Of all the celestial bodies in our solar system, Jupiter’s icy moon Europa may hold the most promise for sustaining life. Most scientists agree that the moon’s icy crust conceals a vast underground ocean. A new modeling study now shows how the wide, smooth or faulted bands crisscrossing the moon’s surface likely formed as the crust stretched and cracked over a deeper, more fluid layer, possibly transporting ocean matter to the surface. The findings could help scientists determine where future space missions should explore or land to increase the chance of detecting alien life-forms.
Scientists have long puzzled over how Jupiter’s icy moon Europa and bright portions of her larger sibling Ganymede manage to look so young, despite being roughly 4.5 billion years old. Neither moon has terrain that bears the number of craters from space debris that would normally cover celestial bodies that old. The dominant hypothesis is that both moons’ icy crusts have moved in a fashion similar to the movement of Earth’s tectonic plates: As chunks of ice crust shifted, they collided, buckled, and slid underneath one another or spread apart, exposing younger, smoother ice layers that may have subsequently faulted.
To test that hypothesis, Howell and Pappalardo used a computer model to simulate how ice shells similar to those on Europa and Ganymede could stretch, crack, and buckle. Although scientists don’t know precisely how thick either moon’s crust is, the team estimated Ganymede’s thicker, more rigid crust at around 50 kilometers and Europa’s thinner, more pliable crust at about half that thickness. The team also used the model to predict where ocean materials that are attached to the bottom of the ice are likely to end up as the crust deforms.
A relatively thin, weak crust consistently produces wide, smooth bands of ice that are commonly found on Europa’s surface, the model revealed. Contortions of this weaker, thinner lithosphere have the potential to transport fossilized ocean water and any marine organisms, if they exist, to the surface. A thicker, stronger crust was more likely to produce ridges and grooves like those on Ganymede but was unlikely to convey ocean matter from the depths to the moon’s surface.
The study suggests that future space missions would best search for evidence of ancient marine life in these wide, smooth bands of ice. NASA’s Europa Clipper mission and the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission to Ganymede can survey these features from afar for signs of habitability ahead of potential future landers. (Geophysical Research Letters, https://doi.org/10.1029/2018GL077594, 2018)
—Emily Underwood, Freelance Writer