Why is the Giant Red Spot Red?

jupiterganymede_hstThe color of Jupiter’s Great Red Spot is probably the result of simple chemicals being broken apart by sunlight in the planet’s upper atmosphere. At least that’s what’s suggested by analysis of data from lab experiments and from NASA’s Cassini mission. (“Hold it,” I hear you cry. “Cassini is a Saturn mission.” Yes, it is, but it did a Jupiter flyby on the way.) Those results contradict the other leading theory for the origin of the spot’s striking color—that the reddish chemicals are stirred up from beneath Jupiter’s clouds.

Jupiter possesses three main cloud layers which occupy specific altitudes in its skies; from highest to lowest they are ammonia, ammonium hydrosulfide and water clouds. In lab experiments researchers zapped ammonia and acetylene gases, known to be present in that upper layer, with ultraviolet light, simulating the Sun’s effects on those materials. 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. 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.

When the same sort of test were performed on ammonium hydrosulfide which makes up a lower layer, the researchers found that, instead of a red color, the products their experiment produced were a shade of bright green.

The Great Red Spot is a long-lived feature in Jupiter’s atmosphere that is as wide as two earths.

Image Credi: NASA

Three Moons

3MoonsThe Cassini spacecraft has sent us this family photo of three of Saturn’s moons that are different from each other. The largest of the three, Tethys is round and has a variety of terrains across its surface. Hyperion (to the upper-left of Tethys) is the “wild one” with a chaotic spin, and Prometheus (lower-left) is a tiny moon that busies itself shepherding the F ring.

Image Credit: NASA

Crescent Mimas

Crescent Mimas

Death Star MimasCassini has seen back this crescent view of Saturn’s moon Mimas, the long shadows showing off its many craters, indicators of the moon’s violent history. The most famous evidence of a collision on Mimas (just under 400 km across) is the crater Herschel that gives Mimas its Death-Star-like appearance.

Image Credits: NASA

B and C in UV

RingsInUVOn 1 July, 2004, the Cassini spacecraft arrived at Saturn, marking the end of the spacecraft’s nearly seven-year journey through the solar system and the beginning of its tour of Saturn and the planet’s rings and moons.

This picture was taken in ultraviolet on 30 June, 2004 during Cassini’s orbital insertion maneuver. It shows, from left to right, the outer portion of the C ring and inner portion of the B ring which begins a little more than halfway across the image. The “dirty” particles are indicated by red, and “cleaner: ice particles shown in turquoise.

Saturn’s ring system is labeled from the inside out with the D, C, B and A rings followed by the F, G and E rings.

Image Credit: NASA