The Moon is a first step. Mars will test us, but Europa, the prize

In the 2030s, tMoonmbitious mission of the European Space Agency to Jupiter, JUICE will visit Jupiter’s fire-and-ice moons: volcanic Io and icy Europa. Ganymede is a giant; Moon Callisto has craters. It will provide a few close flybys of Europa but not a full view of its surface. Now that the NASA-led Europa Clipper is underway, it appears that a closer look at Europa will be possible.

After so many years of waiting while Mars was the focus of attention, it’s difficult to overstate how excited planetary scientists are. This is a true quest to discover what makes a planet habitable.

Watery World

Europa is the smoothest and smallest of the Galilean Moons. It is 1,940 miles wide and made up of ice, rocks, and a mix of both. In the 1990s, when the Galileo probe flew above Europa, it found evidence of an ocean beneath the surface. It was vast, deep and dark.

Water doesn’t completely freeze because powerful tidal force constantly kneads it as the moon orbits Jupiter every 3.5 days. The ocean, in addition, is thought to be directly in contact with the silicate mantle of the moon and its surface ices, which would provide all the ingredients necessary for a habitable atmosphere: liquid waMoonand energy. Life on Earth has been known to exist even in the most extreme environments (for instance, bacteria called ExtremMoonles). So maybe – Europa’s ocean hidden beneath the ice could be a habitable environment.

Io, Europa, and Ganymede are the four Galilean Moons of Jupiter. NASA

What to Look for

JUICE or Clipper won’t reach the surface of the ocean, nor the sea itself – this is too difficult a technical challenge at the moment. If habitable conditions exist beyond Earth, especially as far as Jupiter and its satellites are from the Sun, then this could indicate that these conditions are widespread throughout our universe.

Europa must be explored via orbital reconnaissance. We need to perform spectral analyses of the composition, geology, and radiation fields of the surface and to measure the magnetic, electrical, and plasma fields. We can use ice-penetrating radio to probe the icy crust and even the ocean beneath it in order to understand better the forces shaping this frozen world.

Europa’s chaotic terrain is caused by repeated melting and freezing. NASA

Europa’s cracked and fractured surface is relatively crater-free and geologically young. Galileo’s observations from orbit indicate that freeze-melt processes trap ice burgs in frozen seas and create the scarred patterns called Chaos terrain. The bright planes are crisscrossed by dark parallel ridges that could be due to geologic processes or tectonics.

Hubble’s 2012 observations were the most surprising. They showed that huge geysers or plumes erupted tens of kilometers over Europa’s South Pole, possibly contributing to an extremely thin atmosphere. We could get a better idea of the composition of the deep ocean if we were able to sample the plumes.

Early rather than Later

For all of these reasons, Europa is still the top priority for any future mission. The fact that there are now two missions to Jupiter’s system is the result of years of research by NASA and ESA. A joint mission called Europa Jupiter System Mission was once planned, but due to financial constraints, it was never carried out.

The Jupiter Icy Moon Explorer (JUICE) and its instruments. ESA

JUICE has now reached full speed ahead. The project has passed the full study and definition phase, allowing it to build the spacecraft. If everything goes according to plan, it will launch in 2022. It should reach Jupiter by 2030. It will be the first human-made orbiter of an Ice Moon, Ganymede, in late 2032, after two years of flybys to explore Jupiter, its rings, moons, and magnetosphere. Europa Clipper could move even faster if NASA’s newly announced funding is confirmed. It would use a new rocket, the Space Launch System, to propel it toward Europa in just a few short years.

Clipper will fly by Europa multiple times (perhaps 45 or more in three years), but it will not enter orbit directly. It will instead provide high-resolution imagery that will be used to select a landing area for a future robotic explorer. Even though funding for a future landing mission may be beyond reach, it is exciting to imagine that one day, we will see images of that harsh and icy environment with Jupiter suspended above.

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