By Sean O'Kane The search for life in our solar system has pointed us in many directions like Mars and Europa. Now, a new study in Nature just made another candidate look even more promising: Enceladus, an icy moon of Saturn, likely has an active hydrothermal system.
Enceladus has been a popular target for the existence of life ever since Cassini first saw plumes of water vapor coming from its south pole back in 2005. Until now, however, it was unclear how those plumes were connected to the potential subsurface ocean. The icy surface is estimated to be over 25 miles thick, and there was little evidence of hydrothermal activity.
But a team led by the University of Colorado's Laboratory for Atmospheric and Space Physics found tiny grains of rock — just 2–8 nm in radius, not much bigger than a strand of human DNA — with the Cassini spacecraft they believe were formed by hydrothermal vents in the ocean of Enceladus. The grains are rich in silicon and are like what is found in sand and quartz here on Earth, which are commonly formed by hydrothermal processes.
The existence of these grains can only mean that there is an active hydrothermal system working on Enceladus, according to the authors of the paper. Here's how the process starts: The gravitational tug of Saturn helps heat the ocean below Enceladus's surface to at least 90 degrees Celsius, or about 200 degrees Fahrenheit.
That helps dissolve minerals from the moon's rocky core.
That water cools on its way towards the surface, and those minerals get trapped in larger grains of ice as they push through vents and out into space. There, the ice erodes, and the tiny silicon-rich grains are left bare, where the scientists were able to detect them with Cassini's dust analyzer.
Hot water wicks minerals away from the core, similar to here on Earth
The paper's authors spent four years studying data from the Cassini spacecraft and performing computer simulations and experiments to reach their conclusions. "We methodically searched for alternative explanations for the nanosilica grains, but every new result pointed to a single, most likely origin," says Frank Postberg in the ESA's release on the study. Postberg is a scientist who works with Cassini's dust analyzer data at the University of Heidelberg in Germany and is a co-author on the paper.
The news is both exciting and important because hydrothermal vents are believed to have spawned life on Earth. Before today we knew that Enceladus had water. Now it looks like that water is heated and has minerals. Those are the most basic ingredients for life as we know it, and it means that Enceladus is about to become a more popular place to explore.