Newly analyzed Galileo data provides “compelling independent evidence that there seems to be a plume on Europa,” said study lead author Xianzhe Jia, an associate professor in the Department of Climate and Space Sciences and Engineering at the University of Michigan.
The Europa plume could offer a way for a spacecraft to sample Europa’s buried ocean of liquid water without even touching down on the moon.
NASA is developing a $2 billion Jupiter-orbiting mission called Europa Clipper, which is scheduled to launch in the early to mid-2020s.
If all goes according to plan, Clipper will make 40 to 45 flybys of Europa over the course of its mission, studying the moon’s ice shell and subsurface ocean in an attempt to better understand Europa’s potential to host life as we know it. Europa Clipper will also scout out locations for a future lander mission, which Congress has directed the space agency to develop as well.
The icy surface of Jupiter’s moon, Europa, is thought to lie on top of a global ocean. Signatures in some Hubble Space Telescope images have been associated with putative water plumes rising above Europa’s surface providing support for the ocean theory. However, all telescopic detections reported were made at the limit of sensitivity of the data, thereby calling for a search for plume signatures in in-situ measurements. Here, we report in-situ evidence of a plume on Europa from the magnetic field and plasma wave observations acquired on Galileo’s closest encounter with the moon. During this flyby, which dropped below 400 km altitude, the magnetometer8 recorded an approximately 1,000-kilometre-scale field rotation and a decrease of over 200 nT in field magnitude, and the Plasma Wave Spectrometer9 registered intense localized wave emissions indicative of a brief but substantial increase in plasma density. We show that the location, duration and variations of the magnetic field and plasma wave measurements are consistent with the interaction of Jupiter’s corotating plasma with Europa if a plume with characteristics inferred from Hubble images were erupting from the region of Europa’s thermal anomalies. These results provide strong independent evidence of the presence of plumes at Europa.
More on the Europa Water Plume
Europa is 1,900 miles (3,100 kilometers) wide. Europa is slightly smaller than Earth’s moon. Jupiter’s moon has about twice as much water as Earth does.
During its time at Jupiter, Galileo performed 11 flybys of Europa. Jia and his team took an in-depth look at information the probe gathered during the closest of these encounters — a 1997 flyby that brought Galileo within 128 miles (206 km) of the moon’s frigid, fractured surface.
The researchers found that, during this flyby, Galileo detected a significant change in Europa’s magnetic field, as well as a brief but big increase in the density of plasma, or ionized gas. Both of these observations provide strong evidence of a plume, Jia said. And these lines of evidence are independent of those gathered by Hubble. For example, in the 2014 and 2016 candidate detections, the possible plumes blocked some ultraviolet light emitted by Jupiter.
Intriguingly, Jia and his colleagues also determined that the 1997 candidate plume emanated from the same general hotspot (or thermal anomaly) as the 2014 and 2016 phenomena.
Why did it take more than two decades to tease this result out of the Galileo data set? For starters, Jia said, the Galileo mission team wasn’t specifically looking for plumes.
In addition, “to make sense of the observations, we had to really go for sophisticated numerical modeling” techniques, he told Space.com. “And I don’t think those were available back 20 years ago.”