Deimos (moon)

Template:Short description Template:Redirect Template:Use dmy dates {{#invoke:infobox|infoboxTemplate | class = vcard | titleclass = fn org | title = Deimos | image = {{#invoke:InfoboxImage|InfoboxImage|image=NASA-Deimos-MarsMoon-20090221.jpg|upright={{#if:||1.1}}|alt=}} | caption = Deimos, captured by the Mars Reconnaissance Orbiter in false color | headerstyle = {{#if:#ffc0c0|background-color:#ffc0c0|background-color:#E0CCFF}} | labelstyle = max-width:{{#if:||11em}}; | autoheaders = y

| header1 = Discovery

| header10 = {{#if:|Designations|Designations}}

| label11 = Template:Longitem | data11 = Mars II | label12 = Pronunciation | data12 = Template:IPAc-en<ref>The Century Dictionary and Cyclopedia (1914)</ref> to Template:IPAc-en<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> or as Greek Δεῖμος (approximated Template:IPAc-en)<ref>Template:Cite dictionary</ref> | label13 = Template:Longitem | data13 = Δεῖμος | label14 = Template:Longitem | data14 = | label15 = Template:Longitem | data15 = | label16 = Adjectives | data16 = Deimian Template:IPAc-en<ref>Harry Shipman (2013) Humans in Space: 21st Century Frontiers, p. 317</ref> | label17 = Symbol | data17 = File:Deimos symbol (bold).svg (rare)

| header20 = Orbital characteristics{{#ifeq:|yes| (barycentric)}}

| data21 = | data22 = {{#if:23 September 2012 (JD 2456191.5) |Epoch 23 September 2012 (JD 2456191.5)}} | data23 = {{#if: | Uncertainty parameter {{{uncertainty}}}}} | label24 = Observation arc | data24 = | label25 = Earliest precovery date | data25 = | label26 = {{#switch:{{{apsis}}} |apsis|gee|barion|center|centre|(apsis)=Apo{{{apsis}}} |Ap{{#if:|{{{apsis}}}|helion}}}} | data26 = | label27 = Peri{{#if:|{{{apsis}}}|helion}} | data27 = | label28 = Peri{{#if:|{{{apsis}}}|apsis}} | data28 = Template:Val | label29 = {{#switch:{{{apsis}}} |helion|astron=Ap{{{apsis}}} |Apo{{#if:|{{{apsis}}}|apsis}}}} | data29 = Template:Val | label30 = Periastron | data30 = | label31 = Apoastron | data31 = | label32 = Template:Longitem | data32 = Template:Val<ref name=Horizons>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> (6.92 Mars radii) | label33 = Template:Longitem | data33 = | label34 = Eccentricity | data34 = Template:Val<ref name="Horizons" /> | label35 = Template:Longitem | data35 = Template:Val<ref name="Horizons" />
(30.312 h) | label36 = Template:Longitem | data36 = | label37 = Template:Longitem | data37 = Template:Val<ref name="NASA" /> | label38 = Template:Longitem | data38 = | label39 = Template:Longitem | data39 = | label40 = Inclination | data40 = 0.93° (to Mars's equator)
1.791° (to the local Laplace plane)<ref name="Horizons" />
27.58° (to the ecliptic) | label41 = Template:Longitem | data41 = | label42 = Template:Longitem | data42 = | label43 = Template:Longitem | data43 = | label44 = Template:Longitem | data44 = | label45 = Template:Longitem | data45 = | label46 = Template:Nowrap | data46 = | label47 = Satellite of | data47 = Mars | label48 = Group | data48 = | label49 = {{#switch: |yes|true=Satellites |Known satellites}} | data49 = | label50 = Star | data50 = | label51 = Earth MOID | data51 = | label52 = Mercury MOID | data52 = | label53 = Venus MOID | data53 = | label54 = Mars MOID | data54 = | label55 = Jupiter MOID | data55 = | label56 = Saturn MOID | data56 = | label57 = Uranus MOID | data57 = | label58 = Neptune MOID | data58 = | label59 = T_Jupiter | data59 =

