VALIDATION TESTS. E. Pierazzo, N. Artemieva, E.C. Baldwin, J. Cazamias, R. Coker, G.S. Collins, D.A. Crawford, T. Davison, K.A. Holsapple, K.R. Housen, D.G. Korycansky, K. Wunnemann, Planetary Science Inst., 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, USA (betty@psi.edu); Inst. Dyn. Geospheres, RAS, Leninsky Pr. 38, 119334 Moscow, Russia; University College London, Gower St., London WC1E 6BT, UK; Univ. of Alabama at Birmingham, Birmingham, AL 35294, USA; Los Alamos Nat. Labs., Los Alamos, NM 87545, USA; Imperial College London, London SW7 2AZ, UK; Sandia Nat. Labs., P.O. Box 5800, Albuquerque, NM 87185, USA; Univ. of Washington, Seattle, WA 98195, USA; The Boeing Company, Seattle, WA 98124, USA; Univ. of Calif. Santa Cruz, S. Cruz, CA 95064, USA; Natural History Museum, Humboldt-Univ., Berlin 10099, Germany.