Worlds in Eruption

A second source is important in providing a slow but continuous source of heat. It’s the natural decay of radioactive elements such as uranium, thorium and potassium. These elements release subatomic particles, which give up heat energy as they are slowed down by the surrounding rock.

Recently, planetary exploration has led to the identification of a third heat source, unsuspected by Earth-based geologists. It is tidal energy released in moons as they orbit in the powerful gravitational field of their parent planet.

Hell-planet Venus

By studying the shape, distribution and location of the plethora of volcanic features on other worlds, we can start to piece together their unique geological jigsaw in the same way we do on Earth. Much has been learnt about extraterrestrial volcanism from missions to Earth’s siblings, Venus and Mars.

Between 1990 and 1994 NASA’s Magellan mission mapped the surface of Earth’s nearest planetary neighbour, Venus. The orbiting spacecraft used radar to cut through the all-enveloping clouds that permanently hide a twisted and tormented surface where volcanism has run rife. Over 80% of the planet’s surface is covered with volcanic plains called planitia - vast coalescing lava flows, subsequently warped and fractured by movements of the planet’s crust. Researchers believe the planitia formed from relatively fluid lava, similar to the Earth’s basaltic lavas that form the Deccan Traps in India and the Columbia River Plateau in America.

NASA The volcano 'Maat Mons' on Venus is 5 miles high and named for an Egyptian goddess of truth and justice.

Magellan mapped huge volcanoes hundreds of kilometres across and thousands of metres high. These are ‘shield’ volcanoes, so called because their convex-upward shape resembles that of a Roman shield, and they are similar to the volcanoes that make up the Hawaiian Islands. Height measurements from Magellan show that the large volcanoes are generally located on large bulges in Venus’s crust. These are thought to represent ‘hot spots’ - plumes of molten rock and heat which well up from deep within the planet’s interior.

Among other volcanic features are coronae, circular blisters on the Venusian surface hundreds of kilometres across which are also formed by up-welling heat from below. And on a smaller scale, 10-20 kilometres across, the surface is peppered with literally millions of cone, dome, and shield volcanoes.