| header60 = Proper orbital elements

| label61 = Template:Longitem | data61 = {{#if: |{{{p_semimajor}}} AU}} | label62 = Template:Longitem | data62 = | label63 = Template:Longitem | data63 = | label64 = Template:Longitem | data64 = {{#if: |{{{p_mean_motion}}} deg Template:\yr}} | label65 = Template:Longitem | data65 = {{#if:|{{#expr:360/1 round 5}} yr
({{#expr:365.25*360/1 round 3}} d) }} | label66 = Template:Longitem | data66 = {{#if:|{{{perihelion_rate}}} arcsec Template:\yr }} | label67 = Template:Longitem | data67 = {{#if:|{{{node_rate}}} arcsec Template:\yr}}

| header70 = Template:Anchor{{#if:| Physical characteristics|Physical characteristics}}

| label71 = Dimensions | data71 = Template:Val km
(± Template:Val km)<ref name="Ernst2023"/> | label72 = Template:Longitem | data72 = | label73 = Template:Longitem | data73 = Template:Val<ref name="Ernst2023"/> | label74 = Template:Longitem | data74 = | label75 = Template:Longitem | data75 = | label76 = Flattening | data76 = | label77 = Circumference | data77 = | label78 = Template:Longitem | data78 = Template:Val<ref name="Ernst2023"/> | label79 = Volume | data79 = Template:Val<ref name="Ernst2023"/> | label80 = Mass | data80 = Template:Val Template:Refn | label81 = Template:Longitem | data81 = Template:Val<ref name="Ernst2023"/> | label82 = Template:Longitem | data82 = Template:Val<ref name="NASA" />
(306 μ g) | label83 = Template:Longitem | data83 = | label84 = Template:Longitem | data84 = Template:Val
(20 km/h)<ref name="NASA" /> | label85 = Template:Longitem | data85 = Synchronous<ref name="Horizons" /> | label86 = Template:Longitem | data86 = | label87 = Template:Longitem | data87 = | label88 = Template:Longitem | data88 = | label89 = Template:Longitem | data89 = | label90 = Template:Longitem | data90 = | label91 = Template:Longitem | data91 = | label92 = Template:Longitem | data92 = | label93 = {{#if: |Template:Longitem |Albedo}} | data93 = Template:Val<ref name="JPLSSD" /> | label94 = Temperature | data94 = ≈ 233 K

| data100 = {{#if:|

Surface temp.	min	mean	max
{{{temp_name1}}}
{{{temp_name2}}}
{{{temp_name3}}}
{{{temp_name4}}}

}}

| label101 = Surface absorbed dose rate | data101 = | label102 = Surface equivalent dose rate | data102 = | label103 = Template:Longitem | data103 = | label104 = Template:Longitem | data104 = | label105 = Template:Longitem | data105 = 12.89<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> | label106 = Template:Longitem | data106 = | label107 = Template:Longitem | data107 =

