![]() ![]() Hubble observations will play a complementary role when the Galileo spacecraft arrives at Jupiter in December of this year. Galileo Galilei did not invent the telescope but was the first to use it systematically to observe celestial objects and record his discoveries. ![]() Hubble ultraviolet observations of Callisto show the presence of fresh ice on the surface that may indicate impacts from micrometeorites and charged particles from Jupiter's magnetosphere. The science of astronomy took a huge leap forward in the first decade of the 1600s with the invention of the optical telescope and its use to study the night sky. Over the past year Hubble has charted new volcanic activity on Io's active surface, found a faint oxygen atmosphere on the moon Europa, and identified ozone on the surface of Ganymede. While the Voyagers provided close-up snapshots of the satellites, Hubble can now follow changes on the moons and reveal other characteristics at ultraviolet and near-infrared wavelengths. Discovering potential 1 meter-scale or smaller satellites that may be exploring Earth, e.g., in polar orbits a few hundred km above Earth, may become feasible with VRO in 2023 and later, but if radar, optical and infrared technologies have been mastered by an ETC, then very sophisticated large telescopes on Earth might be required. Hubble can resolve surface details seen previously only by the Voyager spacecraft in the early 1980s. Located approximately one-half billion miles away, the moons are so small that, in visible light, they appear as fuzzy disks in the largest ground-based telescopes. This is a Hubble Space Telescope "family portrait" of the four largest moons of Jupiter, first observed by the Italian scientist Galileo Galilei nearly four centuries ago. Click the image above for a larger view.Hubble Gallery of Jupiter’s Galilean Satellites ![]()
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