Letters to Nature
Nature 412, 708-712 (16 August 2001) | doi:10.1038/35089010; Received 23 April 2001; Accepted 12 June 2001
Origin of the Moon in a giant impact near the end of the Earth's formation
Robin M. Canup1 & Erik Asphaug2
- Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 426, Boulder, Colorado 80302, USA
- Department of Earth Sciences, University of California, Santa Cruz, California 95064, USA
Correspondence to: Robin M. Canup1 Correspondence and requests for materials should be addressed to R.M.C. (e-mail: Email: robin@boulder.swri.edu).
Abstract
The Moon is generally believed to have formed from debris ejected by a large off-centre collision with the early Earth1, 2. The impact orientation and size are constrained by the angular momentum contained in both the Earth's spin and the Moon's orbit, a quantity that has been nearly conserved over the past 4.5 billion years. Simulations of potential moon-forming impacts now achieve resolutions sufficient to study the production of bound debris. However, identifying impacts capable of yielding the Earth–Moon system has proved difficult3, 4, 5, 6. Previous works4, 5 found that forming the Moon with an appropriate impact angular momentum required the impact to occur when the Earth was only about half formed, a more restrictive and problematic model than that originally envisaged. Here we report a class of impacts that yield an iron-poor Moon, as well as the current masses and angular momentum of the Earth–Moon system. This class of impacts involves a smaller—and thus more likely—object than previously considered viable, and suggests that the Moon formed near the very end of Earth's accumulation.