9781422283707

liquid. Also like those giants, they have rings and many moons circling them. Pluto, since 2006 re-classified as a dwarf planet, is a vastly different world from Uranus and Neptune and indeed from the planets in our Solar System . It is a tiny ball of rock and ice, smaller even than our own Moon. It is so far away that it takes nearly 250 years to circle once around the Sun. Pluto and other nearby dwarf planets are at the outer edge of the Solar System. But some astronomers are convinced that other planets exist far beyond Pluto, orbiting their own suns in their own systems.

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