By 
December 28th, 2023
Korea Moon orbiter.
Credit: KARI
One of the driving questions regarding future Moon exploration is what available resources lurk within lunar permanently shadowed regions (PSRs).
These locales never see direct sunlight and are illuminated only by secondary illumination – light reflected from nearby topography.
Trying to get to the literal bottom of PSRs and what if any water ice may be present is one task of the Korean Pathfinder Lunar Orbiter (KPLO), also known as Danuri.
A preliminary analysis of the floor of Shackleton crater from images acquired over multiple secondary illumination conditions “does not reveal indications of exposed surface ice, even though temperatures are constantly below 110K.”
The new work appears in the Journal of Astronomy and Space, the official publication of the Korean Space Science Society (KSSS), research led by Prasun Mahanti of the School of Earth and Space Exploration at Arizona State University in Tempe, Arizona.
ShadowCam instrument being lifted for mounting to the Korean Pathfinder Lunar Orbiter satellite at the Korean Aerospace Research Institute in Daejeon, Korea.
Credit: Courtesy KARI
No observed evidence
“According to our Shackleton crater interior mapping from ShadowCam images, there is no observed evidence of thick ice deposits or surface ice that could be easily recognized by any relative brightness features observed in multiple illumination geometries,” the research paper explains.
“However, this analysis did not include the estimation of reflectance, nor did it involve reviewing all of the images of Shackleton in this preliminary study,” the researchers report.
A spectacular, specially produced near-ground level oblique view of the “Connecting Ridge” between Shackleton and Henson craters. The lunar south pole (SP) occurs on the rim of Shackleton crater. The ridge along the rim of the South Pole-Aitken impact basin is a potential Artemis landing site (001) and another (004) occurs on the rim of Shackleton crater. (Image credit: ETHZ\LPI\Valentin T. Bickel and David A. Kring)
Hypothesis
Mahanti and colleagues add that their hypothesis, in the context of water frost detections in Shackleton, “is that if ice or frost is present in Shackleton’s interior, then the concentrations are either below the threshold that results in an observable signature in ShadowCam images, or might be mixed with the regolith at the detected areas. At other places where surface temperatures are below 110K, water frost could be hidden in subsurface layers.”
Shackleton crater context, ShadowCam image and simulated secondary illumination image. (A) Shackleton crater near the south pole. The green
dashed line shows the map area for secondary illumination modeling. (B) Parts of the crater and PSR and a reference (yellow text) adopted in this work. (C) Mosaic of ShadowCam images showing the floor and wall (D) Secondary illumination model generated irradiance map, cropped to the PSR extent (yellow circular boundary). Colorbar in (C) and (D) shows ShadowCam radiance and model irradiance, respectively. PSR, permanently shadowed regions. Image credit: Prasun Mahanti, et al.
ShadowCam is a NASA-funded instrument hosted onboard the Korea Aerospace Research Institute (KARI) Korea Pathfinder Lunar Orbiter, built at Arizona State University, an instrument designed and led by Mark Robinson, a professor in Arizona State University’s School of Earth and Space Exploration.
By collecting high-resolution images of the Moon’s permanently shadowed regions, the goal of ShadowCam is to provide critical information about the distribution and accessibility of water ice and other volatiles at spatial scales (1.7 m/pixel) required to mitigate risks and maximize the results of future exploration activities.
For access to the paper – “Preliminary Characterization of Secondary Illumination at Shackleton Crater Permanently Shadowed Region from ShadowCam Observations and Modeling” – go to:
Posted in Space News
In my ever-so-humble opinion, much of the polar ice should be in the form of dirty frost. The water molecules arrive one at a time due to the very low density and can’t form solid ice but instead just stick wherever they hit. Interspersed with the water vapor will be large amounts of fine dust, levitated by solar UV charging in daylight so that it keeps floating until it loses its charge in a place where it never gets hit by enough UV again.
It seems likely that more dust than water arrives in the dark and cold traps, so that the frost is part of a fluffy, very black fine fuzz.