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98-399: An eclipse is an astronomical event. Eclipse may also refer to: Eclipse An eclipse is an astronomical event which occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy . An eclipse
196-531: A corer sampling mechanism, the spacecraft aims to retrieve a minimum 10 g amount of samples. NASA, ESA, DLR, and CNES are also participating in the project, and will provide scientific instruments. The U.S. will contribute the Neutron and Gamma-Ray Spectrometer (NGRS), and France the Near IR Spectrometer (NIRS4/MacrOmega). Although the mission has been selected for implementation and
294-635: A rubble pile held together by a thin crust that is being torn apart by tidal interactions. Phobos gets closer to Mars by about 2 centimetres (0.79 in) per year. Phobos was discovered by the American 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
392-740: A rubble pile . 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. The porosity of Phobos was calculated to be 30% ± 5%, or a quarter to a third being empty. Geological features on Phobos are named after astronomers who studied Phobos and people and places from Jonathan Swift 's Gulliver's Travels . A number of craters have been named, and are listed in
490-565: A saros . Between 1901 and 2100 there are the maximum of seven eclipses in: Excluding penumbral lunar eclipses, there are a maximum of seven eclipses in: As observed from the Earth, a solar eclipse occurs when the Moon passes in front of the Sun. The type of solar eclipse event depends on the distance of the Moon from the Earth during the event. A total solar eclipse occurs when the Earth intersects
588-410: A Phobos-sized object by atmospheric braking. 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. 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. Another hypothesis is that Mars
686-409: 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, although it is not clear that sufficient time is available for this to occur for Deimos. Capture also requires dissipation of energy. The current Martian atmosphere is too thin to capture
784-457: A combination of prefix ἐκ- ( ek- ), from preposition ἐκ ( ek ), 'out', and of verb λείπω ( leípō ), 'to be absent'. For any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, creating a region of shadow around the axis of the line. Typically these objects are moving with respect to each other and their surroundings, so
882-418: A common orbital plane in space. When this plane is very closely aligned with the location of an observer, the stars can be seen to pass in front of each other. The result is a type of extrinsic variable star system called an eclipsing binary . The maximum luminosity of an eclipsing binary system is equal to the sum of the luminosity contributions from the individual stars. When one star passes in front of
980-451: A devout atheist but can't explain why the moon is exactly the right size, and gets positioned so precisely between the Earth and the sun, that total solar eclipses are perfect. It bothers me." The Graeco-Roman historian Cassius Dio , writing between AD 211–229, relates the anecdote that Emperor Claudius considered it necessary to prevent disturbance among the Roman population by publishing
1078-429: A display of God's greatness or even signs of cycles of life and death. However, more ominous eclipses such as a blood moon were believed to be a divine sign that God would soon destroy their enemies. The gas giant planets have many moons and thus frequently display eclipses. The most striking involve Jupiter , which has four large moons and a low axial tilt , making eclipses more frequent as these bodies pass through
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#17327944743171176-417: A hollow iron sphere 16 kilometers (9.9 mi) across but less than 6 centimetres (2.4 in) thick. In a February 1960 letter to the journal Astronautics , 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
1274-602: 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. 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
1372-444: 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. Furthermore, due to Phobos' very weak gravity, the delta-v required to land on Phobos and return
1470-480: 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 casts a shadow on the surface of Mars; this event has been photographed by several spacecraft. Phobos is not large enough to cover the Sun's disk, and so cannot cause a total eclipse . Tidal deceleration
1568-513: A precision of about one part in a million or better. Chinese historical records of solar eclipses date back over 3,000 years and have been used to measure changes in the Earth's rate of spin. The first person to give scientific explanation on eclipses was Anaxagoras [c500BC - 428BC]. Anaxagoras stated that the Moon shines by reflected light from the Sun. In 5th century AD, solar and lunar eclipses were scientifically explained by Aryabhata , in his treatise Aryabhatiya . Aryabhata states that
1666-403: A predictable pattern on the surface of the moon. Faint dust rings produced by Phobos and Deimos have long been predicted but attempts to observe these rings have, to date, failed. 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
1764-454: A prediction for a solar eclipse which would fall on his birthday anniversary [1 August in the year AD 45]. In this context, Cassius Dio provides a detailed explanation of solar and lunar eclipses. Typically in mythology, eclipses were understood to be one variation or another of a spiritual battle between the sun and evil forces or spirits of darkness. More specifically, in Norse mythology , it
