What we know about Venus so far has been gathered from several past probes.
With a slightly smaller diameter than Earth, Venus orbits closer to the Sun. This means that any water on the surface would have evaporated shortly after its formation, starting its greenhouse effect. Early and sustained volcanic eruptions created lava plains and increased the carbon dioxide in the atmosphere — starting the runaway greenhouse effect, which increased the temperature from just a little higher than Earth’s to its current high value of 475°C.
While Venus’s year is shorter than ours (225 days), its rotation is very slow (243 days) and “retrograde” — the other way round to Earth. The slow rotation is related to a lack of magnetic field, resulting in a continuing loss of atmosphere. Venus’ atmosphere “super-rotates” faster than the planet itself. Images from many missions show V-shaped patterns of clouds composed of sulphuric acid droplets.
Despite the harsh conditions, some scientists have speculated that Venus’ clouds might, at some altitudes, harbor habitable conditions. Recent measurements showing phosphine — a potential sign of life as it is continuously produced by microbes on Earth — in Venus’ clouds have been strongly debated. We need more measurements and exploration to work out where it comes from.
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