Volcanology of Mars through the crust to produce volcanic mountains. However, the largest volcano on the planet, Olympus Mons, is thought to have formed when the plates were not moving. Olympus Mons may have formed just after the plate motion stopped. The mare-like plains on Mars are roughly 3 to 3.5 billion years old. The giant shield volcanoes are younger, formed between 1 and 2 billion years ago. Olympus Mons may be "as young as 200 million years." Norman H. Sleep, professor of geophysics at Stanford University, described how the three volcanoes that form a line along the Tharsis Ridge may be extinct
Moons of Uranus spheroid are highlighted in light blue and bolded. Irregular moons with retrograde orbits are shown in dark grey. Margaret, the only known irregular moon of Uranus with a prograde orbit, is shown in light grey. "Sources:" NASA/NSSDC, Sheppard, et al. 2005. For the recently discovered outer irregular moons (Francisco through Ferdinand) the most accurate orbital data can be generated with the Natural Satellites Ephemeris Service. The irregulars are significantly perturbed by the Sun. Moons of Uranus Uranus is the seventh planet of the Solar System; it has 27 known moons, all of which are named after characters from the works