A backward-spinning star with two coplanar planets

The Sun's equator lines up with the orbits of the planets. This fact supports the theory that stars and their planets inherit their angular momentum from the same source: the gravitational collapse of a molecular cloud. Most astronomers expected spin-orbit alignment to be a universal feature of planetary systems. This proved false: many drastic misalignments are known, and many possible reasons have been offered. In one theory, a distant companion star upsets the alignment at an early stage, while the star is still surrounded by a protoplanetary disk. Here, the K2-290 system is shown to be the best-known candidate for such a primordial misalignment. The star rotates backward, and a companion star with suitable properties has been identified.