When Voyager 2 passed by Neptune in 1989, the images it returned surprised scientists; it saw an immense oval dark storm in the planet's southern hemisphere as big as Earth itself! Called the Great Dark Spot, it had measured wind speeds of a staggering 2,100 kph, the fastest wind ever measured in the solar system. Zoom In The sizes of Earth and Neptune to scale. There's a decent gap there, but not in most exoplanet systems. Credit: NASA / jcpag2012 at wikimedia But, when Hubble looked at Neptune in 1994, the spot was gone. Poof. Disappeared. Clearly, unlike Jupiter's Great Red Spot, which has persisted for centuries (at least), storms on Neptune evolve on smaller timescales, though they can last for several years. For example, in the same 1994 Hubble observations a smaller dark spot was seen in Neptune's southern hemisphere, one that must have been born in the intervening time between the Voyager flyby and the Hubble images.