There’s an interesting explanation for the white trails planes leave behind them

The cloud-like streaks we often see trailing behind planes create cool patterns in the sky and make for great Instagram photos, but have you ever wondered what they actually are?

When Austrian physicist Robert Ettenreich first noticed them in 1919, he described them as 'the condensation of a cumulus stripe from the exhaust gases of an aircraft', noting that it was visible for a 'long' time.

Despite resembling smoke or a large cloud, these trails are mostly just condensation, rather than the familiar exhaust fumes we see from cars. Or, in the aerospace industry, they have a more technical name of 'condensation trails' or 'contrails'.

The white trail you see behind planes is made up of mostly condensation / Andrew Holt / Getty Images

They're essentially made up of - you guessed it - condensation, similar to what happens on cold winter days when you can see your breath, only on a much larger and more extreme scale.

As plane engines burn, they expel massive quantities of water and aerosols into the atmosphere.

Aerosols simply consist of tiny solid particles or liquid droplets that are suspended in the air.

However, since the temperature is usually below zero up there, the released particles freeze, via a process called crystalisation, and become visible, which is why we can spot their trails from the ground.

Sometimes there these trails can contain some pollutants, such as carbon dioxide, carbon monoxide, and methane. However the majority of the white trail is water and they evaporate quickly and so, don't pose any real danger to the environment or human health.

Usually 'contrails' are short-lived and don't impact the environment / George Pachantouris / Getty Images

For instance, large aircraft like the Boeing 747 can release around 2.75 kilograms of water per second during flight.

Ulrich Schumann, professor of atmospheric physics at the German Aerospace Center (DLR), explained: 'Contrails have a very strong forcing effect, far stronger than the CO2.

'But contrails are short-lived, they are gone after an hour or so. Whereas the CO2 lives very long, it can live for 100 years.'

Depending on the type of trail, they only tend to last a few minutes, particularly the 'contrails' or 'short-lived trails.'

Unlike 'persistent trails' that linger for much longer, contrails usually emit when the air is dry, making it easier for the ice particles to transform from solids to gas.

Tim Johnson, director of the Aviation Environment Federation (AEF), a UK-based non-profit, said: 'Contrails may only last a few minutes if the surrounding air is dry, but when it's humid, they can persist and spread out to increase cirrus cloudiness.'