Venus is the brightest object in the night sky after the Moon — dazzling enough to cast faint shadows and to be mistaken for a UFO. Beneath its serene glow hides a hellish world: a runaway greenhouse atmosphere of carbon dioxide crushes the surface at 90 times Earth’s pressure and holds it at 465°C, hot enough to melt lead.

When Venus is in view it is unmistakable — the brilliant “star” blazing in the west after sunset or the east before dawn. Through a telescope it shows no surface markings, but it runs through phases like the Moon, from a small bright disc to a large thin crescent as it swings between us and the Sun.