Discovering Greatness in the Great Red Spot
By Samantha Faith VanDeventer, Karlynn Dzik, Alex Forsberg, Broden Galarneau, and Dory Do

Does the largest planet in our solar system hold the biggest mysteries? The gas giant, Jupiter, certainly has its fair share of unanswered questions just begging astronomers to answer. Jupiter’s striped and spotted surface has a commanding presence, but its most striking feature is the large red oval crossing its lower hemisphere. This is the Great Red Spot.  

Figure 1. A look at Jupiter and its Great Red Spot from Voyager 1,, NASA/JPL.

A Background on Jupiter

As the largest planet in our solar system, Jupiter’s striped and spotted surface has a commanding presence. Jupiter has an extremely fast rotation which forces its atmosphere in to a turbulent state, forming storms that dazzle. The extreme speed of Jupiter’s rotation is in part due to the rapid size change between its equator and poles. To put this difference into perspective, the diameter of Jupiter is roughly 11 times that of Earth, but the diameter of the poles is almost 10,000 km shorter.1 This actually gives Jupiter a somewhat squished shape, which is only possible because Jupiter is made up of compressed gases and not solid rock like earth. It is important to note that gas planets like Jupiter use vaporized rock and gas as their starting ingredients,2,3  which could explain why Jupiter’s shape is not uniform. It is theorized that Jupiter was formed with multiple clouds of gases in our solar system, which accounts for the diversity of Jupiter’s gases.3 The gases of Jupiter’s atmosphere are being violently mixed together by its intense wind speeds of over 650 km/hr. These winds act on layers 3,000 km deep into the planet.2 Jupiter’s upper atmosphere has been the easiest to observe and determine its composition. Methods include spacecraft observations at a (relatively) intimate level to Jupiter and observations made through technology here on earth.4 The key elements of Jupiter’s upper atmosphere are carbon, hydrogen, oxygen, helium, and nitrogen,4 components that closely resemble those of earth, but are contained in molecules and states much different than those here at home. Do not let these elements fool your perception of Jupiter’s atmospheric layers. The presence of other gases like methane, argon, neon, sulfur, krypton, and others throughout Jupiter’s gaseous layers show an environment that could not be more shockingly different from Earth.5


What is the Great Red Spot 

Figure 2. A close up of Jupiter’s massive storm as seen from the JunoCam,, NASA/JPL-CALTECH/SWRI/Kevin M.

The Great Red Spot is a massive, violent storm raging across the surface of Jupiter. The discovery of the Great Red Spot could possibly date back to 1664 when Robert Hooke might have observed the storm with a 12-foot telescope. Hooke claimed he saw a large spot one-tenth the size of Jupiter that regularly moved across the planet. There is, however, some controversy over whether he actually observed what we call the Great Red Spot, as his observations of the movements of the spot sound more typical of a transit of a satellite shadow rather than of our modern observations of the storm. A year later, J. D. Cassini made possible observations of the Great Red Spot as well. He was first careful to rule out spots caused by transits of Jupiter’s moons or their shadows. He observed a long-lasting spot on Jupiter that matches the description of the Great Red Spot, but these observations from him and his successors only lasted up until 1713. No more observations were made until the 1800s, which is a reason why scientists wonder if it is the same spot.6 C. W. Pritchett observed the Great Red Spot in 1878 at the Morrison Observatory with a telescope that had a magnification power of 275. Pritchett watched the red storm for almost an hour as it moved about a fourth of the way across Jupiter’s diameter.7

Whether the spot that we know as the Great Red Spot — rather than a different spot on Jupiter — was initially discovered by Hooke, Cassini, or Pritchett, this violent storm has been raging for a century and a half at the very least. The storm is still studied today due to the fact that it is an astonishing phenomenon and because it has importance in the modern scientific world. NASA’s Amy Simon, who specializes in planetary atmospheres, suggests that the study of the Great Red Spot can lead to a better understanding of the Earth’s weather. The idea behind this is that the physics involved in Jupiter’s weather is the same physics that applies to Earth’s weather. She is also hopeful that the studies of the Great Red Spot will improve our understandings of possible conditions for extrasolar planets.8


The Colour of the Great Red Spot 

Figure 3. A close up Image of the Great Red Spot captured by NASA’s Juno Mission,, NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstadt/Justin Cowart.