1862-475: 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
1960-546: 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. 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
2058-430: A sample-return mission for 2024 called Phootprint . 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. A landing on Phobos would be considerably less difficult and expensive than
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#17327944743172156-414: A substantial reservoir of ice. Spectral observations indicate that the surface regolith layer lacks hydration, but ice below the regolith is not ruled out. Surface temperatures range from about −4 °C (25 °F) on the sunlit side to −112 °C (−170 °F) on the shadowed side. Unlike Deimos, Phobos is heavily cratered, with one of the craters near the equator having a central peak despite
2254-441: A sunset, the atmosphere tends to more strongly scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue, thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as eclipses are recorded. Records of solar eclipses have been kept since ancient times. Eclipse dates can be used for chronological dating of historical records. A Syrian clay tablet, in
2352-435: Is 29.7 years, an eclipse is only possible about every 15 years. On Mars , only partial solar eclipses ( transits ) are possible, because neither of its moons is large enough, at their respective orbital radii, to cover the Sun's disc as seen from the surface of the planet. Eclipses of the moons by Mars are not only possible, but commonplace, with hundreds occurring each Earth year. There are also rare occasions when Deimos
2450-521: 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' phases, inasmuch as they can be observed from Mars, take 0.3191 days (Phobos' synodic period) to run their course, a mere 13 seconds longer than Phobos' sidereal period . An observer situated on the Martian surface, in
2548-412: Is believed that there is a wolf by the name of Fenrir that is in constant pursuit of the Sun, and eclipses are thought to occur when the wolf successfully devours the divine Sun. Other Norse tribes believed that there are two wolves by the names of Sköll and Hati that are in pursuit of the Sun and the Moon, known by the names of Sol and Mani, and these tribes believed that an eclipse occurs when one of
2646-471: Is broken up, it will form a planetary ring around Mars. 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. It is predicted that within 30 to 50 million years it will either collide with
2744-851: Is caused by the passage of the dimmer member of the pair in front of the brighter star. The concept that an eclipsing body caused these luminosity variations was introduced by John Goodricke in 1783. Sun – Moon – Earth: Solar eclipse | annular eclipse | hybrid eclipse | partial eclipse Sun – Earth – Moon: Lunar eclipse | penumbral eclipse | partial lunar eclipse | central lunar eclipse Sun – Phobos – Mars: Transit of Phobos from Mars | Solar eclipses on Mars Sun – Deimos – Mars: Transit of Deimos from Mars | Solar eclipses on Mars Other types: Solar eclipses on Jupiter | Solar eclipses on Saturn | Solar eclipses on Uranus | Solar eclipses on Neptune | Solar eclipses on Pluto Phobos (moon) Phobos ( / ˈ f oʊ b ə s / ; systematic designation : Mars I )
2842-467: Is eclipsed by Phobos. Martian eclipses have been photographed from both the surface of Mars and from orbit. Pluto , with its proportionately largest moon Charon , is also the site of many eclipses. A series of such mutual eclipses occurred between 1985 and 1990. These daily events led to the first accurate measurements of the physical parameters of both objects. Eclipses are impossible on Mercury and Venus , which have no moons. However, as seen from
2940-401: Is equal to 1.384 × 10 km , which is much larger than the Moon's semimajor axis of 3.844 × 10 km. Hence the umbral cone of the Earth can completely envelop the Moon during a lunar eclipse . If the occulting object has an atmosphere, however, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during an eclipse of the Moon by
3038-399: Is gradually decreasing the orbital radius of Phobos by approximately 2 m (6 ft 7 in) every 100 years, and with decreasing orbital radius the likelihood of breakup due to tidal forces increases, estimated in approximately 30–50 million years, or about 43 million years in one study's estimate. Phobos' grooves were long thought to be fractures caused by the impact that formed
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3136-445: 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. Subsequently, the systematic data errors that Singer predicted were found to exist, the claim was called into doubt, and accurate measurements of
3234-443: Is much larger. The Moon's umbra will advance eastward at a rate of 1,700 km/h, until it no longer intersects the Earth's surface. During a solar eclipse, the Moon can sometimes perfectly cover the Sun because its apparent size is nearly the same as the Sun's when viewed from the Earth. A total solar eclipse is in fact an occultation while an annular solar eclipse is a transit . When observed at points in space other than from