| header110 = Atmosphere

| below = {{#if:||Template:Reflist }}

}}{{#invoke:Check for unknown parameters|check|unknown=Template:Main other|preview=Page using Template:Infobox planet with unknown parameter "_VALUE_"|ignoreblank=y| abs_magnitude | adjective | adjectives | albedo | allsatellites | alt_names | angular_dist | angular_size | aphelion | apoapsis | apsis | apoastron | arg_peri | asc_node | atmosphere | atmosphere_composition | atmosphere_ref | avg_speed | axial_tilt | background | barycentric | bgcolour | caption | circumference | declination | density | dimensions | discovered | discoverer | discovery_method | discovery_ref | discovery_site | earliest_precovery_date | eccentricity | epoch | equatorial_radius | escape_velocity | exosolar planets | extrasolarplanet | family | flattening | group | image | image_alt | image_scale | inclination | jupiter_moid | label_width | long_periastron | magnitude | mars_moid | mass | max_temp_1 | max_temp_2 | max_temp_3 | max_temp_4 | mean_anomaly | mean_diameter | mean_motion | mean_orbit_radius | mean_radius | mean_temp_1 | mean_temp_2 | mean_temp_3 | mean_temp_4 | mercury_moid | min_temp_1 | min_temp_2 | min_temp_3 | min_temp_4 | minorplanet | moid | moment_of_inertia_factor | mp_category | mp_name | mpc_name | name | named_after | neptune_moid | node_rate | note | observation_arc | orbit_diagram | orbit_ref | p_eccentricity | p_inclination | p_mean_motion | p_orbit_ref | p_semimajor | periapsis | periastron | perihelion | perihelion_rate | period | physical_ref | polar_radius | pole_ecliptic_lat | pole_ecliptic_lon | pronounce | pronounced | right_asc_north_pole | rot_velocity | rotation | satellite_of | satellites | saturn_moid | scale_height | semi-amplitude | semimajor | sidereal_day | single_temperature | spectral_type | star | surface_area | surface_grav | surface_pressure | surface_absorbed_dose_rate | surface_equivalent_dose_rate | symbol | synodic_period | temp_name1 | temp_name2 | temp_name3 | temp_name4 | time_periastron | tisserand | uncertainty | uranus_moid | venus_moid | volume }}

Deimos (Template:IPAc-en; systematic designation: Mars II)<ref name="Blunck" /> is the smaller and outer of the two natural satellites of Mars, the other being Phobos. Deimos has a mean radius of Template:Convert and takes 30.3 hours to orbit Mars.<ref name="Horizons" /> Deimos is Template:Convert from Mars, much farther than Mars's other moon, Phobos.<ref name="SAS-2016">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is named after Deimos, the Ancient Greek god and personification of dread and terror.

Discovery and etymologyEdit

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}

File:T-asaph-hall.jpg

Asaph Hall III, discoverer of Deimos

Deimos was discovered by Asaph Hall at the United States Naval Observatory in Washington, D.C., on 12 August 1877, at about 07:48 UTC.Template:Efn Hall, who also discovered Phobos shortly afterwards, had been specifically searching for Martian moons at the time.

The moon is named after Deimos, a figure representing dread in Greek mythology.<ref name=Blunck>Template:Cite book</ref> The name was suggested by academic Henry Madan, who drew from Book XV of the Iliad, where Ares (Greek counterpart of the Roman god Mars) summons Dread (Deimos) and Fear (Phobos).<ref>Hall, A.; Names of the Satellites of Mars, Astronomische Nachrichten, Vol. 92, No. 2187 (14 March 1878, signed 7 February 1878), p. 47/48</ref>

Planetary moons other than Earth's were never given symbols in the astronomical literature. Denis Moskowitz, a software engineer who designed most of the dwarf planet symbols, proposed a Greek delta (the initial of Deimos) combined with Mars' spear as the symbol of Deimos (File:Deimos symbol (fixed width).svg). This symbol is not widely used.<ref name=moons>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

OriginEdit

The origin of Mars' moons is unknown and the hypotheses are controversial.<ref name="burns">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</ref> The main hypotheses are that they formed either by capture or by accretion.

Because of the postulated similarity to the composition of C- or D-type asteroids, one hypothesis is that the moons may be objects captured into Martian orbit from the asteroid belt, with orbits that have been circularized either by atmospheric drag or tidal forces,<ref name="cazenave" /> as capture requires dissipation of energy. The current Martian atmosphere is too thin to capture a Phobos-sized object by atmospheric braking.<ref name="burns" /> Geoffrey Landis has pointed out that the capture could have occurred if the original body was a binary asteroid that separated due to tidal forces.<ref name="landis">Landis, G. A., "Origin of Martian Moons from Binary Asteroid Dissociation," American Association for the Advancement of Science Annual Meeting; Boston, MA, 2001; abstract.</ref> The main alternative hypothesis is that the moons accreted in the present position. 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 planetesimal.<ref>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</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

In 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 the Mars InSight Mission and other missions, they proposed that the moons were born from the 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.<ref>Template:Cite journal</ref>

