Published yesterday in a paper for Nature Astronomy, a team of scientists led by Dr. Xianzhe Jia unveiled strong evidence that one of Jupiter’s moons, Europa, is venting water into space in the form of plumes. This surprising result comes from anomalies uncovered in decades-old data from NASA’s Galileo mission. Not only does this discovery showcase the importance of past archival data, but it also has critical implications in the search for extraterrestrial life.
For years, Europa has been a promising candidate to host alien life due to its potential habitability. It is the 6th largest moon in the Solar System and boasts a thin, tenuous oxygen atmosphere as well as a magnetic field: important components of a habitable environment. Europa’s most compelling feature, however, lies beneath the miles of ice that form its surface: a massive salt-water ocean. Due to Europa’s non-circular orbit and its resonance with the nearby moons Io and Ganymede, the gravitational forces it experiences change throughout its orbit. These forces stretch and squeeze Europa, causing friction and, consequently, thermal energy. Thanks to this heat, Europa’s surface could still be solid ice while harboring a liquid ocean below.
In addition to the presence of liquid water, Europa has a few other unusual features that make it a crucial place to look for alien life. Research published in the Journal of Geophysical Research: Planets in late 2017 suggested Europa might be the only non-Earth object in our Solar System to have plate tectonics. The movement and interaction of crustal plates is particularly important for Europa because it could be a mechanism by which nutrients and the building blocks of life migrate from the surface to the ocean below. Some of these building blocks have already been detected on Europa’s crust in the form of clay-like minerals called phyllosilicates. Older studies have also proposed that Europa’s ocean is not only as oxygenated as Earth’s but is interacting with the deep sea floor. Simply put, Europa’s ocean has all of the necessary materials to support life: water, heat, and organic materials.
Because of this alluring hint of habitability, the discovery of strong evidence for Europa’s plumes offers a rare opportunity to potentially detect the first signs of alien life. Without the plumes, it would be prohibitively difficult to sample and observe Europa’s ocean, but their presence gives scientists a chance to conduct these experiments on ocean material that is being ejected into space. The possibility of plumes on Europa has been discussed in previous years due to imaging from the Hubble Space Telescope, but the data were at the limit of the observatory’s sensitivity. Instead of waiting for future telescopes, though, Dr. Jia and his team of researchers looked to the past. Specifically, they poured through 20-year-old magnetic field and plasma wave emission data from NASA’s Galileo mission.
From 1995 to 2003, Galileo studied Jupiter and its four largest moons, conducting just 11 flybys of Europa. One of the closest occurred in December of 1997 during which Galileo dipped below 250 miles above Europa’s surface. When Jia and his collaborators reviewed the data from this observation, they knew that, if plumes were present, they would cause changes in the magnetic field and particle density measurements. For three straight minutes, Galileo detected significant anomalies coinciding with the closest pass by regions of unusually elevated temperature on Europa’s surface. Given the known speed of Galileo, this would imply that the plume Jia et al. discovered was over 600 miles wide.
During NASA’s live discussion on Monday, the implication of Jia’s discovery for the upcoming Europa Clipper mission was clearly brought into focus. The Europa Clipper is a mission set to launch in the early to mid-2020s. After a roughly 6 year voyage to Jupiter, it will conduct 45 close flybys of Europa and sample any plumes, confirming their existence and revealing their chemical composition. Whereas Galileo was several hundred miles above Europa’s surface during its closest flyby, the Europa Clipper will skim by at a paltry 16 mile altitude.
Unlike the Cassini mission to Saturn, the Europa Clipper will also have a sounding radar capable of penetrating miles below Europa’s surface. Thus far, all evidence of plumes and the subsurface ocean they result from has been indirect. Like inferring the presence of a frog from ripples that surface in the water, scientists have only measured the effects these features have on their environment. The Europa Clipper will potentially confirm their existence by providing robust direct evidence.
It may be hard to imagine how life could flourish on a seemingly inhospitable moon. Between potentially high radiation, lack of nutrients, frigid temperatures, and distance from the Sun, Europa does not seem like the lush, inviting worlds dreamed up by science fiction. However improbable it seems, similar environments are potentially habitable on Earth and organisms have been discovered that could flourish in even harsher conditions. From Lake Vostok miles below the ice in Antarctica to D. radiodurans‘ resistance to extreme radiation, the ability of life to develop in unthinkably hostile conditions is an ever-evolving surprise. The thought of such a discovery seems to border on impossible, but, as Dr. Margaret Kivelson said during the NASA live talk about the discovery of Europa’s plumes:
“It’s amazing how hard it is to anticipate something that hasn’t happened before.”