Artemieva, NA

Bland, PA

de Souza Filho, CR

Meteoritics and Planetary Science

Spiral - Imperial College Digital Repository

THE PRODUCTION RATE OF SMALL CRATERS ON EARTH, AND THE EXPECTED CRATER POPULATION IN SOUTH AMERICA.  P.A. Bland1, N.A. Artemieva2 and C.R. de Souza Filho3. 1Dept. Earth Sci. & Eng., Imperial College, London SW7 2AZ, UK. E-mail: p.a.bland@imperial.ac.uk. 2Inst. Dyn. Geospheres, Lenin-sky Pr., 38, Bldg.6, 119334, Moscow, Russia. 3Instituto de Geo-ciências, Universidade Estadual de Campinas, Campinas, Brazil.  Introduction: The craters preserved on the lunar mare pro-vide a record of the rate of impacts and the impactor size distribu-tion, over a mass range of ~10-1016kg, for the 3.2-3.5Ga since the mare basalts were emplaced [1]. Constructing a similar curve for number of impacts over a given mass at the Earth’s surface is complicated: the atmosphere disrupts meteoroids [2], and craters are removed by erosion and tectonism, or infilled. Since the ter-restrial small crater record is incomplete, we chose to scale the known impact rate at the upper atmosphere to a flux at the sur-face by modelling how a given bolide behaves in the atmosphere. Methodology: Most semianalytical approaches have consid-ered impactors as strengthless liquid-like objects: so-called ‘pan-cake’ models, in which clouds of fragments are modelled as a continuous, lower-density, deformed impactor [2-4]. Unfortu-nately, these models are not capable of reproducing the cratering behaviour of fragmented asteroids. In contrast, Artemieva and co-workers [6-8] have developed a model that calculates motion, aerodynamic loading, and ablation, for each individual particle or fragment in a disrupted impactor. This approach allows us to pre-dict a mass- velocity-distribution at the Earth’s surface for a given impactor at the top of the atmosphere. The flux at the upper atmosphere has recently been constrained over a large portion of the mass range [9-16]. Our modelling data allows the flux curve for the upper atmosphere to be scaled to an impact rate at the Earth's surface, for objects from meteorites to 1km asteroids [17]. Discussion: Based on our calculated surface flux curve, we estimate that over the last 100Ma the continent of South America has experienced impacts producing ~18 craters >10km, of which 12 would be >20km, and 1 ~75km. Over a 1Ma period we would expect a single 1km crater, and ~200 Campo del Cielo events. The number of confirmed craters in Brazil (Araguainha, Serra da Cangalha, Riachão, Vargeão) is much lower than we would expect given the large area of the country, and the area and age of geologically stable target. It is interesting that the size-frequency distribution of possible craters derived from recent remote sens-ing data is a very close match to the expected population, given estimated impact rate, and the area and age of Brazilian basins. References: [1] Hartmann W.K. et al. (1981) in Basaltic Volcanism on the Terrestrial Planets (Pergamon Press, New York), 1050. [2] Melosh H.J. (1981) in Multi-Ring Basins (Per-gamon Press, New York), 29. [3] Chyba C.F. et al. (1993) Nature 361, 40. [4] Hills J.G., Goda M.P. (1993) Astron. J. 105, 1114. [5] Artemieva N.A., Shuvalov V.V., Shock Waves 5, 359 (1996). [6] Artemieva N.A., Shuvalov V.V. (2001) J. Geophys. Res. 106, 3297. [7] Shuvalov V.V. et al. (2000) SSR 34, 49. [8] Halliday I., Griffin A.A., Blackwell A.T. (1996) MAPS 31, 185. [9] Nem-tchinov I.V. et al. (1997) Icarus 130, 259. [10] Brown P. et al. (2002) Nature 420, 294. [11] ReVelle D.O. (1997) Ann. NY Acad. Sci. 822, 284. [12] Morbidelli A. et al. (2002) Icarus 158, 329. [13] Rabinowitz D. et al. (2000) Nature 403, 165. [14] Stuart J.S. (2001) Science 294, 1691. [15] Harris A.W. (2004) in Proc. As-teroids, Comets, Meteors 2002. [16] Bland P.A., Artemieva N.A. (2003) Nature 424, 288. 67th Annual Meteoritical Society Meeting (2004) 5164.pdf

The production rate of small craters on Earth and the expected crater population in South America

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