Pluto

**Pluto** is a complex with world filled with mountains, valleys, plains, craters and maybe glaciers. Pluto was long considered the ninth planet in our solar system, being discovered in 1930. However, after discovering similar worlds in the Kuiper Belt, Pluto was reclassified as a dwarf planet.

Five known moons are orbiting Pluto, the largest being Charon. Charon is half the size of Pluto making it the largest satellite relative to the planet it orbits in our solar system. Pluto and Charon are often referred to as a "double planet".

Pluto is named after the Roman god of the underworld.

## Size and Distance

Pluto is 1/6 the size of Earth, with a radius of 715 miles (1,151 kilometres). Pluto would be the size of a popcorn kernel if Earth was a nickel.

Pluto is 39 astronomical units away from the Sun. One astronomical unit (abbreviated as 'AU') is the equal distance from the Sun to Earth. Sunlight takes 5.5 hours to travel to Pluto from this distance.

If you were to stand on Pluto at noon, the Sun would be 1/900 the brightness it is here on Earth, or 300 times as bright as a full moon. Each day, near sunset on Earth is the same brightness at noon on Pluto.

## Orbit and Rotation

Pluto's orbit is strange compared other planets in our solar system; it's both elliptical and tilted. Pluto's 248-year-long orbit can take the dwarf planet as far as 49.3 astronomical units (AU) away from the Sun and as close as 30 astronomical units. On average, Pluto is 3.7 billion miles (5.9 billion kilometres) away from the Sun, or 39 astronomical units.

Pluto was near perihelion from 1979 to 199, the time when the planet is closest to the Sun. During this time, Pluto was closer to the Sun than Neptune.

One day on Pluto lasts 153 hours (the time it takes for Pluto to complete one rotation) with a 57 degree tilt. One year on Pluto, however, lasts 248 Earth years (90,520 Earth days). Pluto also experiences a retrograde rotation; spinning from east to west like Venus and Uranus.

## Structure

Pluto is 2/3 the diameter of Earth's moon and probably has a rocky core surrounded by a water ice mantle. Ices like methane and nitrogen frost coat Pluto's surface. Due to its low density, Pluto's mass is 1.6 that of Earth's moon.

## Formation

Pluto is a member of objects that sit in the Kuiper Belt beyond Neptune. This distance realm is filled with thousands of icy worlds, which formed in the early life of our solar system about 4.5 billion years ago. These objects are often referred to as the Kuiper Belt objects, transneptunian objects or plutoids.

## Surface

Pluto's surface is characterised by many mountains, valleys, plains and craters. The temperatures on Pluto can reach as cold as -226 to -240 degrees celsius.

Pluto's mountains can reach as high as 6,500 to 9,800 feet (2 to 3 kilometres) and are big blocks made up of water ice, sometimes coated with frozen methane. Long troughs and valleys that can stretch as long as 370 miles (600 kilometres) add to the interesting features of the dwarf planet.

Craters as large as 162 miles . (260 kilometres) in diameter add a dot on the landscape, with some showing signs of erosion and filling. This means that tectonic forces are slowly resurfacing Pluto.

The most noticeable plains on Pluto appear to be composed of frozen nitrogen gas and show no craters. These plains suggest conventions on the structure (blobs of material circulating up and down).

## Atmosphere

Pluto has a thin, tenuous atmosphere that expands when the Sun comes closer to the planet and collapses as it moves farther away - similar to a comet. Molecular nitrogen is the main constituent, though molecules of methane and carbon dioxide have also been detected.

When Pluto reaches closer to the Sun, its surface changes directly from solid to gas (sublimate) and rise to form a temporary thin atmosphere. The opposite happens when Pluto moves farther away from the Sun. Pluto's low gravity (about 6% of Earth's) causes the atmosphere to be much longer in altitude than our atmosphere. When Pluto is farther away from the Sun, it starts to become colder during that part of the year. During this time, the bulk of the planet's atmosphere may freeze and fall as snow on the surface.

## Magnetosphere

It is unknown whether Pluto has a magnetic field, but is is theorised to be small and slow rotation suggests little or none.

## Moons

Pluto has five known moons in its orbit: Charon, Nix, Hydra, Kerberos and Styx. This moon system might have formed between Pluto and similar object in the early life of the solar system.

Charon, the biggest moon in Pluto's orbit, is about half the size of Pluto itself, making it the largest satellite relative to the planet in our solar system. This moon orbits Pluto at a distance of 12,200 miles (19,640 kilometres). For comparison, our moon is 20 times farther away from Earth. Charon and Pluto are often referred to as the "double planet".

Pluto's other four moons are much smaller, less than 100 miles (160 kilometres) in length. They are also irregularly shaped, not spherical like Charon. Unlike other moons in our solar system, these five moons are no tidally locked to Pluto meaning that they all spin and don't keep the same face towards Pluto.

## Human Life

The extreme temperatures make Pluto very unlikely to be colonised.