With the Cassini mission continuing through 2017, we’ll doubtless have many fine views of Saturn to come, but the images below merit special attention, enough so that I decided to close the week with them. We’re looking at an annotated, panoramic mosaic made by processing 141 wide-angle images, sweeping across 651,591 kilometers. That covers the planet, its inner ring system and all its rings out to the E ring. Moreover, the view presented here is in natural color, so we see the color as it would be seen by human eyes rather than as distorted during observations at other wavelengths.
You may remember the ‘Wave at Saturn’ campaign from last summer, when the word went out that Cassini would be snapping a view of the Earth from Saturn space. In the mosaic (click the image to zoom in) we can see the Earth as a blue dot to the lower right of Saturn, but Venus is visible too to the upper left, and Mars shows up as the faint red dot above and to the left of Venus. A close look will reveal seven of Saturn’s moons, including the intriguing Enceladus to the left. Enceladus is worth mentioning because the E ring, about 240,000 kilometers from Saturn, is made up of fine icy particles from the erupting geysers in Enceladus’ south polar terrain.
“This mosaic provides a remarkable amount of high-quality data on Saturn’s diffuse rings, revealing all sorts of intriguing structures we are currently trying to understand,” said Matt Hedman, a Cassini participating scientist at the University of Idaho in Moscow. “The E ring in particular shows patterns that likely reflect disturbances from such diverse sources as sunlight and Enceladus’ gravity.”
The second image (below) has been brightened and color-enhanced to tease out the ring structure. Note the blue color of the E ring, which is caused by the diffraction of sunlight. In both images, the Earth, Venus, Mars, Enceladus, Epimetheus and Pandora were brightened by a factor of eight and a half relative to Saturn to make them easier to see, although you’ll still need to zoom in by clicking to make them out. The outer rings (from the G to the E ring) were likewise brightened relative to the already bright main rings. Full background on these images can be found on this JPL page.
Getting a view like this is tricky because trying to see the Earth from Saturn means looking close enough to the Sun to endanger sensitive spacecraft detectors. Thus the need to find a time when the Sun is entirely behind Saturn as seen from Cassini. The spacecraft’s wide-angle and narrow-angle cameras were used to capture 323 images in a little over four hours, with the red, green and blue spectral filters combined to create the natural-color view. Although this is the second time Cassini has viewed it, the Earth has only been imaged from the outer Solar System three times, the first being the famous ‘pale blue dot’ image from Voyager. This is also the first time Earth’s inhabitants were told in advance about a photo that would include their entire world.