In order to observe the lunar sodium exosphere out to one-half degree around the Moon, we designed, built and installed a small robotically controlled coronagraph at the Winer Observatory in Sonoita, Arizona. Observations are obtained remotely every available clear night from our home base at Goddard Space Flight Center or from Prescott, Arizona. We employ an And over temperature-controlled 1.5 angstrom wide narrow-band filter centered on the sodium D-2 line, and a similar 1.5 angstrom filter centered blueward of the D-2 line by 3 angstrom for continuum observations. Our data encompass lunation in 2015, 2016, and 2017, thus we have a long baseline of sodium exospheric calibrated images, During the course of three years we have refined the observational sequence in many respects. Therefore this paper only presents the results of the spring, 2017, observing season. We present limb profiles from the south pole to the north pole for many lunar phases. Our data do not fit any power of cosine model as a function of lunar phase or with latitude. The extended Na exosphere has a characteristic temperature of about 2250-6750 K, indicative of a partially escaping exosphere. The hot escaping component may be indicative of a mixture of impact vaporization and a sputtered component.

We present an analytic expression to represent the lunar surface temperature as a function of Sun-state latitude and local time. The approximation represents neither topographical features nor compositional effects and therefore does not change as a function of selenographic latitude and longitude. The function reproduces the surface temperature measured by Diviner to within +/- 10 K at 72% of grid points for dayside solar zenith angles of 100 degrees. The analytic function is least accurate at the terminator, where there is a strong gradient in the temperature, and the polar regions. Topographic features have a larger effect on the actual temperature near the terminator than at other solar zenith angles. For exospheric modeling the effects of topography on the thermal model can be approximated by using an effective longitude for determining the temperature. This effective longitude is randomly redistributed with 1 sigma of 4.5 degrees. The resulting roughened analytical model well represents the statistical dispersion in the Diviner data and is expected to be generally useful for future models of lunar surface temperature, especially those implemented within exospheric simulations that address questions of volatile transport. (c) 2014 Elsevier Inc. All rights reserved.

Our knowledge about the lunar environment is based on a large volume of ground-based, remote, and in situ observations. These observations have been conducted at different times and sampled different pieces of such a complex system as the surface-bound exosphere of the Moon. Numerical modeling is the tool that can link results of these separate observations into a single picture. Being validated against previous measurements, models can be used for predictions and interpretation of future observations results. In this paper we present a kinetic model of the sodium exosphere of the Moon as well as results of its validation against a set of ground-based and remote observations. The unique characteristic of the model is that it takes the orbital motion of the Moon and the Earth into consideration and simulates both the exosphere as well as the sodium tail self-consistently. The extended computational domain covers the part of the Earth's orbit at new Moon, which allows us to study the effect of Earth's gravity on the lunar sodium tail. The model is fitted to a set of ground-based and remote observations by tuning sodium source rate as well as values of sticking, and accommodation coefficients. The best agreement of the model results with the observations is reached when all sodium atoms returning from the exosphere stick to the surface and the net sodium escape rate is about 5.3 x 10(22) s(-1). (C) 2013 Elsevier Inc. All rights reserved.

Helium is one of the first elements clearly identified in the lunar exosphere (Hoffman, J.H., Hodges, R.R., Johnson, F.S., Evans, D.E. [1973]. Proc. Lunar Sci. Conf. 3, 2865-2875). Apollo 17 measured the He density at the surface during four lunations. It confirmed the expected day to night asymmetry of the He exosphere with a maximum density near the dawn terminator on the nightside. Few years later, the first detection of Mercury's He exosphere was successfully obtained by Mariner 10 (Broadfoot, AL., Shemansky, D.E., Kumar, S.[1976]. Geophys. Res. Lett. 3, 577-580). These observations highlighted similar global distribution of the He exosphere at Mercury and at the Moon, but also significant differences that have never been convincingly explained. In this paper, we model the He exosphere at the Moon and Mercury with the same approach. The energy accommodation of the exospheric He particles interacting with the surface can be roughly constrained using Apollo 17 and Mariner 10 measurements. Neither a low energy accommodation, as suggested by Shemansky and Broadfoot (Shemansky, D.E., Broadfoot, A.L. [1977]. Rev. Geophys. 15, 491-499), nor a full energy accommodation, as suggested by Hodges (Hodges Jr., R.R.[1975]. The Moon, 14, 139-157), can fit all the observations. These observations and their modeling suggest a diurnal variation of the energy distribution of the He ejected from the surface that cannot be explained satisfactorily by any of the present theories on the gas-surface interaction in surface-bounded exospheres. (C) 2011 Elsevier Inc. All rights reserved.