2.9 Eruption plumes on Europa?

No visiting spacecraft has seen eruption plumes at Europa like those on Enceladus. However an exciting discovery was announced in December 2013. The Hubble Space Telescope, in orbit about the Earth, had found a faint ultraviolet glow caused by atoms of hydrogen and oxygen rising up to 200 km above Europa’s south pole in December 2012. This probably shows water molecules broken apart in the harsh space environment.

Figure 34 A plume of erupted water above Europa as imaged by the Hubble Space Telescope in Earth orbit (superimposed on a more detailed close-up image of Europa itself).

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This is an image of a plume of erupted water above Europa as imaged by the Hubble Space Telescope in Earth orbit (superimposed on a more detailed close-up image of Europa itself).

Figure 34 A plume of erupted water above Europa as imaged by the Hubble Space Telescope in Earth orbit (superimposed on a more detailed ...

Europa’s plumes are not persistent. Repeat attempts at detection using the same method throughout 2014 were blank. However in 2016 it was announced that by using the Hubble Space Telescope’s ultraviolet camera to watch Europa as it crosses the face of Jupiter, absorption of the sunlight reflected from Jupiter could be detected as it passed parts of Europa’s limb (the edge of its disc). This is most simply explained as plumes blocking out a tiny fraction of the light. The technique found plumes on three occasions out of ten during 2014.

If eruption plumes do indeed occur at Europa, they seem to be less persistent than those currently occurring at Enceladus. Perhaps water escapes in plumes only when certain special cracks in Europa’s ice shell are open.

See also: Europa plumes seen by a new technique (2016 report). [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] An account of plumes detected as Europa transits Jupiter’s disc.

Activity 2 Identify features on Europa for yourself

Timing: Allow approximately 20 minutes.

Now explore these surface features of Europa.

Figure 35 Age relationships.

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This is a 20-km wide image of part of Europa where the surface is made of ‘ball-of-string’ terrain.

Figure 35 Age relationships.

This is a 20-km wide image of part of Europa where the surface is made of ‘ball-of-string’ terrain. Which region do you think is older: the bright region or the dark ‘ball-of-string’ region?

Answer

Figure 36

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This is the same image as Figure 35 but two regions are labelled, 1 and 2.

Figure 36

The brighter band (1) is younger than the darker ‘ball-of string’ textured area. It cuts across the darker area (2), showing that it must have formed later.

Figure 37 Domes

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This is an 80-km wide region of Europa. It is mostly ‘ball-of-string’ terrain, but this has been warped or disrupted by doming from below. Most domes are 5–10 km across.

Figure 37 Domes

This is an 80-km wide region of Europa. It is mostly ‘ball-of-string’ terrain, but this has been warped or disrupted by doming from below. Most domes are 5–10 km across. See if you can identify some domes, and then see what we found.

Answer

Figure 38

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This is the same image as Figure 37, but has the domes circled in three places.

Figure 38

We have pinpointed the three most prominent domes in this image, but there are more.

Figure 39 Offset ridge.

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This is an image of a 15-km wide image of ‘ball-of-string’ terrain in Europa. There is one place where a ridge with a central groove has been offset by sideways slip along a fault.

Figure 39 Offset ridge.

This is a 15-km wide image of ‘ball-of-string’ terrain in Europa. There is one place where a ridge with a central groove has been offset by sideways slip along a fault. Try to find this, and estimate the amount of offset before you click to reveal the annotated version.

Answer

Figure 40

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This is the same image as Figure 39 but the offset ridge is circled.

Figure 40

A ridge has been offset in the centre of the circle. This suggests lateral movement. Given that the image is 15 km wide, the offset is about 0.8 km.

Figure 41 Raft features.

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This image, roughly 34 km by 42 km, is part of a ‘chaos’ region consisting of rafts of ice that have broken apart and drifted into new positions before the slushy matrix between the rafts refroze.

Figure 41 Raft features.

This image, roughly 34 km by 42 km, is part of a ‘chaos’ region consisting of rafts of ice that have broken apart and drifted into new positions before the slushy matrix between the rafts refroze. See if you can distinguish between rafts (still bearing ‘ball-of string’ texture) and matrix (representing the refrozen exposed ocean that was temporarily exposed as the rafts drifted apart), before you click to reveal the annotated version.

Answer

Figure 42

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This is the same image as Figure 41 but has three areas circled.

Figure 42

We have outlined the largest raft (which has neighbours close by to which it could be refitted without too much movement) and circled two other rafts that are more isolated. There are plenty of other rafts in this image. Shadows show that their surface is 100–200 m above the matrix. The matrix is a jumbled mess, lacking ‘ball-of-string’ texture, although there is a groove running through the matrix diagonally from the lower right corner that must have formed after the matrix refroze. Eventually, after many more grooves have formed, the matrix may become indistinguishable from ‘ball-of-string’ terrain.