At a press conference this afternoon, NASA announced that its Cassini space probe detected hydrogen in plumes of water spouting out of Saturn’s moon Enceladus. The discovery checks off another box in the list of ingredients required to support life on the icy world. The presence of hydrogen gas is common around hydrothermal activity and can serve as a valuable source of food for microbial life—just as it does for many creatures that teem around Earth's hydrothermal vents.
“This is the closest we've come, so far, to identifying a place with some of the ingredients needed for a habitable environment,” Thomas Zurbuchen, associate administrator for NASA's Science Mission Directorate says in the press release. “These results demonstrate the interconnected nature of NASA's science missions that are getting us closer to answering whether we are indeed alone or not.”
The Cassini craft detected the hydrogen in 2015 as it flew through hrough one of the hot bursts of spray spurting from four “tiger stripe” cracks near the moon’s south pole. The craft determined that 98 percent of the plume was water, which is heated from Saturn's gravitational pull, while one percent was hydrogen and the rest was a mixture of carbon dioxide, methane and ammonia.
Life as we know it (on Earth) requires three ingredients—energy, liquid water and organic compounds including carbon, hydrogen, nitrogen, oxygen, phosphorous and sulfur. While in most cases the energy component comes from the sun, hydrothermal vents on the deep ocean floor can create energy through a chemical process called “methanogenesis” which supports a whole ecosystem of microbes and animals that rely on them.
“Although we can't detect life, we’ve found that there’s a food source there for it,” says NASA researcher Hunter Waite, lead author of the study which appears in the journal Science. "It would be like a candy store for microbes."
While the new evidence from Enceladus is compelling, in the webcast press briefing, NASA scientists said they currently think they are still more likely to find life on Jupiter's moon Europa. This little moon is at least 4 billion years old, almost as old as the Earth itself, giving it much more time to develop life.
NASA scientists previously suggested that Europa harbored a global ocean under its thick crust of ice, which would contain twice as much water as our own planet's oceans. In the briefing today, agency also revealed that the Hubble Space Telescope detected more evidence of water plumes spouting from Europa. The agency plans to launch a spacecraft, the Europa Clipper, to investigate the moon sometime in the 2020s that will carry an array of instruments able to detect plumes and peer under the moon's icy shell.
The hydrogen on Enceladus is one more great find for the Cassini Spacecraft, which began exploring Saturn and its moons 13 years ago. Over that time, it has provided new data and incredible images of Saturn’s ring system and measured the planet’s magnetosphere. It has also orbited Enceladus and Titan, as well as the smaller moons Dione, Rhea and Helen.
This latest find, however, is going to be one of its last. As Alexandra Witze reports for Nature, Cassini is preparing for its Grand Finale. Next week it will make it’s last pass around Titan, which will slingshot the probe into a new orbit. The craft will zip through the region between the planet’s uppermost clouds and its innermost rings 22 times, allowing it to analyze the particles that make up the rings and study Saturn’s magnetic field. Then, on September 15, the hero of Saturnine science will set out on a crash course with the planet, sending back info the planet’s atmosphere before it meets its spectacular end.