Mysterious Spokes in Saturn's Rings
影像提供: CICLOPS, JPL, ESA, NASA
Explanation:
What causes the mysterious spokes in Saturn's rings? Visible on the left of the above image as ghostlike impressions, spokes were first discovered by the Voyager spacecraft that buzzed by Saturn in the early 1980s. Their existence was unexpected, and no genesis hypothesis has ever become accepted. Oddly, the spokes were conspicuously absent from initial images sent back by the robot Cassini spacecraft now orbiting Saturn. Analyses of archived Voyager images have led to the conclusions that the transient spokes, which may form and dissipate over a few hours, are composed of electrically charged sheets of small dust-sized particles. Some recent images from Cassini like that shown above have now finally shown the enigmatic spokes superposed on Saturn's B ring. Hypotheses for spoke creation include small meteors impacting the rings and electron beams from Saturnian atmospheric lightning spraying the rings. Observations of the puzzling spokes, as well as creative origin speculations, are ongoing.
說明:
土星環上的神祕輻條之成因為何？上面影像左端的幽靈狀的烙印稱為輻條，它們是1980年初由飛掠過土星的航行家太空船首次發現的。它們的存在並未預期，而到現在也未有可信的形成學說。很有意思的是，現在繞行土星的卡西尼號太空船所回傳的首批照片裡，並沒有這種輻條的蹤跡。在分析航行家圖庫影像後，得到這些輻條是種暫發現象的結論，並認為它們可能是種由帶電荷塵埃微粒所聚成之片層狀結構，在形成數個小時後即消失。部份最近由卡西尼號回傳的影像(如上圖)裡，終於顯現土星B環上有這類神祕難解的輻條。輻條產生機制的假說，包括小流星撞擊環系與土星大氣閃電噴灑出來的電子束衝撞環系等。這些神祕難解的輻條的觀測及思索它們成因的工作仍在持續之中。
資料來源: Scientific American
Department of Physics, NCKU
