At the edge of the solar system, far beyond Neptune, hundreds of icy chunks circle the Sun. Some of them move as if an invisible hand had aligned their orbits like compass needles. Ten years ago, this led astronomers to suspect that a massive planet, about ten times heavier than Earth, is hiding there.

But the old calculations had a weakness: telescopes do not scan the sky evenly. Bright regions are easier to see, faint ones harder, and this unevenness could itself create a false impression of alignment. The authors of the new work devised a method that accounts for where telescopes actually pointed. They also checked which distant bodies would not escape the solar system over billions of years and expanded the list of suitable objects from 21 to 25.

The result has cooled the enthusiasm: the alignment is barely noticeable, and the direction it points to is not well determined. This does not mean Planet X does not exist. It means the main argument for it has become shaky.

Soon, the Vera Rubin Observatory in Chile will start operating. It will photograph the entire southern sky every few nights and find thousands of new distant bodies. Then the new method will show whether the alignment was a mirage or whether a real planet lies behind it.