Planets and Rocks

Several different objects orbit around our Sun. From the larger planets and dwarf planets, to the smaller comets, meteoroids and centaurs, the Sun is orbited by countless astronomical bodies. It is only more recently, with new technology, that we can see many of the smaller or more distant objects.

Planets and Dwarf Planets

Around the Sun are 8 planets (see right), ranging from hot rocky planets with sulfuric acid rain to enormous gas giants, drifting around the Sun as they drag their moons.

Officially, a planet is defined as being an object in orbit around the Sun which is almost round and has a clear orbit.

Dwarf planets are objects which are round and in orbit, but haven't yet cleared their orbit. This is particularly evident in Ceres which is within the asteroid belt which definitely isn't clear.

The most significant dwarf planets in our Solar System are Pluto (which was a planet up until 2006) in the Kuiper Belt and Ceres in the Asteroid Belt.

Asteroids, Meteoroids and Comets

Despite being commonly referred to together, asteroids, meteors and comets are completely different. Comets are bodies of ice and gas which come from the Oort Cloud in the outer Solar System. They consist of a tail (made up of an ion tail and a dust tail) and a nucleus which is surrounded by a coma. Comets have highly elliptical orbits with their 'lowest' points being really close to the Sun, whereas their 'highest' points are far away from the Sun. Throughout their orbits, the tails of comets point away from the Sun due to the solar wind.

In contrast to comets, meteors and asteroids are lumps of rock travelling through space. The difference between the two are that asteroids are much larger and that meteors are often produced when asteroids are broken up. Meteoroids have much more round orbits than comets, with meteor showers occurring when these orbits intersect with the Earth's orbit around the Sun. When a meteoroid enters the atmosphere it is called a meteor (or fireball if its magnitude is -3 or brighter) and then once it reaches the ground it is called a meteorite.

James Gooding, 2017

All image credits go to NASA (and respective centers/universities)