This blog provides commentary on interesting geological events occurring around the world in the context of my own work. This work is, broadly, geological fluid dynamics. The events that I highlight here are those that resonate with my professional life and ideas, and my goal is to interpret them in the context of ideas I've developed in my research. The blog does not represent any particular research agenda. It is written on a personal basis and does not seek to represent the University of Illinois, where I am a professor of geology and physics. Enjoy Geology in Motion! I would be glad to be alerted to geologic events of interest to post here! I hope that this blog can provide current event materials that will make geology come alive.

Banner image is by Ludie Cochrane..

Susan Kieffer can be contacted at s1kieffer at gmail.com

Wednesday, December 18, 2013

Europa, emission from oxygen and hydrogen, and inferred jets of water

In the blue areas near the south pole of Europa, a satellite of Jupiter,
aural emissions from oxygen and hydrogen have been
detected by the Hubble Space Telescope. NASA image.
Just as we have aurora at the north pole because charged particles enter Earth's magnetic field, Europa has an aurora at its south pole because it is in the intense magnetic field of Jupiter. When atomic oxygen and hydrogen are excited by the magnetic field, they produce an aural glow that can be detected spectroscopically. The oxygen and hydrogen have been interpreted as being the products of water molecules torn apart by electrons along the magnetic field lines.
Top row: Images of the hemispheres
of Europa; other rows: combined images of
the hydrogen and oxygen emissions. This is
Figure 1 in the Science Express paper

The measurements were made from Hubble Space Telescope in December 2012, nearly a year before reported this week in Science Express and summarized in this NASA press release. The scientists involved (Lorenz Roth et al.) have stressed the need for caution because the Hubble Space Telescope was "pushed to its limits to see this very faint emission." Scientists are excited about this for two reasons. First, if confirmed, it would mean that Europa becomes the second moon spewing out water plumes (Enceladus is the other). Second, because there is good evidence that an ocean of liquid water exists under the surface of Europa, the plumes would be a way to sample its composition without having to drill through a thick crust. (The evidence for subsurface water is in the surface morphology and magnetometer measurements.)
     The plumes vary in intensity with the orbital position of Europa, but not in a way that is easily explained. They are active only when the moon is the farthest from Jupiter, instead of the more logical position closest to Jupiter.  The scientists postulate that the cracks that emit the water are closed when Europa is closest to Jupiter, and open when it is farthest away. The plumes extend up to about 125 miles altitude and the erupted "water" falls back onto the surface rather than escaping into space.  In the figure to the right, the detected "jets" in December 2012 are compared with 1999 and November 2012 images when the particles were not detected. In December 2012 the plume was near apocenter, and the other two times, close to pericenter, lending support to predictions of tidal modeling.

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