Planets
the largest members of the Solar System are the eight major planets. Nearest the Sun are four fairly small, rocky planets - Mercury, Venus, Earth and Mars.
Beyond Mars is the asteroid belt – a region populated by millions of rocky objects. These are left-overs from the formation of the planets, 4.5 billion years ago. On the far side of the asteroid belt are the four gas giants - Jupiter, Saturn, Uranus and Neptune. These planets are much bigger than Earth, but very lightweight for their size. They are mostly made of hydrogen and helium.
Until recently, the furthest known planet was an icy world called Pluto. However, Pluto is dwarfed by Earth’s Moon and many astronomers think it is too small to be called a true planet.
An object named Eris, which is at least as big as Pluto, was discovered very far from the Sun in 2005. More than 1,000 icy worlds such as Eris have been discovered beyond Pluto in recent years. These are called Kuiper Belt Objects. In 2006, the International Astronomical Union decided that Pluto and Eris must be classed as “dwarf planets”.
Definition of planets :-
. It's a body which is in orbit around the sun and not a satellite of a planet. e.g. the moon is ruled out as being a planet because it orbits the earth.
Its shape is close to being the shape if it was made of water - e.g. close to a sphere. If the object is spinning then centrifugal force will cause the radius at the equator to be larger that the radius at the poles - so it's never a perfect sphere.
It has a clear area around it. In other words it has sucked up or pushed away any other objects to become the dominant body in the area. It has been argued that Neptune should be a dwarf planet for the reason that objects like Pluto keep wandering through its orbit space. However Pluto has been locked into a phase in which it orbits the sun twice for every three orbits of Neptune. If this were not the case Pluto's orbit would be unstable. Therefore Neptune's much larger gravitational force is in control.
Beyond Mars is the asteroid belt – a region populated by millions of rocky objects. These are left-overs from the formation of the planets, 4.5 billion years ago. On the far side of the asteroid belt are the four gas giants - Jupiter, Saturn, Uranus and Neptune. These planets are much bigger than Earth, but very lightweight for their size. They are mostly made of hydrogen and helium.
Until recently, the furthest known planet was an icy world called Pluto. However, Pluto is dwarfed by Earth’s Moon and many astronomers think it is too small to be called a true planet.
An object named Eris, which is at least as big as Pluto, was discovered very far from the Sun in 2005. More than 1,000 icy worlds such as Eris have been discovered beyond Pluto in recent years. These are called Kuiper Belt Objects. In 2006, the International Astronomical Union decided that Pluto and Eris must be classed as “dwarf planets”.
Definition of planets :-
. It's a body which is in orbit around the sun and not a satellite of a planet. e.g. the moon is ruled out as being a planet because it orbits the earth.
Its shape is close to being the shape if it was made of water - e.g. close to a sphere. If the object is spinning then centrifugal force will cause the radius at the equator to be larger that the radius at the poles - so it's never a perfect sphere.
It has a clear area around it. In other words it has sucked up or pushed away any other objects to become the dominant body in the area. It has been argued that Neptune should be a dwarf planet for the reason that objects like Pluto keep wandering through its orbit space. However Pluto has been locked into a phase in which it orbits the sun twice for every three orbits of Neptune. If this were not the case Pluto's orbit would be unstable. Therefore Neptune's much larger gravitational force is in control.