3332-554: Is not known how the material stuck to an object with almost no gravity. 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 couldn't be verified because little is known about the exact composition of Phobos. In the late 1950s and 1960s, the unusual orbital characteristics of Phobos led to speculations that it might be hollow. Around 1958, Russian astrophysicist Iosif Samuilovich Shklovsky , studying
3430-531: Is now beyond proposal stage, formal project approval by JAXA has been postponed following the Hitomi mishap. Development and testing of key components, including the sampler, is currently ongoing. As of 2017 , MMX is scheduled to be launched in 2026, and will return to Earth five years later. Russia plans to repeat Fobos-Grunt mission in the late 2020s, and the European Space Agency is assessing
3528-466: Is one of the least reflective bodies in the Solar System, with an albedo of about 0.071. Infrared spectra show that it has carbon-rich material found in carbonaceous chondrites , and its composition shows similarities to that of Mars' surface. Phobos' density is too low to be solid rock, and it is known to have significant porosity . These results led to the suggestion that Phobos might contain
3626-416: Is only 80% of that required for a trip to and from the surface of the Moon. 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
3724-399: 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
3822-480: Is the innermost and larger of the two natural satellites of Mars , the other being Deimos . The two moons were discovered in 1877 by American astronomer Asaph Hall . Phobos is named after 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). It orbits 6,000 km (3,700 mi) from
3920-448: Is the result of either an occultation (completely hidden) or a transit (partially hidden). A "deep eclipse" (or "deep occultation") is when a small astronomical object is behind a bigger one. The term eclipse is most often used to describe either a solar eclipse , when the Moon's shadow crosses the Earth's surface, or a lunar eclipse , when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond
4018-687: 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. 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
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4116-581: The Massachusetts Institute of Technology . The mission is currently in the testing phases, and the team at Stanford plans to launch the mission between 2023 and 2033. 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). Two other Phobos missions that were proposed for
4214-534: The Solar System , with an albedo of 0.071. Surface temperatures range from about −4 °C (25 °F) on the sunlit side to −112 °C (−170 °F) on the shadowed side. The notable surface feature is the large impact crater , Stickney , which takes up a substantial proportion of the moon's surface. The surface is also marked by many grooves, and there are numerous theories as to how these grooves were formed. Images and models indicate that Phobos may be
4312-414: The orbit of the Moon does not give exact integers, the numbers of orbit cycles are close enough to integers to give strong similarity for eclipses spaced at 18.03 yr intervals. An eclipse involving the Sun, Earth, and Moon can occur only when they are nearly in a straight line, allowing one to be hidden behind another, viewed from the third. Because the orbital plane of the Moon is tilted with respect to
4410-420: The secular acceleration of Phobos' orbital motion, suggested a "thin sheet metal" structure for Phobos, a suggestion which led to speculations that Phobos was of artificial origin. 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
4508-426: The "Hall" mission concept, a New Frontiers -class mission under further study as of 2010. 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. 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
4606-431: The 1600s, European astronomers were publishing books with diagrams explaining how lunar and solar eclipses occurred. In order to disseminate this information to a broader audience and decrease fear of the consequences of eclipses, booksellers printed broadsides explaining the event either using the science or via astrology. The American author Gene Weingarten described the tension between belief and eclipses thus: "I am
4704-465: The British academic Henry Madan , a science master at Eton College , who based them on Greek mythology , in which Phobos is a companion to the god, Ares . Phobos has dimensions of 26 by 23 by 18 kilometres (16 mi × 14 mi × 11 mi), 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. It
4802-641: 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. The Japanese Aerospace Exploration Agency (JAXA) unveiled on 9 June 2015 the Martian Moons Exploration (MMX), a sample return mission targeting Phobos. MMX will land and collect samples from Phobos multiple times, along with conducting Deimos flyby observations and monitoring Mars' climate. By using
4900-420: The Earth from the Sun. Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar eclipse from a given location. A lunar eclipse lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour. There are three types of lunar eclipses: penumbral, when
4998-477: The Earth—;producing a faint, ruddy illumination of the Moon even at totality. On Earth, the shadow cast during an eclipse moves very approximately at 1 km per sec. This depends on the location of the shadow on the Earth and the angle in which it is moving. An eclipse cycle takes place when eclipses in a series are separated by a certain interval of time. This happens when the orbital motions of
