Closing in on Saturn after a 7-year journey, the robotic spacecraft Cassini has discovered two storms on the ringed planet merging into a single, larger, hurricanelike disturbance. The only other time that astronomers have observed merging storms on Saturn was in 1981, when the two Voyager spacecraft flew past the planet.
Cassini first spied the storms in mid-February. They appeared as 1,000-kilometer-wide spots in Saturn’s southern hemisphere. Traveling a few meters per second relative to the rotation of Saturn’s gaseous interior, the storms—one moving twice as fast as the other—collided and spun around each other before merging over a 2-day period that began March 19. Cassini scientists posted the findings on the Internet on April 8 (http://saturn.jpl.nasa.gov).
Storms on Earth typically last for a week, fading after they can no longer gather energy from their surroundings. But storms on Saturn and the other giant planets, Jupiter and Uranus, can last from months to years. Merging is a characteristic feature of the atmospheric disturbances, notes Cassini mission scientist Andrew P. Ingersoll of the California Institute of Technology in Pasadena, Calif.
To see storms even before Cassini arrives at Saturn in July is an unexpected bonus, Ingersoll says. With the main mission still ahead, he adds, “the best is yet to come.”