Lunar exploration: opening a window into the history and evolution of the inner Solar System

The lunar geological record contains a rich archive of the history of the inner Solar System, including information relevant to understanding the origin and evolution of the Earth-Moon system, the geological evolution of rocky planets, and our local cosmic environment. This paper provides a brief review of lunar exploration to-date, and describes how future exploration initiatives will further advance our understanding of the origin and evolution of the Moon, the Earth-Moon system, and of the Solar System more generally. It is concluded that further advances will require the placing of new scientific instruments on, and the return of additional samples from, the lunar surface. Some of these scientific objectives can be achieved robotically, for example by in situ geochemical and geophysical measurements and through carefully targeted sample return missions. However, in the longer term, we argue that lunar science would greatly benefit from renewed human operations on the surface of the Moon, such as would be facilitated by implementing the recently proposed Global Exploration Roadmap

Lunar resources: a review

There is growing interest in the possibility that the resource base of the Solar System might in future be used to supplement the economic resources of our own planet. As the Earth’s closest celestial neighbour, the Moon is sure to feature prominently in these developments. In this paper I review what is currently known about economically exploitable resources on the Moon, while also stressing the need for continued lunar exploration. I find that, although it is difficult to identify any single lunar resource that will be sufficiently valuable to drive a lunar resource extraction industry on its own (notwithstanding claims sometimes made for the 3He isotope, which are found to be exaggerated), the Moon nevertheless does possess abundant raw materials that are of potential economic interest. These are relevant to a hierarchy of future applications, beginning with the use of lunar materials to facilitate human activities on the Moon itself, and progressing to the use of lunar resources to underpin a future industrial capability within the Earth-Moon system. In this way, gradually increasing access to lunar resources may help ‘bootstrap’ a space-based economy from which the world economy, and possibly also the world’s environment, will ultimately benefit

A pre-Caloris synchronous rotation for Mercury

The planet Mercury is locked in a spin-orbit resonance where it rotates three times about its spin axis for every two orbits about the Sun. The current explanation for this unique state assumes that the initial rotation of this planet was prograde and rapid, and that tidal torques decelerated the planetary spin to this resonance. When core-mantle boundary friction is accounted for, capture into the 3/2 resonance occurs with a 26% probability, but the most probable outcome is capture into one of the higher-order resonances. Here we show that if the initial rotation of Mercury were retrograde, this planet would be captured into synchronous rotation with a 68% probability. Strong spatial variations of the impact cratering rate would have existed at this time, and these are shown to be consistent with the distribution of pre-Calorian impact basins observed by Mariner 10 and MESSENGER. Escape from this highly stable resonance is made possible by the momentum imparted by large basin-forming impact events, and capture into the 3/2 resonance occurs subsequently under favourable conditions.Comment: Nature Geosci., 201

Laboratory Analysis (Reflectance Spectroscopy) of Terrestrial Analogues

clinopyroxene, olivine, and plagioclase, are the most important constituents of the lunar surface, associated with oxides and rare apatite (e.g., Papike et al. 1991). Though olivine and pyroxene show clear spectral signature and well-defined crystal field absorption bands in the visible and near-infrared (Burns 1993), plagioclase is difficult to recognize, due to very low iron content in its crystal structure. In fact, even if it is widely acknowledged that plagioclase is one of the most important constituents of the lunar surface (Heisenger and Head 2006), its presence has been usually related to featureless spectra and interpreted as shocked plagioclase (Spudis et al. 1984; Bussey and Spudis 2000). Only recently, the spectrometers on board lunar missions (Spectral Profiler (SP), onboard Selene, and Moon Mineralogy Mapper (M3), onboard Chandrayaan), with very high spectral (6–8 and 10 nm, respectively) and spatial (500 and 100 m, respectively) resolution, recognize regions composed of crystalline plagioclase, detecting the plagioclase absorption band in the 1,250 nm spectral region (Ohtake et al. 2009; Pieters et al. 2009; Cheek et al. 2012). Analyzing the plagioclase absorption band depth, Ohtake et al. (2009) recognized areas dominated by plagioclase (plagioclase >98 %), defined pure anorthosite (PAN) regions, mostly in crater central peaks. However, to relate plagioclase absorption band to modal abundance and mineralogical composition can be a difficult task. In fact, on the Moon, several factors such as the mineral chemistry, the presence of different minerals that absorb in a narrow spectral range, the particle size, the space weathering, etc., act in unpredictable ways on the reflectance spectra. For these reasons, studying terrestrial analogues can be fundamental in order to analyze separately the different factors and then superimpose effects to each other