it cannot be seen above the horizon from latitudes greater than 70.4°. Its orbit is so low that its angular diameter, as seen by an observer on Mars, varies visibly with its position in the sky. Seen at the horizon, Phobos is about 0.14° wide; at zenith it is 0.20°, one-third as wide as the full Moon as seen from Earth. By comparison, the Sun has an apparent size of about 0.35° in the Martian sky. Phobos’s phases, inasmuch as they can be observed from Mars, take 0.3191 days (Phobos’s synodic period) to run their course, a mere 13 seconds longer than Phobos’s sidereal period.

Solar transits[edit]

An observer situated on the Martian surface, in a position to observe Phobos, would see regular transits of Phobos across the Sun. Several of these transits have been photographed by the Mars Rover Opportunity. During the transits, Phobos’s shadow is cast on the surface of Mars; an event which has been photographed by several spacecraft. Phobos is not large enough to cover the Sun’s disk, and so cannot cause a total eclipse.^[53]

Predicted destruction[edit]

Tidal deceleration is gradually decreasing the orbital radius of Phobos by approximately two meters every 100 years,^[10] and with decreasing orbital radius the likelihood of breakup due to tidal forces increases, estimated in approximately 30–50 million years,^[10][52] with one study’s estimate being about 43 million years.^[54]

Phobos’s grooves were long thought to be fractures caused by the impact that formed the Stickney crater. Other modelling suggested since the 1970s support the idea that the grooves are more like «stretch marks» that occur when Phobos gets deformed by tidal forces, but in 2015 when the tidal forces were calculated and used in a new model, the stresses were too weak to fracture a solid moon of that size, unless Phobos is a rubble pile surrounded by a layer of powdery regolith about 100 m (330 ft) thick. Stress fractures calculated for this model line up with the grooves on Phobos. The model is supported with the discovery that some of the grooves are younger than others, implying that the process that produces the grooves is ongoing.^{[10][55][inconsistent]}

Given Phobos’s irregular shape and assuming that it is a pile of rubble (specifically a Mohr–Coulomb body), it will eventually break up due to tidal forces when it reaches approximately 2.1 Mars radii.^[56] When Phobos is broken up, it will form a planetary ring around Mars.^[57] This predicted ring may last from 1 million to 100 million years. The fraction of the mass of Phobos that will form the ring depends on the unknown internal structure of Phobos. Loose, weakly bound material will form the ring. Components of Phobos with strong cohesion will escape tidal breakup and will enter the Martian atmosphere.^[58]

Origin[edit]

The origin of the Martian moons is still controversial.^[59] Phobos and Deimos both have much in common with carbonaceous C-type asteroids, with spectra, albedo, and density very similar to those of C- or D-type asteroids.^[60] Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids.^[61][62] Both moons have very circular orbits which lie almost exactly in Mars’s equatorial plane, and hence a capture origin requires a mechanism for circularizing the initially highly eccentric orbit, and adjusting its inclination into the equatorial plane, most probably by a combination of atmospheric drag and tidal forces,^[63] although it is not clear that sufficient time is available for this to occur for Deimos.^[59] Capture also requires dissipation of energy. The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric braking.^[59] Geoffrey A. Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces.^[62][64]

Phobos could be a second-generation Solar System object that coalesced in orbit after Mars formed, rather than forming concurrently out of the same birth cloud as Mars.^[65]

Another hypothesis is that Mars was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal.^[66] The high porosity of the interior of Phobos (based on the density of 1.88 g/cm³, voids are estimated to comprise 25 to 35 percent of Phobos’s volume) is inconsistent with an asteroidal origin.^[27] Observations of Phobos in the thermal infrared suggest a composition containing mainly phyllosilicates, which are well known from the surface of Mars. The spectra are distinct from those of all classes of chondrite meteorites, again pointing away from an asteroidal origin.^[67] Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit,^[68] similar to the prevailing theory for the origin of Earth’s moon.

Some areas of the surface have turned out to be reddish in color, while others are bluish. The hypothesis is that gravity pull from Mars makes the reddish regolith move over the surface, exposing relatively fresh, unweathered and bluish material from the moon, while the regolith covering it over time has been weathered due to exposure of solar radiation. Because the blue rock differs from known Martian rock, it could contradict the theory that the moon is formed from leftover planetary material after the impact of a large object.^[69]

Most recently, Amirhossein Bagheri (ETH Zurich), Amir Khan (ETH Zurich), Michael Efroimsky (US Naval Observatory) and their colleagues proposed a new hypothesis on the origin of the moons. By analyzing the seismic and orbital data from Mars InSight Mission and other missions, they proposed that the moons are born from disruption of a common parent body around 1 to 2.7 Billion years ago. The common progenitor of Phobos and Deimos was most probably hit by another object and shattered to form Phobos and Deimos.^[70]

