Question: What is weather like on other planets?

Susan Cartwright answered on 19 Jun 2015:

Mostly, not as varied as the Earth’s weather.

Mercury has essentially no atmosphere, so it has no weather (the same is true of the Moon).

Venus has a very thick atmosphere, but Venus rotates extremely slowly and has very little axial tilt (i.e. no seasons), so its weather is very stable. The upper layers of Venus’ atmosphere rotate around the planet once every few days, so there is a constant very fast wind (over 200 mph, well above hurricane speed), but this is only at high altitude (like the Earth’s jet stream), and near the surface there’s very little wind. There is no rain because Venus has no water.

Mars does have interesting weather: it has about the same axial tilt as we do, so it has seasons like us, and in addition its orbit is quite oval-shaped, so the seasons are different lengths. It has an atmosphere which is very thin, but enough to support winds. Mars does not have rain – the atmosphere contains very little water – but it does occasionally snow. Clouds can form, although they are frozen carbon dioxide rather than water. The most noticeable Martian weather phenomenon is the dust storm, which is rather like a sandstorm on Earth. Weather on Mars varies from place to place, and can change in a few hours, just like Earth’s weather.

Jupiter and Saturn have incredibly thick atmospheres, tens of thousands of km deep. All we see are the cloud tops. There are weather systems: the Great Red Spot on Jupiter is a gigantic hurricane (big enough to swallow the Earth!) that has been maintained at the same latitude (but not the same longitude: it’s not fixed in the same place) for at least 150 years, and probably more than 350 (something that was probably the Great Red Spot was observed in the 1600s, but not described clearly enough for us to be sure that it was our Great Red Spot). There are many other, more temporary, storm systems in Jupiter’s and Saturn’s atmospheres: we don’t know why the Great Red Spot is so long-lived.

Uranus’ weather is complicated by the fact that the planet has such a large axial tilt that it is basically lying on its side. Therefore, twice a Uranian year one of the poles is facing the Sun, and twice a Uranian year the poles are side on to the Sun and the equator faces the Sun. These extreme seasons drive a unique weather system with extremely fast winds (over 500 mph). Of course, being so far from the Sun, Uranus is also very cold, about -220 C.

Neptune has even faster winds – over 1000 mph – and powerful storm systems. These seem to be driven partly by internal heat – although it is much further from the Sun than Uranus, its temperature is about the same as Uranus’, so some internal source is supplementing the feeble sunlight.

The solar system object with a weather system most like the Earth’s is not a planet, but Saturn’s planet-sized (it’s bigger than Mercury) moon Titan. Titan has a nitrogen atmosphere which can support weather, and it’s the only object apart from the Earth that has seas – though of liquid natural gas (methane), not water: water is a rock on Titan, which is much colder than the freezing point of ice. As a result of having seas, Titan can have clouds and rain like the Earth, though again these are liquid methane and not water.