Moons of Mars

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Phobos colour 2008.jpg
Colour image of Phobos (MRO, 23 March 2008)
Colour image of Deimos (MRO, 21 February 2009)

The two moons of Mars are Phobos and Deimos. [1] They are irregular in shape. [2] Both were discovered by American astronomer Asaph Hall in August 1877 [3] and are named after the Greek mythological twin characters Phobos (fear) and Deimos (terror and dread) who accompanied their father Ares into battle. Ares, god of war, was known to the Romans as Mars.


Compared to the Earth's Moon, the moons Phobos and Deimos are small. Phobos has a diameter of 22.2 km (13.8 mi) and a mass of 1.08×1016 kg, while Deimos measures 12.6 km (7.8 mi) across, with a mass of 2.0×1015 kg. Phobos orbits closer to Mars, with a semi-major axis of 9,377 km (5,827 mi) and an orbital period of 7.66 hours; while Deimos orbits farther with a semi-major axis of 23,460 km (14,580 mi) and an orbital period of 30.35 hours.


Early speculation

Curiosity's view of the Martian moons: Phobos passing in front of Deimos - in real-time (video-gif, 1 August 2013) PIA17352-MarsMoons-PhobosPassesDeimos-RealTime.gif
Curiosity's view of the Martian moons: Phobos passing in front of Deimos – in real-time (video-gif, 1 August 2013)

Speculation about the existence of the moons of Mars had begun when the moons of Jupiter were discovered. When Galileo Galilei, as a hidden report about him having observed two bumps on the sides of Saturn (later discovered to be its rings), used the anagram smaismrmilmepoetaleumibunenugttauiras for Altissimum planetam tergeminum observavi ("I have observed the most distant planet to have a triple form"), Johannes Kepler had misinterpreted it to mean Salve umbistineum geminatum Martia proles (Hello, furious twins, sons of Mars). [4]

Perhaps inspired by Kepler (and quoting Kepler's third law of planetary motion), Jonathan Swift's satire Gulliver's Travels (1726) refers to two moons in Part 3, Chapter 3 (the "Voyage to Laputa"), in which Laputa's astronomers are described as having discovered two satellites of Mars orbiting at distances of 3 and 5 Martian diameters with periods of 10 and 21.5 hours. Phobos and Deimos (both found in 1877, more than a century after Swift's novel) have actual orbital distances of 1.4 and 3.5 Martian diameters, and their respective orbital periods are 7.66 and 30.35 hours. [5] [6] In the 20th century, V. G. Perminov, a spacecraft designer of early Soviet Mars and Venus spacecraft, speculated Swift found and deciphered records that Martians left on Earth. [7] However, the view of most astronomers is that Swift was simply employing a common argument of the time, that as the inner planets Venus and Mercury had no satellites, Earth had one and Jupiter had four (known at the time), that Mars by analogy must have two. Furthermore, as they had not yet been discovered, it was reasoned that they must be small and close to Mars. This would lead Swift to making a roughly accurate estimate of their orbital distances and revolution periods. In addition Swift could have been helped in his calculations by his friend, the mathematician John Arbuthnot. [8]

Voltaire's 1752 short story "Micromégas", about an alien visitor to Earth, also refers to two moons of Mars. Voltaire was presumably influenced by Swift. [9] [10] In recognition of these 'predictions', two craters on Deimos are named Swift and Voltaire, [11] [12] while on Phobos there is one named regio, Laputa Regio, and one named planitia, Lagado Planitia, both of which are named after places in Gulliver's Travels (the fictional Laputa, a flying island, and Lagado, imaginary capital of the fictional nation Balnibarbi). [13] Many of the craters on Phobos are also named after characters in Gulliver's Travels. [14]


The telescope used by Asaph Hall in the discovery of the Martian moons Usno-telescope-equalized-1.png
The telescope used by Asaph Hall in the discovery of the Martian moons

