Asked by: Pearl Goodwin, Lewes

Technically known as contrails, these white trails are created from water vapour produced by the combustion of fuel in aircraft engines.

At their cruising altitude of 10,000m, temperatures are around -55°C. As it’s so cold, the water turns to ice particles, but how long they remain visible depends on humidity.

If the air is relatively humid, the contrails will grow and remain visible long after the aircraft has disappeared.

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Robert is a science writer and visiting professor of science at Aston University.