Physical characteristicsEdit

File:Moon Phobos Deimos.png

Size comparison between Phobos, Deimos and the Moon (right)

Deimos is a gray-colored body. Like most bodies of its size, Deimos is highly non-spherical with triaxial dimensions of Template:Cvt, corresponding to a mean diameter of Template:Cvt which makes it about 57% the size of Phobos.<ref name="Ernst2023"/> Deimos is composed of rock rich in carbonaceous material, much like C-type asteroids and carbonaceous chondrite meteorites.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It is cratered, but the surface is noticeably smoother than that of Phobos, caused by the partial filling of craters with regolith.Template:Citation needed The regolith is highly porous and has a radar-estimated density of only Template:Val.<ref name=Michaelbusch>Template:Cite journal</ref>

Escape velocity from Deimos is 5.6 m/s.<ref name=NASA>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> This velocity could theoretically be achieved by a human performing a vertical jump.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The apparent magnitude of Deimos is 12.45.<ref name=JPLSSD>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Template:Clear left

Named geological featuresEdit

Only two geological features on Deimos have been given names. The craters Swift and Voltaire are named after writers who speculated on the existence of two Martian moons before Phobos and Deimos were discovered.<ref>{{#invoke:citation/CS1|citation |CitationClass=web

}}</ref>

{{safesubst:#invoke:Check for unknown parameters|check|unknown=|preview=Page using Template:Center with unknown parameter "_VALUE_"|ignoreblank=y| 1 | style }}

Template:DeimosCraterNames

Template:Anchor

Craters	Coordinates	Diameter (km)	Approval Year	Eponym	Ref
Swift	Template:Coord	1	1973	Jonathan Swift; Irish writer (1667–1745)	Template:WGPSN
Voltaire	Template:Coord	1.9	1973	Voltaire; French writer (1694–1778)	Template:WGPSN

Orbital characteristicsEdit

File:Orbits of Phobos and Deimos.gif

Orbits of Phobos and Deimos (to scale)

Deimos's orbit is nearly circular and is close to Mars's equatorial plane. Deimos is possibly an asteroid that was perturbed by Jupiter into an orbit that allowed it to be captured by Mars, though this hypothesis is still controversial and disputed.<ref name="burns" /> Both Deimos and Phobos 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 likely by a combination of atmospheric drag and tidal forces;<ref name="cazenave">Template:Cite journal</ref> it is not clear that sufficient time was available for this to have occurred for Deimos.<ref name="burns" />

File:PIA17352-MarsMoons-PhobosPassesDeimos-RealTime.gif

Curiosity's view of the Mars moons: Phobos passing in front of Deimos in real-time (video-gif, 1 August 2013)

As seen from Mars, Deimos would have an angular diameter of no more than 2.5 minutes (sixty minutes make one degree), one twelfth of the width of the Moon as seen from Earth, and would therefore appear almost star-like to the naked eye.<ref name="richardson">Template:Citation</ref> At its brightest ("full moon") it would be about as bright as Venus is from Earth; at the first- or third-quarter phase it would be about as bright as Vega. With a small telescope, a Martian observer could see Deimos's phases, which take 1.2648<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> days (Deimos's synodic period) to run their course.<ref name="richardson" />

Unlike Phobos, which orbits so fast that it rises in the west and sets in the east, Deimos rises in the east and sets in the west, slower than Mars's rotation speed. The Sun-synodic orbital period of Deimos of about 30.4 hours exceeds the Martian solar day ("sol") of about 24.7 hours by such a small amount that 2.48 days (2.41 sols) elapse between its rising and setting for an equatorial observer. From Deimos-rise to Deimos-rise (or setting to setting), 5.466 days (5.320 sols) elapse.Template:Citation needed

Because Deimos's orbit is relatively close to Mars and has only a very small inclination to Mars's equator, it cannot be seen from Martian latitudes greater than 82.7°.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Deimos's orbit is slowly getting larger, because it is far enough away from Mars and because of tidal acceleration. It is expected to eventually escape Mars's gravity.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Solar transitsEdit