Asaph Hall discovered Deimos on August 12, 1877 at about 07:48 UTC and Phobos on August 18, 1877, at the US Naval Observatory (the Old Naval Observatory in Foggy Bottom) in Washington, D.C., at about 09:14 GMT (contemporary sources, using the pre-1925 astronomical convention that began the day at noon, [15] give the time of discovery as 11 August 14:40 and 17 August 16:06 Washington mean time respectively). [16] [17] [18] At the time, he was deliberately searching for Martian moons. Hall had previously seen what appeared to be a Martian moon on 10 August, but due to bad weather, he could not definitively identify them until later.

Hall recorded his discovery of Phobos in his notebook as follows: [19]

"I repeated the examination in the early part of the night of 11th [August 1877], and again found nothing, but trying again some hours later I found a faint object on the following side and a little north of the planet. I had barely time to secure an observation of its position when fog from the River stopped the work. This was at half-past two o'clock on the night of the 11th. Cloudy weather intervened for several days.
"On 15 August the weather looking more promising, I slept at the Observatory. The sky cleared off with a thunderstorm at 11 o'clock and the search was resumed. The atmosphere however was in a very bad condition and Mars was so blazing and unsteady that nothing could be seen of the object, which we now know was at that time so near the planet as to be invisible.
"On 16 August the object was found again on the following side of the planet, and the observations of that night showed that it was moving with the planet and if a satellite, was near one of its elongations. Until this time I had said nothing to anyone at the Observatory of my search for a satellite of Mars, but on leaving the observatory after these observations of the 16th, at about three o'clock in the morning, I told my assistant, George Anderson, to whom I had shown the object, that I thought I had discovered a satellite of Mars. I told him also to keep quiet as I did not wish anything said until the matter was beyond doubt. He said nothing, but the thing was too good to keep and I let it out myself. On 17 August between one and two o'clock, while I was reducing my observations, Professor Newcomb came into my room to eat his lunch and I showed him my measures of the faint object near Mars which proved that it was moving with the planet.
"On 17 August while waiting and watching for the outer moon, the inner one was discovered. The observations of the 17th and 18th put beyond doubt the character of these objects and the discovery was publicly announced by Admiral Rodgers."

The telescope used for the discovery was the 26-inch (66 cm) refractor (telescope with a lens) then located at Foggy Bottom. [20] In 1893 the lens was remounted and put in a new dome, where it remains into the 21st century. [21]

The names, originally spelled Phobus and Deimus, respectively, were suggested by Henry Madan (18381901), Science Master of Eton, from Book XV of the Iliad , where Ares summons Fear and Fright. [22] The granddaughter of Henry Madan's brother Falconer Madan was Venetia Burney, who first suggested the name of the planet Pluto.

Mars moon hoax

In 1959, Walter Scott Houston perpetrated a celebrated April Fool's hoax in the April edition of the Great Plains Observer, claiming that "Dr. Arthur Hayall of the University of the Sierras reports that the moons of Mars are actually artificial satellites". Both Dr. Hayall and the University of the Sierras were fictitious. The hoax gained worldwide attention when Houston's claim was repeated in earnest by a Soviet scientist, Iosif Shklovsky, [23] who, based on a later-disproven density estimate, suggested Phobos was a hollow metal shell.

Recent surveys

Searches have been conducted for additional satellites. In 2003, Scott S. Sheppard and David C. Jewitt surveyed nearly the entire Hill sphere of Mars for irregular satellites. However scattered light from Mars prevented them from searching the inner few arcminutes where the satellites Phobos and Deimos reside. No new satellites were found to an apparent limiting red magnitude of 23.5, which corresponds to radii of about 0.09 km using an albedo of 0.07. [24]


