Mars in opposition in 2018 (annotated)

This annotated image of Mars shows features of the planet that were visible in summer 2018 despite a global dust storm. During the time of observation it was spring in Mars’ southern hemisphere, where a dust storm erupted and ballooned into a global event that is blanketing the entire planet. Even so, several distinctive features can be identified.

The large oval area at the lower right is the bright Hellas Basin. About 2200 kilometres across and nearly eight kilometres deep, it was formed about four billion years ago by an asteroid impact. Many global dust storms originate in this region.

The orange area in the upper centre of the image is Arabia Terra, a vast upland region in northern Mars. The landscape is densely cratered and heavily eroded, indicating that it could be among the oldest terrains on the planet.

South of Arabia Terra, running east to west along the equator, are the long dark features known as Sinus Sabaeus and Sinus Meridiani. These regions are covered by dark bedrock and fine-grained sand deposits ground down from ancient lava flows and other volcanic features. These sand grains are coarser and less reflective than the fine dust that gives the brighter regions of Mars their rusty appearance.

Because it is autumn in the northern hemisphere, a bright blanket of clouds covers the north polar region. Clouds also can be seen over the southern polar cap.

The two small moons of Mars, Phobos and Deimos, appear in the lower half of the image.