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Pluto

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Pluto is a fascinating dwarf planet located in the Kuiper belt. This is a wide ring of many objects found far beyond the orbit of Neptune.

Outersolarsystem objectpositions labels comp
Outersolarsystem objectpositions labels comp

Pluto is a very small world compared to the big planets. It is the ninth-largest object to orbit the Sun directly. However, it is much less massive than the object named Eris.

Pluto, Earth & Moon size comparison
Pluto, Earth & Moon size comparison

Pluto is mostly made of ice and rock. It has about one-sixth the mass of our Moon. It also has about one-third of the Moon's volume.

Nh-pluto moons family portrait
Nh-pluto moons family portrait

Pluto moves in a very specific way through space. Its orbit is shaped like an oval and is tilted. This is called an eccentric and inclined orbit.

Animation of Pluto orbit
Animation of Pluto orbit

Because of this path, Pluto sometimes gets closer to the Sun than Neptune does. A stable orbital resonance keeps Pluto and Neptune from hitting each other. It takes a long time for light to reach Pluto. Sunlight takes 5.5 hours to reach it.

Plutoorbit1.5sideview
Plutoorbit1.5sideview

Pluto also has five known moons. These are Charon, Styx, Nix, Kerberos, and Hydra.

Nh-pluto moons family portrait
Nh-pluto moons family portrait

Charon is the largest moon. It is so big that it is over half the diameter of Pluto.

Finding Pluto was a long journey for astronomers. In 1906, Percival Lowell began looking for a ninth planet. He called this mystery object "Planet X."

Clyde W. Tombaugh
Clyde W. Tombaugh

He used math to help find it. After he died, a young man named Clyde Tombaugh took over the search.

Pluto discovery plates
Pluto discovery plates

Tombaugh looked at pairs of photos to find moving objects. He used a tool called a blink comparator. This tool made objects look like they were moving. On February 18, 1930, he found a moving object. This object was Pluto.

Pluto discovery plates
Pluto discovery plates

People had many ideas for what to name the new world. An eleven-year-old girl named Venetia Burney suggested the name Pluto.

Pluto monogram (bold)
Pluto monogram (bold)

She liked the name from Roman mythology. The name was chosen because it was a unanimous vote.

Pluto symbol (large orb, bold)
Pluto symbol (large orb, bold)

Pluto was considered the ninth planet for a long time. But scientists later found many other objects in the Kuiper belt. They also found Eris in 2005. In 2006, the International Astronomical Union changed the rules. They decided Pluto is a dwarf planet.

Pluto symbol (southern Europe)
Pluto symbol (southern Europe)

Some astronomers still think Pluto should be a planet.

We know much more about Pluto thanks to space travel. A spacecraft named New Horizons visited Pluto in 2015.

PIA21590 – Blue Rays, New Horizons' High-Res Farewell to Pluto
PIA21590 – Blue Rays, New Horizons' High-Res Farewell to Pluto

It flew by on July 14, 2015. This mission gave us detailed measurements and beautiful pictures.

We can see that Pluto has icy mountains and flat plains.

MVIC sunset scan of Pluto
MVIC sunset scan of Pluto

Pluto and its moon Charon are very close. They orbit a point between them. This is called a barycenter.

Pluto-Charon system-new
Pluto-Charon system-new

Because they are tidally locked, they always face each other. This makes them look like a special pair in the dark sky.

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🖼️ Images & Media (24)
File:Pluto monogram (bold).svg
Pluto monogram (bold).svg
File:Pluto symbol (large orb, bold).svg
Pluto symbol (large orb, bold).svg
File:Pluto discovery plates.gif
Pluto discovery plates.gif
File:Clyde W. Tombaugh.jpeg
Clyde W. Tombaugh.jpeg
File:Pluto monogram (fixed width).svg
Pluto monogram (fixed width).svg
File:Pluto symbol (large orb, fixed width).svg
Pluto symbol (large orb, fixed width).svg
File:Pluto symbol (southern Europe).svg
Pluto symbol (southern Europe).svg
File:Pluto symbol (northern Europe).svg
Pluto symbol (northern Europe).svg
File:Pluto symbol (northern Europe, variant).svg
Pluto symbol (northern Europe, variant).svg
File:Charon symbol (fixed width).svg
Charon symbol (fixed width).svg
File:Animation of Pluto orbit.gif
Animation of Pluto orbit.gif
File:Plutoorbit1.5sideview.gif
Plutoorbit1.5sideview.gif

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