Apparent sizes of the moons of Mars, Deimos and Phobos, and the Moon as viewed from the surface of their respective planets (Mars' moons imaged by the Curiosity rover, 1 August 2013) PIA17351-ApparentSizes-MarsDeimosPhobos-EarthMoon.jpg
Apparent sizes of the moons of Mars, Deimos and Phobos, and the Moon as viewed from the surface of their respective planets (Mars' moons imaged by the Curiosity rover, 1 August 2013)

If viewed from Mars's surface near its equator, full Phobos looks about one-third as big as a full moon on Earth. It has an angular diameter of between 8' (rising) and 12' (overhead). Due to its close orbit, it would look smaller when the observer is further away from the Martian equator and is below the horizon and thus not visible from Mars's polar ice caps. Deimos looks more like a bright star or planet for an observer on Mars, only slightly bigger than Venus looks from Earth; it has an angular diameter of about 2'. The Sun's angular diameter as seen from Mars, by contrast, is about 21'. Thus there are no total solar eclipses on Mars, as the moons are far too small to completely cover the Sun. On the other hand, total lunar eclipses of Phobos happen almost every night. [25]

The motions of Phobos and Deimos would appear very different from that of Earth's Moon. Speedy Phobos rises in the west, sets in the east, and rises again in just eleven hours, while Deimos, being only just outside synchronous orbit, rises as expected in the east but very slowly. Despite its 30-hour orbit, it takes 2.7 days to set in the west as it slowly falls behind the rotation of Mars.

Both moons are tidally locked, always presenting the same face towards Mars. Since Phobos orbits Mars faster than the planet itself rotates, tidal forces are slowly but steadily decreasing its orbital radius. At some point in the future, when it approaches Mars closely enough (see Roche limit), Phobos will be broken up by these tidal forces and form a ring around Mars or will crash into Mars. [26] [27] Several strings of craters on the Martian surface, inclined further from the equator the older they are, suggest that there may have been other small moons that suffered the fate expected of Phobos, and that the Martian crust as a whole shifted between these events. [28] Deimos, on the other hand, is far enough away that its orbit is being slowly boosted instead, [29] as in the case of Earth's Moon.

Orbital details

Name and pronunciationImageDiameter (km)Surface

Area (km2)

Mass (kg)Semi-major
axis (km)
period (h)
Average moonrise
period (h, d)
Mars I Phobos /ˈfbəs/
Phobos moon (large).jpg
22.2 km (13.8 mi)(27×21.6×18.8 km)1,548 km210.8×10159,377 km (5,827 mi)7.6611.12 h (0.463 d)
Mars II Deimos /ˈdməs/
12.6 km (7.8 mi)
(10×12×16 km)
483 km21.5×101523,460 km (14,580 mi)30.35131 h (5.44 d)
Mars Moons Orbit distance.jpeg
The relative sizes of and distance between Mars, Phobos, and Deimos, to scale

(Load the image in full size to see both Moons of Mars.)


Animation illustrating the asteroid-belt origin for the moons MoonsOfMarsImproved3.gif
Animation illustrating the asteroid-belt origin for the moons

The origin of the Martian moons is still controversial. [30] 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. [31] Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids. [6] [32] 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, [33] although it is not clear that sufficient time is available for this to occur for Deimos. [30] Capture also requires dissipation of energy. The current atmosphere of Mars is too thin to capture a Phobos-sized object by atmospheric braking. [30] Geoffrey Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces. [32]

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. [34]

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. [35] 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' volume) is inconsistent with an asteroidal origin. [36] 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. [37] Both sets of findings support an origin of Phobos from material ejected by an impact on Mars that reaccreted in Martian orbit, [38] similar to the prevailing theory for the origin of Earth's moon.

