The giant red spot on Jupiter is a 400-year-old storm raging in the atmosphere of Jupiter's southern hemisphere. Known as the Great Red Spot, the storm rotates counter-clockwise and is more than three times the size of Earth.
The Great Red Spot on Jupiter rotates every six days and has winds that reach 432 km/h at its edges, with weaker, stagnant winds inside the storm. Higher and cooler than other clouds in Jupiter's atmosphere, the spot remains on the same track around the planet due to an eastward jet stream to its south and a westward jet stream to its north. The storm has circled Jupiter about 10 times since the early 19th century.
A theory indicates that organic molecules, red phosphorus or sulfur compounds cause the Great Red Spot's iconic color, which shifts in hue, possibly due to changes in its environment.
According to NASA, the Great Red Spot is shrinking. Observations by the Hubble Space Telescope in 2014 indicate a diameter of 10,250 miles at the spot's widest points. Voyager 1 and 2 measured the spot at 14,500 miles in diameter in 1979. Observations from the late 19th century estimated a size of 25,500 miles wide, indicating that the spot has decreased in size by about half.