Here’s another intriguing look at Helene, lit by sunlight from the right while some reflected light from its own highlands illuminates the interior of a valley/crater. Its dark side appears pitch black against the slightly brighter region of space behind, possibly lightened by the diffuse reflected light from ice particles in Saturn orbit.
This is from a raw image acquired by Cassini as it was approaching Helene on June 18, 2011. For more information on that flyby, see my previous post.
I brightened the image a bit so it would be more visible on most monitors, and added a layer to give a slight glow effect from the sunlit area. I also had to clean up some CCD noise and artifacting around the edges of the moon. The original downlink can be seen here.
Credit: NASA / JPL / SSI. Edited by J. Major.
First of all, get your mind out of the gutter. 😉 21-mile (35 km) -wide Helene is a “Trojan” moon of the much larger Dione, so called because it orbits Saturn within the path of Dione, 60º ahead of it. (Its little sister Trojan, 3-mile-wide Polydeuces, trails Dione at the rear 60º mark.) The Homeric term comes from the behavioral resemblance to the Trojan asteroids which orbit the Sun within Jupiter’s path…again, 60º in front and behind. These orbital positions are known as Lagrangian points (L4 and L5, respectively.)
The image here shows some really interesting texture on Helene…grooves running outwards from a central point on the little moon. I’m not sure what side of Helene we are looking at here, but it would make sense if this were its leading face that we are seeing the result of motion into its orbit, perhaps the result of meteorite weathering or some other debris falling onto it along its path, maybe material ejected from Dione?
This is a crop of a raw image acquired by the Cassini spacecraft on January 31, 2011, during a flyby of several moons in the Saturnian system. Cassini also visited Mimas and Enceladus, getting some very nice images of those worlds as well…I’ll post some of those later today!
This isn’t the closest Cassini has come to Helene, either…that happened back in March of 2010 when it passed by at a distance of about 1,200 miles (1,900 km).
Image: NASA / JPL / Space Science Institute. Edited by J. Major.
Update: the image above is now an RGB color version, assembled from three separate raw images.
On March 3 the Cassini spacecraft flew by the 22-mile-wide Helene, an irregularly-shaped moon orbiting Saturn in the same path as the much larger Dione. Cassini was about 1,200 miles from the moon when this image was taken.
See more photos of Helene on the Cassini imaging center website here.