The moons of Mars may have started with a huge collision with a protoplanet one third the mass of Mars that formed a ring around Mars. The inner part of the ring formed a large moon. Gravitational interactions between this moon and the outer ring formed Phobos and Deimos. Later, the large moon crashed into Mars, but the two small moons remained in orbit. This theory agrees with the fine-grained surface of the moons and their high porosity. The outer disk would create fine-grained material. [39] [40] Simulations suggest the object colliding with Mars had to be within the size range of Ceres and Vesta because a larger impact would have created a more massive disc and moons that would have prevented the survival of tiny moons like Phobos and Deimos. [41]

Most recently, Amirhossein Bagheri and his colleagues from ETH Zurich and US Naval Observatory, 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. [42]


While many Martian probes provided images and other data about Phobos and Deimos, only few were dedicated to these satellites and intended to perform a flyby or landing on the surface.

Two probes under the Soviet Phobos program were successfully launched in 1988, but neither conducted the intended jumping landings on Phobos and Deimos due to failures (although Phobos 2 successfully photographed Phobos). The post-Soviet Russian Fobos-Grunt probe was intended to be the first sample return mission from Phobos, but a rocket failure left it stranded in Earth orbit in 2011.

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. These samples would be returned to Earth for study three years later. Ultimately, NASA rejected this proposal in favor of MESSENGER , a probe to Mercury.

In 2007, the European Space Agency and EADS Astrium proposed and developed a mission to Phobos in 2016 with a lander and sample return, but this mission was never flown. Since 2007 the Canadian Space Agency has been considering the PRIME mission to Phobos with orbiter and lander. Since 2008 NASA Glenn Research Center began studying a Phobos and Deimos sample return mission. Since 2013 NASA developed the Phobos Surveyor mission concept with an orbiter and a small rover that is proposed to launch sometime after 2023.[ citation needed ] Proposed NASA's PADME mission proposes to launch in 2020 and reach Mars orbit in 2021 to conduct multiple flybys of the Martian moons.[ citation needed ] Also, NASA is assessing the OSIRIS-REx II, concept mission for a sample return from Phobos. [43] Another sample return mission from Deimos, called Gulliver. has been conceptualized. [44] Russia plans to repeat Fobos-Grunt mission around 2024.[ citation needed ]

Orbits of moons and spacecraft orbiting Mars. PIA19396-PlanetMars-OrbitsOfMoonsAndOrbiters-20150504.jpg
Orbits of moons and spacecraft orbiting Mars.

See also

Related Research Articles

Phobos (moon) Larger, inner moon of Mars

Phobos is the innermost and larger of the two natural satellites of Mars, the other being Deimos. Both moons were discovered in 1877 by American astronomer Asaph Hall. Phobos is named after the Greek god Phobos, a son of Ares (Mars) and Aphrodite (Venus) and twin brother of Deimos. Phobos was the god and personification of fear and panic.

Natural satellite Astronomical body that orbits a planet

A natural satellite is in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small solar system body. While natural satellites are often colloquially referred to as moons, there is only the Moon of Earth.

Deimos (moon) Smaller, outer moon of Mars

Deimos is the smaller and outermost of the two natural satellites of Mars, the other being Phobos. Deimos has a mean radius of 6.2 km (3.9 mi) and takes 30.3 hours to orbit Mars. Deimos is 23,460 km (14,580 mi) from Mars, much farther than Mars's other moon, Phobos. It is named after Deimos, the Ancient Greek god and personification of dread and terror, and who is also a son of Ares and Aphrodite and the twin brother of Phobos.

Lander (spacecraft) Type of spacecraft

A lander is a spacecraft that descends towards, comes to rest on, the surface of an astronomical body. In contrast to an impact probe, which makes a hard landing that damages or destroys the probe upon reaching the surface, a lander makes a soft landing after which the probe remains functional.

Asaph Hall American astronomer

Asaph Hall III was an American astronomer who is best known for having discovered the two moons of Mars, Deimos and Phobos, in 1877. He determined the orbits of satellites of other planets and of double stars, the rotation of Saturn, and the mass of Mars.

