Enceladus is an icy moon of Saturn that hides an ocean and sprays its water into space. NASA’s Cassini spacecraft detected gases in the water that some Earth-based bacteria feed on. The gases likely come from hydrothermal vents on the seafloor. The discovery raises the likelihood that we could find alien life.
If alien life exists, it will likely be found in a place with three key ingredients: water, warmth, and food.
Scientists have long thought such conditions may exist under the icy shell of Enceladus, a moon of Saturn that’s about 272 miles (505 kilometers) wide.
Those suspicions grew after NASA’s Cassini spacecraft found plumes of water shooting out fissures in the ice.
The probe repeatedly flew through the plumes, leading to the discovery of the moon’s global subsurface ocean.
But Cassini also “sniffed” and “tasted” the water of Enceladus, and on April 13, scientists revealed they’d found traces of hydrogen – a gas that deep-sea microbes on Earth can eat for energy.
Scientists behind the new research, which was published in the journal Science, also think the gases likely form and bubble up from hydrothermal vents that litter the dark seafloor of Enceladus.
“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, the head of NASA’s science mission directorate, said in a press release.
While the discovery does represent any evidence of aliens, the space agency says the new information “will help inform future ocean world exploration … and the broader search for life beyond Earth.”
‘A candy store for microbes’
On Earth, hydrothermal vents form in the darkness of the deep ocean, where seawater seeps into the planet’s rocky crust, meets volcanically active rock, and blasts back toward the surface.
The intense heat and chemistry of rocks can rip molecules of water apart to form hydrogen, carbon dioxide, and other chemicals, which gush out of holes in the seabed. Where sunlight is lacking, this chemistry can be a lifesaver: Certain microbes can process the hydrogen into sugar.
When Cassini tasted the plumes coming out of Enceladus, about 99% was water and 1% was hydrogen.
That amount of hydrogen “is considered to be one of the most powerful chemical energy sources that could support life,” Alexis S. Templeton, a geologist and microbiologist at the University of Colorado at Boulder, told Business Insider in an email.
“It would be like a candy store for microbes,” Hunter Waite, a space scientist and lead author of the new study, said in NASA’s press release.
Christopher Glein, a research scientist at the Southwest Research Institute and a co-author of the study, put it a little differently: Enceladus is generating about 300 pizzas’ worth of calories an hour through hydrogen production, he said during a televised press briefing about the discovery.
However, while many scientists think life on Earth may have started out at hydrothermal vents more than 3.7 billion years ago, the new evidence of hydrothermal vents at Enceladus doesn’t mean we’ve found extraterrestrial life.
In fact, Cassini finding as much hydrogen leaking into space as it did should dishearten fans of aliens.
“Normally when you put a stack of pizzas in a cafeteria, they disappear quickly,” Mary Voytek, an astrobiologist at NASA, said during a televised press briefing. “So we have this build-up of food that’s not being used.”
Still, many scientists we contacted were optimistic about the findings.
Kevin Hand, a planetary scientist at NASA JPL who wasn’t involved in the research, told Business Insider that if Enceladus does indeed harbor such microbes, they could form the base of a food chain within the moon that could be “somewhat similar to what we see at sites like the Lost City hydrothermal site on Earth.”
And Mark Sykes, director of the Planetary Science Institute, says the discovery of hydrogen gas at Enceladus backs up computer models of how subsurface oceans work on icy worlds across the solar system, including Europa (a moon of Jupiter), Ceres (a dwarf planet in the asteroid belt), Pluto, and possibly Titan (another moon of Saturn).
“For decades we have been asking the question, ‘Does water equal life’?” Sykes told Business Insider in an email. “Enceladus is making the contents of its subsurface ocean directly available to us so we can drill further into this question.”
An icy barrier to humanity’s biggest questions
The new study isn’t foolproof, though.
One of its big unanswered questions, says Philipp Heck, a cosmochemist at the Field Museum, is whether Enceladus’ water jets are actually a good representation of its ocean water.
“As that liquid escapes, some of it forms ice and stays behind, and some of it doesn’t and continues into the vacuum of space,” Heck, who wasn’t part of the research team, told Business Insider. “So the composition Cassini sampled may be different than the original liquid.”
This makes it much harder to know if the water sampled by Cassini in 2015 was representative of Enceladus’ long history. If the mix of chemicals in the jets and the ocean are similar, then it’s likely Enceladus has harbored a life-friendly environment for millions of years.
To best answer the pressing question about the habitability of Enceladus – and worlds like it – researchers believe we’ll have to launch a multi-billion-dollar robot, find a way through the moon’s icy crust, and taste its liquid ocean water.
Some scientists even want to drop nuclear-powered robots into the ocean to map its sea floor, but this could be difficult since the moon’s icy crust is probably 2 to 3 miles (3.2 to 4.8 kilometers) thick.
However, the cracks that spew out water from Enceladus may offer shortcuts.
“Wouldn’t it be great to dive into those ice fractures with a robotic spacecraft and swim through that ocean?” Hand said.
NASA hasn’t announced any plans to re-visit Enceladus, though it is working on the Europa Clipper mission. That probe will orbit Jupiter’s moon, map its icy crust, and look for water plumes similar to those spewed out by Enceladus. (Images by the Hubble space telescope suggest plumes exist at Europa, but the photos are too grainy to say for certain.)
A previous version of the mission to Europa called for a lander, but a recently approved NASA budget axed it.
Assuming NASA could scrape together enough financial support to scout for signs of life in an alien ocean world, however, Voytek knows which one she’d pick.
“My money for the moment is still on Europa,” Voytek said, “but it could be on any of these moons.”
Note: This story was updated with new information after it was published.