Saturn’s main rings, seen here on their “lit” face, appear much darker than normal. That’s because they tend to scatter light back toward its source — in this case, the Sun.
Usually, when taking images of the rings in geometries like this, exposures times are increased to make the rings more visible. Here, the requirement to not over-expose Saturn’s lit crescent reveals just how dark the rings actually become. Scientists are interested in images in this sunward-facing (“high phase”) geometry because the way that the rings scatter sunlight can tell us much about the ring particles’ physical make-up.
This Cassini image shows Jupiter from an unusual perspective. If you were to float just beneath the giant planet and look directly up, you would be greeted with this striking sight: red, bronze and white bands encircling a hazy south pole. The multicoloured concentric layers are broken in places by prominent weather systems such as Jupiter’s famous Great Red Spot, visible towards the upper left, chaotic patches of cloud and pale white dots. Many of these lighter patches contain lightning-filled thunderstorms.
Jupiter has very dramatic weather – the planet’s axis is not as tilted (towards or away from the Sun) as much as Earth’s so it does not have significant seasonal changes, but it does have a thick and tumultuous atmosphere filled with raging storms and chaotic cloud systems. Continue reading →
A very nice Cassini image of the Saturn moons Rhea and Tethys. The orientation of the pair is such that we can see what looks like large matching craters on each moon. I believe the crater on Rhea (the moon in front) is Tirawa. The crater is 360 km / 220 mile wide and makes up the Tirawa impact basin. The crater on Tethys is even larger, a true giant considering it is has a diameter 400 km / 249 miles or about 40 percent of the moons diameter.
Tethys appears to be peeking out from behind Rhea, watching the watcher.
Scientists believe that Tethys’ surprisingly high albedo is due to the water ice jets emerging from its neighbor, Enceladus. The fresh water ice becomes the E ring and can eventually arrive at Tethys, giving it a fresh surface layer of clean ice.
Lit terrain seen here is on the anti-Saturn side of Rhea. North on Rhea is up. The image was taken in red light with the Cassini spacecraft narrow-angle camera on April 20, 2012.
A nice image of the moon Enceladus seen with the back drop of the planet Saturn. This is the same sort of alignment Cassini was in to get the image of Tethys and Mimas posted here a last week (see Ring Shadows).
Enceladus is 504 km / 313 miles across and Cassini was 948,000 km / 589,000 miles away (about twice the Earth – Moon distance) so we can see how massive Saturn is. Learn more about Enceladus here,
Aside from Enceladus, the image shows wonderful detail in Saturn’s atmosphere. In particular the two dark round spots (center and upper right) and the interesting cloud feature about half way between Enceladus and the larger round spot. The cloud features look like they are rising vertically from the planet but probably are not. The round spots are disturbances in the atmosphere, much like Jupiter’s Great Red Spot only smaller.
Click the image to get a larger version and it scales pretty well so if you download it you can make it larger yet. You can get a full-res version and more details at the “Mighty Little Dot“.
This view looks toward the sunlit side of the rings from slightly above the ringplane. The image was taken in visible light with the Cassini spacecraft wide-angle camera on Aug. 14, 2014.
The view was obtained at a distance of approximately 1.1 million miles (1.7 million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 23 degrees. Image scale is 63 miles (102 kilometers) per pixel.
There are two moons in the image: the most obvious one is Tethys, seen at the lower right below the rings. The other is Mimas. Can you spot it? You may need to click the image to see the large version. Funny how it sticks right out once you find it. Give it a try.
Originally meant to publish yesterday: Cassini took this image of the Saturn swirling atmosphere. Planetary atmospheres (including our own) are a study in fluid dynamics and that is clearly evident here.
The image was taken on 23 August 2014 in red light from about 1.8 million km / 1.1 million miles with the narrow-angle camera.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
New research on the Great Red Spot of Jupiter based on Cassini’s flyby nearly 14 years ago (Dec 2000) suggests the red color is from the “sunburn” of particles and the variable color comes from cloud altitudes.
The ruddy color of Jupiter’s Great Red Spot is likely a product of simple chemicals being broken apart by sunlight in the planet’s upper atmosphere, according to a new analysis of data from NASA’s Cassini mission. The results contradict the other leading theory for the origin of the spot’s striking color — that the reddish chemicals come from beneath Jupiter’s clouds.
The results are being presented this week by Kevin Baines, a Cassini team scientist based at NASA’s Jet Propulsion Laboratory, Pasadena, California, at the American Astronomical Society’s Division for Planetary Science Meeting in Tucson, Arizona.
Baines and JPL colleagues Bob Carlson and Tom Momary arrived at their conclusions using a combination of data from Cassini’s December 2000 Jupiter flyby and laboratory experiments.
In the lab, the researchers blasted ammonia and acetylene gases — chemicals known to exist on Jupiter — with ultraviolet light, to simulate the sun’s effects on these materials at the extreme heights of clouds in the Great Red Spot. This produced a reddish material, which the team compared to the Great Red Spot as observed by Cassini’s Visible and Infrared Mapping Spectrometer (VIMS). They found that the light-scattering properties of their red concoction nicely matched a model of the Great Red Spot in which the red-colored material is confined to the uppermost reaches of the giant cyclone-like feature.
“Our models suggest most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material,” said Baines. “Under the reddish ‘sunburn’ the clouds are probably whitish or grayish.” A coloring agent confined to the top of the clouds would be inconsistent with the competing theory, which posits that the spot’s red color is due to upwelling chemicals formed deep beneath the visible cloud layers, he said. If red material were being transported from below, it should be present at other altitudes as well, which would make the red spot redder still. Continue reading →
NASA has produced global mosaics of Saturn’s moon Dione from Cassini spacecraft images. The image here is a trailing hemisphere which is darker than the leading hemisphere possibly because to “alteration by magnetospheric particles and radiation striking those surfaces”. It is also thought the leading hemisphere “is coated with icy dust from Saturn’s E-ring, formed from tiny particles ejected from Enceladus’ south pole. These satellites are all being painted by material erupted by neighboring Enceladus”.
The image is best enjoyed by looking at the high resolution verions at NASA’s Photojournal site you can see down to 250 meters per pixel – amazing!
Image Credit: NASA/JPL-Caltech/Space Science Institute/Lunar and Planetary Institute
A look at a dark Saturn and Titan in this Cassini image. This view is looking pretty much towards the Sun providing a look at the atmosphere of Titan and a very nice crescent on both.
These observations can tell us something of the compositions and physical states of the atmospheres. You will notice the crescent goes almost all the way around Titan, this is due to small haze particles in the upper atmosphere refracting the sunlight.
For a sense of scale the view is from 1.7 million km or 1.1 million miles from Saturn and yet we don’t see the entire planet.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Another very nice look at the north polar hexagon of Saturn from the Cassini spacecraft. This view is from 973,000 km/605,000 miles from about 33 degrees above the ring plane on 24 July 2013.
What causes the hexagon is not fully understood, the thinking is a “meandering” polar jet stream. Apparently wind speed is less important than the gradient of the winds flowing around the area in the formation of the hexagon which seem a little counter intuitive.
Another nice part of the photo is the detail in the atmosphere. Storms on Saturn are thought to occur when relatively warm atmospheric gas in the depths of the planet rise and cool, causing gaseous ammonia to form crystals and white clouds. This is analogous to thunderstorms here on Earth.