It is a common conception that Venus is so warm simply because it’s nearer the sun than the Earth but its clouds actually reflect around 70% of the incoming solar radiation. The prime reason Venus is hot is that it has been subject to a runaway greenhouse gas effect.

Although the nature of its atmosphere has made the surface of Venus inhospitable, it is the atmosphere itself, particularly at temperate altitudes, which has received renewed attention following the suggestion that it may include phosphine gas (now contested). This gas is one indicator of the potential presence of microbial life.