Europa. Long imagined as one of the most promising places in the solar system where life might have arisen, our observations of the Jovian moon have been limited to a few flyby missions and long-range telescopes on Earth. New data modeling suggests that Europa may have even more energy to play with than we thought it did — and energy is critical for any life that might exist.
We already know that Europa is covered in a thick ice crust and that there’s almost certainly a vast liquid ocean underneath all the ice. That ice covering isn’t a uniform blanket — instead, it’s in constant motion and subject to tectonic forces similar to the continental crust on Earth. These forces are part of what keeps the liquid ocean underneath the crust from freezing — Jupiter exerts tremendous force on Europa, and that tidal heating and flexing keeps the planet’s core molten.
According to researchers from Brown University, previous scientists who studied this behavior used models that weren’t sophisticated enough to account for all the variables.”People have been using simple mechanical models to describe the ice,” said Christine McCarthy, a faculty member at Columbia University who led this new research as a graduate student at Brown. While those calculations suggested liquid water under Europa’s surface, “they weren’t getting the kinds of heat fluxes that would create these tectonics. So we ran some experiments to try to understand this process better.”
The team at Brown tested the amount of energy released by the frozen tectonics on Europa by subjecting ice on Earth to the kinds of stresses its counterpart would experience. According to their work, water ice generates the most energy not due to grains of ice rubbing on each other, but by defects in the crystal lattice formation that forms as water freezes. More heat dissipation means more energy is released, and that means there’s more energy being produced on Europa than previously thought.
One of the basic requirements for life, from single-celled prokaryotes to blue whales, is the presence of an energy gradient. There must be some form of energy available, and that energy must be of a type that an organism can plausibly use. That energy can be geothermal, solar, or chemical (among many other types), but there’s got to be energy in the system that can be repurposed in some fashion.
We already know that life on Earth can persist in the deepest parts of the ocean where no light penetrates. We also know that some life at these depths is driven by events like whale falls, in which the corpse of a whale descends to the depths of the ocean and is then colonized by undersea life. Current estimates are that colonies of this type can survive for up to a century on the corpse of the largest whales. The discovery of rich patches of microorganisms living happily near undersea volcanic vents further proved that yes, life can exist without the sun.
All of these events, however, occurred on Earth, and in an ecosystem where there’s plenty of energy at the top of the surface, even if it descends below only occasionally. It’s less clear how energy might be distributed across Europa or how warm the planet’s liquid ocean actually is. Hopefully we’ll find out the answer to some of these questions in the near future; NASA is planning to launch the Europa Multiple Flyby Mission between 2022 and 2025. If Europa indeed has periodic water eruptions from its surface, as our observations have indicated, it might be possible to sample these plumes from the probe rather than trying to land directly on the surface to do so.