Forty years ago, a Voyager spacecraft made the first close-up images of Europa, one of Jupiter’s 79 moons, which revealed brown cracks cutting through the moon’s icy surface, giving it a veiny eyeball appearance. Subsequent missions have gathered enough additional information about Europa to make it a priority research target in NASA’s search for life.
Why is this moon so special? Because it has all the necessary ingredients for life, a promising alien nursery.
Planetary scientists suspected that Europa, Jupiter’s largest moon, could harbor a vast ocean of liquid water beneath its thick icy crust. We couple this ocean with an energy source (like hydrothermal vents) and some chemical elements, and we find a decent chance that the moon can support basic life forms.
Now, an international team of astronomers has announced the direct detection of water vapor in Europa’s atmosphere for the first time in history. As detailed in the study published in the journal Nature Astronomy, this detection method is strong evidence that liquid water exists below the surface of Europa.
“This does not necessarily mean that the water vapor comes from an ocean,” says NASA planetary scientist Lucas Paganini. “But it appears that this detection is connected to liquid water below the surface.”
The NASA team found that Europa releases enough water vapor to fill an Olympic-size swimming pool in a matter of minutes. It sounds strange to us or not, it has been enough to be detected from Earth.
Where does this water come from?
Of the 17 observations at the WM Keck Observatory in Hawaii, which uses a spectrograph to detect the chemical compositions of the atmospheres of other planets by scanning infrared light, either released or absorbed, the scientists only detected water vapor in one. Molecules like water emit specific frequencies of infrared light when they interact with solar radiation.
“We suggest that water vapor degassing in Europe occurs at lower levels than previously estimated, with localized and rare events of stronger activity,” the authors wrote.
Because they only saw the water vapor once, the scientists trusted that the water came from a plume. And where there are plumes, there is a good chance that there is liquid water. The next step is to determine what is producing the plumes and if they are indicative of large amounts of liquid water in Europe. A plume can come from degassing of liquid water deep below Europa’s surface or friction caused by ice, among other things. But to solve the mystery, we will have to send some robots to see for ourselves. “If we want to get more knowledge about this oceanic world, we really need to get closer,” Paganini clarifies.
What’s to come
NASA’s upcoming Europa Clipper mission will take a much closer view of the icy moon’s surface. The mission will be launched in 2025 and will be the largest probe ever created, Clipper will be equipped with a set of instruments designed to look under the ice cap of Europa (cameras, spectrometers, radar …) that will also determine the composition of the moon and will offer us images never seen before. If Clipper finds evidence of life during the 45 scheduled flybys, it could finally justify a lander on this huge moon.
Referencia: A measurement of water vapour amid a largely quiescent environment on Europa. L. Paganini, G. L. Villanueva, L. Roth, A. M. Mandell, T. A. Hurford, K. D. Retherford & M. J. Mumma. Nature Astronomy (2019) DOI: doi:10.1038/s41550-019-0933-6