Exploration of Mars Overview of the exploration of Mars

The planet Mars has been explored remotely by spacecraft. Probes sent from Earth, beginning in the late 20th century, have yielded a large increase in knowledge about the Martian system, focused primarily on understanding its geology and habitability potential. Engineering interplanetary journeys is complicated and the exploration of Mars has experienced a high failure rate, especially the early attempts. Roughly sixty percent of all spacecraft destined for Mars failed before completing their missions and some failed before their observations could begin. Some missions have met with unexpected success, such as the twin Mars Exploration Rovers, Spirit and Opportunity which operated for years beyond their specification.

Discovery Program Ongoing solar system exploration program by NASA

The Discovery Program is a series of solar system exploration missions funded by the US National Aeronautics and Space Administration (NASA) through its Planetary Missions Program Office. The cost of each mission is capped at a lower level than missions from NASA's New Frontiers or Flagship Programs. As a result, Discovery missions tend to be more focused on a specific scientific goal rather than serving a general purpose.

Stickney (crater) Largest crater on Phobos

Stickney is the largest crater on Phobos, which is a satellite of Mars. It is 9 km (5.6 mi) in diameter, taking up a substantial proportion of the moon's surface.

An areostationary orbit or areosynchronous equatorial orbit is a circular areo­synchronous orbit (ASO) in the Martian equatorial plane about 17,032 km (10,583 mi) above the surface, any point on which revolves about Mars in the same direction and with the same period as the Martian surface. Areo­stationary orbit is a concept similar to Earth's geo­stationary orbit (GEO). The prefix areo- derives from Ares, the ancient Greek god of war and counterpart to the Roman god Mars, with whom the planet was identified. The modern Greek word for Mars is Άρης (Áris).

Astronomy on Mars

In many cases astronomical phenomena viewed from the planet Mars are the same or similar to those seen from Earth but sometimes they can be quite different. For example, because the atmosphere of Mars does not contain an ozone layer, it is also possible to make UV observations from the surface of Mars.

North Polar Basin (Mars) Large basin in the northern hemisphere of Mars

The North Polar Basin, more commonly known as the Borealis Basin, is a large basin in the northern hemisphere of Mars that covers 40% of the planet. Some scientists have postulated that the basin formed during the impact of a single, large body roughly 2% of the mass of Mars, having a diameter of about 1,900 km. However, the basin is not currently recognized as an impact basin by the IAU. The basin is one of the flattest areas in the Solar System, and has an elliptical shape. Chryse Planitia, the landing site of the Viking 1 lander, is a bay that opens into this basin.

Mars has two moons, Phobos and Deimos. Due to their small size, both moons were discovered only in 1877, by astronomer Asaph Hall. Nevertheless, they frequently feature in works of science fiction.

Mars Fourth planet from the Sun in the Solar System

Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. In English, Mars carries the name of the Roman god of war and is often referred to as the "Red Planet". The latter refers to the effect of the iron oxide prevalent on Mars's surface, which gives it a reddish appearance, that is distinctive among the astronomical bodies visible to the naked eye. Mars is a terrestrial planet with a thin atmosphere, with surface features reminiscent of the impact craters of the Moon and the valleys, deserts and polar ice caps of Earth.

Planetary Science Decadal Survey Publication of the United States National Research Council

The Planetary Science Decadal Survey is a publication of the United States National Research Council produced for NASA and other United States Government Agencies such as the National Science Foundation. The document identifies key questions facing planetary science and outlines recommendations for space and ground-based exploration ten years into the future. Missions to gather data to answer these big questions are described and prioritized, where appropriate. Similar Decadal Surveys cover astronomy and astrophysics, earth science, and heliophysics.

Asteroid Redirect Mission 2013–2017 proposed NASA space mission

The Asteroid Redirect Mission (ARM), also known as the Asteroid Retrieval and Utilization (ARU) mission and the Asteroid Initiative, was a space mission proposed by NASA in 2013. The Asteroid Retrieval Robotic Mission (ARRM) spacecraft would rendezvous with a large near-Earth asteroid and use robotic arms with anchoring grippers to retrieve a 4-meter boulder from the asteroid.

