Europa was first glimpsed up-close by the Pioneer and Voyager probes in the 1970s, but it wasn’t until the Galileo mission in the 1990s and early 2000s that our current understanding of Europa as a potentially habitable world developed. We now have good reason to believe that Europa contains a vast ocean of liquid water beneath its icy surface, and a central goal of two upcoming missions is to understand whether this ocean might harbour conditions suitable for life.

Figure 1 The launch of the JUICE spacecraft onboard an ESA Ariane 5 rocket from Guiana Space Centre on 14 April 2023Show descriptionA photograph of a rocket, standing vertical. It is a long tube-shape with a pointed end facing upwards. At ground-level is a bright white cloud, indicating flames, with smoke billowing upwards. To the right of the rocket is a small rectangular building and behind the rocket and to the left and right are tall metal constructs that taper to the top.In the 2030s, the European Space Agency’s JUpiter ICy moons Explorer (JUICE) spacecraft (which launched in 2023, Figure 1) will be joined by NASA’s Europa Clipper – currently planned for launch in October 2024 – in studying Europa. Together, these missions stand to revolutionise our knowledge of Europa and its ocean.

There is a plethora of science planned for both missions. They will use radar to peer below the ice and search for liquid water, and they will study how Europa affects Jupiter’s magnetic field, providing information on the depth and salinity of its ocean. To learn more about ocean chemistry, the spacecraft will use infrared and ultraviolet cameras to seek chemical compounds from the ocean at Europa’s surface.

While Europa’s ocean is hidden underneath kilometres of solid ice, it’s young surface is covered in evidence for recent geological activity that could have brought ocean water up from below. Salts and other chemical compounds have recently been detected on Europa’s surface by the Hubble and James Webb Space Telescopes, a sign that water from the deep has, at some point, made its way to the surface. By conducting many flybys of Europa (Figure 2), Clipper and JUICE will map such compounds in exquisite, unprecedented detail, allowing scientists to investigate where, when, and how material from the ocean might have emerged and frozen onto the surface.

Europa Clipper will also aim to collect tiny, microscopic fragments of the surface that have been ejected into their flight paths. Because Europa lacks a proper atmosphere, such specks of dust are expected to be constantly kicked up by micrometeorite impacts. Another exciting possibility is that icy plumes, like the spectacular geysers discovered by the Cassini mission at Saturn’s icy moon Enceladus, could deliver frozen droplets of water from beneath the surface into space, which the spacecraft could collect and study. However, the existence of such plumes at Europa is not yet confirmed.

Figure 2 The trajectories of Europa Clipper's 44 planned flybys of Europa, which will allow it to achieve near-global coverage. The red portions of some lines show the lowest altitude flybys, some as low as 25 km above the surfaceShow descriptionAn image showing an artist’s impression of Europa as a 2D disk, coloured brown-grey, in the centre. To the right and behind is Jupiter, identifiable from the round, red spot in the southern hemisphere. Drawn across Europa’s face are 44 lines across all latitudes of the moon. Some are horizontal and others are at an angle.

One challenge the spacecraft face is the intense level of radiation found near Europa, a consequence of Jupiter’s magnetic field. By staying in Jupiter’s orbit, they will spend most of their time far from Europa, only coming in for close flybys and avoiding the worse effects of the intense radiation (Video 1). Even so, electronics on the spacecraft must be engineered to withstand high doses of radiation. JUICE will then ultimately go into orbit at Ganymede – another ocean-bearing moon of Jupiter where the radiation is much lower – making it the first spacecraft to ever orbit a moon of another planetary body.

Video 1 Animation showing Europa Clipper’s planned trajectories (pink line) to avoid Jupiter’s intense radiation.  The green dot is Jupiter, and the cyan circle is Europa’s orbit.  The orange and yellow circles represent the orbits of two other of Jupiter’s moons, Io and Callisto.

A major challenge for space scientists is to learn how to interpret all the new data these missions will provide. For example, we must understand how ice moves and buckles under extremely low temperatures, how Jupiter’s gravity might squash and squeeze the moon’s interior, and how radiation can change the chemistry of the surface. To allow us to assess the prospects for life in Europa’s ocean, we need to answer questions like: how can we recognise chemical compounds from the ocean and distinguish them from dust or molecules that might have been delivered from space? How might compounds from the ocean change during their journey from the ocean to the surface? And, what do they tell us about Europa’s ocean throughout its history?

Answering these questions is a central focus of our icy worlds research in AstrobiologyOU. We run laboratory simulation experiments and computer models that simulate the conditions found in the deep oceans and icy layers of icy moons like Europa. We study forms of ice and salt in the laboratory that exist only under extremely low temperatures. These icy minerals don’t form naturally on Earth, but could be important components of the geology of worlds like Europa. We also explore regions on Earth’s surface that bear some similarities to Europa (an approach we also use to learn about Mars). We use these regions, which include locations in Iceland and the High Arctic, to learn more about the traces of life that could exist in Europa’s ice, or how evidence of ocean chemistry might appear at the surface. Another aspect of our work is to use knowledge of life in extreme environments on Earth to learn how to protect Europa from contamination from future spacecraft.

Within a decade, a treasure trove of new data will emerge from Europa, but it’s only through the work we do here on Earth that we can turn this data into understanding of Europa’s potential for life.