Volcanoes in the Solar System

Tuesday 15th March, 2016

Our speaker for the evening was Dr Paul Olver who had come to talk to us about "Alien Volcanoes: A Journey Through Our Solar System." Dr Olver had originally wanted to become an astronomer but decided to study geology as he considered his job prospects would be better. However, he still kept up his love of the stars as a hobby and, as technology advanced and various spacecraft were sent out into space to explore neighbouring worlds, he was able to combine his passion with his profession.

For his degree he had studied plate tectonics and seafloor spreading, which at the time had been relatively new developments in earth science. He explained that plate tectonics was the study of the movement of the Earth's outer layers which are split up into areas known as "plates"; somewhat like a spherical jigsaw. The term seafloor spreading referred to long linear features, usually in the centre of oceanic plates, where crust was actually being created and so these plates would be growing in area. At the edges of these growing plates the crust dives underneath other plates surrounding it.

Of the 450 active volcanoes on Earth most are found along the edges of plates where one plate is going underneath another. The exceptions to this are places such as Hawaii where underground lava (known as magma) breaks through forming hot spots or in places such as Iceland where the lava is forming new crustal material. On average the Atlantic Ocean grows by about 2cm a year as new crust is formed underneath the sea and Spain and Florida are moving apart. In contrast the Pacific Ocean is shrinking at a rate of 16cm a year.

Having given us an overview of Earth's volcanic activity, Dr Olver then turned our attention to the other planets and their moons. He said that Io, the innermost moon of Jupiter, was the most active volcanic body in the Solar System. The moon orbits so close to Jupiter that it is stretched and squeezed by the gravitational pull of its parent body leading to volcanoes erupting constantly all over its surface. Io's eruptions were first imaged by the Voyager 1 spacecraft as it flew past the moon and captured a plume of material shooting up from its surface.

The only other bodies in our Solar System that are known to be currently having active volcanism (apart from Earth and Io) are Neptune's moon Triton and Saturn's moon Enceladus. In 1989 the Voyager 2 spacecraft returned images of dark plumes emanating from Triton's surface and then in 2005 the Cassini spacecraft imaged jets of material coming from fractures in Enceladus' south polar region. Unlike Earth and Io these are not eruptions of hot molten rock but are outbursts of liquids and gases produced when pressurised subsurface liquid finds its way to the surface via vents or crustal cracks. The sudden release of pressure can turn some of the liquid into gas which then cools in the low temperatures of space before falling back to the moon's surface. This type of icy volcanism is known as cryovolcanism.