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Dwarf Planet Pluto

Dwarf Planet Pluto
Dwarf Planet Pluto.
Source: NASA.
What is Pluto Like?

Up until 2006, Pluto was considered the 9th planet of the Solar System. At that time the IAU (International Astronomical Union) gave an official definition of a planet. Pluto no longer qualified as a planet under this definition and was re-classified as a "dwarf planet".

Pluto is a relatively small planetoid, smaller than the Earth's moon. It is thought that Pluto is made up of a mantle of ice (mostly Nitrogen ice), which is about 50% of its mass, and a rocky core, which makes up the other 50% of its mass.

Pluto has a unique orbit around the sun. Rather than a round or circular orbit around the sun, like the 8 planets, Pluto's orbit is more egg-shaped. At its closest point to sun, Pluto is around 2.8 billion miles away. At its furthest point, it is around 5 billion miles from the sun. When Pluto is closest to the sun, it has a thin atmosphere. As Pluto moves away from the sun, it gets so cold that the atmosphere starts to freeze and fall to the ground.

Pluto and its largest moon Charon
Pluto and its largest moon Charon.
Source: NASA.

Pluto has five named moons: Charon, Styx, Nix, Kerberos, and Hydra. The largest is Chiron. Charon's diameter is around half the size of Pluto's. This makes it the largest moon in the Solar System in relation to the planet it orbits. Pluto and its moons are part of the Kuiper belt.

Pluto compared to Earth
Pluto is much smaller than Earth
Source: NASA.
How does Pluto compare to Earth?

Pluto has a hard, rocky surface like Earth. It is much smaller than Earth. Pluto is so far away from the sun, that it gets very little energy from the sun and is extremely cold.

How do we know about Pluto?

For nearly 100 years scientists had suspected there was a 9th planet somewhere beyond Neptune. This was based on changes in Neptune's and Uranus' orbit that indicated a large mass was tugging on the planets. They called this mysterious 9th planet Planet X.

In 1930 a young astronomer, Clyde Tombaugh, found Planet X after a year of searching.

Since then much more has been learned about Pluto using telescopes. The first space probe to visit Pluto was the New Horizons in 2015. The New Horizons flew past Pluto coming within 7,800 miles of the dwarf planet's surface. It took pictures and mapped the chemical compositions of the surface of Pluto and its moon Charon.

Mountains on Pluto
Giant mountains on the surface of Pluto.
Source: NASA. Picture taken by the New Horizons space probe.

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