Exploration[edit]

Launched missions[edit]

Phobos has been photographed in close-up by several spacecraft whose primary mission has been to photograph Mars. The first was Mariner 7 in 1969, followed by Mariner 9 in 1971, Viking 1 in 1977, Phobos 2 in 1989^[71] Mars Global Surveyor in 1998 and 2003, Mars Express in 2004, 2008, 2010^[72] and 2019, and Mars Reconnaissance Orbiter in 2007 and 2008. On 25 August 2005, the Spirit rover, with an excess of energy due to wind blowing dust off of its solar panels, took several short-exposure photographs of the night sky from the surface of Mars, and was able to successfully photograph both Phobos and Deimos.^[73]

The Soviet Union undertook the Phobos program with two probes, both launched successfully in July 1988. Phobos 1 was accidentally shut down by an erroneous command from ground control issued in September 1988 and lost while the craft was still en route. Phobos 2 arrived at the Mars system in January 1989 and, after transmitting a small amount of data and imagery but shortly before beginning its detailed examination of Phobos’s surface, the probe abruptly ceased transmission due either to failure of the onboard computer or of the radio transmitter, already operating on the backup power. Other Mars missions collected more data, but no dedicated sample return mission has been performed.^{[citation needed]}

The Russian Space Agency launched a sample return mission to Phobos in November 2011, called Fobos-Grunt. The return capsule also included a life science experiment of The Planetary Society, called Living Interplanetary Flight Experiment, or LIFE.^[74] A second contributor to this mission was the China National Space Administration, which supplied a surveying satellite called «Yinghuo-1», which would have been released in the orbit of Mars, and a soil-grinding and sieving system for the scientific payload of the Phobos lander.^[75][76] However, after achieving Earth orbit, the Fobos–Grunt probe failed to initiate subsequent burns that would have sent it to Mars. Attempts to recover the probe were unsuccessful and it crashed back to Earth in January 2012.^[77]

On 1 July 2020, the Mars orbiter of the Indian Space Research Organisation was able to capture photos of the body from 4,200 km away.^[78]

Missions considered[edit]

In 1997 and 1998, the Aladdin mission was selected as a finalist in the NASA Discovery Program. The plan was to visit both Phobos and Deimos, and launch projectiles at the satellites. The probe would collect the ejecta as it performed a slow flyby (~1 km/s).^[79] These samples would be returned to Earth for study three years later.^[80][81] The Principal Investigator was Dr. Carle Pieters of Brown University. The total mission cost, including launch vehicle and operations was $247.7 million.^[82] Ultimately, the mission chosen to fly was MESSENGER, a probe to Mercury.^[83]

In 2007, the European aerospace subsidiary EADS Astrium was reported to have been developing a mission to Phobos as a technology demonstrator. Astrium was involved in developing a European Space Agency plan for a sample return mission to Mars, as part of the ESA’s Aurora programme, and sending a mission to Phobos with its low gravity was seen as a good opportunity for testing and proving the technologies required for an eventual sample return mission to Mars. The mission was envisioned to start in 2016, was to last for three years. The company planned to use a «mothership», which would be propelled by an ion engine, releasing a lander to the surface of Phobos. The lander would perform some tests and experiments, gather samples in a capsule, then return to the mothership and head back to Earth where the samples would be jettisoned for recovery on the surface.^[84]

Proposed missions[edit]

In 2007, the Canadian Space Agency funded a study by Optech and the Mars Institute for an uncrewed mission to Phobos known as Phobos Reconnaissance and International Mars Exploration (PRIME). A proposed landing site for the PRIME spacecraft is at the «Phobos monolith», a prominent object near Stickney crater.^[85][86][87] The PRIME mission would be composed of an orbiter and lander, and each would carry 4 instruments designed to study various aspects of Phobos’s geology.^[88]

In 2008, NASA Glenn Research Center began studying a Phobos and Deimos sample return mission that would use solar electric propulsion. The study gave rise to the «Hall» mission concept, a New Frontiers-class mission under further study as of 2010.^[89]

Another concept of a sample return mission from Phobos and Deimos is OSIRIS-REx II, which would use heritage technology from the first OSIRIS-REx mission.^[90]

As of January 2013, a new Phobos Surveyor mission is currently under development by a collaboration of Stanford University, NASA’s Jet Propulsion Laboratory, and the Massachusetts Institute of Technology.^[91] The mission is currently in the testing phases, and the team at Stanford plans to launch the mission between 2023 and 2033.^[91]

In March 2014, a Discovery class mission was proposed to place an orbiter in Mars orbit by 2021 to study Phobos and Deimos through a series of close flybys. The mission is called Phobos And Deimos & Mars Environment (PADME).^[92][93][94] Two other Phobos missions that were proposed for the Discovery 13 selection included a mission called Merlin, which would flyby Deimos but actually orbit and land on Phobos, and another one is Pandora which would orbit both Deimos and Phobos.^[95]

