By Alexandra Witze
NASA’s Cassini spacecraft continues to yield surprising discoveries, more than a month after it burned up on its mission-ending dive into Saturn. New data from the probe suggest that Saturn’s majestic rings are showering tiny dust particles into the planet’s upper atmosphere, where they form a complicated and unexpected chemical mix.
A mass spectrometer aboard Cassini detected the strange chemistry as the probe spent its final five months looping between Saturn and its rings.
“We really hit the jackpot,” said Mark Perry, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. He reported the findings on 17 October at a meeting of the American Astronomical Society’s Division for Planetary Sciences in Provo, Utah.
Mission scientists had expected Cassini’s mass spectrometer to spot the signature of water molecules as the spacecraft slipped between the planet and its rings. In the 1970s and 1980s, NASA’s Pioneer and Voyager missions found fewer charged particles than expected in Saturn’s uppermost atmosphere. Based on that data, researchers proposed in 1984 that water molecules coming off the rings — mostly in the form of ice — acted as a catalyst to strip charged particles from the atmosphere1. Cassini’s final months gave scientists their first opportunity to test this idea directly.
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