Eighty years ago today — February 18, 1930 — astronomer Clyde W. Tombaugh of the Lowell Observatory in Flagstaff, Arizona, discovered Pluto.
(Hubble Space Telescope image of Pluto and its moons, Charon, Nix and Hydra. NASA image.)
Pluto is about 39 times as far from the sun as Earth is. Its average distance from the sun is about 3,647,240,000 miles (5,869,660,000 kilometers). Pluto travels around the sun in an elliptical (oval-shaped) orbit. At some point in its orbit, it comes closer to the sun than Neptune, the outermost planet. It stays inside Neptune’s orbit for about 20 Earth years. This event occurs every 248 Earth years, which is about the same number of Earth years it takes Pluto to travel once around the sun.
Many of us grew up knowing Pluto as a planet: a cold, distant planet but a planet nonetheless. Now, thanks to the inexorable forward march of scientific progress, Pluto is no longer a planet in its own right. It’s too small, the critics said, to fit the definition. In 2006, the International Astronomical Union named Pluto a “dwarf planet.”
But, Pluto does have the distinction of being the largest (so far) of the Kuiper Belt Objects, those far-flung chunks of whatever that orbit the far reaches of our solar system. And, as such, it is the namesake of a class of celestial objects known as “plutoids.” So, little Pluto got some redemption after being stripped of its title.
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