On a small but very bright Saturn moon called Enceladus, scientists from San Antonio’s Southwest Research Institute have found hydrogen gas, a “tantalizing” discovery that, combined with the moon’s water and organic molecules, provides it with life’s three basic ingredients.
Data from NASA’s Cassini spacecraft indicate that the hydrogen on Enceladus, an ice-covered body discovered orbiting the ringed planet in 1789, is best explained by chemical reactions between its rocky core and warm water from its subsurface saltwater ocean.
The discovery by the SwRI-led team, according to its press release, suggests that Enceladus’ ocean floor could include features analogous to hydrothermal vents on Earth, which are known to support life on the sea floor. Though the hydrogen plumes were first detected by Cassini in a close flyby on Oct. 28, 2015, their significance was not widely publicized until described in the current issue of the journal Science.
“This is really an important step forward in the search for life in our solar system,” said SwRI planetary scientist Kelly Miller, one of the article’s co-authors. “This is the first time we’ve found those three key ingredients to life anywhere outside the Earth’s environment.”
SwRI’s Hunter Waite, principal investigator of Cassini’s Ion Neutral Mass Spectrometer (INMS), said scientists have not found “evidence of the presence of microbial life in the ocean of Enceladus, but the discovery of hydrogen gas and the evidence for ongoing hydrothermal activity offer a tantalizing suggestion that habitable conditions could exist beneath the moon’s icy crust.”
Hydrogen is a source of chemical energy for microbes that live in the Earth’s oceans near hydrothermal vents, Waite said. “Our results,” he added, “indicate the same chemical energy source is present in the ocean of Enceladus.”
Pictures from the Voyager spacecraft in the 1980s helped explain why the relatively tiny moon— just 310 miles across — is considered the most reflective object in the solar system. It is covered in white ice that looks about as smooth as a hockey rink.
“It would be a dramatic vacation destination,” Miller said. “You’d get beautiful views of its poles, then right adjacent are Saturn’s rings and when the angle is just right you could wave hello to Earth.”
Previous flybys by Cassini provided evidence for a global subsurface ocean, said SwRI researchers. Molecular hydrogen in the plumes could serve as a marker for hydrothermal processes, which could provide the chemical energy necessary to support life.
“The amount of molecular hydrogen we detected is high enough to support microbes similar to those that live near hydrothermal vents on Earth,” said SwRI’s Christopher Glein, another co-author on the paper and a pioneer of extraterrestrial chemical oceanography. “If similar organisms are present in Enceladus, they could ‘burn’ the hydrogen to obtain energy for chemosynthesis, which could conceivably serve as a foundation for a larger ecosystem.”
Scientists also considered other sources of hydrogen from the moon itself, a SwRI press release stated, such as a pre-existing reservoir in the ice shell or ocean. Analysis determined that it was unlikely that the observed hydrogen was acquired during the formation of Enceladus or from other processes on the moon’s surface or in the interior.
“Everything indicates that the hydrogen originates in the moon’s rocky core,” Waite said. “We considered various ways hydrogen could leach from the rock and found that the most plausible source is ongoing hydrothermal reactions of rock containing reduced minerals and organic materials.”
Miller said Enceladus is probably about 4 billion years old, younger than the Earth, which is believed to be about 4.5 billion years old. “That’s really exciting for me,” Miller said, “because there are many moons that have this structure of an icy shell, liquid water ocean and solid core, which is quite unlike Earth.”
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Cassini orbiter was designed, developed, and assembled at NASA’s Jet Propulsion Laboratory in Pasadena, California, a division of Caltech that manages the mission for NASA’s Science Mission Directorate in Washington, D.C.