Evidence for water ice on the Moon: Results for anomalous polar craters from the LRO Mini‐RF imaging radar

Abstract

[1] The Mini-RF radar instrument on the Lunar Reconnaissance Orbiter spacecraft mapped both lunar poles in two different RF wavelengths (complete mapping at 12.6 cm S-band and partial mapping at 4.2 cm X-band) in two look directions, removing much of the ambiguity of previous Earth-and spacecraft-based radar mapping of the Moon's polar regions. The poles are typical highland terrain, showing expected values of radar cross section (albedo) and circular polarization ratio (CPR). Most fresh craters display high values of CPR in and outside the crater rim; the pattern of these CPR distributions is consistent with high levels of wavelength-scale surface roughness associated with the presence of block fields, impact melt flows, and fallback breccia. A different class of polar crater exhibits high CPR only in their interiors, interiors that are both permanently dark and very cold (less than 100 K). Application of scattering models developed previously suggests that these anomalously high-CPR deposits exhibit behavior consistent with the presence of water ice. If this interpretation is correct, then both poles may contain several hundred million tons of water in the form of relatively "clean" ice, all within the upper couple of meters of the lunar surface. The existence of significant water ice deposits enables both long-term human habitation of the Moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant.

The Main Belt Comets and ice in the Solar System

“…Water ice has also been hypothesised to exist on the Moon in permanently shadowed craters near the poles (Spudis et al 2013;Hayne et al 2015), although a debate about alternative interpretations of data is on-going (Eke et al 2014;Haruyama et al 2013). Hydroxyl-and/or water-bearing materials are widely spread across the lunar surface (Pieters et al 2009).…”

The Miniature Radio Frequency instrument’s (Mini-RF) global observations of Earth’s Moon

“…One of these instruments, and the dominant focus of this study, is the Mini-RF hybrid polarization synthetic aperture radar. Mini-RF has built upon its predecessor, ChandrayaanMini-SAR (which observed almost exclusively the lunar poles [Spudis et al, 2010]), by observing ~67% of the lunar surface at Sband (12.6 cm), including ~99% of the North and South polar regions (±70° to ±90°) [McAdam et al, 2011;Cahill et al, 2012;Spudis et al, 2013] (FIGURE 2 and 3). This includes never before observed radar coverage of western Orientale, the farside Feldspathic Highlands Terrane (FHT), and the South Pole Aitken Terrane (SPA).…”

Bistatic radar observations of the Moon using Mini-RF on LRO and the Arecibo Observatory

“…One of its primary objectives was the collection of radar data in the permanently shadowed regions of the lunar poles sufficient to determine the presence and distribution of water ice. Monostatic Sband (12.6 cm) and X-band (4.2 cm) data collected by Mini-RF have been interpreted, using radar scattering models [Thompson et al, 2011], as consistent with the presence of water ice in at least 80 permanently shadowed polar craters [Spudis et al , 2013. While the monostatic scattering models are supportive of the presence of water ice, ambiguities do permit alternative interpretations [e.g., Fa A C C E P T E D M A N U S C R I P T 6 et al, 2011;Eke et al, 2014].…”