Archive for September 27, 2016

The Possible Plumes of Europa

Posted in The Universe and Stuff with tags , , , , , , , on September 27, 2016 by telescoper

I was too busy yesterday to write a post about the latest hot news from the NASA Hubble Space Telescope, so here’s a quick catch-up.

It seems that Europa, the smallest of the four Galilean moons of Jupiter, may from time to time be releasing “plumes” of water vapour. It has long been speculated that there might be large quantities of liquid water under Europa’s extremely smooth icy crust. Here’s a picture of possible plumes (to the bottom left of the image) in which a high-resolution picture of the surface of Europa has been superimposed.

europa

Picture Credits: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center

There’s also short video explaining the possible discovery here.

It’s not obvious at first sight that features like that shown above are caused by water erupting through Europa’s surface. On the face of it they could, for example, be caused by the impact of a smaller body. However,  long-term observations of this phenomenon suggest out-gassing is much more likely.  The Hubble Space Telescope’s Imaging Spectrograph was used to study what are essentially Aurorae powered by Jupiter’s strong magnetic field in which the presence of excited states of hydrogen and oxygen provide evidence for the disintegration of water molecules through interaction with electrons in this highly energetic environment. The images were taken when Europa was in front of Jupiter so they are seen were seen in silhouette.

There is also evidence that these appearance of these plumes is periodic, and that they are more likely to occur when Europa is further from Jupiter than when it is closer. A plausible theory is that water is released from cracks in Europa’s surface which open and close owing to a combination of tidal gravitational and magnetic effects.

I wouldn’t say this was definite proof of the water interpretation. These observations push the capability of the Hubble Space Telescope to the limit because the features are so faint. For information here’s what the raw image looks like (left)  and with enhanced contrast (right):

raw_image

 

Verification of these results through independent means is clearly an important priority, though likely to prove challenging. The plume interpretation is possible, but whether it is yet probable I couldn’t say!

 

 

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