The Japanese Aerospace Exploration Agency (JAXA) unveiled on 9 June 2015 the Martian Moons Exploration (MMX), a sample return mission targeting Phobos.^[96] MMX will land and collect samples from Phobos multiple times, along with conducting Deimos flyby observations and monitoring Mars’s climate. By using a corer sampling mechanism, the spacecraft aims to retrieve a minimum 10 g amount of samples.^[97] NASA, ESA, DLR, and CNES^[98] are also participating in the project, and will provide scientific instruments.^[99][100] The U.S. will contribute the Neutron and Gamma-Ray
Spectrometer (NGRS), and France the Near IR Spectrometer (NIRS4/MacrOmega).^[97][101] Although the mission has been selected for implementation^[102][103] and is now beyond proposal stage, formal project approval by JAXA has been postponed following the Hitomi mishap.^[104] Development and testing of key components, including the sampler, is currently ongoing.^[105] As of 2017, MMX is scheduled to be launched in 2024, and will return to Earth five years later.^[97]

Russia plans to repeat Fobos-Grunt mission in the late 2020s, and the European Space Agency is assessing a sample-return mission for 2024 called Phootprint.^[106][107]

Human missions[edit]

Phobos has been proposed as an early target for a human mission to Mars. The teleoperation of robotic scouts on Mars by humans on Phobos could be conducted without significant time delay, and planetary protection concerns in early Mars exploration might be addressed by such an approach.^[108]

Phobos has been proposed as an early target for a crewed mission to Mars because a landing on Phobos would be considerably less difficult and expensive than a landing on the surface of Mars itself. A lander bound for Mars would need to be capable of atmospheric entry and subsequent return to orbit without any support facilities, or would require the creation of support facilities in-situ. A lander instead bound for Phobos could be based on equipment designed for lunar and asteroid landings.^[109] Furthermore, due to Phobos’s very weak gravity, the delta-v required to land on Phobos and return is only 80% of that required for a trip to and from the surface of the Moon.^[110]

It has been proposed that the sands of Phobos could serve as a valuable material for aerobraking during a Mars landing. A relatively small amount of chemical fuel brought from Earth could be used to lift a large amount of sand from the surface of Phobos to a transfer orbit. This sand could be released in front of a spacecraft during the descent maneuver causing a densification of the atmosphere just in front of the spacecraft.^[111][112]

While human exploration of Phobos could serve as a catalyst for the human exploration of Mars, it could be scientifically valuable in its own right.^[113]

Phobos as a space elevator for Mars[edit]

Phobos is synchronously orbiting Mars, where the same face stays facing the planet at 6,000 km (3,700 mi) above the Martian surface. A space elevator could extend down from Phobos to Mars 6,000 km, about 28 kilometers from the surface, and just out of the atmosphere of Mars. A similar space elevator cable could extend out 6,000 km the opposite direction that would counterbalance Phobos. In total the space elevator would extend out over 12,000 km which would be below areostationary orbit of Mars (17,032 km). A rocket launch would still be needed to get the rocket and cargo to the beginning of the space elevator 28 km above the surface. The surface of Mars is rotating at 0.25 km/s at the equator and the bottom of the space elevator would be rotating around Mars at 0.77 km/s, so only 0.52 km/s of delta-v would be needed to get to the space elevator. Phobos orbits at 2.15 km/s and the outermost part of the space elevator would rotate around Mars at 3.52 km/s.^[114]

See also[edit]

• List of natural satellites
• List of missions to the moons of Mars
• Phobos and Deimos in fiction
• Phobos monolith
• Transit of Phobos from Mars

References[edit]

External links[edit]

• Phobos Profile at NASA’s Solar System Exploration site
• HiRISE Phobos
• USGS Phobos nomenclature
• Asaph Hall and the Moons of Mars
• Flight around Phobos (movie)
• Animation of Phobos
• Scale of Phobos [1] [2]
• Mars Express view of Phobos
• Phobos cartography (MIIGAiK Extraterrestrial Laboratory)

ФОБОС

Синонимы:

Фобос – что означает? Определение, значение, примеры употребления

Ищешь, что значит слово фобос? Пытаешься разобраться, что такое фобос? Вот ответ на твой вопрос:

Значение слова «фобос» в словарях русского языка

Фобос это:

Фобос

Фо́бос ( «страх») — один из двух спутников Марса (наряду с Деймосом). Был открыт американским астрономом Асафом Холлом в 1877 году и назван в честь древнегреческого бога Фобоса (переводится как «Страх»), сына бога войны Ареса.

