Asked by: Peter Alexander, Altrincham
The ingredients required to make a rainbow are sunlight and raindrops. Currently, there is no other planet known to have liquid water on its surface or in sufficient quantities in the atmosphere to make rain. However, other liquid droplets could refract sunlight and spread it out into its component colours, just as water droplets do on Earth.
On Saturn’s moon Titan, for example, the atmosphere is rich in liquid methane droplets that almost certainly form rain. Titan’s atmosphere is extremely hazy, meaning that direct sunlight is probably uncommon, but there is still a chance that methane rainbows could form. If they do exist, they would look very similar to terrestrial rainbows, but would be somewhat broader due to the different refractive index of methane compared to water.
Another similar phenomenon, called a ‘glory’, occurs on Venus (pictured) and is caused by droplets of sulphuric acid that are present in the planet’s atmosphere.