Moons of Mars
[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 panic) and Deimos (terror and dread) who accompanied their father Ares (Mars in Roman mythology, hence the name of the planet) into battle.
Both hypotheses are compatible with current data, though upcoming sample return missions may be able to distinguish which hypothesis is correct.
When Galileo Galilei (1564–1642), as a hidden report about his 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 (1571–1630) had misinterpreted it to mean Salve umbistineum geminatum Martia proles (Hello, furious twins, sons of Mars).
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.
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.
[22] The names, originally spelled Phobus and Deimus, respectively, were suggested by Henry Madan (1838–1901), Science Master of Eton, from Book XV of the Iliad, where Ares summons Fear and Fright.
The hoax gained worldwide attention when Houston's claim was repeated in earnest by a Soviet scientist, Iosif Shklovsky,[24] who, based on a later-disproven density estimate, suggested Phobos was a hollow metal shell.
At some point in the future, when it falls within the Roche limit, Phobos will be broken up by these tidal forces and either crash into Mars or form a ring.
[7][34] 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,[35] although it is not clear that sufficient time is available for this to occur for Deimos.
[32] Geoffrey Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated under tidal forces.
[43] Most recently, Amirhossein Bagheri and his colleagues from ETH Zurich and US Naval Observatory, proposed a new hypothesis on the origin of the moons.
[44] But a recent paper suggests that it seems unlikely that Phobos and Deimos are split directly from a single ancestral moon.
Another suggestion is that Mars was hit by an object from beyond the orbit of Saturn or Neptune, about 3% the mass of the planet and consisting of at least 30% and up to 70% water ice.
This would create a disc around the planet with large amounts of water that cooled it down and changed the chemical composition of the rocks, likely producing a type of minerals called phyllosilicates.
[46] 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.
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.
Efforts to reactivate the craft were unsuccessful, and it fell back to Earth in an uncontrolled re-entry on 15 January 2012, over the Pacific Ocean, west of Chile.
[55] JAXA plans to launch Martian Moons eXploration (MMX) mission in 2026 to bring back the first samples from Phobos.
[56][57] The spacecraft will enter orbit around Mars, then transfer to Phobos,[58] and land once or twice and gather sand-like regolith particles using a simple pneumatic system.
[60][61] The spacecraft will then take off from Phobos and make several flybys of the smaller moon Deimos before sending the Return Module back to Earth, arriving in July 2029.
