Cosmic Paparazzi: Dione Flyby

Cassini flyby of Saturn moon Dione

(Click for full-size version)
[Image credit: NASA/JPL-Caltech/Space Science Institute] – Flying past Saturn’s moon Dione, Cassini captured this view which includes two smaller moons, Epimetheus and Prometheus, near the planet’s rings.

Dione (698 miles, or 1,123 kilometers across) is closest to Cassini here and is on the left of the image. Potato-shaped Prometheus (53 miles, or 86 kilometers across) appears above the rings near the center top of the image. Epimetheus (70 miles, or 113 kilometers across) is on the right.

This view looks toward the northern, sunlit side of the rings from less than one degree above the ring plane. The view was acquired at a distance of approximately 67,000 miles (108,000 kilometers) from Dione. Image scale is 2,122 feet (647 meters) per pixel on Dione.

Cosmic Paparazzi: Saturn Storm


Saturn Storm - Credit: Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA; Color Composite: Jean-Luc Dauvergne

Explanation: Late last year, a new, remarkably bright storm erupted in Saturn’s northern hemisphere. Amateur astronomers first spotted it in early December, with the ringed gas giant rising in planet Earth’s predawn sky. Orbiting Saturn, the Cassini spacecraft was able to record this close-up of the complex disturbance from a distance of 1.8 million kilometers on December 24th. Over time, the storm has evolved, spreading substantially in longitude, and now stretches far around the planet. Saturn’s thin rings are also seen slicing across this space-based view, casting broad shadows on the planet’s southern hemisphere. – NASA Astronomy Picture Of The Day

Pac-Man On Mimas

Saturn’s icy moon, Mimas, has long been remarked for its large Herschel Crater giving it the appearance of the Death Star, the fictional space station of Star Wars fame.


Death-Star-esque Mimas, imaged by Cassini -- Click for high-resolution view

Perhaps Mimas inspired George Lucas when creating the Death Star? Nope; Voyager was the first to give us close-up views of Mimas, a few years after ‘A New Hope’ was in theatres.

But earlier this year, Mimas revealed another uncanny secret resemblance to something out of recent pop-culture history: Pac-Man!

Mimas Temperature Map

Mimas Temperature Map - Click for a Pac-tastic Larger Version

So what we’re seeing here is a map of temperature differences placed over a visual-light image of Mimas. If you think it’s curious that the highest temperatures seem to vary in such a way, you’re not alone:

“Even though we can’t explain the observed pattern of surface temperatures on Mimas, the giant Herschel crater is a leading suspect[.]” “The energy of impact that created it several billion years ago has been estimated to be one-seventh of Mimas’s own gravitational energy. Anything much larger would likely have torn the moon apart. We really would like to see if there is also an anomalous temperature pattern on the other side of Herschel, which has not been observed so closely.” – Dr. Mike Flasar, composite infrared spectrometer principal investigator from NASA Goddard Space Flight Center.

The following image gives an idea of how what’s actually occurring on Mimas compared to what would previously be expected:

Comparison of different images of Mimas.

Comparison between expected temperature-map, actual temperature-map, visual light, and actual temperature-map layered on visual light images. - Click for full version.

A leading theory is that different textures of surface materials (mostly water ice with small amounts of rock) are holding on to heat from the Sun differently, but what is still not understood is why such sharp boundaries exist between these textures — giving the Pac-Man shape. It’s possible that the impact that caused the Herschel Crater distributed the more heat-absorbent materials in that pattern, but Mimas is constantly bombarded by impacts (as can be clearly seen when viewing the high resolution image of Mimas above), which you’d expect to destroy long ago any non-uniform surface make-up.

So for now, no definite answer is available. Luckily, we have the amazing Cassini orbiter up there, collecting more data for the scientists to work with.

Cosmic Paparazzi – Saturn and Tethys

Saturn and moon Tethys

Saturn and moon Tethys

(Click image for full resolution)

This view of Saturn, its rings and the moon Tethys represents “Target 1” in the fall 2009 edition of the Cassini Scientist for a Day contest. (See The contest is designed to give students a taste of life as a scientist by challenging them to write an essay describing the value of one target choice among three for Cassini to image.

A bonus feature in the image is the presence of bright spokes on and just above the ansa, or curved edge of the darkened ringplane. The spokes are made visible here by sunlight scattering through the dust-sized icy particles and toward Cassini’s cameras.

Images taken using red, blue and green spectral filters were combined to create this color view. The images were acquired with the Cassini wide-angle camera on Oct. 11, 2009 at a distance of 1.7 million kilometers (1 million miles) from Saturn. – NASA

The Deathstar…. Err… Mimas

Cassini never ceases to amaze me.

Saturn has moons. Lots of moons (at least 62). And I find each one of those moons to be equally interesting.

Recently, the orbiter, Cassini, snapped the following photo of one of Saturn’s moons, Mimas.

(Click image to BIGGIFY)
Mimas is the twentieth largest moon in our solar system, yet is the smallest astronomical body that is believed to be round in shape due to its self-gravitation. Mimas has an interesting feature in a huge crater named Herschel. Compared to Mimas, this crater is huge. It is 80 miles (130km) wide, which is about a third of the total size of the moon itself (wider than Canada). As Phil Plait points out, the impact that created this crater was just about as big as it could have been without obliterating Mimas.

The results are beautiful. Some see the crater resembling a big eye. To many, including myself, it looks like the Deathstar:
(That’s no moon. It’s a space station. – Obi-Wan Kenobi)

For a mission that began in 1997, Cassini (Cassini-Huygens originally, until the Huygens probe was sent to land on the surface of Titan) just keeps on keepin’ on. It has had its missions and extended multiple times, and will most likely keep snapping these shots until it makes a flaming plunge into Saturn’s atmosphere in 2017. NASA, and its counterparts from around the globe, have done a fantastic job of completing their main missions, and then coming up with ways to continue using them for additional missions. We’re learning new and amazing things on a regular basis, and I think that’s just grand.