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

The Eye of Jupiter

jupitereye_0Not really. The trick is that the planet seems to be looking back at us because Hubble happened to catch the shadow of Ganymede, Jupiter’s largest moon, as it moved across the Giant Red Spot. Hubble was monitoring changes in that huge storm last April when the moon’s shadow moved across the center of the storm. For a moment, Jupiter became Cyclops.

Image Credit: NASA


IDL TIFF fileThis isn’t a picture of the Earth. It’s Jupiter as seen in ultraviolet light by the Hubble Space Telescope. Just as on Earth, Jupiter’s aurorae are curtains of light resulting from high energy electrons following the planet’s magnetic field into the upper atmosphere. Collisions with atmospheric atoms and molecules produce the observed light.

Image Credit: NASA

A Day in a Life …

… of Jupiter. A collection of Hubble images taken in 2007 was used to assemble this full, even coverage of Jupiter. The resulting mosaic has been mapped onto a sphere, and one full rotation is presented in the visualization.

Video Credit: NASA


The Not-So-Giant Red Spot

HubbleJGRS_900The most prominent feature on Jupiter is a storm called the Giant Red Spot. The most recent Hubble observations measure the spot to be about 16,500 km across. That’s the smallest ever measured by Hubble and big decrease from the 23,300 km measured by the Voyager 1 and Voyager 2 flybys in 1979. Telescopic observations during the 19th-century indicated a width of about 41,000 lm on its long axis. Current indications are that the rate of shrinking is increasing for the long-lived storm.

Image Credit: NASA