Hydrothermal Activity On Saturn’s Moon

Enceladus, one of Saturn’s many moons, may undergo similar processes that are going on in Earth’s deep oceans, as new evidence gathered by NASA’s Cassini spacecraft suggests. Hydrothermal activity, a natural occurrence in Earth’s oceans when seawater reacts with the crust and then emerges as a mineral-enriched solution, might also be taking place on Enceladus.

New information indicates that Enceladus may contain a subsurface ocean. The Cassini spacecraft has detected miniscule grains of rock that are formed when cooler water comes into contact with hot water that contains dissolved minerals. The hot water comes from the rocky interior of the moon that has shot up to the surface. A temperature of 194 degrees Fahrenheit (90 degrees Celsius) would have been needed to form the particles. These findings were published in the journal, Nature, by lead author Sean Hsu, after conducting comprehensive data analyses, computer simulations and laboratory experiments, which ranged over four years.

The spacecraft detected these particles well before it was even in Saturn’s orbit using its Cosmic Dust Analyzer (CDA). The particles are rich in silicon, and range in size from 6 to 9 nanometers. The scientist concluded that they were silica grains, equivalent to Earth’s sand and mineral quartz, which is achieved through a hydrothermal process when super-saturated, slightly alkaline and salty water and silica undergo a big increase in temperature.

According to Frank Postberg, co-author, no matter how many times they look at it, they could only find one plausible explanation for the origin of the silica grains.

In another paper, written by Alexis Buoquet, it is suggested that the methane found in the erupting plumes of gas and ice particles in Enceladus’ south polar region also originates from hydrothermal activity. The paper was published in Geophysical Research Letters only recently.

Clathrates, icy materials found in the moon’s ocean, could imprison methane molecules inside crystalline structures of water ice with the help of the ocean’s pressure. This process efficiently depletes methane in the moon’s ocean.

Scientists hypothesize that hydrothermal activity produces methane rapidly, compared to its conversion into clathrates, due to its super-saturated state. Another hypothesis is that the plumes may have dragged methane clathrates from the ocean, and methane is released when the plumes erupt.

Both authors agree that this likely occurs, and that the presence of the nanosilica grains favors the hydrothermal approach.

Cassini first introduced Enceladus’ active geologic activity in the year 2005, using the spray of ice found in the moon’s south polar region and higher than anticipated temperatures as evidence. In addition, after some years, it revealed information about plumes of water ice and vapor, minerals and salts, coming from fractures in the surface. Moreover, a presence of an ocean, about 6 miles long, hidden beneath a 19-25 mile ice shell was suggested in 2014.