Stunning images of Jupiter’s moon Europa show it has a floating icy shell

NASA’s Juno mission is busy studying not only the planet of Jupiter, with its strange weather and strong magnetic field, but also several of its icy moons, including the intriguing Europa. Often a top target of habitability research, Europa is exciting as a potential host for life because it is thought to have a liquid water ocean — although this ocean is beneath an icy crust up to 15 miles thick. Juno has taken high-definition photos of Europa’s surface, and scientists have recently analyzed this data to identify fractures and other features running across the icy shell.

The researchers expected to find marks in the surface like ridges and troughs, but what they were surprised to see were large pits up to 30 miles wide. The surface features suggest that the icy crust is not locked into place, but is floating on top of the ocean and can move — a theory called true polar wander.

“True polar wander occurs if Europa’s icy shell is decoupled from its rocky interior, resulting in high stress levels on the shell, which lead to predictable fracture patterns,” said Candy Hansen, a Juno co-investigator who leads planning for JunoCam at the Planetary Science Institute, in a statement. “This is the first time that these fracture patterns have been mapped in the southern hemisphere, suggesting that true polar wander’s effect on Europa’s surface geology is more extensive than previously identified.”

In addition to the color images of Europa taken by Juno’s JunoCam instrument, there are also black-and-white images taken by its Stellar Reference Unit (SRU) camera. The SRU was originally designed to help point the spacecraft in the right direction, but researchers have found that they can also use it for science, as it is particularly useful for studying features in lowlight conditions.

The Juno team used the SRU to take pictures of Europa’s nightside, when it faced away from the sun and the only light it received was sunlight that was reflected from Jupiter. That helped them to see features like ridges and stains that appear to be caused by water plumes jetting up from the ocean beneath the icy crust. That means there are potentially still ice volcanoes active on Europa, which is exciting for future missions planned to visit the moon.

“These features hint at present-day surface activity and the presence of subsurface liquid water on Europa,” said Heidi Becker, lead co-investigator for the SRU at NASA’s Jet Propulsion Laboratory. “The SRU’s image is a high-quality baseline for specific places NASA’s Europa Clipper mission and ESA’s [European Space Agency’s] Juice missions can target to search for signs of change and brine.”

The research is published in the Planetary Science Journal and JGR Planets.