The Mars Express orbiter has taken new images of the large extinct volcano Tharsis Tholus on Mars. At about 8 km (5 miles) tall and with a base that stretches about 155 km x 125 km (96 miles x 78 miles), it is a medium-sized volcano for Mars, but is a giant compared to volcanoes on Earth. It has been noticeably battered over the eons.
The caldera on top is almost circular, thought to have formed when the magma chamber below finally emptied, causing the chamber roof to collapse under its own weight. Two other sections have also collapsed on the volcano’s western and eastern flanks, forming scarps up to several kilometres high.
Tharsis Tholus is just one of many volcanoes on the planet, although all of them are believed to have become extinct millions of years ago.