Discovery of interstellar dust entering the Earth's atmosphere

Abstract

ALL known asteroids and comets are believed to have been gravitationally bound to the Sun since they formed (together with the Sun and planets) from the solar nebula. This is because no such object has been observed with a speed exceeding the solar escape velocity, although some comets have been close to this limit¹. As comets are occasionally ejected from the Solar System, interstellar comets might be expected to arrive every few centuries, having been ejected from similar systems around other stars². The flux of interstellar dust into the Solar System should be much higher, but its detection poses significant technological challenges. Recently, the Ulysses spacecraft detected a population of dust particles near Jupiter, identified as being of interstellar origin on the basis of their speeds and trajectories^3,4. Here we report the radar detection of interstellar particles in the Earth's atmosphere. From intra-annual variations in particle flux, we infer the existence of two discrete sources, one associated with nearby A-type stars, and the other with the Sun's motion about the Galactic Centre. The data also suggest the presence of a third source, possibly associated with local B-type stars and young stellar clusters.