Facts about Callisto
- 09
Callisto's subsurface ocean may contain twice as much water as all of Earth's oceans combined, according to models based on NASA Galileo spacecraft data.
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Callisto's dark surface reflects only 20 percent of sunlight, making it one of the dimmest moons in Jupiter's system due to its composition of ancient rock and ice mixed with dark material.
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Callisto's surface lacks the geological activity seen on Jupiter's moon Io because its interior never underwent sufficient tidal heating to sustain volcanism or plate tectonics.
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Callisto orbits Jupiter once every 16.69 days at a distance of 1.88 million kilometers, making it the outermost of the four large Galilean moons.
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Galileo Galilei discovered Callisto on January 7, 1610, as one of the four large moons he observed orbiting Jupiter through his telescope.
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Callisto's extreme radiation environment receives 126 times more radiation than Earth's surface, making it inhospitable for known life forms despite potentially harboring a subsurface ocean.
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With a diameter of 4,821 kilometers, Callisto is Jupiter's second-largest moon and slightly smaller than the planet Mercury.
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Callisto's thin oxygen atmosphere, detected by NASA's Hubble Space Telescope in 1997, is produced when ultraviolet radiation splits water ice on its surface.
- 01
Jupiter's second-largest moon Callisto has a heavily cratered surface with impact basins dating back 4.2 billion years, making it one of the oldest geological surfaces in our solar system.