Enjoying EarthSky? Subscribe.

221,463 subscribers and counting ...

What makes Jupiter’s Red Spot red?

A new analysis suggests that sunlight – not chemicals beneath Jupiter’s clouds – give the Great Red Spot its ruddy color.

Research suggests effects of sunlight produce the color of Jupiter's Great Red Spot. The feature's clouds are much higher than those elsewhere on the planet, and its vortex nature confines the reddish particles once they form. Image credit: NASA/JPL-Caltech/ Space Science Institute

Why is the Great Red Spot red? The intense red color is seen only in the Red Spot and a few much smaller spots on the planet. Researchers think altitude plays a key role. The Red Spot is extremely tall. It reaches to much higher altitudes than clouds elsewhere on Jupiter. Image via NASA/JPL-Caltech/ Space Science Institute

A new analysis of data from NASA’s Cassini mission suggests that reddish color of planet Jupiter’s Great Red Spot is likely a product of simple chemicals being broken apart by sunlight in the planet’s upper atmosphere.

These 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 (JPL), at the American Astronomical Society’s Division for Planetary Science Meeting in Tucson, Arizona.

Image credit : NASA, ESA, and A. Simon (Goddard Space Flight Center)

The Great Red Spot has been shrinking. Image at top – taken in 1995 – shows the Spot at a diameter of just under 21,000 km. Middle image from 2009 shows it at a diameter of just under 18,000 km. Bottom image taken in 2014 shows the Spot at its smallest yet, with diameter of just 16,000 km. Read more about the shrinking of the Red Spot from Hubble. Image via NASA, ESA, and A. Simon

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.

Baines said:

Our models suggest most of the Great Red Spot is actually pretty bland in color, beneath the upper cloud layer of reddish material. 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.

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

As for why the intense red color is seen only in the Great Red Spot and a few much smaller spots on the planet, the researchers think altitude plays a key role. Baines said:

The Great Red Spot is extremely tall. It reaches much higher altitudes than clouds elsewhere on Jupiter.

Bottom line: A new analysis suggests that reddish 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, rather than due to chemicals come from beneath Jupiter’s clouds.

Read more from NASA

EarthSky

MORE ARTICLES