Zac Powlowicz, of Port Chalmers School, asks :-

Do other planets have seasons?

Alan Gilmore an astronomer at the University of Canterbury's Mt John Observatory, responded:-

The answer depends on the planet. Earth and Mars have obvious seasons. Through a telescope we can see Mars's seasons as frost caps form at the north pole then at the south pole. Mars also has dust storms at a particular season.

The seasons on Earth and Mars happen because the spin axis of the each planet is tilted a bit to its path around the sun. So, for half an orbit, the northern hemisphere of the planet gets more sunshine than the southern hemisphere. Then, for another half orbit, the south gets more sunshine. If the spin axes of Earth and Mars weren't tilted then we wouldn't have seasons.

Venus doesn't have seasons partly because its spin axis is vertical to its orbit, but mostly because it has a dense atmosphere of carbon dioxide. Carbon dioxide is a 'greenhouse gas' that traps the heat from the sunshine. Venus's thick clouds also help to keep the heat in. So Venus is very hot everywhere all the time.

Mercury and the moon have no air to trap the heat so they have no seasons. The big planets, Jupiter to Neptune, have cloudy atmospheres and no solid surfaces. So our everyday ideas of seasons don't really apply to them.