Википедия

Фобос

(от греч. phobos — страх), спутник Марса. Открыт А. Холлом (США,
1877). Расстояние от Марса 9400 км, синодический период обращения 7 ч 39 мин 27 с. Имеет неправильную форму, наибольший поперечник 26 км. — (Фоб) , в греческой мифологии божество, олицетворявшее страх, сын Ареса и Афродиты. У римлян — Павор.

Современный толковый словарь, БСЭ

Фобос

спутник планеты Марс , ближайший к планете (среднее расстояние 9380 км ) . Как показали изображения Ф., полученные при помощи космического зонда ‘Маринер-9’ (1971v
72), Ф. представляет собой тело неправильной формы (размерами 26 км в длину и 21 км в ширину), покрытое многочисленными кратерами. Период обращения Ф. вокруг Марса 7 ч 39 мин, т. е. меньше периода вращения Марса вокруг оси. Альбедо поверхности Ф. близко к альбедо наиболее тёмных участков Луны (около 5%). Открыт А. Холлом в

1877.

Большая советская энциклопедия, БСЭ

Фобос

сын бога Ареса в греческой мифологии спутник планеты Марс

Викисловарь

Где и как употребляется слово «фобос»?

Кроме значения слова «фобос» в словарях, рекомендуем также ознакомиться с примерами предложений и цитат из классической литературы, в которых употребляется слово «фобос».

Так вы сможете гораздо легче понять и запомнить, как правильно употребляется слово «фобос» в тексте и устной речи.

Примеры употребления слова «фобос»

Однажды в баре на орбитальной станции «Фобос» ему повстречался пилот, только что прибывший из пояса астероидов.

Фобос отвечает за еальную и непосредственную опасность.

Атлантов приютил ближайший спутник четвёртой планеты, который сегодня получил название – Фобос (Ужас).

Синонимы, антонимы и гипонимы к слову «фобос»

Синонимы к слову «фобос»:

• спутник
• страх

Разбор слова «фобос»

Фобос является ответом на вопросы из кроссвордов

• «Страшный» спутник воинственной планеты
• Спутник Марса
• Сын Ареса и Афродиты
• Российская АМС «…. — грунт»
• Бог страха и спутник Марса
• Российская автоматическая межпланетная станция «…-Грунт»
• Этот спутник обращается вокруг Марса столь быстро, что один оборот совершает за треть марсианских суток, обгоняя суточное вращение планеты
• «Страшный» спутник
• Один из спутников Марса
• (Фоб) в греческой мифологии божество, олицетворявшее страх, сын Ареса и Афродиты

У этого термина существуют и другие значения, см. Фобос (значения).

Фо́бос (др.-греч. φόβος «страх») — один из двух спутников Марса (наряду с Деймосом).

Спутник был открыт американским астрономом Асафом Холлом в 1877 году^[3] и назван в честь древнегреческого бога Фобоса (переводится как «Страх»), сына бога войны Ареса.

Описание

Фобос вращается на среднем расстоянии 6006 км от поверхности Марса и 2,77 радиуса Марса от центра планеты (9400 км), что в 41 раз меньше расстояния между центрами Земли и Луны (384 400 км); перицентр составляет 9235,6 км, апоцентр — 9518,8 км. Фобос делает оборот за 7 ч 39 мин 14 с, что примерно в три раза быстрее вращения Марса вокруг собственной оси. В результате на марсианском небе Фобос восходит на западе и заходит на востоке.

Фобос имеет форму, близкую к трёхосному эллипсоиду, большая ось которого направлена на Марс^[4]. Размеры Фобоса составляют 26,8×22,4×18,4 км.

Вследствие крайне малой массы атмосфера у Фобоса отсутствует. Чрезвычайно низкая средняя плотность Фобоса (около 1,86 г/см³) указывает на пористую структуру спутника с пустотами, составляющими 25—45 % объёма.^[5]

Период вращения Фобоса вокруг своей оси совпадает с периодом его обращения вокруг Марса, поэтому Фобос всегда повёрнут к планете одной и той же стороной. Его орбита находится внутри предела Роша для «жидкого» спутника, однако приливные силы не разрывают его, поскольку он имеет рыхлую структуру, и его орбита в настоящее время лежит вне предела Роша для «твёрдого» спутника. Тем не менее, в силу такого положения орбиты невозможно создать искусственный спутник Фобоса^[6].

