Jupiter's moon Europa has long been one of the most attractive potential homes for life in the solar system. Well, apart from Earth. While the Earth is in the habitable zone with liquid water and a thick atmosphere, Europa is a small icy moon that orbits around a gas giant. However, lurking beneath its frozen surface could be liquid water. Scientists have even speculated about tectonic activity in Europe. It looks nothing like the tectonic plates on Earth, but it could fuel the development of life, according to a new analysis.
According to researchers at Brown University in Rhode Island, it is possible that Europe's ice sheet shows Earth-like tectonic activity. Specifically, the team led by assistant professor Brandon Johnson observed subduction. It's when one tectonic plate slides under another, which can cause volcanic activity and earthquakes on Earth. In Europe, it could deliver much needed nutrients to a biosphere on the planet.
Researchers used computer simulations to determine if subduction is possible in Europe. It is a very different environment for geological activity for two reasons. First, we are talking about ice sheets on the surface of the water instead of rock on molten rock. Second, subduction on Earth is driven by temperature differentials (ie, density) between the plates and the mantle. Europe does not have that, but Johnson's team showed that varying the salt content could lead to the same process.
There is good evidence that Europe's ice sheet consists of two layers: a hard outer shell and an inner convection layer slightly warmer to the tidal forces of Jupiter's gravity. The model developed for this study assumed variable amounts of salt content in the surface shell. The salt is denser than the ice, so it would allow the ice of the hard surface to be submerged in the warm inner layers of Europe.
This process could be vital for the development of life in Europe because the surface is known to be rich in oxidants, substances that extract electrons from other molecules. These include oxygen, iodine, bromine and more complicated molecules such as nitric acid. Oxidants can provide chemical energy for life that does not depend on the sun's energy.
Subduction is a very slow process that is difficult to observe, but a future probe could prove or disprove this hypothesis. The team suggests that tectonic activity in Europe is due to telltale signs such as ice rising with high salt content and cryo-canonics. We still do not know if there is anything alive in Europe, but this could be another piece of the puzzle.