The surface of the Moon is a critical boundary that shapes our understanding of the Moon as a whole. All geologic mapping and remote sensing techniques utilize only the outermost portion of the Moon. Before leaving the Moon for study in our laboratories, all lunar samples that have been studied existed at or very near the surface. With the exception of the deeply probing geophysical techniques, our understanding of the interior of the Moon is derived from surficial, but not superficial, information, coupled with boundary of the lunar crust, it is the lower boundary layer of the tenuous lunar atmosphere and constitutes both a source and a sink for atmospheric gases. The surface is also where the Moon interacts with the space environment, causing changes in the physical nature of lunar materials, and provides a laboratory for the study of processes that occur on all airless bodies.

The data obtained remotely by the Galileo, Clementine, and Lunar Prospector missions, as well as data derived from lunar meteorites, have resulted in major changes to our understanding of global distributions of chemistry and rocks. This chapter summarizes the current understanding of this critical interface, the surface of the Moon, in its role as the lower boundary of the lunar atmosphere, the upper boundary of the crust, and the window through which we view, through remote sensing, the composition of the crust and the history of the Moon. In this post-Lunar Prospector time, the view of the Moon has changed, lending new perspectives to lunar samples and lunar processes. But the New View will likely remain in flux as we continue to digest the results from these recent space missions and move forward to a new era of lunar exploration.

Despite the freshness of our perspective, this is an important moment to capture, …

Understanding the Lunar Surface and Space-Moon Interactions

Plots of reflectance slope between 0402 and 0564 μm versus the intensity ratio between 0564 and 0948 μm are used to quantitatively define the mare, mare crater, upland, and bright upland crater spectral types previously presented by McCord et al (1972a) An additional spectral type, dark mantling material, has also been found Quantification of lunar spectral types allows direct comparison of the spectral units with geologic units established by the US Geological Survey, including the dark mantling material unit Unit age-color relationships are observed in the upland and mare crater spectral types However, explicit correlation in the maria between stratigraphy and color measurements is not apparent An empirical relationship is derived relating TiO2 content of the bulk lunar soils to the slope of the spectral curve between 0402 and 0564 μm The relationship is noted in both laboratory and telescopic measurements and is governed by optical absorption in the glassy material of the soils Hence the slope of the spectral curves (0402–0564 μm) may be useful as a new basis for establishing mappable geologic units on the moon Examples are presented for the mare regions

Application of Remote Spectral Reflectance Measurements to Lunar Geology Classification and Determination of Titanium Content of Lunar Soils

X-rays from solar system objects

A wide variety of solar system bodies are now known to radiate in the soft x-ray energy ( 10 keV) x-rays mainly result from the electron bremsstrahlung process. In this paper we present a brief review of the x-ray observations on each of the planetary bodies and discuss their characteristics and proposed source mechanisms. 1. INTRODUCTION The usually-defined range of x-ray photons spans 0.1-100 keV. Of this wide energy extent the soft x-ray energy band (<5 keV) is an important spectral regime for planetary remote sensing, as a large number of solar system objects are now known to shine at these wavelengths. These include Earth, Moon, Jupiter, Saturn, comets, Venus, Galilean satellites, Mars, Io plasma torus, and (of course) the Sun. Since Earth's thick atmosphere efficiently absorbs x-ray radiation at lower altitudes (<30 km, even for hard x-rays), x-rays can only be observed from space by high-altitude balloon-, rocket-, and satellite-based instruments. But to observe most of the soft x-ray band one has to be above ~100 km from Earth's surface. Terrestrial x-rays were discovered in the 1950s. The launch of the first x-ray satellite UHURU in 1970 marked the beginning of satellite-based x-ray astronomy. Subsequently launched x-ray observatories - Einstein, and particularly Rontgensatellit (ROSAT), made important contributions to planetary x-ray studies. With the advent of th el a sn dm p ic x- ry b -Chandra and XMM-Newton - the field of planetary x-ray astronomy is advancing at a much faster pace. Earth and Jupiter, as magnetic planets, are observed to emanate strong x-ray emissions from their auroral (polar) regions, thus providing vital information on the nature of precipitating particles and their energization processes in planetary magnetospheres [1,2,3]. X-rays from low latitudes have also been observed on these planets. Saturn sho ul d a p rc ex- y in tm w J ,although the intensity is expected to be weaker. Lunar x-rays have been observed from the sunlit hemisphere; and a small number of x-rays are also seen from the Moon's nightside [4]. Cometary x-rays are now a well-established phenomena; more than a dozen comets have been observed at soft x-ray energies [5,6]. The Chandra X-ray Observatory (CXO) has recently captured soft x-rays from Venus [7,8]. Martian x-rays are expected to be similar to those on Venus. More recently, using CXO [9] have discovered soft x-rays from the inner moons of Jupiter - Io, Europa, and probably Ganymede. The Io Plasma Torus (IPT) was also discovered recently

Soft X-ray emissions from planets, moons, and comets

A wide variety of solar system bodies are now known to radiate in the soft x-ray energy ( 10 keV) x-rays result mainly from the electron bremsstrahlung process. In this paper we present a brief review of the x-ray observations on each of the planetary bodies and discuss their characteristics and proposed source mechanisms.

P. Gorenstein

Papers

Results of the Apollo 15 and 16 X-Ray Fluorescence Experiment