Jupiter’s moons harbor giant underground oceans – Europa Clipper is one of two missions on the way to see if these moons could support life

This article was originally published at The conversation. The publication contributed the article to Space.com Expert Voices: Op-Eds and Perspectives.

Mike Sori is an assistant professor of planetary science at Purdue University.

On October 14, 2024, NASA launched a robotic spacecraft called the Europa Clipper to the moons of Jupiter. Clipper will arrive at the ice-covered Jovian moon Europe in 2030 and spend several years collecting and sending valuable data about potential lunar habitation back to Earth.

Clipper is not the only mission that highlights the interest of researchers Jupiter and his months.

On April 13, 2023, European Space Agency launched a rocket carrying a spacecraft destined for Jupiter. The Jupiter Icy Moons Explorer – or JUICE – will spend at least three years on Jupiter’s moons after it arrives in 2031.

I’m a planetarian who studies the structure and evolution of the solid planets and moons in the solar system.

There are many reasons why my colleagues and I look forward to getting the data Europa Clipper and JUICE will hopefully be sent back to Earth in the 2030s. But perhaps the most interesting information will have to do with water. Three of Jupiter’s moons – Europa, Ganimed and Callisto – host large, underground oceans of liquid water that could support life.

Four of Jupiter's moons—from left to right, top to bottom: Io, Europa, Ganymede, and Callisto—are shown at their relative sizes.

Four of Jupiter’s moons—from left to right, top to bottom: Io, Europa, Ganymede, and Callisto—are shown at their relative sizes. (Image credit: JPL/NASA)

Meet Io, Europa, Ganymede and Callisto

Jupiter has dozens of moons. Four of them in particular are of interest to planetary scientists.

Io, Europa, Ganymede, and Callisto are, like Earth’s Moon, relatively large, spherical complex worlds. Two previous ones GODMOTHER missions sent spacecraft to orbit the Jupiter system and collected data on these moons. The The Galileo mission orbited Jupiter between 1995 and 2003 and led to geological discoveries on all four large moons. The The Juno mission it still orbits Jupiter today and has given scientists an unprecedented view of Jupiter’s composition, structure and structure. space-bar medium.

These missions and other observations revealed that Yothe closest of the four to the host planet, is rumble with geological activityincluding lava lakes, volcanic eruptions and tectonically formed mountains. But it does not hold large amounts of water.

Europa, Ganymede and Callisto, on the other hand, have icy landscapes. Europa’s surface is a frozen wonderland with a young but complex history, possibly including frozen analogues of tectonic plates and volcanoes. Ganymede, the largest moon in the entire world solar systemis greater than Mercury and has its own magnetic field internally generated from a liquid metal core. Callisto seems somewhat inert compared to the others, but it serves as a valuable time capsule of an ancient past that is no longer accessible on the young surfaces of Europa and Io.

Most interesting of all: Europa, Ganymede and Callisto almost certainly possess it underground oceans of liquid water.

An illustration of Europa with an iron core surrounded by a rocky mantle believed to be in direct contact with a vast, interior ocean with a volcanic seafloor.

Heat from Europa’s interior and tidal energy from Jupiter likely maintain a massive liquid ocean beneath the moon’s icy surface. (Image credit: NASA/JPL-Caltech/Michael Carroll)

Ocean worlds

Europa, Ganymede, and Callisto have cold surfaces that are hundreds of degrees below zero. At these temperatures, ice behaves like solid rock.

But just like Earththe deeper you go underground during these months, the warmer it gets. Go down far enough and you eventually reach the temperature at which ice melts into water. How far this transition occurs on each of the months is a subject of debate which scientists hope to solve with JUICE and the Europa Clipper. Although the exact depths are still uncertain, scientists are confident that these oceans exist.

The best evidence of these oceans comes from Jupiter’s magnetic field. Salt water is electrically conductive. So as these moons travel through Jupiter’s magnetic field, they it generates a secondary, smaller magnetic field which signals to researchers the presence of an underground ocean. Using this technique, planetary scientists were able to demonstrate that the three moons contain underground oceans. And these oceans are not small – Europa’s ocean alone might have more than that double the water of all the Earth’s oceans combined.

A next obvious and tantalizing question is whether these oceans can support extraterrestrial life. Liquid water is an important part of what makes for a habitable world, but far from the only requirement for life. And life needs it energy and certain chemical compounds beside the water to bloom. Because these oceans are hidden under miles of solid ice, sunlight and photosynthesis are eliminated. But other sources may provide the necessary ingredients.

On Europa, for example, the liquid water ocean overlays a rocky interior. That rocky floor could provide energy and chemicals via underwater volcanoes that could make Europa’s ocean habitable. But it’s also possible that Europa’s ocean is a barren, inhospitable place—scientists need more data to answer these questions.

An artist rendering of the JUICE spacecraft traveling through the Jupiter system.

The Jupiter Icy Moons Explorer spacecraft will travel for eight years before reaching Jupiter. (Image credit: ESA)

Future missions from ESA and NASA

Europa Clipper and JUICE were established to provide scientists with game-changing information about the potential habitability of Jupiter’s moons. While both missions will gather data over several months, JUICE will spend time orbiting and focusing on Ganymede, and the Europa Clipper will make dozens of close flybys of Europa.

Both spacecraft will carry a suite of scientific instruments built specifically to investigate the oceans. The onboard radar will enable Europa Clipper and JUICE to probe in months’ outer layers of solid ice. The radar could reveal any small pockets of liquid water in the ice or, in the case of Europa, which has a thinner outer ice layer than Ganymede and Callisto, we hope to detect the larger ocean.

Magnetometers will be too in both missions. These instruments will give scientists the opportunity to study the secondary magnetic fields produced by the interaction of the conducting oceans with Jupiter’s field in detail, and hopefully give researchers clues about the salinity and volumes of the oceans.

Scientists will also observe small variations in the moon’s gravitational pulls by tracking subtle movements in the orbits of both spacecraft, which could help determine whether Europa’s sea floor has volcanoes that provides the necessary energy and chemistry for the ocean to support life.

Ultimately, both craft will carry an array of cameras and light sensors that will provide unprecedented images of the geology and composition of the moons’ icy surfaces.

Perhaps one day, a spacecraft will be able to drill through the miles of solid ice on Europa, Ganymede or Callisto and explore the oceans directly. Until then, observations from spacecraft like Europa Clipper and JUICE are scientists’ best bet for learning about these ocean worlds.

When Galileo discovered these moons in 1609, they were the first objects known to directly orbit another planet. Their discovery was the final nail in the coffin of the theory that Earth – and humanity – is at the center of the universe. Perhaps these worlds have another humiliating surprise in store.