Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer. The individual images were recorded over the last year by NASA's Galileo spacecraft and are scaled to the moons' relative sizes. All these moons orbit in the zone between Io and Jupiter's rings , are bombarded by high-energy ions within the Jovian magnetosphere , and are probably locked in synchronous rotation by Jupiter's strong gravity. Like the asteroids and the diminutive moons of Mars , their own gravity is not strong enough to mold them into spheres.
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