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Letters to Nature

Nature 420, 294-296 (21 November 2002) | doi:10.1038/nature01238; Received 9 October 2002; Accepted 21 October 2002

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The flux of small near-Earth objects colliding with the Earth

P. Brown1,2, R. E. Spalding3, D. O. ReVelle2, E. Tagliaferri4 & S. P. Worden5

  1. Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada
  2. Los Alamos National Laboratory, PO Box 1663, MS J577, Los Alamos, New Mexico 87545, USA
  3. Sandia National Laboratory, Org. 5740, MS 0973, PO Box 5800, Albuquerque, New Mexico 87185, USA
  4. ET Space Systems, 5990 Worth Way, Camarillo, California 93012, USA
  5. Directorate of Operations, United States Space Command, Peterson Air Force Base, Colorado Springs, Colorado 80914-3190, USA

Correspondence to: P. Brown1,2 Correspondence and requests for materials should be addresses to P.B. (e-mail: Email: pbrown@uwo.ca).

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Asteroids with diameters smaller than ~50–100 m that collide with the Earth usually do not hit the ground as a single body; rather, they detonate in the atmosphere1. These small objects can still cause considerable damage, such as occurred near Tunguska2, Siberia, in 1908. The flux of small bodies is poorly constrained, however, in part because ground-based observational searches pursue strategies that lead them preferentially to find larger objects3. A Tunguska-class event—the energy of which we take to be equivalent to 10 megatons of TNT—was previously estimated to occur every 200–300 years, with the largest annual airburst calculated to be ~20 kilotons (kton) TNT equivalent (ref. 4). Here we report satellite records of bolide detonations in the atmosphere over the past 8.5 years. We find that the flux of objects in the 1–10-m size range has the same power-law distribution as bodies with diameters >50 m. From this we estimate that the Earth is hit on average annually by an object with ~5 kton equivalent energy, and that Tunguska-like events occur about once every 1,000 years.

  1. Department of Physics and Astronomy, University of Western Ontario, London, Ontario N6A 3K7, Canada
  2. Los Alamos National Laboratory, PO Box 1663, MS J577, Los Alamos, New Mexico 87545, USA
  3. Sandia National Laboratory, Org. 5740, MS 0973, PO Box 5800, Albuquerque, New Mexico 87185, USA
  4. ET Space Systems, 5990 Worth Way, Camarillo, California 93012, USA
  5. Directorate of Operations, United States Space Command, Peterson Air Force Base, Colorado Springs, Colorado 80914-3190, USA

Correspondence to: P. Brown1,2 Correspondence and requests for materials should be addresses to P.B. (e-mail: Email: pbrown@uwo.ca).