Фобос постепенно приближается к Марсу. Как установил в 1945 году Б. П. Шарплесс^[en] на основе обработки наблюдений Г. О. Струве и более поздних, Фобос испытывает вековое ускорение орбитального движения. И. С. Шкловский в 1959 году на основании расчётов высказал, как он сам заметил, «весьма радикальное и необычное» предположение, что Фобос — полый внутри и имеет искусственное происхождение, именно этим можно было объяснить принятое тогда значение векового ускорения, если считать причиной его торможение Фобоса весьма разреженной атмосферой Марса. Тщательный анализ наблюдательных данных Дж. Уилкинсом (1967), С. Н. Вашковьяк и Э. Синклером (1972) вообще указывал на отсутствие векового ускорения. Но анализ В. А. Шора (1973) показал, что вековое ускорение всё-таки есть, но значительно более слабое, чем считал Шарплесс. Теоретические выводы Шора подтвердили результаты измерений АМС «Маринер-9». Поэтому предположение Шкловского было отвергнуто, и была принята высказанная в том же 1959 году^[7] Н. Н. Парийским гипотеза, что причиной векового ускорения является приливное воздействие Марса^[8]. Именно оно постепенно приближает Фобос к Марсу. В будущем это приведёт к столкновению Фобоса с Марсом.

В настоящее время Фобос приближается к Марсу на 1,8 метра за столетие. Скорость приближения, однако, зависит непростым образом от оставшегося расстояния. Согласно расчётам, столкновение произойдёт через 43 миллиона лет^[9]. Причём ещё до него Фобос разрушится на многие куски, что произойдёт уже через 10—11 миллионов лет, когда он перейдёт свой предел Роша^[10][11].

Из-за близости Марса сила тяготения на различных сторонах спутника различна, причём на марсианской и противоположной сторонах она практически отсутствует, а там где Марс постоянно виден на горизонте спутника — максимальна, в силу близости Фобоса к пределу Роша.

Детали рельефа Фобоса

Наиболее заметным образованием на Фобосе является кратер Стикни диаметром 9 км. Кратер образовался в результате столкновения Фобоса с небольшим астероидом, возможно миллион лет назад, и это столкновение почти разрушило спутник.

Также, на Фобосе была обнаружена система загадочных параллельных борозд возле кратера Стикни. Они прослеживаются на расстояниях до 30 км в длину и имеют ширину 100—200 метров при глубине 10—20 метров.

Монолит на Фобосе^[en] — валун высотой около 90 метров^[12]. Обнаружен Эфраином Палермо после изучения снимков Фобоса, сделанных в 1998 году миссией «Mars Global Surveyor».

Происхождение

Гипотезы происхождения марсианских спутников по-прежнему противоречивы. Фобос и Деймос имеют много общего с астероидами класса С: их спектр, альбедо и плотность в целом характерны для астероидов класса C или D. Так, по старой гипотезе Фобос, как и Деймос — это астероиды, образовавшиеся около 4,5 миллиардов лет назад в главном поясе астероидов, которые постепенно перемещаясь из внешней его части в сторону Солнца, впоследствии стали спутниками Марса^[13]. Захват Марсом сразу двух астероидов представляется маловероятным, поэтому возникла гипотеза^[14], что Фобос и Деймос — это остатки расколовшегося надвое более крупного, единственного астероида, захваченного планетой. Однако Фобос и Деймос обращаются вокруг Марса по круговым орбитам почти точно в плоскости экватора планеты^[15], а их плотности нехарактерны для астероидов и настолько малы, что захват Марсом привёл бы к разрушению таких астероидов. Всё это опровергает гипотезу захвата астероидов.

Точный анализ данных с европейского аппарата Марс-экспресс показал также существенное отличие спектра Фобоса от спектра астероидов главного пояса. По новой гипотезе, Фобос — объект второго поколения Солнечной системы, то есть объект, не образовавшийся одновременно с Марсом, а вновь собравшийся на околомарсианской орбите^[16]. Возможно, в прошлом Марс пережил столкновение с крупной планетезималью, которые во времена молодости Солнечной системы встречались часто, выбросив на орбиту огромную массу пород Марса. Часть этого вещества впоследствии собралась на орбите в виде спутников^{[источник не указан 1268 дней]}.

Вид с Марса

Фобос при наблюдении с поверхности Марса имеет видимый диаметр около 1/3 от диска Луны на земном небе и видимую звёздную величину порядка −9 (приблизительно как Луна в фазе первой четверти)^[17]. Фобос восходит на западе и садится на востоке Марса, чтобы снова взойти через 11 часов, таким образом, дважды в сутки пересекая небо Марса. Движение этой быстрой луны по небу будет легко заметно в течение ночи, так же, как и смена фаз. Невооружённый глаз различит крупнейшую деталь рельефа Фобоса — кратер Стикни. Оба спутника могут наблюдаться на ночном небе одновременно, в этом случае Фобос будет двигаться навстречу Деймосу.

Яркость и Фобоса, и Деймоса достаточна для того, чтобы предметы на поверхности Марса ночью отбрасывали чёткие тени. На Марсе может наблюдаться затмение Фобоса и Деймоса при их входе в тень Марса, а также затмение Солнца, которое бывает только кольцеобразным из-за малого углового размера Фобоса по сравнению с диском Солнца.

