The states of matter on Earth The states of matter in the Universe What makes one state different from another? Changing state does not change the substance

All matter (anything made up of atoms) is divided into four physical "states": solid, liquid, gas and plasma. The chemical composition of a substance determines its state at any particular temperature.

All substances start as solids at the very lowest possible temperature, absolute zero (-273°C) and go through changes of state as they are heated. As a solid is heated, it will generally melt to become a liquid, boil to form a gas and finally, at extreme temperatures like those found on the Sun or a very hot flame, its atoms will break apart to become a plasma.

The states of matter on Earth
Plasma, in the form of ionised gas, is very rare on Earth and usually only exists fleetingly as the glowing gas in a flame or as a bolt of lightning. Gases are mainly found in the Earth's atmosphere, although small pockets of gas are also caught in the Earth's mantle. Most of the outer part of our planet is solid; this solid mantle sits on an outer liquid core and a solid inner core. Two thirds of the Earth's surface is covered in liquid water.

The states of matter in the Universe
The most common state in the Universe is plasma. This is because most of the atomic matter in the Universe is found in stars and stars are massive, extremely hot balls of ionised gas or plasma.

Gas is the next most universally common state. It is found in vast gas nebula clouds spread throughout space and in the giant gas planets like Jupiter and Saturn.

Solid forms the third most common state. It is found in the form of cosmic dust, Earth-like planets, comets and other stray pieces of rock.

Liquid is probably the rarest state in the Universe, with the only discovered naturally occurring liquids being the Earth's surface water and our liquid metal core. Some astronomists believe that there may be water on a few of the moons in the outer Solar System and that water may have once existed on Mars and carved out its extensive canyons.

What makes one state different from another?
The state of a substance at any particular temperature and pressure is dependent on how big its particles are and how strongly they bond together. For example, substances which are solids under normal conditions (25°C and 1 atmosphere pressure) are usually made of large heavy atoms or molecules and are tightly bonded together. On the other hand, gases under these same conditions tend to be made of small, light atoms or very small molecules that do not stick together well. Liquids generally have particles which are somewhere in between these two extremes.

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