Pluto's crescent imaged by NASA's New Horizons interplanetary space probe

© NASA/JHUAPL/SWRI/Science Photo Librar

Too awesome to be a planet

Pluto was first spotted on this day in 1930 by Clyde Tombaugh, a 23-year-old astronomer at Lowell Observatory in Flagstaff, Arizona. Because it’s so far away - about 40 times as far from the Sun as Earth is - scientists knew relatively little about Pluto until the New Horizons spacecraft reached it in 2015. In a flyby study, the craft spent more than five months gathering detailed information about Pluto and its moons. What did they find out? There’s a heart-shaped glacier, blue skies, spinning moons, mountains as high as the Rockies, and it snows - but the snow is red.

Once thought to be one of nine full-fledged planets orbiting the Sun, in 2006, Pluto was stripped of its planetary status and reclassified as merely a 'dwarf planet'. (Sorry, Pluto.) Though it may no longer be considered a true planet, it’s still the largest dwarf planet of our solar system and holds plenty of mysteries waiting to be discovered.