Introduction
Pluto is the solar system's mystery planet. At nearly 5,900 million km from the sun, it has never been visited by a probe. Pluto is smaller than our moon, and some even question its claim to be a planet at all. Many astronomers believe that Pluto is a large asteroid, little bigger than those found in the Kuiper Belt beyond the planets.
Twin Planets
In 1978, Pluto was found to have a companion moon, which was named charon. The moon is one third the size of Pluto, making it the biggest moon in comparison to its parent planet in the solar system. They are a mere 20,000 km apart, and are caught in the gravitational head lock, forming what scientists call a dual planet system. Nobody knows Pluto managed to adopt so large a moon. Some believe charon is made from ice chipped off Pluto by a collision, others that the worlds formed in different places and were somehow caught by on another later on.
Planet or not?
Many scientists have questioned Pluto's status as a planet, arguing that it is too small and its orbit too elongated to be classified as a proper planet. Some scientists claim that Pluto is the largest of the objects in the Kuiper Belt, a collection of rocky and icy debris orbiting beyond Neptune. Others argue that Pluto and charon were actually moons of Neptune that broke free billions of years ago and were caught in their own orbit around the sun. However, there are no plans to demote Pluto from a planet to trans- Neptunian object. Instead, it has been given a dual classification as both.
A dark planet
In summer, Pluto has a slight atmosphere because the surface warms up enough to melt some of its ice, turning it to gas. As Pluto moves away from the sun, the gas freezes and becomes ice again. This means that in winter, Pluto's weather doesn't just become worse, it completely disappears! On Pluto it is always dark and cold, even in the middle of the day. This is because the sun appears 1,000 times fainter from the surface of Pluto than it does from Earth,little more than a faint star.
Some important facts
1) Pluto takes 248 years to orbit the sun. Amazingly, This means that not even half a year has elasped on the planet since its discovery in 1930.
2) Pluto is a mystery planet. It is different to the inner planets, which are much denser and composed of large amounts of iron and nickel, and it is vastly different to the gas giants.
3) The Pluto Express is due to fly by the planet between 2006 and 2008. It will consist of small spacecraft that will pass the planet at a height of 15,000km.
4) Pluto's strange orbit means that for periods of around 20 years it moves closer to sun than the Neptune. It was like this between 1979 and 1999.
5) Pluto's orbit is more elongated than any other planet in the solar system. It is tilted against the plane of its neighbours, so that Pluto spends half its year above the other planets, then half its year below.
6) Pluto is smaller than many of the moons in the solar system. It is less than one fifth the mass of Earth's moon. However, it is 10 times the mass of ceres, the largest known asteroid.
Facts and figures
Diameter: 2,274km
Distance from sun : 5,899 million km
Surface temperature : -230oC (-380oF)
Surface gravity : 0.067 x Earth
Length of orbit : 90,800 Earth days
Length of day : 153 Earth hours
Mass : 0.002 x Earth
Density(water=1) : 2.03
Number of moons : 1
Number of rings : 0
Pluto is the solar system's mystery planet. At nearly 5,900 million km from the sun, it has never been visited by a probe. Pluto is smaller than our moon, and some even question its claim to be a planet at all. Many astronomers believe that Pluto is a large asteroid, little bigger than those found in the Kuiper Belt beyond the planets.
Twin Planets
In 1978, Pluto was found to have a companion moon, which was named charon. The moon is one third the size of Pluto, making it the biggest moon in comparison to its parent planet in the solar system. They are a mere 20,000 km apart, and are caught in the gravitational head lock, forming what scientists call a dual planet system. Nobody knows Pluto managed to adopt so large a moon. Some believe charon is made from ice chipped off Pluto by a collision, others that the worlds formed in different places and were somehow caught by on another later on.
Planet or not?
Many scientists have questioned Pluto's status as a planet, arguing that it is too small and its orbit too elongated to be classified as a proper planet. Some scientists claim that Pluto is the largest of the objects in the Kuiper Belt, a collection of rocky and icy debris orbiting beyond Neptune. Others argue that Pluto and charon were actually moons of Neptune that broke free billions of years ago and were caught in their own orbit around the sun. However, there are no plans to demote Pluto from a planet to trans- Neptunian object. Instead, it has been given a dual classification as both.
A dark planet
In summer, Pluto has a slight atmosphere because the surface warms up enough to melt some of its ice, turning it to gas. As Pluto moves away from the sun, the gas freezes and becomes ice again. This means that in winter, Pluto's weather doesn't just become worse, it completely disappears! On Pluto it is always dark and cold, even in the middle of the day. This is because the sun appears 1,000 times fainter from the surface of Pluto than it does from Earth,little more than a faint star.
Some important facts
1) Pluto takes 248 years to orbit the sun. Amazingly, This means that not even half a year has elasped on the planet since its discovery in 1930.
2) Pluto is a mystery planet. It is different to the inner planets, which are much denser and composed of large amounts of iron and nickel, and it is vastly different to the gas giants.
3) The Pluto Express is due to fly by the planet between 2006 and 2008. It will consist of small spacecraft that will pass the planet at a height of 15,000km.
4) Pluto's strange orbit means that for periods of around 20 years it moves closer to sun than the Neptune. It was like this between 1979 and 1999.
5) Pluto's orbit is more elongated than any other planet in the solar system. It is tilted against the plane of its neighbours, so that Pluto spends half its year above the other planets, then half its year below.
6) Pluto is smaller than many of the moons in the solar system. It is less than one fifth the mass of Earth's moon. However, it is 10 times the mass of ceres, the largest known asteroid.
Facts and figures
Diameter: 2,274km
Distance from sun : 5,899 million km
Surface temperature : -230oC (-380oF)
Surface gravity : 0.067 x Earth
Length of orbit : 90,800 Earth days
Length of day : 153 Earth hours
Mass : 0.002 x Earth
Density(water=1) : 2.03
Number of moons : 1
Number of rings : 0
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