In the enduring search for life in the universe, new evidence is pointing researchers toward Saturn's moon Enceladus.
Enceladus is Saturn's sixth largest moon with a diameter equal to roughly the width of Arizona, and it's thought to have a massive subsurface ocean that spouts plumes of water out into space. One of 145 known moons around the planet, Enceladus has intrigued scientists searching for extraterrestrial life in our solar system. And, according to new research, they could be looking in the right place. New evidence from multiple new papers suggests microscopic life could survive in Enceladus' ocean and that the planet's plumes essentially "organize" the compounds and minerals inside. What this means is it could be easier to explore what's in the moon's ocean than previously thought.
"That is great news in the search for life," Frank Postberg, lead author of one and co-author of the other of these new studies and professor at Freie Universität Berlin, said in a statement. "Future spacecraft will have to analyze many individual ice particles in the plume. But if they come across one with microbial material in it, they could identify biosignatures in the particle relatively easy with already available technology."
Planet-prepared samples
Enceladus isn't the only place in our solar system with water — so, why is it so exciting in the search for life? Well, it has to do with the seafloor of its extensive, liquid ocean.
Down deep at the bottom of this body of water, scientists think hydrothermal processes, or movement or reactions with hot water under the surface, are taking place. The plumes shooting upward from the ocean also contain trace amounts of salts and organic compounds. NASA's Cassini spacecraft found these traces when it flew through the plumes over a decade ago. Between the hydrothermal activity and the organics and minerals in the water, this moon's ocean has a number of aspects that could be involved in supporting life.
What's more, using a combination of Cassini data, theoretical models and laboratory experimentation, in Postberg's new study the team found that the plume's water droplets blasting out into space at up to 621 miles per hour (1,000 kilometers per hour) don't freeze as quickly as expected. Before, scientists thought the freeze would happen instantaneously once the droplets reached space, but Postberg and fellow researchers say they found the freezing would actually happen much slower.
They also found that during this freezing process, the salt, organic compounds (and maybe possible signs of life) in the water droplets separate from one another. Not only that, but the team says that as the particles are blasted out into space, they should often collide with the icy cracks of the planet's surface. This ultimately would leave behind tiny shards of frozen droplets with individually separated out components.
Essentially, it's like the planet has organized its oceanic ingredients into tiny, frozen particle fragments.
"Enceladus actually does a lot of the work for us in preparing samples for analysis that usually take a lot of effort in chemical labs on Earth," Postberg said in the same statement. "The oceanic constituents are separated from each other and simultaneously concentrated into individual ice particles."
Looking to the future, researchers could theoretically take advantage of this knowledge to more easily collect samples from the planet. With Enceladus-bound missions like the European Space Agency's L4 in development, we could know more about what lies in Enceladus' oceans (and if it's life) sooner rather than later.
Creating Enceladus in a lab
While we wait to see if future spacecraft are able to collect shards of frozen droplets from Enceladus' ocean, researchers in another study have replicated the conditions of the moon's ocean in a laboratory and tested how well it supported life.
While we don't know everything about this ocean, and the mystery remains of whether or not it contains life — or even the ingredients to support life — from previous observations with missions like Cassini we do know some things. For instance, we know the ocean is fairly basic and alkaline, has very little oxygen, and hosts an abundance of carbonate and hydrothermal activity.
This second paper's team of researchers included all of these elements to create a mini Enceladus ocean in a lab. And to see if life could survive in the faux Enceladus ocean, the crew added a microscopic species into the mix: Methanothermococcus okinawensis. On Earth, this microbe is often found near hydrothermal vents. Additionally, the species doesn't need oxygen (it relies on hydrogen and carbon dioxide). It was a very reasonable choice of species to introduce, seeing as Enceladus also has hydrothermal activity and very little oxygen.
The group of microbes actually did well in the faux Enceladus ocean, growing and taking in hydrogen from the environment. In fact, even though there wasn't a lot of carbon dioxide in the tank, the microbes persisted, adapting to the conditions relatively quickly.
"This was really a surprise to us," study contributor Nozair Khawaja, a planetary scientist at Freie Universität Berlin, said in the same statement. "This was an experiment for which we did not expect such a successful outcome."
Between this study showing that life can sustain itself in an environment similar to Enceladus' ocean and the other study demonstrating how easily future spacecraft could examine samples from the planet, these new results give scientists hope for the continued search for life on this moon.
"On Enceladus the specific geochemical conditions might allow one of the oldest known metabolic systems on Earth to work, even in very alkaline environments," Postberg said. "While that doesn't mean that there is life on Saturn’s moon, our first study shows that — in the event that there is — future space missions might have a good chance of finding traces if they analyze individual ice grains from Enceladus’s plume."
This work is described in two new studies published in the journal Science Advances here and here.
