11 awesome facts about Pluto that you probably don’t know

11 awesome facts about Pluto that you probably don’t know

Pluto may be small, but the love people have shown for the former ninth planet is anything but. NASA’s New Horizons probe recently visited Pluto, becoming the first spacecraft to do so. It adds to our knowledge of Pluto, which was the first Kuiper Belt object ever discovered by humanity. While that distinction may seem less important than being a planet, it has the potential to teach us a great deal about the nature of the solar system. Let’s take a look at what we know about Pluto now with the added revelations from New Horizons.

It’s bigger than we thought, but not very dense

Pluto was the smallest planet in our solar system until it was demoted in 2006, but in 2005 a more distant dwarf planet named Eris was discovered. Eris was slightly larger than Pluto, but New Horizons now tells us that Pluto is 2% to 3% larger than we thought (1,476 miles), making it a bit larger than Eris’ 1,445 mile diameter. Pluto is still considerably less massive than Eris, as it’s about one third ice.

It hasn’t even completed one orbit since its discovery

As you’ve probably heard a million times in recent weeks, Pluto was discovered in 1930 by astronomer Clyde W Tombaugh. In the 85 years since its discovery, it has yet to complete a single orbit of the Sun. A single Plutonian year is 247.68 Earth years.

It has five known moons

Pluto has five moons, not because it’s particularly massive, but because there’s a lot more debris at the edge of the Kuiper Belt. Its inability to clear the surrounding space is one of the reasons Pluto is a dwarf planet. The five natural satellites of Pluto are Charon, Styx, Nix, Kerberos, and Hydra. Several of them can be thought of as large-ish asteroids. For example, Hydra is only five miles across.

Pluto and its moon Charon are actually a binary system

Charon is the largest moon of Pluto, and it’s actually very large compared to the dwarf planet — it’s about one eighth the mass of Pluto. That’s big enough that the center of mass between the two bodies (the barycenter) is outside of Pluto. Thus, Pluto and Charon are both orbiting around that center, making it the only binary system we’ve directly observed.

It has an atmosphere

The New Horizons probe confirms that Pluto does indeed have an atmosphere. It’s thin and almost entirely nitrogen. The planet’s low mass means that the gas envelope has spread far out into space, allowing the solar wind to strip much of it away.

The heart of Pluto is caused by frost

The now-famous image of Pluto from New Horizons has a large heart-shaped feature toward the lower right. Astronomers believe this lighter-colored region is caused by frost, specifically frozen methane, nitrogen, and carbon monoxide.

Pluto’s orbit crosses that of Neptune

Unlike the eight planets of the solar system, Pluto has a highly eccentric orbit. It even crosses the orbit of Neptune and remains closer to the Sun than the gas giant for about 20 years. That last happened in 1979 and won’t happen again until 2207. So why doesn’t Neptune’s huge mass eject Pluto from orbit? They have orbital resonance, meaning they’re never in the same region of space at the same time.

It rotates very slowly and backward

A single day on Pluto is equal to 6.4 Earth days, and it rotates backward compared to Earth and most other planets. Pluto goes from east to west like Venus and Neptune. It also rotates on its side, like Neptune.

Pluto surface is young and has ice mountains taller than the Rockies

Pluto is small and frozen, but astronomers studying the New Horizons data have been fascinated to see that much of its surface appears to be less than 100 million years old and mostly free of impact craters. The vast planes of Pluto also have mysterious ice mountains rising as high as 11,000 feet above the surface. Geophysicists are super interested in getting the rest of that New Horizons data.

It was almost discovered more than a dozen times before 1930

While Clyde Tombaugh was the first to identify Pluto as a planet (this was the correct conclusion at the time), that wasn’t the first time someone laid eyes on it. After Tombaugh’s discovery was announced, other astronomers rushed to their telescopes to see if they too had sighted the planet. More than a dozen images of Pluto from before the 1930 discovery have been found, but no one realized what they had. There’s even a probable Pluto sighting from 1909.

It’s probably brighter on Pluto than you thought

Pluto’s distance from the sun varies thanks to its eccentric orbit, but the average distance is still almost 40 times further from the sun than Earth. Still, it’s brighter on Pluto than you might think. At “noon” on Pluto when the sun exposure is at its maximum, it’s bright enough to read a book. The image above was taken at “Pluto time.”

Its real name is “134340 Pluto”

When Pluto was demoted from a planet to a dwarf planet, it got a new official name. See, dwarf planets are in the same class of objects as asteroids and use the same MPC (minor planet designation) naming system. Therefore, Pluto’s official name is “134340 Pluto.” Doesn’t quite roll of the tongue, does it?