title: Lunar formation. Dating the Moon-forming impact event with asteroidal meteorites.
abstract: The inner solar system's biggest and most recent known collision was the Moon-forming giant impact between a large protoplanet and proto-Earth. Not only did it create a disk near Earth that formed the Moon, it also ejected several percent of an Earth mass out of the Earth-Moon system. Here, we argue that numerous kilometer-sized ejecta fragments from that event struck main-belt asteroids at velocities exceeding 10 kilometers per second, enough to heat and degas target rock. Such impacts produce ~1000 times more highly heated material by volume than do typical main belt collisions at ~5 kilometers per second. By modeling their temporal evolution, and fitting the results to ancient impact heating signatures in stony meteorites, we infer that the Moon formed ~4.47 billion years ago, which is in agreement with previous estimates.
authors.affiliation: Southwest Research Institute and NASA Solar System Exploration Research Virtual Institute (SSERVI)-Institute for the Science of Exploration Targets (ISET), Boulder, CO, USA. bottke@boulder.swri.edu.
authors.forename: W F
authors.initials: WF
authors.lastname: Bottke
authors.affiliation: Institute of Astronomy, Charles University, V Holešovičkách 2, CZ-18000, Prague 8, Czech Republic.
authors.forename: D
authors.initials: D
authors.lastname: Vokrouhlický
authors.affiliation: Southwest Research Institute and NASA Solar System Exploration Research Virtual Institute (SSERVI)-Institute for the Science of Exploration Targets (ISET), Boulder, CO, USA.
authors.forename: S
authors.initials: S
authors.lastname: Marchi
authors.affiliation: Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA. SSERVI Center for Lunar Science Exploration, Houston, TX, USA.
authors.forename: T
authors.initials: T
authors.lastname: Swindle
authors.affiliation: Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Manoa, Honolulu, Hawai'i 96822, USA.
authors.forename: E R D
authors.initials: ER
authors.lastname: Scott
authors.affiliation: Department of Earth Sciences, Western University, London, ON, Canada.
authors.forename: J R
authors.initials: JR
authors.lastname: Weirich
authors.affiliation: Southwest Research Institute and NASA Solar System Exploration Research Virtual Institute (SSERVI)-Institute for the Science of Exploration Targets (ISET), Boulder, CO, USA.
authors.forename: H
authors.initials: H
authors.lastname: Levison