Открытие

Спутники Марса пытался отыскать ещё английский королевский астроном Уильям Гершель в 1783 году, но безрезультатно. В 1862 и 1864 гг. их искал директор обсерватории Копенгагенского университета Генрих (Анри) Луи Д’Арре с помощью 10-дюймового (25-сантиметрового) телескопа-рефрактора, но также не смог их обнаружить^[18].

Фобос — внутренний спутник — был открыт в серии наблюдений американского астронома Асафа Холла ночью 17 августа^[19][20] 1877 года. Наблюдения проводились в военно-морской обсерватории в Вашингтоне, и поэтому, если перевести местное солнечное время к гринвичскому, то официальная дата открытия — это 18 августа 1877 года. В письме Глейшеру от 28 декабря 1877 года Холл пишет^[21]:

Из различных имен, которые были предложены для этих спутников, мне больше всего нравятся имена из Гомера, предложенные мистером Маданом из Итона, а именно: Деймос для внешнего спутника и Фобос для внутреннего.

Of the various names that have been proposed for these satellites I like best those suggested from Homer by Mr. Madan, of Eton, viz. Deimos for the outer satellite, and Phobos for the inner one.

Таким образом, имена для спутников Марса предложил Генри Джордж Мадан^[en] в 1877 году, и взял он их из «Илиады» Гомера^[22]. Окончательный выбор в пользу предложения Мадана Холл сделал 7 февраля 1878 года^[23].

Исследование Фобоса

На одном из снимков «Маринера-7» с близкого расстояния зафиксирована тень Фобоса на диске Марса. При анализе снимка определено, что Фобос в сечении эллиптический, его размеры вдвое больше вычисленных Дж. Койпером и альбедо его поверхности 5—6 %.

Фобос был сфотографирован крупным планом несколькими космическими аппаратами, основной целью которых являлось фотографирование Марса. Первым был «Маринер-9» в 1971 году, за ним «Викинг-1» и «Викинг-2» в 1977 году, Mars Global Surveyor в 1998 и 2003 годах, «Марс-экспресс» в 2004 году и Mars Reconnaissance Orbiter в 2007 и 2008 годах.

В 1988 году были запущены две автоматические межпланетные станции «Фобос» для исследования Марса и его спутников. Один из аппаратов был потерян через 2 месяца после запуска, второй успешно достиг Марса и успел выполнить часть исследовательской программы до того, как контакт с ним прекратился. 21, 27 и 28 февраля 1989 года АМС «Фобос-2» провела съёмку Фобоса — получено 38 изображений Фобоса высокого качества с удаления от 300 км до 1100 км, максимальное разрешение составило примерно 40 метров^[24].

9 января 2011 года «Марс-экспресс» приблизился к Фобосу на 100 км и сделал снимки с разрешением 16 м. Впервые были получены стереоизображения спутника^[25][26].

9 ноября 2011 года в рамках программы «Фобос-Грунт» Российского космического агентства, состоялся запуск очередной экспедиции к Фобосу автоматической межпланетной станции, которая должна была в 2014 году доставить образцы грунта со спутника Марса на Землю; но в результате нештатной ситуации (предположительно программного сбоя), станция не была выведена на расчётную траекторию, и 15 января 2012 года упала в Тихий океан^[27][28]. В течение нескольких лет после этого Роскосмос планировал повторную миссию «Фобос-Грунт 2», однако на 2020 год этот проект не планируется к реализации в ближайшем будущем^[29].

Японское агентство аэрокосмических исследований (JAXA) разрабатывает автоматический аппарат Martian Moons Exploration (MMX) для исследования Фобоса и Деймоса, включающую доставку образцов грунта Фобоса на Землю. NASA, ESA и CNES планируют предоставить отдельные приборы для аппарата. Запуск планируется в 2024 году, прибытие образцов грунта на Землю — к 2029 году.

Зонд Mars Odyssey с помощью инфракрасной камеры определил, что когда Фобос полностью освещён Солнцем температура на его поверхности достигает 27 °C. Во время полного затмения температура на поверхности Фобоса составляет −123 °C^[30].

Предсказание о двух спутниках

Предположение о существовании у Марса двух спутников высказал Иоганн Кеплер в 1611 году. Он ошибочно расшифровал анаграмму Галилео Галилея smaismrmilmepoetaleumibunenugttauiras как лат. Salue, umbistineum geminatum Martia proles^[31] («Привет вам, близнецы, Марса порождение»^[32]) и, таким образом, посчитал, что Галилей открыл два спутника Марса. В то время, как правильной её расшифровкой было лат. Altissimum planetam tergeminum obseruaui («Высочайшую планету тройною наблюдал»^[32], опубликована в письме Галилея Джулиано де Медичи 13 ноября 1610 года) — Галилей увидел Сатурн тройным — с кольцами^[33].

