in diameter -- about one-fourth the size of the planet Pluto. The object is classified as a minor planet, like thousands of other asteroids and comets in our solar system. It is second in size ...

Far from being flat and boring, Pluto seemed to be full of mountains, plains and maybe even "snow". By measuring the size of the shadows, we could estimate the height of these peaks at over 4,000m ...

Why was Pluto reclassified as a dwarf planet? One might think that it’s purely a matter of size. Mercury, the smallest of the ...

Neither one is “big.” Earth’s moon is 2,160 miles in diameter. Some scientists believe Pluto should be upheld, but others suggest that Pluto, UB313 and other icy denizens of the Kuiper Belt ...

Ganymede, Jupiter's largest moon and the solar system's largest, is bigger than Mercury and the dwarf planet Pluto, with a diameter of 5,268 kilometers.

Size alone doesn't bestow planethood. Moons of Jupiter and Saturn are wider than Mercury, and Pluto is smaller than Earth's moon. For years, astronomers tried to define a planet by shape ...