On-site evidence of plumes on Europa from the Galileo spacecraft

The existence of plumes transporting material from the internal ocean of Jupiter’s moon Europa out into space is strengthened by on-site evidence taken by the late Galileo probe, reports a study published online this week in Nature Astronomy. Such plumes could allow a spacecraft orbiting Europa to sample ocean material directly and determine the ocean’s habitability.

Europa is archetypical of the outer Solar System’s ‘ocean worlds’ - bodies that host a warm liquid ocean under several kilometres of ice. To study this ocean, one option might be to land on Europa and drill through the ice, but this would be costly and technically challenging. A better option may lie in studying the plumes believed to spew material from the ocean to the surface. The Hubble Space Telescope observed phenomena on Europa in both 2012 and 2016 that may be plumes, although this interpretation is debated.

Looking instead at locally sampled data, taken by the Galileo spacecraft during its 1997 flyby of Europa, Xianzhe Jia and colleagues find the best evidence of plumes to date. The authors report that the changes they observe in the magnetic field and plasma around Europa are easily explained by the presence of a plume. Reconstructing Galileo’s path, they also pinpoint the location of the plume on Europa’s surface, which coincides with a region of anomalous temperatures due owing to the transport of heat from Europa’s interior.

These findings will help plan future missions to Europa, such as NASA’s Europa Clipper and ESA’s Jupiter Icy Moons Explorer spacecraft, both of which are expected to arrive at Jupiter between the late 2020s and early 2030s.

doi: 10.1038/s41550-018-0450-z

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