This snapshot was taken by the Cassini spacecraft. The small moon that seems to be hovering over Saturn’s rings is Janus. It’s only about 180 km across. The larger moon is Rhea, which is around 1500 km across. Saturn’s thin outer F ring is visible in front of Rhea, and the top of the moon is visible between the larger A and B rings.
Back in 2009, the Cassini spacecraft took this picture of Saturn’s moons Titan and Rhea. The two large moons are very different. Rhea is airless, cratered, and rocky. Titan has a lakes of liquid hydrocarbons and a nitrogen-rich atmosphere even denser that Earth’s.
Saturn 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.
This 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.
Saturn’s two largest moons, Titan and Rhea, seem to be stacked together in this true-color picture taken by the Cassini spacecraft. This view looks toward the Saturn-facing side of Rhea. North on Rhea is up and rotated 35 degrees to the right.
Separate images taken with red, green and blue filters using Cassini‘s narrow-angle camera were combined to create this natural-color view. The spacecraft was approximately 1.8 million km away from Rhea and 2.5 million km from Titan.
Rhea, Enceladus, and Dione are three of Saturn’s moons. This is what they looked like as seen from the Cassini spacecraft on 25 April, 2011. Saturn is also present in the picture on the left but is too dark to see. Rhea is closest to Cassini. It is the largest moon in center of the image. Enceladus is to the right of Rhea. Dione is to the left of Rhea and is partially covered by Saturn.
A quintet of Saturn’s moons appear in this image taken by the Cassini spacecraft.
Janus (179 kilometers, or 111 miles across) is on the far left. Pandora (81 kilometers, or 50 miles across) orbits between the A ring and the thin F ring near the middle of the image. Brightly reflective Enceladus (504 kilometers, or 313 miles across) appears above the center of the image. Part of Saturn’s second largest moon Rhea (1,528 kilometers, or 949 miles across) is visible at the right edge of the image. The smaller moon Mimas (396 kilometers, or 246 miles across) can be seen beyond Rhea also on the right side of the image.
This view looks toward the sunlit side of the rings from just above the ringplane. Rhea is closest moon to Cassini here. The rings are beyond Rhea and Mimas. Enceladus is beyond the rings.
The image was taken by Cassini spacecraft narrow-angle camera on 29 July, 2011. The view was acquired at a distance of approximately 1.1 million kilometers (684,000 miles) from Rhea and 1.8 million kilometers (1.1 million miles) from Enceladus.