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#17327944743175096-503: The Earth's surface, the Sun can be eclipsed by bodies other than the Moon. Two examples include when the crew of Apollo 12 observed the Earth to eclipse the Sun in 1969 and when the Cassini probe observed Saturn to eclipse the Sun in 2006. Lunar eclipses occur when the Moon passes through the Earth's shadow. This happens only during a full moon , when the Moon is on the far side of
5194-536: The Earth, both have been observed to transit across the face of the Sun. Transits of Venus occur in pairs separated by an interval of eight years, but each pair of events happen less than once a century. According to NASA, the next pair of Venus transits will occur on December 10, 2117, and December 8, 2125. Transits of Mercury are much more common, occurring 13 times each century, on average. A binary star system consists of two stars that orbit around their common centre of mass . The movements of both stars lie on
5292-492: The Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if the plane of the orbit of its constituent stars intersects the observer's position. For the special cases of solar and lunar eclipses, these only happen during an " eclipse season ",
5390-504: The Mars-facing side to the edge of Mars' atmosphere, the other extending 6,000 km (3,700 mi) from the other side and away from Mars. A spacecraft launching from Mars' surface to the lower space elevator would only need a delta-v of 0.52 km/s (0.32 mi/s), as opposed to the over 3.6 km/s (2.2 mi/s) needed to launch to low Mars orbit. The spacecraft could be lifted up using electrical power and then released from
5488-425: The Martian surface, closer to its primary body than any other known natural satellite to a planet. 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
5586-572: The Moon and planets shine by reflected sunlight and explains eclipses in terms of shadows cast by and falling on Earth. Aryabhata provides the computation and the size of the eclipsed part during an eclipse. Indian computations were very accurate that 18th-century French scientist Guillaume Le Gentil , during a visit to Pondicherry, India, found the Indian computations of the duration of the lunar eclipse of 30 August 1765 to be short by only 41 seconds, whereas Le Gentil's charts were long by 68 seconds. By
5684-418: The Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's umbra ; and total, when the Moon crosses entirely into the Earth's umbra. Total lunar eclipses pass through all three phases. Even during a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere enters the umbra and provides a faint illumination. Much as in
5782-421: The Moon's orbit around the Earth were both in the same plane with each other, then eclipses would happen every month. There would be a lunar eclipse at every full moon, and a solar eclipse at every new moon. It is because of the non-planar differences that eclipses are not a common event. If both orbits were perfectly circular, then each eclipse would be the same type every month. Lunar eclipses can be viewed from
5880-461: The PRIME spacecraft is at the " Phobos monolith ", a prominent object near Stickney crater. The PRIME mission would be composed of an orbiter and lander, and each would carry 4 instruments designed to study various aspects of Phobos' geology. 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
5978-413: The Solar System" in terms of orbits completed. 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. Therefore, from the point of view of an observer on the surface of Mars, it rises in the west, moves comparatively rapidly across
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#17327944743176076-544: 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
6174-435: The Sun and thus cannot produce an annular eclipse. The same terms may be used analogously in describing other eclipses, e.g., the antumbra of Deimos crossing Mars , or Phobos entering Mars's penumbra. The first contact occurs when the eclipsing object's disc first starts to impinge on the light source; second contact is when the disc moves completely within the light source; third contact when it starts to move out of
6272-547: The Ugaritic language, records a solar eclipse which occurred on March 5, 1223, B.C., while Paul Griffin argues that a stone in Ireland records an eclipse on November 30, 3340 B.C. Positing classical-era astronomers' use of Babylonian eclipse records mostly from the 13th century BC provides a feasible and mathematically consistent explanation for the Greek finding all three lunar mean motions (synodic, anomalistic, draconitic) to
6370-448: The bodies form repeating harmonic patterns. A particular instance is the saros , which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years. Because this is not a whole number of days, successive eclipses will be visible from different parts of the world. In one saros period there are 239.0 anomalistic periods, 241.0 sidereal periods, 242.0 nodical periods, and 223.0 synodic periods. Although
6468-569: 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 shortly before beginning its detailed examination of Phobos' surface, the probe abruptly ceased transmission due either to failure of the onboard computer or of the radio transmitter, already operating on backup power. Other Mars missions collected more data, but no dedicated sample return mission has been successfully performed. The Russian Space Agency launched
