The mottled surface of Europa has fascinated scientists ever since Voyager 2 returned high-resolution images of the Jovian moon in 1979. Opportunities to look closely at this frozen world have been few and far between, but NASA's Juno probe has delivered the best snapshots yet. The spacecraft revealed new structures, possible evidence of water plumes, and confirmed a supposed crater was just a trick of light.
Juno was sent to study Jupiter, conducting a series of elongated orbits that limit the time spent being fried by the planet's radiation belts. The mission has long passed its original design life, so the team has used that opportunity to conduct close flybys of several moons, like the volcanic Io and icy Europa.
The five new Europa images were captured on Sep. 29, 2022, and are the first new close-ups of the moon since the Galileo spacecraft flew by in 2000. Juno passed within just 220 miles (355 kilometers) of the moon’s frozen surface, giving scientists a close look at the alien landscape.
Juno zipped right over the moon's equator, returning four detailed JunoCam images of the deep impressions on the surface, known as lineae. Europa is believed to have a global subsurface ocean of salty water, which occasionally bubbles up to the surface. One of the four JunoCam frames also helped delete a crater from maps. Because the surface is constantly remodeled, there are very few impact craters. A feature called Crater Gwern turns out to have been a set of intersecting ridges that created a round shadow.
The lineae may be fractures in the thick icy shell associated with true polar wander, a theory that posits Europa's surface ice is free-floating. If disconnected from the rocky core, the shell will be put under intense pressure and cause predictable fracture patterns. "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," said Juno investigator Candy Hansen from the Planetary Science Institute.
In addition to the JunCam images, the probe also took one photo (above) with the Stellar Reference Unit (SRU). This highly sensitive camera detects dim stars for navigational purposes. To avoid overexposing the image, JPL pointed the SRU at Europa's nightside.
The black and white SRU sensor captures incredible detail, illuminated only by sunlight reflecting off Jupiter. Near the top, a pair of ridges run east to west, surrounded by dark stains. The team speculates these could be locations where plumes of water escaped from the ocean as briny plumes. Thirty-one miles (50 kilometers) south is a feature dubbed "The Platypus," which features a complex swirl of ridges, hummocks, and spires. The SRU image reveals ice blocks within The Platypus that are several miles wide, interrupting lineae in the area.
This is just a taste of what we'll get in a few years. NASA plans to launch the Europa Clipper in late 2024. The spacecraft will arrive at Europa in 2030 and begin looping around the moon to map its surface and internal structure. It might even determine if the ocean has conditions that could support life.