Phobos And Deimos & Mars Environment NASA Mars orbiter mission concept

Phobos And Deimos & Mars Environment (PADME) is a low-cost NASA Mars orbiter mission concept that would address longstanding unknowns about Mars' two moons Phobos and Deimos and their environment.

The selection process for Mission 13 and 14 of the Discovery program began in February 2014, as NASA drafted an Announcement of Opportunity (AO) for the next Discovery mission. The winning mission proposals received $450 million in funding towards mission development and construction, along with bonus funding if missions were able to incorporate certain technologies. For Discovery Mission 13 and 14, NASA received 28 proposals, 16 of which notably centered around small Solar System bodies. Lucy, a multiple-flyby mission to the Jupiter trojans, and Psyche, a mission to the metallic asteroid 16 Psyche, were announced as the winners of the competition in January 2017, with launches in October 2021 and October 2023, respectively.

Martian Moons eXploration (MMX) Planned sample-return mission by Japan to Phobos

The Martian Moons eXploration (MMX) is a robotic space probe set for launch in 2024 to bring back the first samples from Mars' largest moon Phobos. Developed by the Japanese Aerospace Exploration Agency (JAXA) and announced on 9 June 2015, MMX will land and collect samples from Phobos once or twice, along with conducting Deimos flyby observations and monitoring Mars' climate.

Deimos and Phobos Interior Explorer (DePhine) is a European mission concept to use a dedicated orbiter to explore the two Moons of Mars: Phobos and Deimos. The mission concept was proposed in 2016 to the European Space Agency's Cosmic Vision programme for launch in 2030, but it was not chosen as a finalist for the M5 mission class.


