Jupiter’s ice-encrusted moon Europa is increasingly looking just like the best place within the solar system to search for extraterrestrial life.
New modeling suggests that the rocky mantle, deep below the thick ice and salty ocean, could actually be hot enough for volcanic activity. Moreover, it might have this hot over most of its 4.5-billion year lifespan.
The finding has direct implications for the likelihood of life lurking on Europa’s seafloor.
“Our findings provide additional evidence that Europa’s subsurface ocean could also be an environment suitable for the emergence of life,” said geophysicist Marie Běhounková of Charles University in Czechia.
“Europa is one among the rare planetary bodies which may have maintained volcanic activity over billions of years, and possibly the sole one beyond Earth that has large water reservoirs and a long-lived source of energy.”
You might think an icy world faraway from the life-sustaining warmth of the Sun – where surface temperatures tend to peak at around -140 degrees Celsius (-225 degrees Fahrenheit) – would be an unlikely place to seek out living organisms, but there’s actually precedent right here on Earth.
True, most life here does believe a food cycle supported photosynthesis… but in some extreme environments, where the Sun never shines, life has found differently .
In the dark depths of the ocean, too deep for sunlight to penetrate, volcanic vents seep heat into the waters around them. There, life is made on chemosynthesis, bacteria that harness the energy within geochemistry instead of solar power to supply food.
With the bacteria come other organisms which will eat them, thus creating a whole ecosystem down there within the dark.
We know that Europa, beneath its thick shell of ice, harbors a worldwide ocean – we have seen liquid water shooting out of cracks within the ice within the sort of geysers. We’ve also detected what’s very probably salt. This answers a number of the conditions for chemosynthetic hydrothermal life as we all know it.
What we do not know is whether or not Europa has volcanic activity below its seafloor, opening into vents like they are doing here on Earth.
It’s possible; Jupiter’s moon Io is that the most volcanic world within the solar system , thanks to the constant stresses placed by Jupiter’s gravitational tugging (and possibly the gravitational tugging of the other Jovian moons) that heat the inside .
Given that Europa is farther from Jupiter than Io, though, doubt remains – so Běhounková and her colleagues decided to undertake and figure it out.
They used detailed modeling to simulate the evolution and heating of Europa’s interior from the time of its formation. They found several mechanisms at play that would be working to stay the earth from freezing completely.
Firstly, heat released by radio-active decay of elements within the mantle likely contributed a big fraction of the moon’s internal heat, especially early in Europa’s history.
Over time, though, the changing stresses generated by tidal forces exerted by the moon’s elliptical orbit around Jupiter should have produced ongoing flexing in Europa’s interior.
This flexing, in turn, produces heat – and it should be sufficient heat to melt rock into magma, leading to volcanic activity that would be ongoing today, especially within the higher latitudes on the brink of the polar regions.
These simulations have given scientists signs of this activity to seem for when probes like NASA’s Europa Clipper and therefore the European Space Agency’s JUpiter ICy moons Explorer (JUICE) mission (due to launch in 2024 and next year respectively)get up close & private with Europa.
Gravitational anomalies could suggest the presence of deep magmatic activity, and therefore the anomalous presence of hydrogen and methane in Europa’s thin atmosphere might be the results of chemical reactions occurring at hydrothermal vents. Deposits of fresh oceanic materials on Europa’s surface could indicate subsurface activity too.
“The prospect for a hot, rocky interior and volcanoes on Europa’s seafloor increases the prospect that Europa’s ocean might be a habitable environment,” said Europa Clipper Project Scientist Robert Pappalardo of NASA’s Jet Propulsion Laboratory, who wasn’t involved within the research.
“We could also be ready to test this with Europa Clipper’s planned gravity and compositional measurements, which is an exciting prospect.”
First, however, we’ll need to wait a couple of more years for the spacecraft to urge there. Curse the tyranny of distance!
The team’s research has been published in Geophysical Research Letters.