Pluto is a dwarf planet in the Kuiper Belt, a donut-shaped region of icy bodies beyond the orbit of Neptune. There may be millions of these icy objects, collectively referred to as Kuiper Belt objects (KBOs) or trans-Neptunian objects (TNOs), in this distant region of our solar system.
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 ›
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.
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.
A year on Pluto is 248 Earth years. A day on Pluto lasts 153 hours, or about 6 Earth days.
Small in Size, But Not in Importance
Pluto is officially classified as a dwarf planet.
Pluto has a thin atmosphere of nitrogen, methane and carbon monoxide. The atmosphere has a blue tint and distinct layers of haze.
Pluto has 5 moons. The largest, Charon, is so big that Pluto and Charon orbit each other like a double planet.
Pluto has no ring system.
The only spacecraft to visit Pluto is NASA’s New Horizons, which passed close by in July 2015.
Pluto’s surface is far too cold, -378 to -396 degrees F (-228 to -238 C), to sustain life as we know it.
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
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!"
- New Horizons Mission Website
- Pluto and the Developing Landscape of Our Solar System (International Astronomical Union)
- NASA Planetary Photojournal: Pluto
- For Kids: About Pluto