Keck II image of the close passage of Red Spot Junior as it moved past the Great Red Spot on 20 July 2006. On the left is a visible light false colour image and on the right is a closeup of the two spots in infrared light. Image: Imke de Pater, Michael Wong (UC Berkeley), Al Conrad (Keck), Chris Go (Cebu, Philippines) Astronomers have used the giant Keck II telescope to take sharp infrared pictures of Jupiter’s famous and 350-year old Great Red Spot being overtaken by its smaller cousin, nicknamed Red Spot Junior. The latter formed in the late 1990s from the merger of several smaller storms and turned red in December 2005.

Both spots are thought to be giant storms. The Great Red Spot is big enough to hold several Earths, while Red Spot Junior is ‘only’ as big as our planet. One idea is that the red originates from material being dredged up from lower in the Jovian atmosphere that changes colour when exposed to the ultraviolet light of the Sun.

Amateur image of Jupiter's two red spots in visible light, March 2006. © Mike Salway The close encounter of the two spots took place on July 20 and astronomers used it to compare them, as well as improving the sharpness of the Keck infrared images. Although the two spots appear similar in visible light, Red Spot Junior is much darker than its cousin in the Keck pictures, suggesting that infrared light is scattered into the region above its cloud tops.

Scientists will watch how Red Spot Junior develops – it may disappear or could survive for decades to come.