The most promising places to look for life in the Solar System are in the ocean moons Europa and Enceladus. But all that warm, salty, potentially life-supporting water is under thick sheets of ice: up to 30 km thick on Europa and up to 40 km thick for Enceladus.
The main obstacles to exploring all that water are the thick ice barriers. Assuming a spacecraft can be designed and built to melt its way through all that ice, what then?
Submarines can do the actual exploring, and they needn’t be large.
Saturn is best known for two things: its iconic ring structures and its large system of natural satellites. Currently, 146 moons and moonlets have been discovered orbiting the ringed giant, 24 of which are regular satellites. These include the seven largest moons, Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, and Mimas, which are icy bodies believed to have interior oceans. In addition, there are unresolved questions about the age of these satellites, with some suspecting that they formed more recently (like Saturn’s rings, which are a few hundred million years old).
To address these questions, an international team of astronomers created a series of high-resolution simulations coupled with improved estimates of Trans-Neptunian Object (TNO) populations. This allowed them to construct a chronology of impacts for Saturn’s most heavily cratered regular satellites – Mimas, Enceladus, Tethys, Dione, and Rhea. This established age limits of 4.1 and 4.4 billion years for all five, with the two innermost moons appearing more youthful than the outer three. These results could have significant implications for our understanding of the formation and tidal evolution of moons in the outer Solar System.
In our search for life on other worlds, the one we’ve most explored is Mars. But while Mars has the makings for possible life, it isn’t the best candidate in our solar system. Much better are the icy moons of Jupiter and Saturn, which we know have liquid water. And of those, perhaps the best candidate is Saturn’s moon Enceladus.
The James Webb Space Telescope has observed a huge water vapor plume emanating from Saturn’s moon Enceladus. Astronomers say the plume reaches nearly 10,000 kilometers (6,200 miles) into space, which is about the equivalent distance as going from Ireland to Japan. This is the largest plume ever detected at Enceladus.
If you’ve ever played Kerbal Space Program, you know how difficult it can be to get your spacecraft into the orbit you want. It’s even more difficult in real life. This is why it’s pretty impressive to see a proposal to study all of Saturn’s large inner moons in one go.
The European Space Agency’s (ESA) recently launched Jupiter Icy Moons Explorer (JUICE) mission and NASA’s upcoming Europa Clipper mission could allow scientists to image landslides on the icy moons of Europa and Ganymede due to potential moonquakes on these small worlds. This comes after a recent study examined fault scarps on Europa and Ganymede orbiting Jupiter and Enceladus and Dione orbiting Saturn with the goal of drawing a connection between tectonic activity (quakes) and observed mass wasting (landslides) on these surfaces. The researchers “consider whether such smooth material can be generated by mass wasting triggered from local seismic shaking”, according to the study.
For astrobiologists, the scientists dedicated to the search for life beyond Earth, the moons of Saturn are a virtual treasure trove of possibilities. Enceladus is especially compelling because of the active plumes of water emanating from its southern polar region. Not only are these vents thought to be connected directly to an ocean beneath the moon’s icy surface, but the Cassini mission detected traces of organic molecules and other chemicals associated with biological processes. Like Europa, Ganymede, and other “Ocean Worlds,” astrobiologists think this could indicate hydrothermal activity at the core-mantle boundary.
Both NASA and the ESA are hoping to send missions to Enceladus that could study its plumes in more detail. These include the Enceladus Orbitlander recommended in the Planetary Science and Astrobiology Decadal Survey 2023-2032 and the ESA’s Enceladus Moonraker, which could depart Earth in the next decade, taking advantage of a favorable alignment between the planets. In anticipation of what these missions could find, an international team of researchers used data from the Cassini mission to establish how samples of plume material could constrain how much biomass Enceladus has within it.
There are plenty of exciting places in the solar system to explore. But few are more interesting than Saturn’s moon Enceladus. It’s one of the only planetary bodies known to have all six necessary components of Earth-based life. It has an active ocean and most likely hydrothermal vents, similar to those on Earth, where some species exist entirely separately from any solar-powered biosphere. All of this makes it one of the most likely candidates for life in the solar system – and the center of much astrobiological attention. Now a team from a variety of European countries and the US has proposed a mission to the moon that could profoundly impact our understanding of our place in the universe – if the European Space Agency (ESA) funds it.
We recently examined how and why the planet Mars could answer the longstanding question: Are we alone? There is evidence to suggest that it was once a much warmer and wetter world thanks to countless spacecraft, landers, and rovers having explored—and currently exploring—its atmosphere, surface, and interior. Here, we will examine another one of Saturn’s 83 moons, an icy world that spews geysers of water ice from giant fissures near its south pole, which is strong evidence for an interior ocean, and possibly life. Here, we will examine Enceladus.
“We’re coming up on the plumes!” The co-pilot announced over the intercom.
The other six passengers and I took our positions along the viewing cupola at the belly of the “Tour Bus”, and each grabbed on to the hand and foot restraints to keep ourselves in place in the weightlessness. We were traveling about 400 km (250 miles) above the south pole of Enceladus looking down at the highly reflective surface that was so bright it took about a minute for our eyes to adjust. We all remained silent, and my heart was pounding in anticipation. The Tour Bus silently coasted for a few more minutes as we took in the breathtaking view of Saturn’s sixth-largest moon.