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Mars and Phobos; terrestrial planet; telluric planet; rocky planet; moon - Space Art Illustration

Mars and Phobos

This is how Mars and its tiny satellite Phobos might appear from a distance of about 100 miles from Phobos' surface. In this image Phobos is passing over the low martian plains of Syrtis Major. Below the plains extending down to Mars' terminator and beyond is the heavily cratered Terra Sabaea. Clouds of water-ice crystals are forming at the terminator between light and dark.

Looking more like a common potato than a celestial body, Phobos is actually the larger of Mars' two satellites, with a length of about 16 miles and about 11 miles across its smallest dimension. Phobos does not have enough mass for gravity to pull it into a uniform sphere like the larger satellites and planets in the Solar System.

Phobos may be an asteroid long ago captured by Mars' gravity, orbiting a mere 5,800 miles above Mars' surface, making it the closest satellite to its host planet in the Solar System. Phobos' orbit is so low that it completes one revolution in less than eight hours, easily outpacing by threefold Mars' rotation period of 24 hours, 40 minutes. The resulting tidal forces are causing Phobos' altitude to decay at the relatively rapid rate of 6 feet per century; in about 50 million years Phobos will either be torn apart by Mars' gravity or crash into the martian surface.


What's in a name?

Phobos (Greek for panic/fear) is named after the son of Ares (Roman Mars) from Greek Mythology. Phobos was discovered by American astronomer Asaph Hall in 1877.

Syrtis is the classical Roman name for the Gulf of Sidra on the coast of Libya.

Terra Sabaea translates as Cratered Highlands of Sabaea, though it was probably originally christened Sinus Sabeus (Bay of Sabaea) as Mars was not known to be cratered until the 1970s. The historic Sabaeans lived in the1st millennium BC in what is today Yemen. The Sabaean Kingdom may be the  same nation as the biblical Sheba.

Special thanks to James Hastings-Trew for his Mars & Moons digital data.

Copyright Walter B. Myers. All rights reserved.

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