File:Transit of Deimos from Mars.jpg

Deimos transits the Sun Template:Snd as viewed by the Mars rover Opportunity (4 March 2004)

{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} Deimos regularly passes in front of the Sun as seen from Mars. It is too small to cause a total eclipse, appearing only as a small black dot moving across the Sun. Its angular diameter is only about 2.5 times the angular diameter of Venus during a transit of Venus from Earth. On 4 March 2004 a transit of Deimos was photographed by Mars rover Opportunity, and on 13 March 2004 a transit was photographed by Mars rover Spirit.Template:Citation needed

ExplorationEdit

File:PIA17351-ApparentSizes-MarsDeimosPhobos-EarthMoon.jpg

Deimos and Phobos as seen from Mars, compared to the Moon as seen from Earth (in angular sizes)

Overall, its exploration history is similar to those of Mars and of Phobos.<ref>Mars Phobos and Deimos Survey (M-PADS)–A Martian Moons Orbiter and Phobos Lander (Ball, Andrew J.; Price, Michael E.; Walker, Roger J.; Dando, Glyn C.; Wells, Nigel S; and Zarnecki, John C. (2009). Mars Phobos and Deimos Survey (M-PADS)–A Martian Moons Orbiter and Phobos Lander. Advances in Space Research, 43(1), pp. 120–127.)</ref> Deimos has been photographed close-up by several spacecraft whose primary mission has been to photograph Mars, including in March 2023 during a rare close encounter by the Emirates Mars Mission.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> No landings on Deimos have been made.

In 1997 and 1998, the proposed 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).<ref>Template:Cite book</ref> These samples would be returned to Earth for study three years later.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The principal investigator was Carle M. Pieters of Brown University. The total mission cost, including launch vehicle and operations was $247.7 million.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Ultimately, the mission chosen to fly was MESSENGER, a probe to the planet Mercury.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

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 currently under further study.<ref>Lee, P. et al. 2010. Hall: A Phobos and Deimos Sample Return Mission. 44th Lunar Planet. Sci. Conf., The Woodlands, TX. 1–5 Mar 2010. [#1633] Template:Bibcode.</ref>

Also, the sample-return mission called Gulliver has been conceptualized and dedicated to Deimos,<ref name=britt>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> in which 1 kilogram (2.2 pounds) of material from Deimos would be returned to Earth.<ref name="britt" />

Another concept of sample-return mission from Phobos and Deimos is OSIRIS-REx 2, which would use heritage from the first OSIRIS-REx.<ref>Template:Cite journal</ref>

In March 2014, a Discovery class mission was proposed to place an orbiter in Mars orbit by 2021 and study Phobos and Deimos. It was called Phobos And Deimos & Mars Environment (PADME).<ref name="lpsc 2014">Template:Cite conference</ref><ref name="Reyes 2014">Template:Cite news</ref>

Human exploration of Deimos could serve as a catalyst for the human exploration of Mars. Recently, it was proposed that the sands of Deimos or Phobos could serve as a valuable material for aerobraking in the colonization of Mars.<ref name="arias16">Template:Cite conference</ref> See Phobos for more detail.

ISRO's Mars Orbiter Mission captured the first pictures of the far side on Deimos.Template:Citation needed

In April 2023, astronomers released close-up global images, for the first time, of Deimos that were taken by the Mars Hope orbiter.<ref>Template:Cite journal</ref><ref name="SPC-20230424">Template:Cite news</ref> Observations reported by this mission contravene the captured asteroid hypothesis and indicate basaltic planetary origin of Deimos.<ref>Template:Cite news</ref>

During its gravity assist from Mars en route to 65803 Didymos, the ESA's Hera took observations of Deimos in March 2025, approaching at a distance of 300 km (190 mi).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The JAXA MMX Mission to Phobos and Deimos is planned for launch in October 2026.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It will make flybys of Deimos to investigate its composition and structure, as well as performing a sample return on Phobos and placing a rover on that moon.