This is a color composite image of Rhea (pronounced REE-ah) I made from raw images acquired by the Cassini spacecraft on March 9, 2013, during its most recent — and final — close pass of the moon. The visible-light colors of Rhea’s frozen surface have been oversaturated to make them more apparent… even so, it’s still a very monochromatic place.
If someone were to ask you today what the most heavily-cratered world in the Solar System is, you can’t go wrong with saying “why, Rhea of course!”
(I don’t know why someone would ask you that, but if anyone does you can now consider yourself well-prepared.)
Here’s a color-composite image of Rhea, made from raw images acquired by Cassini during a flyby on March 10, 2012. The color is derived from images taken in infrared, green and ultraviolet light.
Here’s a color-composite image of Rhea and Titan, Saturn’s largest moons. Made from raw images acquired by the Cassini spacecraft on June 16, 2011, this really shows the vast difference in size and appearance of the two moons.
Rhea, seen in the foreground, is an icy, airless and heavily-cratered world 950 miles wide. Titan, on the other hand, is over three times larger at 3,200 miles across and covered in a thick atmosphere of methane and hydrocarbons. Its surface features mountains and valleys, with lakes and streams of liquid methane… and it may even have a liquid subsurface ocean.
Titan’s atmosphere and high-level haze can be seen in this image, and you can also see where the moon’s shadow cuts through the haze at the south pole (up and to the right in this image.)
Raw images taken in red, green and blue visible-light channels were combined to make this color version. The spacecraft was 1,828,949 km (1,136,456 miles) from Rhea when the images were taken.
Credit: NASA / JPL / Space Science Institute. Edited by Jason Major.
This image from Cassini shows no less than five of Saturn’s moons in the same frame: Rhea (1,528 kilometers, or 949 miles across) is largest in the foreground; Dione (1,123 kilometers, or 698 miles across) can be seen just above the rings below Rhea near the center; Prometheus (86 kilometers, or 53 miles across) is just barely visible in the rings to the right of Dione; Epimetheus (113 kilometers, or 70 miles across) is to the right of the rings and Tethys (1,062 kilometers, or 660 miles across) is on the extreme right below the ringplane.
Cassini was approximately 61,000 km (38,000 miles) from Rhea when this image was acquired.
Read more on the Cassini mission site here.
Credit: NASA / JPL / Space Science Institute
Assembled from 29 raw images taken by the Cassini orbiter on Monday, April 25, this animation brings us along an orbital ride with Rhea as it crosses Saturn’s nighttime face, the planet’s shadow cast across the ringplane. Sister moons Dione and Tethys travel the opposite lane in the background, eventually appearing to sink into Saturn’s atmosphere.
Every six to nine months or so the Cassini Imaging Center dumps orbiter image data into NASA’s Planetary Data System, or PDS. This data is accessible to anyone with an internet connection, but it can be a little awkward to find exactly what you’re looking for (unless you’re familiar with the technical nomenclature of the dozen imaging filter codes and timestamps of Cassini data…in which case, dig in!) Luckily the SETI institute has set up a more user-friendly search engine that allows desktop astronomers to zero in on image collections with less data entry involved.
(More photos after the jump…)