  1. Andrews, Robin George (25 July 2020). "Why the 'Super Weird' Moons of Mars Fascinate Scientists - What's the big deal about little Phobos and tinier Deimos?". The New York Times . Archived from the original on 25 July 2020. Retrieved 25 July 2020.
  2. "NASA - Under the Moons of Mars". Archived from the original on 29 March 2014. Retrieved 28 February 2013.
  3. "The Planet Mars: A History of Observation and Discovery. Chapter 5: 1877. University of Arizona Press". Archived from the original on 3 November 2017. Retrieved 28 February 2013.
  4. "Galileo, Kepler, & Two Anagrams: Two Wrong Solutions Turn Into Two Correct Solutions". Judge Starling. Archived from the original on 13 October 2018. Retrieved 29 October 2018.
  5. "Galileo's Anagrams and the Moons of Mars". Archived from the original on 12 June 2018. Retrieved 29 October 2018.
  6. 1 2 "Close Inspection for Phobos". Archived from the original on 14 January 2012. Retrieved 2 April 2011. One idea is that Phobos and Deimos, Mars's other moon, are captured asteroids.
  7. V. G. Perminov (1999). The Difficult Road to Mars (Report). NASA. ISBN   0-16-058859-6. NP-1999-06-251-HQ. Retrieved 29 October 2018.
  8. Lamont, Roscoe (1925). "The moons of Mars". Popular Astronomy. 33: 496. Bibcode:1925PA.....33..496L.
  9. Sheehan, William (1 September 1996). The Planet Mars: A History of Observation and Discovery (2nd ed.). Tucson: University of Arizona Press. ISBN   9780816516414.
  10. Voltaire explained that since Mars is further from the Sun than Earth is, it could not make do with less than two moons. (Patrick Moore, 2000, The Wandering Astronomer)
  11. "Swift". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
  12. "Voltaire". Gazetteer of Planetary Nomenclature. USGS Astrogeology Research Program.
  13. Gazetteer of Planetary Nomenclature Archived 15 January 2021 at the Wayback Machine USGS Astrogeology Research Program, Phobos
  14. "Gazetteer of Planetary Nomenclature, Phobos Craers". International Astronomical Union. Archived from the original on 9 January 2017. Retrieved 10 January 2018.
  15. Campbell, W.W. (1918). "The Beginning of the Astronomical Day". Publications of the Astronomical Society of the Pacific. 30 (178): 358. Bibcode:1918PASP...30..358C. doi: 10.1086/122784 .
  16. "Notes". The Observatory. 1: 181. 1877. Bibcode:1877Obs.....1..181.
  17. Hall, Asaph (1877). "Observations of the Satellites of Mars". Astronomische Nachrichten. 91 (1): 11–14. Bibcode:1877AN.....91...11H. doi:10.1002/asna.18780910103. Archived from the original on 1 October 2021. Retrieved 1 July 2021.
  18. Morley, T. A. (1989). "A catalogue of ground-based astrometric observations of the Martian satellites, 1877-1982". Astronomy and Astrophysics Supplement Series. 77 (2): 209. Bibcode:1989A&AS...77..209M.
  19. Hall, A. (1878). "Discovery of satellites of Mars". Monthly Notices of the Royal Astronomical Society. 38: 205. Bibcode:1878MNRAS..38..205H. doi:10.1093/mantras/38.4.205 (inactive 31 October 2021).CS1 maint: DOI inactive as of October 2021 (link)
  20. "Telescope: Naval Observatory 26-inch Refractor". Archived from the original on 18 October 2013. Retrieved 29 October 2018.
  21. "The 26-inch "Great Equatorial" Refractor". United States Naval Observatory. Archived from the original on 29 October 2018. Retrieved 29 October 2018.
  22. Knorre, V. (1878). "Entdeckung zweier Planeten". Astronomische Nachrichten. 92 (3): 47–48. Bibcode:1878AN.....92...47K. doi:10.1002/asna.18780920305. Archived from the original on 1 October 2021. Retrieved 1 July 2021.
  23. Jefferson City Post-Tribune 4 May 1959
  24. Sheppard, Scott S.; Jewitt, David; Kleyna, Jan (November 2004). "A Survey for Outer Satellites of Mars: Limits to Completeness". The Astronomical Journal. 128 (5): 2542–2546. arXiv: astro-ph/0409522 . Bibcode:2004AJ....128.2542S. doi:10.1086/424541. ISSN   1538-3881. S2CID   45681283.
  25. "Astrobiology Exclusive News You Can't Afford to Miss -". Astrobiology Magazine. Archived from the original on 20 February 2021. Retrieved 29 October 2018.
  26. Nemiroff, R.; Bonnell, J., eds. (14 April 2008). "Phobos: Doomed Moon of Mars". Astronomy Picture of the Day . NASA. In 100 million years or so Phobos will likely be shattered by stress caused by the relentless tidal forces, the debris forming a decaying ring around Mars.
