Scientists have long speculated that Juptiter’s moon Europa has an icy crust covering a vast, global ocean –what Caltech’s Mike Brown describes as a “miniature Earth” ocean. The rocky layer underneath may be hot enough to melt, leading to undersea volcanoes.
“Whales of Europa”
Europa’s ocean, some 15 miles below its chaotic terrain of the surface lies the rocky sea floor, with plate tectonics, continents, deep trenches, and active spreading centers, says Caltech’s Brown. “Think about mid-ocean ridges on Earth,” he says, “with their black smokers belching scalding nutrient-rich waters into a sea floor teeming with life that is surviving on these chemicals. It doesn’t take much of an imagination to picture the same sort of rich chemical soup in Europa’s ocean leading to the evolution of some sort of life, living off of the internal energy generated inside of Europa’s core. If you’re looking for Europa’s whales – which many of my friends and I often joke that we are – this is the world you want to look for them.”
Underwater volcanoes, if present, could power hydrothermal systems like those that fuel life at the bottom of Earth’s oceans. On Earth, when seawater comes into contact with hot magma, the interaction results in chemical energy. And it is chemical energy from these hydrothermal systems, rather than from sunlight, that helps support life deep in our own oceans. Volcanic activity on Europa’s seafloor would be one way to support a potential habitable environment in that moon’s ocean.
Existence of Protocells?
In 2019, a University College London (ULC)-led research team added to evidence that the origin of life could have been in deep-sea hydrothermal vents rather than shallow pools by creating protocells in hot, alkaline seawater –protocells are seen as a key stepping stone to the development of cell-based life—in such environments, the ULC study found that heat and alkalinity might be necessary to get life started. Some of the world’s oldest fossils discovered originated in such underwater vents
“There are multiple competing theories as to where and how life started. Underwater hydrothermal vents are among most promising locations for life’s beginnings—our findings now add weight to that theory with solid experimental evidence,” said the ULC study’s lead author, evolutionary biochemist Nick Lane.
“Our findings provide additional evidence that Europa’s subsurface ocean may be an environment suitable for the emergence of life,” said lead author Marie Běhounková, referring to new research that models in detail how Europa’s rocky part may flex and heat under the pull of Jupiter’s gravity. It shows where heat dissipates and how it melts that rocky mantle, increasing the likelihood of volcanoes on the seafloor.
“Europa is one of the rare planetary bodies,” Běhounková added, “that might have maintained volcanic activity over billions of years, and possibly the only one beyond Earth that has large water reservoirs and a long-lived source of energy.”
NASA’s upcoming Europa Clipper mission, targeting a 2024 launch, will swoop close to the icy moon and collect measurements that may shed light on the recent findings.
3D modeling of Europa’s internal heat
Scientists have strong evidence that Europa harbors an enormous ocean between its icy crust and rocky interior. “The water ocean of Europa is generally believed (not only in our work) to be global — extending to the polar areas,” wrote Běhounková in reply to an email from The Daily Galaxy. “The arguments supporting the global ocean usually involve global energy and heat transfer considerations and evidence of the ice shell’s mechanical decoupling (for example, making possible a slightly faster rotation of the ice shell compared to the interior).”
The new work shows how the moon may have enough internal heat to partially melt this rocky layer, a process that could feed volcanoes on the ocean floor. The recent 3D modeling of how this internal heat is produced and transferred is the most detailed and thorough examination yet of the effect this interior heating has on the moon.
Volcanic activity most likely to occur near Europa’s poles
The key to Europa’s rocky mantle being hot enough to melt lies with the massive gravitational pull Jupiter has on its moons. As Europa revolves around the gas giant, the icy moon’s interior flexes. The flexing forces energy into the moon’s interior, which then seeps out as heat (think of how repeatedly bending a paperclip generates heat). The more the moon’s interior flexes, the more heat is generated.
Volcanic activity on Europa has been a topic of speculation for decades. By comparison, Jupiter’s moon Io is obviously volcanic. Hundreds of volcanoes there erupt lava fountains and eject volcanic gas and dust up to 250 miles (400 kilometers) high—activity that is due to the same kind of internal heating caused by Jupiter’s pull. But Europa is farther away than Io is from its host planet, so scientists have wondered whether the effect would be similar under the icy surface.
Led by Marie Běhounková of Charles University in the Czech Republic, the authors further predicted that volcanic activity is most likely to occur near Europa’s poles—the latitudes where the most heat is generated. They also looked at how volcanic activity may have evolved over time. Long-lived energy sources give more opportunity for potential life to have developed.
Europa Clipper reaches its target in 2030
NASA scientists will have the opportunity to put the new predictions to the test when Europa Clipper reaches its target in 2030. The spacecraft will orbit Jupiter and perform dozens of close flybys of Europa to map the moon and investigate its composition. Among the science data it collects, the spacecraft will survey the surface in detail and sample the moon’s thin atmosphere.
Scientists believe the exchange of material between the ocean and the crust would leave traces of seawater on the surface. They also believe the exchange may emit gas, and possibly even plumes of water vapor, with ejected particles that could contain materials coming from the seafloor.
As Europa Clipper measures the moon’s gravity and magnetic field, anomalies in those areas, especially toward the poles, could help confirm the volcanic activity predicted by the new research.
“The prospect for a hot, rocky interior and volcanoes on Europa’s seafloor increases the chance that Europa’s ocean could be a habitable environment,” said Europa Clipper Project Scientist Robert Pappalardo of NASA’s Jet Propulsion Laboratory in Southern California. “We may be able to test this with Europa Clipper’s planned gravity and compositional measurements, which is an exciting prospect.”
Image credit: NASA, Europa Clipper Mission