# The Simplest Way to Tell a Planet From a Brown Dwarf: Listen to It Spin - Date: 2026-04-02 - Category: Space & Aerospace In the HR 8799 system, a planet seven times Jupiter's mass spins six times faster than a nearby brown dwarf. That contrast is now the clearest evidence yet that planets and brown dwarfs form differently — and spin is the diagnostic astronomers have been missing. ---