Видимо, Кеплер также основывал своё предположение на логике, что если у Земли есть один спутник, а у Юпитера — четыре (известных в то время Галилеевых спутников), то количество спутников планет по мере удаления от Солнца возрастает в геометрической прогрессии. По этой логике у Марса должно быть два спутника.

В третьей части главы 3 «Путешествий Гулливера» (1726) Джонатана Свифта, которая описывает летающий остров Лапута, говорится, что астрономы Лапуты открыли два спутника Марса на орбитах, равных 3 и 5 диаметрам Марса с периодом обращения соответственно 10 и 21,5 часов. В действительности Фобос и Деймос находятся на расстоянии 1,4 и 3,5 диаметра Марса от центра планеты, а их периоды — 7,6 и 30,3 часа^[34].

Примечания

Литература

• Силкин Б.И. В мире множества лун. — М.: Наука, 1982. — 208 с. — 150 000 экз.

Ссылки

• Бурба Г. Приёмный сын Марса. Научно-популярная статья о Фобосе // Вокруг света, № 10, 2011
• Спутник Марса — Фобос
• Автореферат диссертации Т. В. Шингарёвой «Геологическое строение и вещественный состав Фобоса»
• Phobos Profile at NASA (англ.)

Эта страница в последний раз была отредактирована 28 февраля 2023 в 20:21.

Как только страница обновилась в Википедии она обновляется в Вики 2.
Обычно почти сразу, изредка в течении часа.

Фобос – спутник Марса. Это необычный космический объект, гораздо меньше других планетарных спутников. Название он получил в честь бога страха – сына бога войны.

Открытие спутника Фобос

Первым существование спутником Марса предположил Иоганн Келлер в 1611 году. Но на тот момент не было технических возможностей их увидеть. Телескопы не имели достаточно мощных линз. С тех пор начались поиски марсианских лун. Их пытались увидеть в 1783 году Уильям Гершель и в 1830 году Иоганн Генрих. Первым человеком, увидевшим Деймос и Фобос был Асаф Холл в 1877 году. Он дождался максимального приближения Марса к Земле, которое бывает примерно раз в 15 лет и наблюдал за нужным участком неба.
12 августе Холл увидел малый спутник Деймос. Спустя почти неделю, только 18 августа в объектив телескопа попал Фобос. С этого момента существование марсианских лун было официально доказанным фактом.

Основные параметры

Фобос спутник имеет неправильную форму и его часто сравнивают с картофелиной. Поверхность серого цвета, покрыта кратерами и глубокими бороздками. Параметры Фобоса — 26,8 × 22,4 × 18,4 км, средний диаметр около 22.5 км.

Интересные факты

• Площадь Фобоса — 1 600 км², что очень мало для планетарного спутника. Для сравнения, площадь Москвы — 2 561 км².
• Фобос находится в зоне приливного притяжения, поэтому с поверхности планеты видна только одна сторона, так же как с Земли видна только одна сторона Луны.
• Спутник Фобос приближается к планете и скоро, по космическим меркам, он развалиться и его осколки упадут на поверхность Марса.
• Происхождения Фобоса до сих пор не известно, в научной среде сохраняются споры.

Физические характеристики

Масса	1,072⋅10*16 кг
Размеры	26,8 × 22,4 × 18,4 км
Радиус	11,25 км
Площадь поверхности	1600 км²
Температура	233 К
Видимая звёздная величина	11,8

Фобос и Деймос крайне малы, Фобос – крупнейший спутник Марса. Масса равна 1,072∙10 в 16 степени кг. Это небольшой вес для его размера, что приводит к выводам о низкой плотности — 1,87 г/см³. Исследователи предполагают, что он состоит из пористого материала и, вероятно, имеет внутри много полостей.
На поверхности воды нет, но есть вероятность, что она есть где-то в недрах Фобоса в форме льда. Температура на поверхности -40°С. Внутри она отличается незначительно. Серый цвет поверхности обуславливает слабую способность к светоотражению, поэтому светится он не ярко, что долгое время затрудняло поиски самих спутников.