There is no doubt that the Great Red Spot would not be as distinct if it did not possess such a striking colour against Jupiter’s swirling atmosphere. In truth, the source behind the red of the Great Red Spot has not yet positively been identified, and scientists have been relying on theory and recreation assessments to try to determine how this colour is formed in Jupiter’s atmosphere.9 Right now the leading theory about the Great Red Spot’s colour is that it is not actually red, but white. It is the UV light hitting the gases of the Great Red Spot that makes it appear red. In a mock experiment, researchers formed clouds of ammonia and acetylene, their number one suspects of the Great Red Spot’s composition, to represent the clouds at the top of Jupiter’s atmosphere near the Great Red Spot. When they reproduced the Sun’s effect by shining UV light on the experimental clouds, a red effect formed with the same light-scattering properties as the Great Red Spot. 




Figure 4. Experiments conducted by Baines and colleagues on the composition of Jupiter’s atmosphere,, Mark Loeffler/Cosmic Ice Laboratory, NASA GSFC.

NASA’s Cassini team scientist, Kevin Baines, first had other thoughts about the source of the red colour. He theorized models that proposed the Great Red Spot is a white or grey colour under the red layer that forms from the Sun’s rays. This means that the red we see is only thin top layer to the spot that is red due to interactions with solar rays. To test this theory, Baines and his team members had initially hypothesized that it was the breakdown of ammonium hydrosulfide — which is part of one of Jupiter’s major cloud layers — that caused the red colour. After testing this hypothesis with the application of UV light however, the substance was green instead of red. They then turned to combinations of ammonia and hydrocarbons before discovering that ammonia and acetylene, when hit by UV radiation, would cause an effect that was the same as the red colour of the storm.10 These experimental results are shown in Figure 4, which display images taken during Baines’ experiments. Over 200 experiments on composition and conditions have been conducted in an attempt to determine why the Great Red Spot has such an intense colour,9 but all of this is only theoretical and speculative. Until a probe can be sent into the spot and collect actual samples, we may never have a definitive answer on the colour of the Great Red Spot.


Jupiter’s Weather and how it Favours the Great Red Spot


Juno Mission to Jupiter

Watch NASA scientist Candy Hansen explain the Juno Project HERE

The Juno mission has been able to do what has not been done before, and that is to involve the public in the gathering of data. This concept is called citizen science and allows members of the public to access and analyze the images that are taken by Juno in an open database. In this database, called JunoCam, there is the ability for anyone to contribute to what they would like to see the Juno spacecraft cover, the images that have been captured of Juno, and to discuss findings and research related to the Juno project. This is an important development in astronomical research as it allows more data to be processed than would be possible in the time that scientists have, as well as bridging a relationship between the average person and the scientific community. These opportunities are critical to fostering care and support from people on a global level, and we can only hope that citizen scientists will be able to contribute answers to the mystery of the Great Red Spot throughout this project. If you would like to contribute to NASA’s Juno mission, its homepage can be found here: 

Juno was able to figure out more properties than the previous missions to Jupiter and the Great Red Spot. While passing over the Great Red Spot, as of April 3, 2017, Juno recorded the size of the storm to be 16,350 km, or 1.3 times the size of Earth.10 Juno was also able to determine that the roots of the storm go as deep as about 300 km into the atmosphere. This is between 50 and 100 times deeper than the oceans on Earth reach. It was also found that the base of the storm is warmer than at the top.11



1Jupiter, The World Almanac and Book of Facts, New York, 2004, (99)

2P. Voosen, Missions expose surprising differences in the interiors of Saturn and Jupiter, (Accessed 8 March 2019).

3N.T. Redd, How Was Jupiter Formed?, (Accessed 8 March 2019).

4L. Bjoraker, H.P. Larson, V.G. Kunde, Icarus, The gas composition of jupiter derived from 5- μm airborne spectroscopic observations ( Volume 66, issue 3, 1986) pg. 579-609

5H.B. Niemann, S.K. Atreya, G.R. Carignan, T.M. Donahue, J.A. Haberman, D.N. Harpold, R.E. Hartle, D.M Hunten, W.T. Kasprzak, P.R. Mahaffy, T.C. Owen, N.W. Spencer, S.H. Way, Science 272, 846 – 849 (1996)

6M. Falorni, Journal of the British Astronomical Association 97, 215 – 219, (1987).…97..215F/0000215.000.html (Accessed 9 March 2019).

7Royal Society of South Australia, Transactions and Proceedings and Report of the Royal Society of South Australia, Adelaide, 1886, (1-9)

8NASA, Jupiter’s Great Red Spot: A Swirling Mystery, (Accessed 6 February 2019).

9N.T Redd, What Makes Jupiter’s Great Spot Red? It’s Still a Mystery, (Accessed 8 March 2019).

10NASA, NASA’s Juno Spacecraft Spots Jupiter’s Great Red Spot, (Accessed 12 March 2019).

11NASA, NASA’s Juno Probes the Depths of Jupiter’s Great Red Spot, (Accessed 12 March 2019).