Pluto
Pluto is a complex and mysterious world with mountains, valleys, plains, craters, and maybe glaciers.
It is located in the distant Kuiper Belt.
Discovered in 1930, Pluto was long considered our solar system's ninth planet.
after the discovery of similar intriguing worlds deeper in the Kuiper Belt, tiny Pluto was reclassified as a dwarf planet.
Pluto is only about 1,400 miles wide. At that small size, Pluto is only about half the width of the United States.
It's about 3.6 billion miles away from the Sun,
and it has a thin atmosphere composed mostly of nitrogen, methane, and carbon monoxide.
On average, Pluto’s temperature is -387°F (-232°C), making it too cold to sustain life.
Pluto is orbited by five known moons, the largest of which is Charon.
Charon is about half the size of Pluto itself, 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."
The surface of Pluto is extremely cold, so it seems unlikely that life could exist there.
At such cold temperatures, water, which is vital for life as we know it, is essentially rock-like.
Pluto's interior is warmer, however, and some think there could even be an ocean deep inside.
With a radius of 715 miles (1,151 kilometers), Pluto is about 1/6 the width of Earth.
From an average distance of 3.7 billion miles (5.9 billion kilometers), Pluto is 39 astronomical units away from the Sun. One astronomical unit (abbreviated as AU), is the distance from the Sun to Earth.
From this distance, it takes sunlight 5.5 hours to travel from the Sun to Pluto.
If you were to stand on the surface of Pluto at noon, the Sun would be 1/900 the brightness it is here on Earth, or about 300 times as bright as our full moon.
There is a moment each day near sunset here on Earth when the light is the same brightness as midday on Pluto.
Pluto's orbit around the Sun is unusual compared to the planets: it's both elliptical and tilted.
Pluto's 248-year-long, oval-shaped orbit can take it as far as 49.3 astronomical units (AU) from the Sun, and as close as 30 AU.
One day on Pluto takes about 153 hours. Its axis of rotation is tilted 57 degrees with respect to the plane of its orbit around the Sun, so it spins almost on its side.
Pluto also exhibits a retrograde rotation; spinning from east to west like Venus and Uranus.
Pluto has five known moons: Charon, Nix, Hydra, Kerberos, and Styx.
This moon system might have formed by a collision between Pluto and another similar-sized body early in the history of the solar system.
Charon, the biggest of Pluto's moons, is about half the size of Pluto itself, making it the largest satellite relative to the planet it orbits in our solar system. It orbits Pluto at a distance of just 12,200 miles (19,640 kilometers). For comparison, our Moon is 20 times farther away from Earth. Pluto and Charon are often referred to as a double planet.
Charon's orbit around Pluto takes 153 hours – the same time it takes Pluto to complete one rotation. This means Charon neither rises nor sets, but hovers over the same spot on Pluto's surface. The same side of Charon always faces Pluto, a state called tidal locking.
Pluto's other four moons are much smaller, less than 100 miles (160 kilometers) wide. They're also irregularly shaped, not spherical like Charon. Unlike many other moons in the solar system, these moons are not tidally locked to Pluto. They all spin and don’t keep the same face towards Pluto.
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
The small moon Nix is named for the goddess of darkness and night, who is also the mother of Charon.
Hydra is named for the nine-headed serpent that guards the underworld.
Kerberos is named after the three-headed dog of Greek mythology
And Styx is named for the mythological river that separates the world of the living from the realm of the dead.
