Triple Crescent


Triple CrescentSaturn has many moons. The three shown here—Titan, Mimas, and Rhea—show marked contrasts in their surface features. Titan, Saturn’s largest moon and the largest moon in this image, appears fuzzy because we only see its clouds. Because Titan’s atmosphere refracts light around the moon, its crescent is wrapped just a little further around the moon than it would on an airless body. Rhea (upper left) appears rough because its icy surface is heavily cratered. A close inspection of Mimas, though difficult to see at this scale, would show surface irregularities because of its violent history.

Image Credit: NASA

One more thing … If it’s clear where you are this evening, go outside and look up in the western sky just after sunset. There’s a conjunction of Venus and Jupiter tonight. They will be separated by less than half the diameter of the Full Moon.

Tethys Eyes Saturn


Tethys and SaturnIn this picture taken by the Cassini spacecraft last April, the two large craters on Tethys near the line where day fades to night seem to be looking at Saturn. (Click the image to embiggen it.)

The shadowing on the craters caused by being near Tethys’ terminator throws their topography into sharp relief. The larger, southernmost of the two shows a more complex structure. Its central peak is  probably the result of the surface reacting to the violent post-impact excavation of the crater. The northern crater doesn’t have a similar feature. The impact was likely too small to form a central peak, or the composition of the material in the immediate vicinity couldn’t support the formation of a central peak.

Image Credit: NASA

Odysseus


Tethys with craterOdysseus is the name of the huge crater on Saturn’s moon Tethys. Tethys is a bit more than 1000 km in diameter, and the crater is roughy 450 km across. To put that into scale, a crater that covered the same percentage of the Earth’s surface would be about the size of Africa.

Image Credit: NASA

Hyperion Close Up


hyperion20150531This picture of Saturn’s moon Hyperion was taken by Cassini during a fly by last Sunday. Hyperion is the largest of Saturn’s irregular, potato-shaped moons. It may be left over from a violent collision that shattered a larger object.

Image Credit: NASA

UPDATE—Broken link to image fixed.

Hyperion


HyperionThe Cassini spacecraft will make its last close approach to Saturn’s large, irregularly shaped moon Hyperion tomorrow. Cassini will pass by Hyperion at a distance of about 34,000 km at around 13:36  UTC. Images should arrive from the encounter to within 24 to 48 hours.

Hyperion rotates chaotically, tumbling unpredictably as it orbits Saturn. That makes it  challenging to target a specific region of the moon’s surface, and most of Cassini‘s previous close approaches have seen the same side of the craggy moon. The view above is from the closest encounter back in 2005. Mission scientists have hopes of seeing different terrain on Hyperion than the mission has previously explored in detail during tomorrow’s encounter, but this is not guaranteed.

BTW, the first time I saw this picture, I was reminded of a wasps’ nest.

Image Credit: NASA

Rhea on Edge


Rhea HorizonThis image looking at the horizon of Saturn’s moon Rhea was taken by the Cassini spacecraft at a range of about 56,000 km from the small (~1500 km) moon. The surface of Rhea has been mostly shaped by impact cratering. On more geologically active worlds like Earth or moons such as Titan, craters are erased by erosion, volcanoes, or tectonics. On quieter worlds like Rhea, craters remain until they are disrupted or covered up by the ejecta of subsequent impacts.

Image Credit: NASA