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Next stop, Europa! Scheduled to launch sometime in the 2020s, NASA has decided on the nature and scope of a mission to Jupiter’s moon Europa. All that’s left is to actually build the probe, and wait for an appropriate launch window. Using a technique called the gravity assist the travel time for a fully equipped probe is about three years before the probe reaches orbit around Jupiter. That’s when the difficulty really begins.

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Even for the outer solar system, Europa is not an easy place to visit. The reason is Jupiter’s fearsome radiation belt. Jupiter has an immensely strong magnetic field, which tends to capture high-energy particles from the solar wind and trap them in belts around the giant planet. These energized particles play havoc on electronics and communications (even for a shielded spacecraft) and Europa is well inside the hot zone. The radiation will prevent the Europa probe from entering into orbit around Europa. Instead, it will need to take a very wide orbit around Jupiter, and perform numerous quick flybys in and out of the radiation zone, transmitting its information in the clear. Each pass will be brief, but the technique will prolong the life of the probe so it may perform numerous passes over a long period.

Ideally the probe will get the most out of each pass, as NASA has very good reasons for wanting to go to Europa. A major objective of many recent space missions is to find liquid water, and Europa almost certainly has that—a whole ocean in fact. Europa’s surface is water ice, kilometers thick, but the tidal forces caused by gigantic Jupiter cause heat and friction, enough to keep the water beneath the ice in a liquid state. What’s more, the strong gravity of Jupiter flexes its moon, so there may well be volcanic vents or similar features beneath the ocean, and volcanism can provide energy for a living ecosystem, as life thrives around Earth’s deep sea vents. In shallower portions of the sea, faults and deformation cracks, also caused by tidal forces, might allow access between the ocean and the surface, potentially allowing light and some oxygen to penetrate.

Taken together, if there is life elsewhere in the solar system, Europa is the place to look. The evidence suggests that the needs of life as we understand them will be best met in Europa’s ocean. If there is life in Europa’s seas, a flyby probe might be able to detect some molecular evidence, but a lander that can try to collect water samples will have the best shot. Such a mission would still be in the discussion phase, but the flyby mission is ready to enter R&D.


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Science News, Vol. 104, No. 21 (Nov. 24, 1973), p. 325
Society for Science & the Public
American Scientist, Vol. 90, No. 1 (JANUARY-FEBRUARY 2002), pp. 48-55
Sigma Xi, The Scientific Research Society