NASA’s Cassini mission is no longer with us, but its legacy lives on in the research using its data. Today, that research takes a closer look at Enceladus – one of the most intriguing places to hunt for life. The icy shell covering its surface hides an ocean. Jets of water vapor erupt from the moon’s south polar region.
Cassini measured salts and silica dust during its close flybys of the icy moon. This makeup suggests an interaction between rocks and hot water measuring at least 90 degrees Celsius (that’s 194 degrees Fahrenheit for us).
One of the biggest mysteries for scientists is figuring out where this source of heat is. According to the ESA, the heat source would need to be about 100 times more than what is generated by the natural decay of radioactive elements in rocks in the moon’s core.
Tidal friction could heat the water (the gravitational pull from nearby Saturn). But the heat produced from the gravitational pushing and pulling in the ice wouldn’t be enough to offset the heat loss from the ocean itself.
“Where Enceladus gets the sustained power to remain active has always been a bit of mystery, but we’ve now considered in greater detail how the structure and composition of the moon’s rocky core could play a key role in generating the necessary energy,” says Choblet.
The researchers crafted a simulation of Enceladus’ core made up of porous rock. That is, a core where water could seep through it. Picture a core resembling a pile of gravel. Cool water seeps into the core, tidal friction heats it up, and then rises back towards the surface as its warmer than its surroundings.
The simulations deliver a one-two punch for explaining what is going on Enceladus today. “Our simulations can simultaneously explain the existence of an ocean at a global scale due to large-scale heat transport between the deep interior and the ice shell, and the concentration of activity in a relatively narrow region around the south pole, thus explaining the main features observed by Cassini,” says co-author Gabriel Tobie.
A porous core combined with tidal friction could produce up to 30 GW of heat over millions, maybe even billions of years according to the researchers.
Here’s how Enceladus’ south pole looked during Cassini’s last flyby.
There’s still a lot we don’t know about the icy moon, but it’s active. Today. Wherever there’s water on Earth, we’ve found life. Cassini showed us the hunt for life can begin right in our own cosmic backyard. Future missions will only reveal more about this intriguing moon. And potentially, answer the ultimate mystery. Are we alone?