Astronomers Find Three Smallest Planets Outside Solar System

The three planets, which all orbit a single star, are smaller than Earth and appear to be rocky with a solid surface. Until now, astronomers have found at most only four other rocky planets, also called terrestrial planets, around other stars.

The trio of new planets is too close to the central star to be in its habitable zone—the ring-shaped region around a star where the temperature is mild enough for liquid water, and possibly life, to exist. But the planets are the first rocky ones to be found orbiting a type of dim, small star called a red dwarf, the most common kind in the Milky Way. Their existence suggests that the galaxy could be teeming with similarly rocky planets—and that there's a good chance that many are in the habitable zone.

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