For the better part of a century, we believed there were nine planets in our solar system, with Pluto being the farthest from the sun. Since the discovery of more Pluto-sized dwarf planets, that outlook has changed. Fortunately, there’s far more to Pluto than its unique history among the other planets.
Our solar system has gotten a little bit more crowded, both closer to home and out beyond Pluto’s neck of the woods. Pluto can handle the competition. It has a distinct and exciting presence, guaranteeing the planet an outsized place in our minds and in our hearts.
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Pluto Is the 10th Planet From the Sun
Many of us grew up knowing Pluto as the ninth planet from the sun. Turns out, that wasn’t exactly true.
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Pluto is one of several dwarf planets floating around in our solar system. One of these dwarf planets actually orbits in between Mars and Jupiter. Its name is Ceres. This little rock is around 590 miles (950km) long and its days are roughly nine Earth hours. Since Ceres is the fifth planet from the sun, that bumps Pluto out to number ten.
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But Sometimes Pluto’s the Ninth
Each planet goes around the sun in an elliptical orbit. Pluto is unique. While its orbit is elliptical like all the others, it is the only planet that sometimes crosses inside the orbit of another. So, rather than floating out in the deep reaches of space all by its lonesome, Pluto sometimes dips inside of Neptune’s orbit to temporarily become the ninth planet from the sun.
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The First Probe Reached Pluto in 2015
Humankind has known about the existence of Pluto since most of us have been alive, but despite seeing drawings in science textbooks, we didn’t actually know how Pluto looked for most of that time. We didn’t get our first photos of Pluto until 2015.
The New Horizons spacecraft left Earth in 2006 and began a 9-year journey that would result in it flying over Pluto on July 14, 2015, at a height of 7,800 miles (12,550km) above the planet’s surface. Since data takes a long time to travel such distances, we received our final images of Pluto from the spacecraft over a year later, on October 25, 2016.
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Pluto Has the Biggest Heart in the Solar System
It was only after images from 2015 arrived that Pluto secured a place in my heart. That’s because Pluto, it turns out, has a heart bigger than mine, yours, or anything else in the solar system. When looking at a photo of the planet, there’s a heart-shaped landscape that easily occupies around a third of the planet’s visible surface.
This heart is named Tombaugh Regio, named after Clyde Tombaugh, the 24-year-old who discovered Pluto in 1930. The region sits just north of Pluto’s equator. The western lobe is a 620-mile (1,000km) plain of nitrogen and other ices lying within a basin. The eastern lobe consists of uplands that may be coated by nitrogen deposited in the form of ice.
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A Year on Pluto Is Over Two Centuries Long
The farther you get from the sun, the longer it takes to complete an orbit. Mercury has the shortest orbit, consisting of only 88 Earth days. By contrast, it takes Pluto nearly two and a half centuries to orbit the sun.
Pluto’s long years are due to the planet being over three and a half billion miles away from the center of our solar system. We Earthlings have it made, living just a mere 93 million miles from the sun. A year on Mars, by comparison, is roughly only twice as long as our own.
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Pluto Has Five Moons
Pluto is smaller than Earth’s moon, yet it still manages to have five moons of its own. Their names are Styx, Nix, Kerberos, Hydra, and Charon.
Most of Pluto’s moons are positively tiny. Nix is only 20 miles (32km) in diameter, while Hydra is 70 miles (113km). Both were discovered in 2005. Styx is even smaller, at a mere four and a half miles long (7km). Kerberos is shaped like a lopsided peanut, with the larger lobe being five miles in diameter (8km) while the smaller is only three (5km).
Charon, discovered decades before the others, absolutely dwarfs them in size.
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Some Consider Pluto and Charon a Double-Planet System
Charon is by far Pluto’s largest moon. With a diameter of 754 miles (1,213km), it is roughly half the size of Pluto. Pluto’s diameter is 1,477 miles (2,377km).
With both celestial bodies being so similar in size, some consider Pluto and Charon to actually form a double-planet system. A double-planet system is one where two planetary bodies orbit each other. In 2006, there was a proposal to classify Pluto and Charon as a binary system, before the International Astronomical Union opted to reclassify Pluto as a dwarf planet instead.
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Pluto Almost Spins on Its Side—and Backwards
Part of Uranus’ claim to fame is that it spins on its side compared to all the other large planets. Apparently, Pluto rotates very similarly to Uranus, with a tilt of 57 degrees from its elliptical plane.
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That alone would make Pluto seem unusual compared to Earth, but that’s not all. Pluto also spins backwards. It has a retrograde rotation like Venus and Uranus.
Pluto is so far from us, it can be hard to fathom inhabiting that corner of space. Yet planets can be just as foreign, and captivating, closer to home. What better way to illustrate this than by comparing extremes and finding out what’s so compelling about Mercury?
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