Category Archives: Moons
On May 12, 2016, the Hubble Space Telescope captured a series of images of Mars and in them the planet’s moon Phobos can be seen appearing from behind the western limb. This was just 10 days before opposition which, in 2016, was the closest Mars had been to Earth since 2005, lending particularly good opportunity for picking out its largest—yet still quite small—moon.
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.
The HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter (MRO) is specifically designed to take super high-resolution images of the surface of Mars but it also does a pretty darn good job capturing pictures of other objects too—like Jupiter and its Galilean moons, several hundred million miles away! The image above was captured in expanded color (that is, it includes wavelengths in infrared) by HiRISE on January 11, 2007, and shows the giant planet from Mars orbit.
Mars and Jupiter were at opposition at the time, only about 345 million miles apart.
Discovered in June 2005, distant Pluto’s outermost moon Hydra it thought to have formed during the same collision four billion years ago that created the Pluto-Charon system that we see today. Yet despite its age this 31-mile (50-km) -long moon appears remarkably clean and bright, as witnessed by New Horizons during its close pass through the Pluto system in July 2015.
Turns out there is something new under the Sun, at least to us; on Tuesday, April 26 scientists announced the discovery of a new moon in the Solar System—but it’s not around Earth, or Jupiter, or Saturn, or any of the planets that you’ve long been familiar with. This new moon is orbiting a distant world even farther away and smaller than Pluto: the dwarf planet Makemake (pronounced mah-kay mah-kay), located deep in the Kuiper Belt and currently over 52 times farther away from the Sun than we are.