Thirty-four years ago Linda Morabito saw a crescent-shaped object on Io, the moon nearest to Jupiter. Her discovery was the first extraterrestrial siting of a volcanic eruption. Nighttime infrared images soon confirmed the presence of many active volcanoes on the moon. Now the colorful Swiss cheese surface of Io is a well-known image.
[frame type=”lifted” align=”none”][/frame]
Io is so close to Jupiter and three of its other moons, it suffers severe gravitational stresses. The eleven kilometer thick silicate crust flexes over distances up to 100 meters, Expansion and contraction generate surface tides every 43 hours. In addition, Ion absorbs strong magnetic fields and has been whacked by more meteors than its share. Who could possibly live there?
Exhibiting 12 or more active volcanoes at any one orbital pass, Io puts out huge plumes of sulfur, sulfur dioxide, magnesium and other gases that can rise 300 km from the surface. Of course, this indicates high subsurface pressures. In spite of all this activity, the thin atmosphere retains very small amounts of sulfur dioxide, carbon dioxide, carbon monoxide and an assortment of ions.
The lava fallout quickly freezes, melting the crust first, then creating a variety of flat surface features of condensed and frozen sulfur dioxide. Gorges, thrust faults and jagged blocks add to the landscape of lava fields and wide plains. The huge Amerani lava field puts out 100 tons per second in two dozen areas, pushing outward 300 km over the frozen sulfur dioxide surface.
Away from active volcanoes, the surface temperature of Io is –180 º C. Lava emerges at 1500° C, and long-term temperature gradients are extensive both horizontally and vertically. Temperatures range around the volcanoes at a cool 0° at 50 km, 47° C at about 3 km, and 2000° C where magma appears.
Does this mean that life could move along the lava borders in a reasonable temperature range? Possibly, but Io orbits very rapidly within Jupiter’s deadly magnetosphere. Radiation is a problem for most life, but some radiation-resistant forms of DNA are known on Earth in the bacteria Deinococcus. Other possibilities for life could be like the extremeophiles
found in Yellowstone’s hot springs—probably thermophiles or anaerobes.
On Io, such life would most likely exist at the zone where lava flows over the cold surface. With so little water on Io, other solvents for life should be considered. Maybe liquid sulfur dioxide. It is liquid around –70° C. but is not very good at forming large bio-capable molecules. Irwin and Shulze-Makuch in Cosmic Biology suggest that sulfur dioxide would serve best as an exterior casing for living microbes. The interior of life forms would do better with hydrogen sulfide as solvent, since it binds better with hydrogen and can form the kind of macromolecules necessary for life as we know it.