Lunar cold traps: Effects of double shielding

V. Carruba et A. Coradini, Lunar cold traps: Effects of double shielding, ICARUS, 142(2), 1999, pp. 402-413
Citations number
Categorie Soggetti
Space Sciences
Journal title
ISSN journal
0019-1035 → ACNP
Year of publication
402 - 413
SICI code
This paper deals with the problem of water permanence on the surface of the Moon Possible zones where water ice can survive are called cold traps (K. Watson, B. C. Murray, and H. Brown 1961, J. Geophys. Res. 66, 3033-3045). T hese are zones of the Moon permanently obscured where the temperatures are low enough to preserve ice far billions of years. In this work we developed a model for the topographic temperatures of complex craters whose shape wa s approximated by a capsized frustum of a circular right cone. Double-shade d areas were simulated by embedding a small hemispherical crater in the sha dowed part of the previous one. Their temperatures were calculated using th e R. R. Hedges, Jr. (1980, Proc. Lunar Planet. Sci. Conf. 11th, 2463-2477) model. First we verified that our results were in agreement with those of p revious models. Our results confirm those obtained by J. R. Salvail and F. P. Fanale (1994, Icarus 111, 441-445), and in agreement with Hedges (1980), we found that the lowest temperatures are reached by Tycho-like craters th at are the larger and shallower among the examined cases. When small crater s are embedded in the shaded area of larger ones, their temperatures are lo w enough to preserve other volatiles like CO2 (Hodges 1980). In particular, if we consider double-shaded areas in Blot-like craters, the temperatures are lower than 103 K in a shell of almost 20 degrees around the poles, thus allowing the preservation of ices. For geometrical reasons a hemispherical crater embedded in the bottom of a Biot-like crater cold remain in the sha dowed area for latitude values lower than those reached by an analogous cra ter embedded in Sosigene or Tycho-like craters. Therefore the latitudinal r adius of polar frost caps could be greater than that predicted by previous models that did not consider double-shaded areas. However double shielding occurs in only a fraction of the secondary craters; therefore, in this case eventual deposits of ice would be of smaller dimensions compared with the case of primary shielding. Analysis of the Clementine radar data (S. Nozett e, C. L. Lichtenberg, P. Spudis, R. Bonner, W. Ort, E. Malaret, M. Robinson , and E. hi. Shoemaker 1996, Science 274, 5292-5300) and the Lunar Prospect or neutron spectrometer data seems to be consistent with the presence of wa ter ice in very low concentrations across a significant number of craters, thus confirming the old hypothesis of Watson et ai. (1961). (C) 1999 Academ ic Press.