Olympus Mons, extinct Martian volcano, 1976.
© National Aeronautics & Space Administration / Science & Society
Olympus Mons is the largest volcano in the Solar System. Mars has a number of volcanoes, which are generally larger than those on Earth. This is thought to be due to the lower gravity on Mars and more importantly, the fact that because Mars has never been tectonically active, magma welling up from the planet's interior continued to erupt from a volcano at the same location. There is currently no volcanic activity on Mars, but with the most recent volcanic features dated at between 10 and 100 million years ago, relatively recently in geological terms, scientists have not ruled out the posibility of volcanoes erupting again in the future. This false colour image taken from the Viking 1 Orbiter shows the differences in the lava flows that have accumulated over time.