Enric Pallé

Every clear night, a telescope on the island of La Palma looked at the sky and recorded how much the air dimmed starlight. This was routine work for astronomers measuring stellar positions. But in these records, like in an old diary, traces of a different story remained: the arrivals of dust from the Sahara.

350 light-years away, four planets orbit the star V1298 Tau. They are 5–10 times larger than Earth but lighter than they appear. For nine years, astronomers tracked their motion to understand what they are made of and how they lived in the past. The planets are lined up in a chain: their orbital periods are nearly in 3:2, 2:1, and 3:1 ratios.

A quarter-century ago, Michel Mayor and Didier Queloz discovered the first hot Jupiter, and shattered all the rules of planet formation. A gas giant on a days-long orbit couldn't have formed next to the star: it's far too hot and lacks building material. So, it must have been born far away and then migrated.