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.
Just to remind you that things are still indeed going “boom” in our Solar System, here is a cluster of fresh craters on Mars created by an impact that occurred sometime between 2008 and 2014.
The craters are a result of a meteorite that broke apart during entry, striking the surface as fragments within a localized area. The largest crater’s ejecta field spans about 100 meters across.
It’s kinda like Mars’ way of saying “how’s that space program coming along?”
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.
Here’s a view of our home planet and its lovely Moon captured from 127 million miles away by NASA’s Mars Reconnaissance Orbiter on November 20, 2016. The sunlit part of Earth shows eastern Asia, the Indian Ocean, and Australia with ice-covered Antarctica visible as a bright white spot. The Moon has been brightened in this image, since it would be too dark in relation to a properly-exposed Earth to be readily visible (and I added more dark background to frame them a bit better.) But the positions and sizes of the two worlds are as captured by the HiRISE instrument, which was designed to map the surface of Mars in exquisite detail but occasionally is aimed to take a look back homeward.
Here’s a view of a section of a crater on Mars filled with a lacework of bright spidery fractures, acquired on Sept. 20, 2015 with the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter. The crater is approximately 3 miles (5 km) wide and located in Mars’ north polar region, and its old, infilled interior has undergone countless millennia of freeze/thaw cycles that have broken the surface into polygons of all sizes, outlined by frost-filled cracks.
The fractured segments get increasingly more compressed closer to the crater rim, which contains the outward freeze expansion.
According to the image description from the HiRISE team:
The crater rim constrains the polygon formation within the crater close to the rim, creating a spoke and ring pattern of cracks. This leads to more rectangular polygons than those near the center of the crater. The polygons close to the center of the crater display a more typical pattern. A closer look shows some of these central polygons, which have smaller polygons within them, and smaller polygons within those smaller polygons, which makes for a natural fractal!
Source: HiRISE/University of Arizona