Surficial water ice has been detected in the permanently shaded regions (PSRs) near the lunar poles. Water ice can be detected by its diagnostic absorption features of ice at 1.0, 1.25, 1.5, and 2.0 mu m, as well as high reflectance in the VIS region. However, the effects of particle size and shape, ice abundance, and phase angle on the VNIR spectra of ice mixtures remain poorly understood, posing a challenge for detections of water ice on the lunar surface. In this study, we measured the VNIR spectra of pure water ice and mixtures of water ice and a lunar highland regolith simulant (HRS). We investigated the effects of particle size of ice (0-250 mu m), particle shape of ice (angular vs. spherical), phase angle (0-105 degrees), and ice abundance (0-50 wt%) on the VNIR spectra of water ice and HRS mixtures from 350 to 2500 nm. Our results show that coarser ice particles exhibit stronger NIR absorptions and lower VIS reflectance, attributable to increased photon absorptions due to longer optical pathlengths. Similarly, the longer optical pathlengths of spherical particles relative to angular ones result in lower VIS reflectance. The forward scattering nature of water ice leads to increased VIS reflectance at high phase angles (>90 degrees), suggesting that high phase angles are optimal for lunar water ice detection. Phase angles have a negligible effect on the strength of the NIR absorptions of ice, especially when ice is present at low ice abundances (<20 wt%) in intimate mixtures with the HRS. Lastly, our findings suggest that the NIR absorptions near 1.25, 1.5, and 2.0 mu m rapidly deepen at very low ice concentrations (0-5 wt%). We also find a linear relationship between VIS reflectance and ice content in intimate mixtures with a HRS containing 0-50 wt% ice. The findings of this study offer a detailed framework for detecting and analyzing water ice on the lunar surface via VNIR spectroscopy.

Volatile organic molecules and a complex organic refractory material were detected on the Moon and on lunar samples. The Moon's surface is exposed to a continuous flux of solar UV photons and fast ions, e.g. galactic cosmic rays (GCRs), solar wind (SW), and solar energetic particles (SEPs), that modify the physical and chemical properties of surface materials, thus challenging the survival of organic compounds. With this in mind, the aim of this work is to estimate the lifetime of organic compounds on the Moon's surface under processing by energetic particles. We performed laboratory experiments to measure the destruction cross of selected organic compounds, namely methane (CH4), 4 ), formamide (NH2CHO), 2 CHO), and an organic refractory residue, under simulated Moon conditions. Volatile species were deposited at low temperature (17- 18 K) and irradiated with energetic ions (200 keV) in an ultra-high vacuum chamber. The organic refractory residue was produced after warming up of a CO:CH4 4 ice mixture irradiated with 200 keV H+ + at 18 K. All the samples were analyzed in situ by infrared transmission spectroscopy. We found that destruction cross sections are strongly affected (up to one order of magnitude) by the dilution of a given organic in an inert matrix. Among the selected samples, organic refractory residues are the most resistant to radiation. We estimated the lifetime of organic compounds on the surface of the Moon by calculating the dose rate due to GCRs and SEPs at the Moon's orbit and by using the experimental cross values. Taking into account impact gardening, we also estimated the fraction of surviving organic material as a function of depth. Our results are compatible with the detection of CH4 4 in the LCROSS eject plume originating from layers deeper than about 0.7 m at the Moon's South Pole and with the identification of complex organic material in lunar samples collected by Apollo 17 mission.