Moons of Mars

Enhanced color image of Phobos (MRO, 23 March 2008)

Enhanced color image of Deimos (MRO, 21 February 2009)

The two moons of Mars are Phobos and Deimos.^[1] They are irregular in shape.^[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.

Compared to the Earth's Moon, the moons Phobos and Deimos are small. Phobos has a diameter of 22.2 km (13.8 mi) and a mass of 1.08×10¹⁶ kg, while Deimos measures 12.6 km (7.8 mi) across, with a mass of 1.5×10¹⁵ kg. Phobos orbits closer to Mars, with a semi-major axis of 9,377 km (5,827 mi) and an orbital period of 7.66 hours; while Deimos orbits farther with a semi-major axis of 23,460 km (14,580 mi) and an orbital period of 30.35 hours.

Two major hypotheses have emerged as to the origin of the moons: The first suggests that they originated from Mars itself, perhaps from a giant impact event suggested to have created the Martian dichotomy and the Borealis Basin. The second suggests that they are captured asteroids. Both hypotheses are compatible with current data, though upcoming sample return missions may be able to distinguish which hypothesis is correct.^[4]

^ Andrews, Robin George (25 July 2020). "Why the 'Super Weird' Moons of Mars Fascinate Scientists - What's the big deal about little Phobos and tinier Deimos?". The New York Times. Archived from the original on 25 July 2020. Retrieved 25 July 2020.
^ "NASA - Under the Moons of Mars". Nasa.gov. Archived from the original on 29 March 2014. Retrieved 28 February 2013.
^ Sheehan, William (1996). "Chapter 5: 1877". The Planet Mars: A History of Observation and Discovery. University of Arizona Press. Bibcode:1996pmho.book.....S. Archived from the original on 3 November 2017. Retrieved 28 February 2013.
^ Kuramoto, Kiyoshi (23 July 2024). "Origin of Phobos and Deimos Awaiting Direct Exploration". Annual Review of Earth and Planetary Sciences. 52 (1): 495–519. Bibcode:2024AREPS..52..495K. doi:10.1146/annurev-earth-040522-110615. ISSN 0084-6597.

[NYT-20200725-1] Andrews, Robin George (25 July 2020). "Why the 'Super Weird' Moons of Mars Fascinate Scientists - What's the big deal about little Phobos and tinier Deimos?". The New York Times. Archived from the original on 25 July 2020. Retrieved 25 July 2020.

[2] "NASA - Under the Moons of Mars". Nasa.gov. Archived from the original on 29 March 2014. Retrieved 28 February 2013.

[3] Sheehan, William (1996). "Chapter 5: 1877". The Planet Mars: A History of Observation and Discovery. University of Arizona Press. Bibcode:1996pmho.book.....S. Archived from the original on 3 November 2017. Retrieved 28 February 2013.

[4] Kuramoto, Kiyoshi (23 July 2024). "Origin of Phobos and Deimos Awaiting Direct Exploration". Annual Review of Earth and Planetary Sciences. 52 (1): 495–519. Bibcode:2024AREPS..52..495K. doi:10.1146/annurev-earth-040522-110615. ISSN 0084-6597.

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