Introduction
Pluto is not the most distant thing to orbit the sun by a long way. The solar system extends for millions of kilometres beyond the "last" planet, stretching as far as the sun's gravity will allow. Clouds containing trillions of comets and asteroids have been found orbiting the sun from great distances, and some scientists even believe that a tenth planet may lie beyond Pluto.
Oort cloud
Many scientists believe that the boundary of the solar system could be an immense cloud of comets called the Oort cloud, which surrounds the panet like a cage. The spherical halo consists of tens of trillions of orbiting comets dating back to the origin of the solar system 4.6 billion years ago. The Oort cloud is nearly eight million million km in diameter. Objects beyond this are pulled away from the solar system because the sun's gravity is no longer strong enough to hold them.
Minor members
An astronomer named Gerard Kuiper suggested that beyond Neptune lay belt of celestial bodies made from rock and ice. Astronomers now think that there may be up to 100,000 large, comet like objects in the Kuiper Belt ], including Pluto and Charon. The largest of these, apart from the ninth planet and its moon, is called 1992QBI, otherwise known as Smiley, and is 200 km across. The icy bodies in the Kuiper Belt are called minor members, or "plutinos" because they act like little Plutos and are very difficult to spot from Earth, even with the most powerful telescopes.
Planet X
For many years before Pluto was discovered, astronomers were looking for a planet beyond Neptune, because the orbits of Uranus and Neptune suggested they were being distorted by the gravity from a distant, invisible source. Even when Pluto was discovered, it was believed to be too small a planet to affect orbits of its neighbours, and scientists instead thought it was a tenth planet that was responsible. The recent discovery of minor members beyond Pluto means that a tenth planet is unlikely. However, new planets are being discovered all the time, not in our solar system, but orbiting other stars.
Some important facts
1) If all the objects in the Kuiper belt, joined together, they would form a planet the size of Earth.
2) Astronomers believe that the Oort cloud could contain upto 10 million million comets. These pieces of debris are the left over material from when the planets formed billions of years ago.
3) A comet orbiting the sun from the outskirts of the Oort cloud would take millions of years to complete one year.
4) Smiley gets its name from a character in a book by a british thriller writer John Le Carre. Smiley's discoverer was reading this book when he came across it.
Facts and Figures
Kuiper Belt:
Age : 4.6 billion years
Composition : comets and asteroids
Oort cloud :
Age : 4.6 billion years
Diameter : 7.6 million million km
Composition : icy comets
Pluto is not the most distant thing to orbit the sun by a long way. The solar system extends for millions of kilometres beyond the "last" planet, stretching as far as the sun's gravity will allow. Clouds containing trillions of comets and asteroids have been found orbiting the sun from great distances, and some scientists even believe that a tenth planet may lie beyond Pluto.
Oort cloud
Minor members
An astronomer named Gerard Kuiper suggested that beyond Neptune lay belt of celestial bodies made from rock and ice. Astronomers now think that there may be up to 100,000 large, comet like objects in the Kuiper Belt ], including Pluto and Charon. The largest of these, apart from the ninth planet and its moon, is called 1992QBI, otherwise known as Smiley, and is 200 km across. The icy bodies in the Kuiper Belt are called minor members, or "plutinos" because they act like little Plutos and are very difficult to spot from Earth, even with the most powerful telescopes.
Planet X
For many years before Pluto was discovered, astronomers were looking for a planet beyond Neptune, because the orbits of Uranus and Neptune suggested they were being distorted by the gravity from a distant, invisible source. Even when Pluto was discovered, it was believed to be too small a planet to affect orbits of its neighbours, and scientists instead thought it was a tenth planet that was responsible. The recent discovery of minor members beyond Pluto means that a tenth planet is unlikely. However, new planets are being discovered all the time, not in our solar system, but orbiting other stars.
Some important facts
1) If all the objects in the Kuiper belt, joined together, they would form a planet the size of Earth.
2) Astronomers believe that the Oort cloud could contain upto 10 million million comets. These pieces of debris are the left over material from when the planets formed billions of years ago.
3) A comet orbiting the sun from the outskirts of the Oort cloud would take millions of years to complete one year.
4) Smiley gets its name from a character in a book by a british thriller writer John Le Carre. Smiley's discoverer was reading this book when he came across it.
Facts and Figures
Kuiper Belt:
Age : 4.6 billion years
Composition : comets and asteroids
Oort cloud :
Age : 4.6 billion years
Diameter : 7.6 million million km
Composition : icy comets
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