Pergamon www.elsevier.com/locate/asr A& Space Rex Vol. 28, No. 10, pp. 1527-1532,200l 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain 0273-l 177/01 $20.00 + 0.00 PII: SO273.1177(01)00365-9 LABORATORY INVESTIGATIONS OF THE TEMPERATURE DEPENDENCE OF HYPERVELOCITY IMPACT CRATERING IN ICE zyxwvutsrq I.D.S. Grey, M.J. Burchell and N.R.G. Shrine Unit for Space Sciences and Astrophysics, University of Kent at Canterbury, Canterbury, Kent, CT2 7NR, UK. ABSTRACT Laboratory investigations by hypervelocity impact cratering in water ices are usually carried out at temperatures of approximate 250-265 K. However, icy surfaces in the Solar System are typically at lower temperatures. Accordingly a study of the temperature dependence of cratering in water ice has been carried out using a two-stage light gas gun firing mm-sized projectile at 5 - 6 km s-l. The temperature of the water ice targets has been varied in the range 152-253 K. The variation in depth, diameter and volume of the resulting craters is presented as a function of temperature. 0 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved. INTRODUCTION Spectra data from the satellites of Jupiter and the other outer planetary bodies have indicated that ice dominates the surfaces of many of the Satellites beyond 4 AU from the Sun (Grundy, et al 1999). For this reason, much work on understanding the cratering process on these satellites has been carried out on HZ0 ice of temperatures 250-265 K (Cintala, et al 1985 and Kato, et al 1995) which is the most abundant. CO* ice has also been investigated by Burchell et al (1998). However, these target temperatures do not represent typical surface temperatures on the icy satellites. Encrenez (1995) tabulated from either observed data from Voyager or estimated from calculation that the surface temperatures of the icy satellites ranged from 122 K on Callisto to as little as 37 K on Pluto and Charon. Work by Lange and Al-n-ens (1986) investigated crater morphologies at temperatures 81 and 257 K but at low projectile velocities (SO.64 km s-l). An investigation to see how crater morphologies alter with target temperature for hypervelocity impacts could prove important as any changes in crater morphology will help to better understand and develop current scaling laws further. Rheologic properties of H20 ice at low temperatures could give clues to why the cratering process produces morphologies obtained in this study. The mechanical deformation and compressive strength of polycrystalline lh Hz0 ice has been investigated by a number of groups and will be discussed later in the paper. EXPERIMENTAL PROCEDURE Distilled water was boiled so to expel any dissolved gases. The water was then allowed to cool before siphoning into a specially created container that consisted of a thermally conductive bottom and insulated top and sides and placed in a freezer. Heat sources in the upper portions of the container cause the water to freeze from the bottom up. Ice was created in this method so to allow any dissolved gas remaining in the water to escape and to allow the ice once formed to expand naturally without restriction. Stresses within the ice are therefore kept to a minimum. Polycrystalline lh Hz0 ice targets, 10 cm in depth and 18 cm in diameter were created using this method. The targets once deep enough are removed from the 1527