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Planetary History

Pluto's Status

Pluto’s classification as a planet has had a history of changes. Since 2006, per the International Astronomical Union’s planetary criteria, Pluto isn’t considered a planet because it hasn’t cleared the neighborhood around its orbit of other objects. However, it does meet IAU’s criteria for what constitutes a dwarf planet.

Pluto – which is smaller than Earth’s Moon – has a heart-shaped glacier that’s the size of Texas and Oklahoma. This fascinating world has blue skies, spinning moons, mountains as high as the Rockies, and it snows – but the snow is red.

On July 14, 2015, NASA’s New Horizons spacecraft made its historic flight through the Pluto system – providing the first close-up images of Pluto and its moons and collecting other data that has transformed our understanding of these mysterious worlds on the solar system’s outer frontier.

In the years since that groundbreaking flyby, nearly every conjecture about Pluto possibly being an inert ball of ice has been thrown out the window or flipped on its head.

“It’s clear to me that the solar system saved the best for last!” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, Boulder, Colorado. “We could not have explored a more fascinating or scientifically important planet at the edge of our solar system. The New Horizons team worked for 15 years to plan and execute this flyby and Pluto paid us back in spades!”

Go farther. Explore Pluto In Depth ›

10 Things to Know About Pluto

10 Need-to-Know Things About Pluto

1

Small World

Pluto is about 1,400 miles (2,380 km) wide. That's about half the width of the United States, or 2/3 the width of Earth's moon.

2

Deep Space

Pluto orbits the Sun about 3.6 billion miles (5.8 billion km) away on average, about 40 times as far as Earth, in a region called the Kuiper Belt.

3

Slow Journey

A year on Pluto is 248 Earth years. A day on Pluto lasts 153 hours, or about 6 Earth days.

Natural Color

4

Small in Size, But Not in Importance

Pluto is officially classified as a dwarf planet.

5

Hazy Days

Pluto has a thin atmosphere of nitrogen, methane and carbon monoxide. The atmosphere has a blue tint and distinct layers of haze.

6

Moon Dance

Pluto has 5 moons. The largest, Charon, is so big that Pluto and Charon orbit each other like a double planet.

7

Ringless

Pluto has no ring system.

8

Sole Encounter

The only spacecraft to visit Pluto is NASA’s New Horizons, which passed close by in July 2015.

9

Harsh Habitat

Pluto’s surface is far too cold, -378 to -396 degrees F (-228 to -238 C), to sustain life as we know it.

10

From the Mouths of Babes

Venetia Burney, just 11 years old at the time, suggested the name Pluto in 1930.

Majestic Mountains and Frozen Plains

How Pluto Got Its Name

How Pluto Got its Name

Pluto is the only world (so far) named by an 11-year-old girl. In 1930, Venetia Burney of Oxford, England, suggested to her grandfather that the new discovery be named for the Roman god of the underworld. He forwarded the name to the Lowell Observatory and it was selected.

Picture of Venetia Burney
Picture of Venetia Burney

Pluto's moons are named for other mythological figures associated with the underworld. Charon is named for the river Styx boatman who ferries souls in the underworld (as well as honoring Sharon, the wife of discoverer James Christy); Nix is named for the mother of Charon, who is also the goddess of darkness and night; Hydra is named for the nine-headed serpent that guards the underworld; Kerberos is named after the three-headed dog of Greek mythology (and called Fluffy in the Harry Potter novels); and Styx is named for the mythological river that separates the world of the living from the realm of the dead.

Pluto's place in mythology can get a little muddled, so we asked Dr. Elizabeth Vandiver, chair of the Department of Classics in Whitman College in Walla Walla, Washington, to clarify the origins of the name: "Pluto is the name of the Roman god of the Underworld, equivalent to the Greek Hades. However, the Greek name "Plouton" (from which the Romans derived their name "Pluto") was also occasionally used as an alternative name for Hades. But Pluto is definitely the Roman spelling."

Planetary Features

Interesting Facts About Pluto

  • Pluto is only about 1,400 miles wide. At that small size, Pluto is only about half the width of the United States.
  • Pluto is about 3.6 billion miles away from the Sun and has five moons.
  • Pluto’s atmosphere is thin and composed mostly of nitrogen, methane and carbon monoxide.
  • Pluto and its largest moon, Charon, are so similar in size that they orbit each other like a double planet system.
  • On average, Pluto’s temperature is -387°F (-232°C), making it too cold to sustain life, but it does have a heart-shaped glacier bigger than Texas.

Pop Culture

Pop Culture

When Pluto was reclassified in 2006 from a planet to a dwarf planet, there was widespread outrage on behalf of the demoted planet. As the textbooks were updated, the internet spawned memes with Pluto going through a range of emotions, from anger to loneliness. But since the release of New Horizons images showing a very prominent heart-shaped feature on the surface, the sad Pluto meme has given way to a very content, loving Pluto that would like to once again be visited by a spacecraft.

The Disney cartoon character Pluto, Mickey's faithful dog, made his debut in 1930, the same year Tombaugh discovered the dwarf planet. There is speculation that Walt Disney named the animated dog after the recently discovered planet to capitalize on its popularity, but other accounts are less certain of a direct link. But either way, the joke connecting the two, as told in the 1987 Mel Brooks film Spaceballs remains:

We were lost. None of us knew where we were. Then Harry starts feeling around on all the trees, and he says, "I got it! We're on Pluto." I say, "Harry, how can ya tell?" And he says, "From the bark, you dummies. From the bark!"

Kid-Friendly Pluto

Kid-Friendly Pluto

Pluto is a dwarf planet that lies in the Kuiper Belt, an area full of icy bodies and other dwarf planets out past Neptune. Pluto is very small, only about half the width of the United States and its biggest moon Charon is about half the size of Pluto.

Almost all the planets travel around the Sun in nearly perfect circles. But not Pluto. It takes an oval-shaped path with the Sun nowhere near its center. What's more, its path is quite tilted compared to the planets.

Visit NASA Space Place for more kid-friendly facts.

NASA Space Place: All About Pluto ›

Resources

Resources

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