Исследования Фобоса

Марс всегда интересовал землян и как только началась космическая эпоха началось и исследование этой планеты включая спутник Фобос. Еще в 1962 г. СССР отправила исследовательский аппарат Марс -1. Но он сбился с курса и не достиг цели.
В 1971 г. Аппарат НАСА Маринер-9 отправил первые денные с Марса, в том числе несколько снимков Фобоса. В 1977 г. данные прислали уже аппараты Викинг-1 и 2. В 1988г. Был запущен исследовательский аппарат Фобос-1, но он не смог достичь цели и затерялся в космическом пространстве. В том же году был запущен Фобос-2. Аппарат работал не долго, но успел прислать качественные снимки спутника, некоторую информацию о его составе.
В 2003 году Европейское космическое агентство запустило станцию «Марс -экспресс». Она проработала долгое время на орбите Марса и в 2011 году прислала уникальные снимки Фобоса. Ученые, наконец, смогли рассмотреть еще не изученную сторону Фобоса.
В 2011 году Россия планировала запустить аппарат Фобос-грунт, но миссия оказалась провальной, аппарат сгорел, не покинув атмосферу. Повторный запуск планируется только в 2025 году.

Орбитальные характеристики

Орбита Фобоса – это эллипсоид. Спутник делает полный оборот вокруг планеты за 7 ч 39 мин, что намного быстрее скорости вращения Марса. За марсианские сутки Фобос успевает сделать 3 оборота вокруг планеты. Расстояние от поверхности Марса до спутника всего 9377км. Это привело к некоторым интересным эффектам. Фобос вертеться вокруг Марса быстрее, чем Марс вокруг своей оси. С Марса лучше всего наблюдать спутник в зоне экватора, а чем дальше от экватора, тем хуже видимость. На полюсах марсианских лун совсем не видно.
Вращения вокруг Марса и вокруг своей оси синхронизировано, а значит с планеты видно только одну сторону. По сути, Фобос двигается не по кругу, а по спирали, постепенно приближаясь к Марсу. Ему предрекают судьбу Танатоса – предполагаемого третьего спутника, который уже упал на поверхность планеты. Самые смелые ученые предполагают что именно Танатос убил жизнь на Марсе.

Геологические особенности поверхности

Фобос спутник похож на продолговатый валун серого цвета. Поверхность покрыта множеством кратеров разных размеров и бороздками. Ученые полагают, что бороздки – это трещины. Они являются первыми признаками дальнейшего разрушения Фобоса под действием приливных сил Марса. Спутник имеет пористую структуру. По последним данным, 40% полостей остается незаполненными.
Сегодня есть достаточно снимков, чтобы составить полную карту поверхности Фобоса. Основа рельефа – это кратеры и трещины. На этом фоне выделяет монолит, который по расчетам возвышается примерно на 90 м. Происхождение этого объекта установить сложно. Возможно, это обломок крупного метеорита, когда-то упавшего на Фобос. Форма основания монолита близка к правильному квадрату, что дает возможность для многочисленных предположения криптозоологов.

Формирование и состав

Есть несколько теорий формирования Фобоса:

• Это космическое тело Марс некогда захватил из пояса астероидов между Юпитером и Марсом. В поддержание данной теории говорит форма, размер, структура и состав Фобоса, имеющий некоторое сходство с астероидами.
• Спутники, Марс получил в результате столкновения с крупным космическим телом. Часть материи было выбито из планеты, и эти куски постепенно сформировали спутники Марса.

Обе теории имеют своих сторонников и общепризнанного мнения пока нет. В 2030 г. исследователи планируют получить образцы грунта. После анализа можно будет решить этот многолетний спор ученых.

Кратеры Фобоса

Вся поверхность Фобоса испещрена кратерами разного размера, от огромных до самых маленьких. Это отличает его от Деймоса, практически гладкого и покрытого толстым слоем реголита. В основном кратеры называли в честь персонажей Джонатана Свифта и известных астрономов. Персонажей Свифта используют не просто так. В своей книге «Путешествия Гулливера» он написал о двух спутниках Марса еще до того, как Холл увидел их в телескоп.
Самый большой кратер назван в честь жены первооткрывателя Асафа Холла – Стикни. Его диаметр 9 тыс. км. Внутри этого кратера, еще один, тоже довольно крупный – Лимтоком.
В честь астрономов названы:

• Д’Арре,
• Холл,
• Эпик,
• Рош,
• Шарплесс,
• Шкловский,
• Тод,
• Уэнделл.

В честь персонажей Джонатана Свифта названы кратеры:

• Флимнап,
• Гильдрик,
• Друнло,
• Рудрезал,
• Гулливер,
• Кластрил,
• Скайкрас.

Множество кратеров Фобоса до сих пор не имеют имен. Их очень много, и специально этим никто не занимается. Названия получили только самые крупные кратеры.

Фобос в мифологии

Деймос и Фобос спутник и сын Ареса — римского бога войны, греческим аналогом которого является Марс . По легенде, братья всегда сопровождают отца на поле битвы. Страх и Ужас, вот что сеяли они. Фобоса часто представляли с головой льва. Он являлся армии врага еще до начала боя, стремясь породить в их сердцах страх, а значит неуверенность в собственных силах и сомнения. Редкий смертный мог противостоять его воздействию.

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