No escaping this winter Lynn Hilton/Alamy Stock Photo

A nebular winter could have doomed the dinosaurs. The clue is a thick layer of an extraterrestrial element on the ocean floor, now claimed to be the result of Earth colliding with a galactic cloud.

The most-heard explanation for the dinosaurs’ demise is an asteroid impact, which left a crater off the coast of Mexico and a worldwide 30-centimetre-thick layer of iridium, an element otherwise rare on Earth.

But every so often, astronomers suspect, the solar system ploughs into a giant nebula of molecular gas and dust much denser than typical …