Finding Saturn

pia08387_croppedAstronomers have paired the Cassini spacecraft with the National Science Foundation’s Very Long Baseline Array (VLBA) radio-telescope system to pinpoint the position of Saturn and its family of moons to within about 4 km. That’s about 50 times more precise than those provided by ground-based optical telescopes, improving out knowledge of Saturn’s orbit and benefiting spacecraft navigation and basic physics research.

Image Credit: NASA

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