Tuesday, October 27, 2009

Murky Views of Umbriel

When Voyager 2 flew by Uranus in 1986, the extreme tilt of Uranus, the "planet on its side," and the need to continue on to Neptune meant that it would not be able to fly close to all of the planet's major moons, because it would make its closest approach to all of them at about the same time.  Additionally, the best images of Umbriel are smeared. 

While Umbriel is black as a lump of coal, a bright spot can be seen in a large basin near the terminator in this distant view.

In this view, Umbriel has rotated significantly, but because the south pole is pointed almost straight at the spacecraft, it appears to rotate like a pinwheel.  More features can been, including the fact that the basin seen earlier is a double basin.  A large lineament can be seen just to the lower right of the center of the disk.
This view is the closest color view of Umbriel (the closest view is colorized based on this image).   Thank to spacecraft motion, the phase angle is growing, and the heavily cratered, dark moon can be seen to have several bright spots, most notably the extremely bright crater rim near the top of the disk, Wunda.

This is Voyager's best view of Umbriel and its cratered surface. It appears that their is a degraded tectonic feature near the bottom of the terminator.  Wunda sits prominently at the top of the disk, and another crater, Skynd, on the upper terminator lacks a bright rim but has a bright central peak.

This view of Wunda, produced using the last two images shown here and reprojected to be seen as if viewed from above, shows the doughnut-like shape (with a tiny segment missing pointing diagonally down and left).


While of very limited quality, this crescent image, taken as Voyager receded, speaks to the rugged surface of this battered moon via its lumpiness.  A bright spot can be seen toward the bottom of the crescent, possibly another bright spot. 

Processed Images Copyright Ted Stryk, Raw Data Courtesy NASA/JPL

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