Since Vera Rubin first convincingly showed that galaxies are surrounded by invisible matter, the quest to understand the nature of dark matter has remained one of physics' greatest challenges. New research suggests that ultralight dark matter could be screened by Earth's atmosphere if it has a special 'quadratic' interaction with Standard Model particles (like a double handshake). Near our planet, the density of these particles changes, and the atmosphere acts as a shield, limiting the signal in ground-based laboratories.

At the orbital altitude of the International Space Station, the atmosphere is gone, and the 'rain' falls unimpeded. Ultra-precise optical clocks could pick up shifts in fundamental constants caused by passing dark matter. If the particles' de Broglie wavelength is smaller than Earth's radius, a dipole pattern forms around the planet, which oscillates as the station moves. This creates a distinctive signal that's hard to mistake for noise.

Orbital clocks might place the tightest constraints yet on the properties of ultralight dark matter, and future nuclear clocks will extend the search even further.