Abstract

The Little Red Spot (LRS) in Jupiter's atmosphere was investigated in unprecedented detail by the New Horizons spacecraft together with the Hubble Space Telescope (HST) and the Very Large Telescope (VLT). The LRS and the larger Great Red Spot (GRS) of Jupiter are the largest known atmospheric storms in the solar system. Originally a white oval, the LRS formed from the mergers of three smaller storms in 1998 and 2000, and became as red as the GRS between 2005 and 2006. Here we show that circulation and wind speeds in the LRS have increased substantially since the Voyager and Galileo eras when the oval was white. The maximum tangential velocity of the LRS is now 172 18 m s -1, close to the highest values ever seen in the GRS, which has also evolved both in size and maximum wind speed. The cloud-top altitudes of the GRS and LRS are similar, both storms extending much higher in the atmosphere than other Jovian anti-cyclonic systems. The similarities in wind speeds, cloud morphology, and coloring suggest a common dynamical mechanism explaining the reddening of the two largest anticyclonic systems on Jupiter. These storms will not be observed again from close range until at least 2016. © 2008. The American Astronomical Society. All rights reserved.