Deimos (moon)

Deimos (moon)
NASA/JPL/University of Arizona · Public domain · source
Name	Deimos
Caption	Deimos as imaged by spacecraft
Discoverer	Asaph Hall
Discovered	12 August 1877
Major moons	Phobos (moon)
Mean radius	6.2 km
Mass	1.8×10^15 kg
Satellites	none
Orbital period	30.3 hours
Eccentricity	0.00033
Inclination	1.8°

Deimos (moon) Deimos is the smaller and outermost of the two natural satellites of Mars and one of the smallest known moons in the Solar System. It is irregular in shape, has a heavily cratered, dusty surface, and follows a near-circular, low-inclination orbit that keeps it well outside the synchronous rotation radius of Mars. Deimos has been the subject of observations by terrestrial astronomers, planetary probes, and missions associated with NASA and European Space Agency science programs.

Overview

Deimos orbits Mars as the outer companion to Phobos (moon), completing a full revolution roughly every 30.3 hours while exhibiting synchronous rotation relative to Mars. Its small size and low gravity make surface retention of ejecta difficult, a trait shared with other small bodies such as 433 Eros and 243 Ida. Deimos’s appearance—dominated by regolith and a set of shallow craters—links its study to work on asteroid belt objects like C-type asteroids and captured-body hypotheses advanced in comparisons with D-type asteroids and members of the Trojan asteroid population.

Discovery and Naming

Deimos was discovered on 12 August 1877 by Asaph Hall during an observational campaign at the United States Naval Observatory in Washington, D.C., which also yielded the discovery of Phobos (moon). The name derives from classical sources tied to Greek mythology and the retinue of Ares—the counterpart of Mars in Roman tradition—and follows scholarly naming conventions used by organizations such as the International Astronomical Union. Subsequent designations and catalog entries appeared in catalogs maintained by institutions like the Smithsonian Institution and observatory records tied to nineteenth-century surveys.

Orbit and Rotation

Deimos follows a near-circular orbit with eccentricity and inclination values that keep it nearly equatorial relative to Mars. Its semimajor axis places it at a distance where tidal interactions with Mars are weak compared with those acting on Phobos (moon), leading to long-term orbital stability on timescales constrained by perturbations from Jupiter and solar tides from Sun. Deimos is locked in synchronous rotation, presenting the same face toward Mars like many satellites studied in the context of tidal locking such as Europa and Moon. Perturbation analyses reference gravitational models used in studies of orbital resonance and planetary satellite dynamics developed by researchers at institutions like Jet Propulsion Laboratory and universities engaged in celestial mechanics.

Physical Characteristics

Deimos’s dimensions (approximately 15×12×11 km) yield a mean radius near 6.2 km and a bulk density consistent with a porous, primitive body comparable to carbonaceous chondrite parent bodies studied in meteoritics at museums such as the Natural History Museum, London. Its mass produces surface gravity orders of magnitude lower than that of Mars or Moon, influencing regolith behavior relevant to laboratories at Caltech and measurement teams at NASA Jet Propulsion Laboratory. Spectral measurements from telescopes including Keck Observatory and missions like Mars Global Surveyor and Mars Reconnaissance Orbiter indicate a low-albedo surface consistent with organic-rich or hydrated minerals similar to those found on C-type asteroids and certain Trojan asteroids.

Surface and Geology

The surface of Deimos is dominated by fine regolith and a small number of relatively shallow impact craters; the largest feature, a broad depression named after classical figures, displays subdued relief unlike the fresh, bowl-shaped craters seen on objects such as 511 Davida. The regolith’s physical properties have been modeled by teams at Imperial College London and MIT to understand cohesion and dust lofting under microgravity, drawing comparisons to measurements from Hayabusa and NEAR Shoemaker. Surface spectral heterogeneity observed by instruments on Mars Express and imaging from Viking program-era spacecraft contributes to debates over space weathering processes explored by researchers affiliated with Smithsonian Astrophysical Observatory.

Origin and Evolution

Competing hypotheses for Deimos’s origin include capture of a primitive asteroid from the outer main belt or formation from impact-generated debris following a giant collision into Mars, with proponents at institutions such as Brown University and University of Arizona testing models using numerical simulations and isotopic analogs from meteorite studies. The capture scenario invokes dissipative mechanisms such as gas drag in a primordial protoplanetary disk or three-body interactions examined in dynamical studies at Max Planck Institute for Astronomy, while the impact-origin scenario parallels formation theories applied to Earth’s Moon and proposes compositional ties to martian ejecta studied by planetary geologists at Lunar and Planetary Institute.

Exploration and Observations

Deimos has been imaged and analyzed by missions including the Mariner 9 spacecraft, the Viking program orbiters, Mars Global Surveyor, Mars Reconnaissance Orbiter, and the Mars Odyssey mission, with instrumental teams at NASA facilities producing high-resolution datasets. Proposals for future investigation include sample-return concepts and lander missions proposed by teams at JAXA, ESA, and NASA Jet Propulsion Laboratory, leveraging technologies developed for missions like Hayabusa2 and OSIRIS-REx. Earth-based telescopic campaigns using facilities such as Hubble Space Telescope and ground-based observatories continue to refine Deimos’s photometric, spectral, and dynamical parameters in coordination with planetary science programs at universities and space agencies.

Category:Moons of Mars Category:Natural satellites