NASA / JPL / SSI
The spiky shadow of Saturn's moon Mimas dips onto the planet's rings and
straddles the Cassini Division in this natural color image taken by the Cassini
spacecraft on April 8, 2009. Click on the image for a larger view.
Those shadows are taking on an especially eerie look as the planet nears equinox, an event that happens only twice during Saturn's 29.5-year-long orbit. In August, Saturn's rings will be facing the sun exactly edge-on. During the buildup to that event, the Cassini orbiter has been focusing on the shadows cast by moons as well as structures on the rings themselves.
The shadows are stretched to bizarre lengths, just as earthly shadows are elongated right before sunset. And because the moons are in motion, the mini-eclipses slide across the rings like dark ghosts. Four pictures showing the phenomenon were released today to celebrate the approaching Saturnian equinox as well as a "Visions of Saturn" exhibit at Britain's Royal Observatory in Greenwich.
"It has been a scientist's delight to watch this almost wafer-thin collection of icy debris, that we have come to know so well, change in character and spring into the third dimension," Carolyn Porco, the leader of Cassini's imaging team and director of the Cassini Imaging Central Laboratory for Operations, said in an image advisory.
Today's bonus image is another kind of mini-eclipse, involving two of Saturn's moons. The time-lapse animation shows the shadow of one Saturnian moon, Enceladus, passing over the face of another moon, Mimas.
Both moons are intriguing, but for different reasons: Ice-covered Enceladus possesses a set of geysers that spew water into space. Those geysers hint at a subsurface ocean, and perhaps alien marine life as well. You'll be hearing more about that as Cassini's mission continues.
Icy Mimas, meanwhile, is less than 250 miles (400 kilometers) wide, but still retains a round shape. That has led astronomers to suppose that the smallest dwarf planets (as defined three years ago by the International Astronomical Union) are around Mimas' size. But I'll bet that exceedingly few dwarf planets have the cool "Death Star" profile that Mimas has.
For more Cassini coolness, check out these links:
- Slideshow: Cassini's greatest hits
- Slideshow: Cassini's 10th birthday
- Cassini's closest encounter
- A mystery glows on Saturn
- Winners from Saturn
Join the Cosmic Log corps by signing up as my Facebook friend or hooking up on Twitter. And if you really want to be friendly, ask me about my upcoming book, "The Case for Pluto."