6566-408: The day at noon, give the time of discovery as 17 August at 16:06 Washington mean time , meaning 18 August 04:06 in the modern convention.) Hall had discovered Deimos , Mars' other moon, a few days earlier . The discoveries were made using the world's largest refracting telescope , the 26-inch "Great Equatorial". The names, originally spelled Phobus and Deimus respectively, were suggested by
6664-456: The descent maneuver causing a densification of the atmosphere just in front of the spacecraft. 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. First discussed in fiction in 1956 by Fontenay, Phobos has been proposed as a future site for space elevator construction. This would involve a pair of space elevators: one extending 6,000 km from
6762-426: The eclipse magnitude is the ratio of the angular sizes of the Moon to the Sun. Solar eclipses are relatively brief events that can only be viewed in totality along a relatively narrow track. Under the most favorable circumstances, a total solar eclipse can last for 7 minutes, 31 seconds, and can be viewed along a track that is up to 250 km wide. However, the region where a partial eclipse can be observed
6860-589: The eclipse, and many people of the Hindu religion refuse to eat during an eclipse to avoid the effects of the evil spirits. Hindu people living in India will also wash off in the Ganges River , which is believed to be spiritually cleansing, directly following an eclipse to clean themselves of the evil spirits. In early Judaism and Christianity , eclipses were viewed as signs from God, and some eclipses were seen as
6958-494: The entire nightside half of the Earth. But solar eclipses, particularly total eclipses occurring at any one particular point on the Earth's surface, are very rare events that can be many decades apart. The term is derived from the ancient Greek noun ἔκλειψις ( ékleipsis ), which means 'the abandonment', 'the downfall', or 'the darkening of a heavenly body', which is derived from the verb ἐκλείπω ( ekleípō ) which means 'to abandon', 'to darken', or 'to cease to exist',
7056-484: The far side of the Sun. Ole Rømer deduced that the delay was caused by the time needed for light to travel from Jupiter to the Earth. This was used to produce the first estimate of the speed of light . The timing of the Jovian satellite eclipses was also used to calculate an observer's longitude upon the Earth. By knowing the expected time when an eclipse would be observed at a standard longitude (such as Greenwich ),
7154-553: The following map and table. 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 ). The only named ridge on Phobos is Kepler Dorsum , named after the astronomer Johannes Kepler . The orbital motion of Phobos has been intensively studied, making it "the best studied natural satellite in
7252-399: 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. Given Phobos' 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. When Phobos
7350-529: The impact of a large object. In February 2021, 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
7448-415: The light; and fourth or last contact when it finally leaves the light source's disc entirely. For spherical bodies, when the occulting object is smaller than the star, the length ( L ) of the umbra's cone-shaped shadow is given by: where R s is the radius of the star, R o is the occulting object's radius, and r is the distance from the star to the occulting object. For Earth , on average L
7546-577: The moon's small size. 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 ' crater Herschel , the impact that created Stickney must have nearly shattered Phobos. 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
7644-456: The observer is within the umbra, an annular eclipse when the observer is within the antumbra, and a partial eclipse when the observer is within the penumbra. During a lunar eclipse only the umbra and penumbra are applicable, because the antumbra of the Sun-Earth system lies far beyond the Moon. Analogously, Earth's apparent diameter from the viewpoint of the Moon is nearly four times that of
7742-625: The orbit available by 1969 showed that the discrepancy did not exist. Singer's critique was justified when earlier studies were discovered to have used an overestimated value of 5 centimetres (2.0 in) per year for the rate of altitude loss, which was later revised to 1.8 centimetres (0.71 in) per year. The secular acceleration is now attributed to tidal effects, which create drag on the moon and therefore cause it to spiral inward. The density of Phobos has now been directly measured by spacecraft to be 1.887 g/cm (0.0682 lb/cu in). Current observations are consistent with Phobos being
7840-662: The orbit of Mars, and a soil-grinding and sieving system for the scientific payload of the Phobos lander. 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. On 1 July 2020, the Mars orbiter of the Indian Space Research Organisation
7938-430: The orbital plane of the Earth (the ecliptic ), eclipses can occur only when the Moon is close to the intersection of these two planes (the nodes ). The Sun, Earth and nodes are aligned twice a year (during an eclipse season ), and eclipses can occur during a period of about two months around these times. There can be from four to seven eclipses in a calendar year, which repeat according to various eclipse cycles , such as
