Another blast from Galileo's past: Europa
Posted by Emily Lakdawalla
24-12-2007 8:29 CST
Here's another set of Ted Stryk's newly reprocessed versions of Galileo's global shots of Jupiter's icy moons (see my previous post on his Callisto and Amalthea images). These are of Europa, the smallest of the Galilean moons, whose icy surface is fractured and grooved and bumped by internally generated forces. The crisscrossing patterns of the fractures and grooves are an intensely interesting puzzle to geologists trying to figure out what they say about the history of Europa's surface.
Galileo got several global views, but as I was uploading them into the image database, trying to figure out what features they showed, I realized that Galileo mostly viewed Europa's trailing hemisphere, the hemisphere that faces backwards along Europa's orbit. This hemisphere has a reddish stain, and the red color is particularly concentrated along some of Europa's long ridges. It's an interesting part of Europa to be sure, but it's a shame that there isn't a good view of the opposite hemisphere. More stuff for a followup Jupiter mission to do! (Though it occurs to me I really need to dig into the Voyager data set to see what there is on the leading hemisphere -- something I don't have time to do on Christmas Eve.) Here's two nearly full-phase views centered on that trailing hemisphere.
Galileo captured this global view of Europa on its 2nd orbit of Jupiter, on September 7, 1996. The filters used for this image cover a broader range of the spectrum than human eyes can see. Galileo was 678,000 kilometers from Europa when it took this image, at a phase angle of just 2°. Image scale is 6.9 kilometers per pixel. Credit: NASA / JPL / Ted Stryk
Europa in color: trailing hemisphereGalileo captured this global view of Europa on its 10th orbit of Jupiter, on September 19, 1997. The filters used for this image cover a broader range of the spectrum than human eyes can see. Only the green channel was returned at full resolution; the other color data was returned at half-resolution. Galileo was 725,000 kilometers from Europa when it took this image, at a phase angle of 27°. Image scale is 7.3 kilometers per pixel.
Here are two more views that swing around to the right (east) of the above views, toward the antijovian hemisphere, the side of Europa that always faces away from Jupiter. Unfortunately, because they are not full-phase, they don't reveal that much new terrain compared to the first two I posted. The first one of them is, however, a really huge global mosaic; if you click to enlarge it you can see a lot of nice topography along the day-night boundary, where slanting sunlight brings low ridges and bumps into relief.Finally, here's two views that swing the other way, to the left (west) of the global views, showing the subjovian hemisphere. If you were standing anywhere on Europa that you can see in these pictures, Jupiter would always be in your sky overhead -- now that would be quite a view! Just for fun, I thought I'd toss in a reminder of what New Horizons saw as it flew by the Jupiter system early this year. Once again, the full-phase views are primarily of the trailing hemisphere.
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