Enceladus ocean may resemble Antarctic lake

Swimming in the sea of the Saturnian moon Enceladus might be like taking a dip in household ammonia.

An ocean hidden beneath the moon’s icy crust is highly alkaline, similar to soda lakes on Earth, researchers have found. The water chemistry provides a peek at how the water interacts with rock in the moon’s core, creating an environment in which life could arise.

Christopher Glein, a geochemist at the University of Toronto, and colleagues used data from the Cassini mission to estimate the ocean’s pH, a measure of how acidic or alkaline the water is. The spacecraft, which has been in orbit around Saturn since 2004, periodically passes through water plumes that are thought to spray saltwater from an ocean beneath the moon’s surface (SN: 9/6/14, p. 15). By combining measurements of carbon dioxide and salts in the plumes, Glein’s team calculated that the ocean has a pH of about 11 to 12. The researchers report the findings February 8 on arXiv.org.

The high pH “makes a certain amount of sense,” says Francis Nimmo, a planetary scientist at the University of California, Santa Cruz. Researchers think the core of Enceladus resembles a pile of rubble, with lots of nooks and crannies where water can interact with the rock. As water percolates through the moon’s core and chemically alters the rocks, it can raise the pH of the ocean.

If the water and rock are interacting to raise the pH, they may also create ingredients that could be beneficial to life, Glein says. The interaction between rock and water might produce molecular hydrogen which, in combination with organic compounds previously detected by Cassini, could be used as a source of energy. “It is a bit speculative,” he says, though life does thrive in similar environments on Earth.

A highly alkaline ocean on Enceladus may resemble Antarctica’s Lake Untersee, says Christopher McKay, a planetary scientist at the NASA Ames Research Center in Moffett Field, Calif. The 170-meter-deep lake is tightly sealed by a 4-meter-thick ice cap, has a pH of 10.4 and is home to unusual cone-shaped microbial mounds (SN: 5/7/11, p. 10). “High pH is a not limiting factor for life,” says McKay, though it does alter the availability of nutrients. “It affects the environment in ways the organisms will have to deal with.”

If life thrives in an alkaline environment on Enceladus, McKay says, scientists may be able to detect evidence for that in the moon’s plumes. Unfortunately, Cassini can’t make the necessary measurements. Glein says that he has submitted a proposal to NASA for a future space mission, named the Enceladus Life Finder, that would fly through the moon’s water geysers with the tools needed to search for possible by-products of life.