  27. December 2017, Nola Taylor Redd 08 (8 December 2017). "Phobos: Facts About the Doomed Martian Moon". Archived from the original on 19 March 2018. Retrieved 13 June 2020.
  28. "NASA - New Map Provides More Evidence Mars Once Like Earth". Archived from the original on 14 September 2012. Retrieved 29 October 2018.
  29. "Mission To Mars - Project-based Learning" (PDF). Archived from the original (PDF) on 17 June 2011. Retrieved 29 October 2018.
  30. 1 2 3 Burns, J. A. "Contradictory Clues as to the Origin of the Martian Moons," in Mars, H. H. Kieffer et al., eds., U. Arizona Press, Tucson, 1992
  31. "New Views of Martian Moons". Archived from the original on 14 November 2011. Retrieved 2 April 2011.
  32. 1 2 Landis, G. A. "Origin of Martian Moons from Binary Asteroid Dissociation," American Association for the Advancement of Science Annual Meeting; Boston, MA, 2001; abstract Archived 4 June 2016 at the Wayback Machine .
  33. Cazenave, A.; Dobrovolskis, A.; Lago, B. (1980). "Orbital history of the Martian satellites with inferences on their origin". Icarus. 44 (3): 730–744. Bibcode:1980Icar...44..730C. doi:10.1016/0019-1035(80)90140-2.
  34. Martin Pätzold & Olivier Witasse (4 March 2010). "Phobos Flyby Success". ESA. Archived from the original on 7 March 2010. Retrieved 4 March 2010.
  35. Craddock, R. A.; (1994); The Origin of Phobos and Deimos, Abstracts of the 25th Annual Lunar and Planetary Science Conference, held in Houston, TX, 14–18 March 1994, p. 293
  36. Andert, T. P.; Rosenblatt, P.; Pätzold, M.; Häusler, B.; et al. (7 May 2010). "Precise mass determination and the nature of Phobos". Geophysical Research Letters . American Geophysical Union. 37 (L09202): n/a. Bibcode:2010GeoRL..37.9202A. doi:10.1029/2009GL041829. Archived from the original on 26 June 2010. Retrieved 1 October 2010.
  37. Giuranna, M.; Roush, T. L.; Duxbury, T.; Hogan, R. C.; et al. (2010). "Compositional Interpretation of PFS/MEx and TES/MGS Thermal Infrared Spectra of Phobos" (PDF). European Planetary Science Congress Abstracts, Vol. 5. Archived (PDF) from the original on 12 May 2011. Retrieved 1 October 2010.
  38. "Mars Moon Phobos Likely Forged by Catastrophic Blast". 27 September 2010. Archived from the original on 30 September 2010. Retrieved 1 October 2010.
  39. Rosenblatt, Pascal; Charnoz, Sébastien; Dunseath, Kevin M.; Terao-Dunseath, Mariko; Trinh, Antony; Hyodo, Ryuki; Genda, Hidenori; Toupin, Stéven (2016). "Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons" (PDF). Nature Geoscience. 9 (8): 581–583. Bibcode:2016NatGe...9..581R. doi:10.1038/ngeo2742. Archived (PDF) from the original on 9 March 2020. Retrieved 29 February 2020.
  40. "A giant impact: Solving the mystery of how Mars' moons formed". ScienceDaily. 4 July 2016. Archived from the original on 15 February 2021. Retrieved 1 August 2021.
  41. "Giant Impact May Have Created Mars Moons | Space". . 18 April 2018. Archived from the original on 26 January 2020. Retrieved 26 January 2020.
  42. Bagheri, Amirhossein; Khan, Amir; Efroimsky, Michael; Kruglyakov, Mikhail; Giardini, Domenico (22 February 2021). "Dynamical evidence for Phobos and Deimos as remnants of a disrupted common progenitor". Nature Astronomy. 5 (6): 539–543. Bibcode:2021NatAs...5..539B. doi:10.1038/s41550-021-01306-2. ISSN   2397-3366. S2CID   233924981. Archived from the original on 5 March 2021. Retrieved 8 April 2021.
  43. Elifritz, T. L. (2012). "OSIRIS-REx II to Mars — Mars Sample Return from Phobos and Deimos". Concepts and Approaches for Mars Exploration. 1679: 4017. Bibcode:2012LPICo1679.4017E.
  44. Britt, D. T.; Robinson, M.; Gulliver Team (2004). "The Gulliver sample return mission to Deimos". 35Th Cospar Scientific Assembly. 35: 3897. Bibcode:2004cosp...35.3897B. Archived from the original on 1 October 2021. Retrieved 3 September 2020.
  45. Ainsworth, Diane (11 September 1998). "Martian moon Phobos hip-deep in powder". JPL. Archived from the original on 12 December 2019. Retrieved 29 October 2018.
  46. Webster, Guy (4 May 2015). "Traffic Around Mars Gets Busy". NASA . Archived from the original on 6 May 2015. Retrieved 5 May 2015.

Further reading