💧 Europa moon: evidence of water plumes called into question

Since 2014, the idea that water vapor plumes erupt from the surface of Europa, Jupiter's icy moon, has captivated astronomers. However, a new analysis of data from the Hubble Space Telescope casts doubt: these long-hoped-for eruptions may never have existed. Nevertheless, the prospect of a hidden ocean beneath the ice remains one of the most promising for the search for life. The researchers themselves, who initially announced this discovery, are behind this reassessment.

Europa is a prime target for those seeking habitable environments elsewhere. Beneath its icy crust lies a global ocean of saltwater, which could contain the ingredients necessary for life. Thus, the possible presence of plumes was very exciting: they would allow sampling of this ocean from space. Moreover, complex organic compounds detected on its surface strengthen interest in this moon. Determining the nature of these eruptions is therefore of great importance for assessing its habitability potential.


The scientists who announced the discovery in 2014 are now revising their conclusions. By re-examining fourteen years of Hubble observations, they have lowered the confidence level. From 99.9% certainty, it has dropped to less than 90%. A threshold insufficient to assert the existence of these plumes with assurance. This reanalysis was led by a team headed by Lorenz Roth from the Royal Institute of Technology in Sweden, and the results were published in the journal Astronomy & Astrophysics. The researchers believe the margin of error is now too large to decide.

The problem came from how Hubble measures light emissions. The researchers were interested in an ultraviolet wavelength called Lyman-alpha. But Europa's positioning in the images was inaccurate by a few pixels, which could create spurious signals. These artifacts may have been mistakenly interpreted as plumes. Kurt Retherford of the Southwest Research Institute explains that even a shift of one or two pixels could distort the interpretation. Thus, the famous eruptions could be nothing more than measurement artifacts.

Despite this doubt, scientists do not entirely rule out the possibility of these eruptions. Other icy moons, such as Enceladus around Saturn, have well-attested plumes. Additionally, Io, another moon of Jupiter, ejects sulfur. Europa could still surprise, but new observations will be needed. The geological similarities between these moons suggest that Europa might also experience similar activity. However, without direct evidence, it is impossible to assert this. The team plans to use other instruments, such as the James Webb Space Telescope, to attempt to confirm or refute the presence of these plumes.


The answer may come in 2030 with the arrival of NASA's Europa Clipper mission. This probe will study the moon up close and will be able to detect possible activity. In the meantime, astronomers remain cautious and continue to analyze data with more precise tools. Europa Clipper will perform several close flybys and will be able to directly measure the composition of the moon's tenuous atmosphere. This mission represents a hope to settle the debate on plumes and explore the subsurface ocean in more detail. Until then, the scientific community remains divided.

Oceans under the ice

Many moons in the Solar System have hidden oceans beneath an icy crust. Europa, Enceladus, Ganymede, and Titan are all worlds where liquid water could exist. These oceans are kept liquid by internal heat, generated by tidal forces from their parent planet. For astrobiologists, these environments are particularly interesting because water is an essential ingredient for life as we know it.

The presence of a global ocean under Europa's ice was deduced from magnetic field measurements and observations of its surface. It is estimated that this ocean could contain more water than all of Earth's oceans combined. Moreover, interactions between water and the rocky floor could provide the chemical elements necessary for life. That is why Europa is a priority target for exploration missions.

Water vapor plumes, if they exist, would offer a unique view of this ocean without having to drill through the ice. By analyzing their composition, scientists could determine whether the ocean contains organic compounds or other signs of potential biological activity. Unfortunately, their existence remains uncertain, as this new study shows.

Limitations of space observations

Telescopes like Hubble are powerful instruments, but they have their limitations. To detect faint phenomena like plumes on Europa, very weak signals must be measured, buried in background noise. Spatial resolution and sensitivity are often insufficient to distinguish a real signal from an artifact. Pointing errors, even tiny ones, can skew results.

The reanalysis of Hubble data on Europa perfectly illustrates these difficulties. Scientists had to account for uncertainty in the moon's exact position in the images. A shift of just a few pixels can create the illusion of an emission where there is none. That is why results must be confirmed by multiple instruments or methods before being considered robust.

To avoid these pitfalls, future missions like Europa Clipper will carry instruments designed specifically for close-up study of icy moons. By flying over Europa at low altitude, they will be able to directly measure particles and gases, without the uncertainties associated with distant telescopes. Collaboration between space observations and in situ missions is key to resolving doubts.