title: A permanent, asymmetric dust cloud around the Moon.
abstract: Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.
authors.affiliation: 1] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA [2] Department of Physics, University of Colorado, Boulder, Colorado 80309, USA [3] Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA.
authors.forename: M
authors.initials: M
authors.lastname: Horányi
authors.affiliation: 1] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA [2] Department of Physics, University of Colorado, Boulder, Colorado 80309, USA [3] Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Szalay
authors.affiliation: 1] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA [2] Department of Physics, University of Colorado, Boulder, Colorado 80309, USA [3] Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA.
authors.forename: S
authors.initials: S
authors.lastname: Kempf
authors.affiliation: Astronomy and Space Physics, University of Oulu, FI-90014 Oulu, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Schmidt
authors.affiliation: 1] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA [2] Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA [3] Max-Planck-Institut für Kernphysik, D-69117 Heidelberg, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Grün
authors.affiliation: Institut für Raumfahrtsysteme, Universität Stuttgart, Raumfahrtzentrum Baden Württemberg, 70569 Stuttgart, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Srama
authors.affiliation: 1] Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado 80303, USA [2] Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT), University of Colorado, Boulder, Colorado 80303, USA [3] Aerospace Engineering Sciences, University of Colorado, Boulder, Colorado 80309, USA.
authors.forename: Z
authors.initials: Z
authors.lastname: Sternovsky