Can you feel the heat? NASA’s Mars Odyssey can see it! This is an image of Mars’ smaller moon Deimos, captured with Odyssey’s THEMIS (Thermal Emission Imaging System) instrument on Feb. 15, 2018. Part of the 7-mile-wide Moon was in shadow, but the sunlit surface area reached temperatures up to 200 K (that’s still pretty cold for us, though… –100ºF / -73ºC!)
Mars isn’t a planet well-known for its natural satellites but it actually does have two small moons. The larger, Phobos, is an irregularly-shaped, heavily grooved and cratered world only about 17 miles (27 km) across at its widest. It orbits Mars so closely that it completes 3 orbits every day, and isn’t even visible from some parts of the planet. But Phobos has an even smaller companion in orbit: Deimos, which at the most 7.5 miles across is half Phobos’ size. Deimos orbits Mars much further away as well, taking about 30 hours to complete one orbit.
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The European Space Agency’s Mars Express has captured footage of Mars’ two tiny moons, Phobos and Deimos, passing each other in what is known as a “mutual event”. Although the moons themselves are in no special positions the images are noteworthy, being the first time the moons have been photographed passing each other.
Mars Express’ High Resolution Stereo Camera (HRSC) took 130 images of the moons on November 5 over a time period of 1.5 minutes. The images were then combined to make this animation.
The moons are separated by a distance of 8,948 miles in these images.
14-mile-wide Phobos is named after the Greek word for fear, 8-mile-wide Deimos is named after the word for dread. Small and irregularly-shaped, they are most likely captured asteroids. Both were discovered in 1877 by American astronomer Asaph Hall.
Credit: ESA / DLR / FU Berlin (G. Neukum)
Released today, this photo from the HiRISE camera aboard the MRO shows the smooth face of Deimos, Mars’ smaller moon. (Its larger brother is Phobos, also photographed by the HiRISE in 2008.) Its surface is covered by a fine layer of rocky soil, called regolith, which gives it its smooth texture.
Deimos is only about 6-7 miles wide. Both it and Phobos are thought to have once been asteroids captured by Mars, perhaps after first being knocked from their own orbits by the massive gravity of Jupiter.
Deimos and Phobos are named after the Greek gods of panic and fear, respectively. Fitting for moons of Mars, whose Roman namesake is the bringer of war.
Image credit: NASA/JPL/University of Arizona