A. Reiners

The tiny star LHS 3844 is trembling. The invisible culprit is a rocky planet that whips around it every 11 hours. The planet pulls on the star, and the star responds with a barely perceptible wobble. Detecting that wobble is like noticing a 100-kilogram weightlifter step forward when a fly lands on his palm.

The star GJ 436 is a dim red dwarf, and orbiting it is a Neptune-sized planet on a nearly vertical, tilted orbit. Astronomers spent 18 years taking spectra of this star to track its spots and flares. Suddenly, a rhythm emerged in the data that matched neither the star's rotation nor its 8-year activity cycle. This rhythm exactly followed the planet's orbit.

A world that for years refused to show its face. Planet GJ 1214 b is exactly such a case. It is larger than Earth but smaller than Neptune, and its dense envelope made the atmosphere invisible to telescopes: starlight passed through it without leaving clear traces. But astronomers' persistence and a new sensitive instrument provided the first clue.