Earth and Space – BBC Bitesize

Pluto and the dwarf planets, asteroids and comets

Scientists have discovered other objects orbiting the Sun. These include comets, asteroids, and dwarf planets like Pluto and Ceres. Pluto used to be considered the ninth planet in our solar system, but in 2006 scientists reclassified it as a dwarf planet.

Asteroids and comets have a few things in common. They both orbit our Sun, and they both can have unusual orbits, sometimes straying close to Earth or the other planets. They are both “leftovers” from when our solar system formed. But there are a few notable differences between these two objects, as well.

The biggest difference between comets and asteroids is what they are made of:

• Asteroids are large lumps of metals and rock that orbit the Sun.
• Comets are smaller and made up of ice, dust and rocky materials.

When comets get closer to the Sun, they lose material with each orbit because some of their ice melts and turns into vapour. We see this as the comet’s tail. This is another difference between asteroids and comets; comets have “tails” while asteroids generally don’t.

A meteoroid is a much smaller rock or particles in orbit around the Sun. If a meteoroid enters the Earth’s atmosphere and vaporizes, it is called a meteor, which is often referred to as a shooting star. Of course, it is not a star, just a very hot piece of rock!