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4顆伽利略衛星當中，以最細小及最接近木星的「木衛一」（木星衛星一號）最為奇特。遠在1979年，太陽系探測器「航行者」一號及二號相繼飛越木星，並拍下大量的木衛高解像照片。當航行者一號高速飛越木星之際，訊息日以繼夜從探測器傳返地球，美國太空署「噴射推進實驗室」的人員須把影像進行數碼處理，提取最大量資訊，負責這項工作是蓮達．摩拉比托，當她處理其中一幀木衛一的影像時，竟意外地成為第一個人發現地球以外的火山爆發（小圖）。其後從航行者一號的影像中共找到9處火山活動，更有趣的是火山噴出的不是熔岩而是硫磺。時至今日，木衛一的火山活動從未休止過。作為對蓮達這項發現的表揚，國際天文聯會把小行星3106命名為摩拉比托。
Extra-Terrestrial volcanoes
Of the four Galilean satellites, Io, the one that orbits closest to Jupiter and also the smallest, is the most wonderful object in the Solar System. During Voyager I's Jupiter flyby in 1979, the spacecraft poured in so much data that the people at Jet Propulsion Laboratory of NASA just couldn't scrutinise them all. A few days later Linda Morabito was processing an image of Io when she suddenly realised what looked like a "plume" jutting out from Io's limb against the dark sky (see small inset). It was later identified as a volcanic eruption. A total of 9 outbursts were counted in all the Io images. What interested scientists most was: all these volcanoes were not erupting lava but sulphur. Io remains the most active Solar System body even today. ■甄枝強 資深天文愛好者
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