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Deimos (moon)

Deimos (or Mars II) is the smaller moon of Mars. Its name comes from the Greek word for terror. Its orbital period is 30.3 hours, which is 1.263 days.

Deimos Deimos symbol (bold).svg (rare)
NASA-Deimos-MarsMoon-20090221.jpg
Deimos, captured by the Mars Reconnaissance Orbiter in false color
Discovery
Discovered byAsaph Hall
Discovery date12 August 1877
Designations
MPC designationMars II
Pronunciation/ˈdaɪməs/[1] to /ˈdiːməs/[2] or as Greek Δεῖμος (approximated /ˈdeɪmɒs/)[3]
Named after
Δεῖμος
AdjectivesDeimian /ˈdaɪmiən/[4]
Orbital characteristics
Epoch 23 September 2012 (JD 2456191.5)
Periapsis23455.5 km
Apoapsis23470.9 km
23463.2 km[5] (6.92 Mars radii)
Eccentricity0.00033[5]
1.263 d[5]
(30.312 h)
1.3513 km/s[6]
Inclination0.93° (to Mars's equator)
1.791° (to the local Laplace plane)[5]
27.58° (to the ecliptic)
Satellite ofMars
Physical characteristics
Dimensions16.08 × 11.78 × 10.22 km
(± 0.16 × 0.12 × 0.10 km)[7]
Mean radius
6.27±0.07 km[7]
522±8 km2[7]
Volume1033±19 km3[7]
Mass1.51×1015 kg[8]
Mean density
1.465±0.051 g/cm3[7]
0.003 m/s2[6]
(306 μ g)
5.556 m/s
(20 km/h)[6]
Synchronous[5]
Albedo0.068±0.007[9]
Temperature≈ 233 K
12.89[10]

Deimos is only 15 kilometers in diameter. It is covered with craters, as Earth's moon and other bodies without an atmosphere are.

Discovery and naming

Deimos was discovered by Asaph Hall at the United States Naval Observatory in Washington, D.C. on 12 August 1877.[11]

It is named after the god Deimos in Greek mythology, who was one of Mars' sons, and means Panic.

Physical characteristics

Deimos is not spherical with triaxial dimensions of 15 × 12.2 × 11 km.[12] Deimos is made up of rock rich in carbonaceous material. It is has lots of craters.[13] Escape velocity from Deimos is 5.6 m/s.[14] The apparent magnitude of Deimos is 12.45.[15]

Exploration

The Soviet Phobos program sent two probes to Phobos. In case Phobos 1 succeeded, Phobos 2 could have been sent to Deimos. Both probes launched successfully in July 1988.

In 1997 and 1998, the proposed Aladdin mission was selected. The plan was to visit both Phobos and Deimos, and launch projectiles at the satellites. The probe would collect the dust kicked into space as it made a slow flyby. These samples would be returned to Earth for study three years later.[16]

Also, the sample-return mission called Gulliver to Deimos, in bringing 1 kilogram (2.2 pounds) of material from Deimos to Earth.[17]

Another concept of sample-return mission from Phobos and Deimos is OSIRIS-REx 2, which would use heritage from the first OSIRIS-REx.[18]

In March 2014, a mission was proposed to place an orbiter on Mars orbit by 2021 and study Phobos and Deimos. It is called Phobos And Deimos & Mars Environment (PADME).[19][20]

Deimos (moon) Media

  • Asaph Hall III, discoverer of Deimos

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

  • The two named craters on Deimos

  • Orbits of Phobos and Deimos (to scale)

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

  • Deimos transits the Sun – as viewed by the Mars rover Opportunity (4 March 2004)

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

References

  1. ↑ The Century Dictionary and Cyclopedia (1914)
  2. ↑ Moons of Mars – the Center for Planetary Science. Retrieved 2025-06-08.
  3. ↑ DeimosOxford University Press.
  4. ↑ Harry Shipman (2013) Humans in Space: 21st Century Frontiers, p. 317
  5. ↑ 5.0 5.1 5.2 5.3 5.4 HORIZONS Web-Interface (21 September 2013)NASA. Retrieved 4 December 2013.
  6. ↑ 6.0 6.1 6.2 Mars:Moons:Deimos (September 30, 2004)NASA Solar SystemExploration. Retrieved June 8, 2025.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 Ernst, Carolyn M.. High-resolution shape models of Phobos and Deimos from stereophotoclinometry. Earth, Planets, and Space (December 2023). Retrieved June 8, 2025.
  8. ↑ Jacobson (2010), as cited in Ernst et al. (2023).[7]
  9. ↑ Planetary Satellite Physical Parameters (July 30, 2006)Jet Propulsion Laboratory (Solar System Dynamics). Retrieved June 8, 2025.
  10. ↑ Mars' Moons.
  11. ↑ Campbell, W. W.. The Beginning of the Astronomical Day (in en). Publications of the Astronomical Society of the Pacific 30 (178) (1918). p. 358. doi:10.1086/122784.
  12. ↑ Deimos, moon of Mars - The Solar System on Sea and Sky. www.seasky.org. Retrieved 2020-10-25.
  13. ↑ Busch, Michael W.. Arecibo radar observations of Phobos and Deimos (in en). Icarus 186 (2) (2007). p. 581–584. doi:10.1016/j.icarus.2006.11.003.
  14. ↑ Solar System Exploration: Planets: Mars: Moons: Deimos: Facts & Figures (2012-10-12). Retrieved 2020-10-25.
  15. ↑ Planetary Satellite Physical Parameters. ssd.jpl.nasa.gov. Retrieved 2020-10-25.
  16. ↑ Barnouin-Jha, O.S.. 1999 IEEE Aerospace Conference. Proceedings (Cat. No.99TH8403) 1 (1999). Snowmass at Aspen, CO, USA: IEEE. p. 403–412 vol.1. ISBN 978-0-7803-5425-8. doi:10.1109/AERO.1999.794346.
  17. ↑ Dr. Britt – The Gulliver Mission: Sample Return from Deimos.
  18. ↑ Elifritz, T. L.. OSIRIS-REx II to Mars --- Mars Sample Return from Phobos and Deimos. Concepts and Approaches for Mars Exploration 1679 (2012-06-01). p. 4017.
  19. ↑ Phobos And Deimos & Mars Environment (PADME): A LADEE-Derived Mission to Explore Mars's Moons and the Martian Orbital Environment.
  20. ↑ Reyes, Tim. Making the Case for a Mission to the Martian Moon Phobos (in en-US). Universe Today (2014-10-01). Retrieved 2020-10-25.
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