Phobos (moon)

This article is about the moon of Mars. For the god, see Phobos (mythology). For other uses, see Phobos.
"Mars I" redirects here. For the Soviet Mars probe, see Mars 1. For other uses, see Mars 1 (disambiguation).

Phobos
A false color image of Phobos, as captured by the Mars Reconnaissance Orbiter in 2008
Discovery
Discovered byAsaph Hall
Discovery date18 August 1877
Designations
Designation
Mars I
Pronunciation/ˈfoʊbɒs/[1] or /ˈfoʊbəs/[2]
Named after
Φόβος
AdjectivesPhobian[3] /ˈfoʊbiən/[4]
Orbital characteristics
Epoch J2000
Periapsis9234.42 km[5]
Apoapsis9517.58 km[5]
9376 km[5] (2.76 Mars radii/1.472 Earth radii)
Eccentricity0.0151[5]
0.31891023 d
(7 h 39 m 12 s)[6]
2.138 km/s[5]
Inclination1.093° (to Mars's equator)
0.046° (to local Laplace plane)
26.04° (to the ecliptic)
Satellite ofMars
Physical characteristics
Dimensions25.90 km × 22.60 km × 18.32 km
(± 0.08 km × 0.08 km × 0.06 km)[7]
11.08±0.04 km[7]
1640±8 km2[7]
Volume5695±32 km3[7]
Mass1.060×1016 kg[8]
Mean density
1.861±0.011 g/cm3[7]
0.0057 m/s2[5]
(581.4 μ g)
11.39 m/s
(41 km/h)[5]
Synchronous
Equatorial rotation velocity
11.0 km/h (6.8 mph) (at longest axis)
0°
Albedo0.071 ± 0.012 at 0.54 μm[9]
Temperature≈ 233 K
11.8[10]

Phobos (/ˈfoʊbəs/; systematic designation: Mars I) 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 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 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 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.

  1. ^ "Phobos". Lexico UK English Dictionary. Oxford University Press. Archived from the original on 2 March 2020.
  2. ^ "Moons of Mars – the Center for Planetary Science".
  3. ^ Harry Shipman (2013) Humans in Space: 21st Century Frontiers, p. 317
  4. ^ The Century Dictionary and Cyclopedia (1914)
  5. ^ a b c d e f g "Mars: Moons: Phobos". NASA Solar System Exploration. 30 September 2003. Archived from the original on 19 October 2013. Retrieved 2 December 2013.
  6. ^ "ESA Science and Technology - Martian moons: Phobos". ESA. Retrieved 5 July 2023.
  7. ^ a b c d e f Cite error: The named reference Ernst2023 was invoked but never defined (see the help page).
  8. ^ Pätzold et al. (2014), as cited in Ernst et al. (2023).[7]
  9. ^ Clark, Beth Ellen (March 1998). Near Photometry of C-Type Asteroid 253 Mathilde (PDF). 29th Lunar and Planetary Science Conference. Lunar and Planetary Institute. Retrieved 27 April 2023.
  10. ^ "Mars' Moons".