8036-405: The other, the luminosity of the system is seen to decrease. The luminosity returns to normal once the two stars are no longer in alignment. The first eclipsing binary star system to be discovered was Algol , a star system in the constellation Perseus . Normally this star system has a visual magnitude of 2.1. However, every 2.867 days the magnitude decreases to 3.4 for more than nine hours. This
8134-476: The planet or break up into a planetary ring . The origin of the Martian moons has been disputed. 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. Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids . Both moons have very circular orbits which lie almost exactly in Mars' equatorial plane , and hence
8232-404: The planet's orbit, due to their higher inclination between the orbits of the moon and the orbital plane of the planet. The moon Titan , for example, has an orbital plane tilted about 1.6° to Saturn's equatorial plane. But Saturn has an axial tilt of nearly 27°. The orbital plane of Titan only crosses the line of sight to the Sun at two points along Saturn's orbit. As the orbital period of Saturn
8330-515: The result of the same impact that created Stickney. Analysis of results from the Mars Express spacecraft, however, revealed that the grooves are not 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
8428-444: The resulting shadow will sweep through a region of space, only passing through any particular location in the region for a fixed interval of time. As viewed from such a location, this shadowing event is known as an eclipse. Typically the cross-section of the objects involved in an astronomical eclipse is roughly disk-shaped. The region of an object's shadow during an eclipse is divided into three parts: A total eclipse occurs when
8526-458: The shadow of the larger planet. Transits occur with equal frequency. It is common to see the larger moons casting circular shadows upon Jupiter's cloudtops. The eclipses of the Galilean moons by Jupiter became accurately predictable once their orbital elements were known. During the 1670s, it was discovered that these events were occurring about 17 minutes later than expected when Jupiter was on
8624-402: 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
8722-431: The surface of Mars. The spectra are distinct from those of all classes of chondrite meteorites, again pointing away from an asteroidal origin. Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, similar to the prevailing theory for the origin of Earth's moon. Some areas of the surface are reddish in color, while others are bluish. The hypothesis
8820-436: The time difference could be computed by accurately observing the local time of the eclipse. The time difference gives the longitude of the observer because every hour of difference corresponded to 15° around the Earth's equator. This technique was used, for example, by Giovanni D. Cassini in 1679 to re-map France . On the other three gas giants ( Saturn , Uranus and Neptune ) eclipses only occur at certain periods during
8918-414: 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. 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
9016-407: The two times of each year when the plane of the Earth's orbit around the Sun crosses with the plane of the Moon's orbit around the Earth and the line defined by the intersecting planes points near the Sun. The type of solar eclipse that happens during each season (whether total, annular, hybrid, or partial) depends on apparent sizes of the Sun and Moon. If the orbit of the Earth around the Sun and
9114-435: The umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occulted, resulting in an annular eclipse. Partial solar eclipses occur when the viewer is inside the penumbra. The eclipse magnitude is the fraction of the Sun's diameter that is covered by the Moon. For a total eclipse, this value is always greater than or equal to one. In both annular and total eclipses,
9212-463: The wolves successfully eats either the Sun or the Moon. In most types of mythologies and certain religions, eclipses were seen as a sign that the gods were angry and that danger was soon to come, so people often altered their actions in an effort to dissuade the gods from unleashing their wrath. In the Hindu religion, for example, people often sing religious hymns for protection from the evil spirits of
9310-484: Was Dr. Carle Pieters of Brown University . The total mission cost, including launch vehicle and operations was $ 247.7 million. Ultimately, the mission chosen to fly was MESSENGER , a probe to Mercury. 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
9408-563: Was able to capture photos of the body from 4,200 km away. 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). These samples would be returned to Earth for study three years later. The Principal Investigator
9506-464: Was most probably hit by another object and shattered to form both moons. 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 Mars Global Surveyor in 1998 and 2003, Mars Express in 2004, 2008, 2010 and 2019, and Mars Reconnaissance Orbiter in 2007 and 2008. On 25 August 2005,
9604-469: Was once surrounded by many Phobos- and Deimos-sized bodies, perhaps ejected into orbit around it by a collision with a large planetesimal . The high porosity of the interior of Phobos (based on the density of 1.88 g/cm , voids are estimated to comprise 25 to 35 percent of Phobos' volume) is inconsistent with an asteroidal origin. Observations of Phobos in the thermal infrared suggest a composition containing mainly phyllosilicates , which are well known from
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