NASA confirms the presence of water vapor on the surface of Europa

The fourth largest natural satellite of Jupiter and sixth largest in the Solar System, Europa has been of interest to planetologists for many years. About forty years ago, the Voyager program provided the first detailed picture of the veined surface of the icy moon. In the last decades, the data collected on Europa has made it a priority target for space agencies in the search for life. And recently, planetologists have confirmed the presence of water vapor in Europe.


What makes this moon so attractive is the possibility that it has all the ingredients necessary for life. Planetologists have evidence that one of these ingredients, liquid water, is present under the icy surface and can sometimes burst into space in the form of gigantic geysers. But so far no one has been able to confirm the presence of water in these plumes by directly detecting the water molecule.

Europa: water vapor and a potential ocean of liquid water

Now, an international research team led by NASA's Goddard Space Flight Center has directly detected water vapor for the first time over the surface of Europa. The team did this detection by surveying Europa through one of the largest telescopes in the world in Hawaii.

By confirming the presence of water vapor over Europa, planetologists can better understand the inner workings of the moon. For example, it helps to support the idea that there is an ocean of liquid water, perhaps twice as large as the Earth's, beneath the thick ice shell of that moon. Some astrophysicists suspect that another source of water for the plumes could be shallow reservoirs of melted water ice.

Although planetologists have still not surveyed the interior of Europe, the predominant hypothesis suggests the existence of an ocean of liquid water beneath its frozen surface. Credits: NASA

" The essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur) and energy sources, two of the three requirements of life, are present throughout the Solar System. But the third - liquid water - is a little hard to find beyond the Earth, "said Lucas Paganini, NASA's planetologist. " Although the scientists have not yet detected the liquid water directly, we have found the second best thing: water in the form of steam ."

First direct detection of water molecules over Europa

In Nature Astronomy , Paganini and his team said they detected enough water ejected from Europa (at a rate of 2360 kilograms per second) to fill an Olympic pool in minutes. However, the authors also discovered that water appears too rarely, at least in sufficient quantity, to be detected from Earth.

" For me, the interest of this work is not only the first direct detection of water over Europa, but also its absence within the limits of our detection method, " says Paganini.

Indeed, Paganini's team detected the weak but distinct signal of water vapor during 17 nights of observation between 2016 and 2017. Looking at the moon from WM Keck observatory at the top of Mauna Kea volcano in Hawaii, researchers have seen water molecules on the main hemisphere of Europa. (Europa, like the Earth's moon, is gravitationally locked on its host planet, so the main hemisphere is always oriented in the direction of the orbit, while the secondary hemisphere is always in the opposite direction).

Differentiate terrestrial water vapor from that of Europa: models in reinforcement

For this, the researchers used a Keck observatory spectrometer, which measures the chemical composition of planetary atmospheres by means of the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light when they interact with solar radiation.

When interacting with solar radiation, water molecules emit specific infrared frequencies. Credits: Michael Lentz / NASA Goddard

Detecting water vapor on other worlds is a challenge. Existing spacecraft have limited capabilities to detect it, and scientists using ground-based telescopes must take into account the distortion effects of the Earth's atmosphere.

To minimize this effect, Paganini's team used complex mathematical and computer modeling to simulate the conditions of the Earth's atmosphere, in order to differentiate between atmospheric water from Earth and Europa from the atmosphere. data returned by the Keck spectrograph.

We conducted rigorous safety checks to eliminate potential contaminants in ground observations, " said Avi Mandell, a planetologist on the Paganini team. " But in the end, we will have to get closer to Europa to see what is really happening ."

Structure of Europa: study it in detail thanks to the Europa Clipper mission

Scientists will soon be able to get close enough to Europa to resolve their outstanding questions about the internal and external functioning of this possibly habitable world. The next mission, Europa Clipper, which is scheduled for launch in the mid-2020s, will complete half a century of scientific discoveries that began with a modest photo.

When it arrives in Europa, the Clipper orbiter will carry out a detailed study of the surface, the deep interior, the weak atmosphere, the submarine ocean and possibly even smaller active vents. Clipper will try to take images of all the plumes and sample the molecules he will find in the atmosphere to study with his mass spectrometers. He will also look for a site from which a future lander could collect a sample.

In this video, NASA returns in detail on the detection of water vapor in Europa:

Bibliography: Article: A measurement of water vapour amid a largely quiescent environment on Europa authors: L. Paganini, G. L. Villanueva, L. Roth, A. M. Mandell, T. A. Hurford, K. D. Retherford & M. J. Mumma Nature Astronomy Source