Exploring the Moon's South Pole
Views of the Moon's South Pole
Fig. 1: Illumination. Lunar Reconnaissance Orbiter Camera Wide Angle Camera Mosaic from pole to 80°S.
Fig. 2: Topography. Lunar Orbiter Laser Altimeter color-shaded digital terrain model from pole to 80°S
Most of the Moon’s polar regions are not visible from Earth, so our knowledge of the lunar south pole comes from spacecraft. The Lunar Reconnaissance Orbiter (LRO) has been collecting data of the poles since 2009, and much of what we understand about the polar environment is derived from illumination (images) and topography (surface features).
Islands in the Dark
Darkness surrounds illuminated peaks between Shackleton crater (at right) and de Gerlache crater (out of scene left). Image width 30 kilometers, Lunar Reconnaissance Orbiter Camera Narrow Angle Camera image M1195011983LR [NASA/GSFC/Arizona State University]
At the south pole of the Moon, elevated peaks are illuminated by the Sun, which is always near the horizon. Low-lying areas near the poles, however, remain in darkness all year. Areas that never receive direct illumination are called permanently shadowed regions (PSRs) and are very cold. The interior of Shackleton crater is a PSR.
Water-Ice Hidden in the Dark
Image of Shackleton crater. Image width 30 kilometers, Lunar Reconnaissance Orbiter Camera Narrow Angle Camera image M1195011983LR.
Fig. 1: Maximum surface temperatures. The Diviner thermal radiometer onboard LRO has mapped the maximum surface temperatures at the poles. Temperatures below 110 K are favorable for the formation of water-ice deposits.
Fig. 2: Water-ice detections (cyan) in PSRs (blue). Li and coauthors (2018) mapped spectral detections of water-ice at the surface using the Moon Mineralogy Mapper (M3) instrument that flew on the Chandraayan-1 spacecraft.
The temperatures at the surface in lunar PSRs are extremely low (<110 K / –267°F) where there is no direct sunlight. Molecules of water that encounter a PSR are frozen and trapped by the low temperatures, mixing into the lunar soil. Over time, significant pockets of waterbearing soil have been created.
Probing the Dark and Cold
Image of northwest rim of Cabeus crater Image width 75 kilometers, Lunar Reconnaissance Orbiter Camera Narrow Angle Camera image M109937747 [NASA/GSFC/Arizona State University]
Fig. 1: LCROSS impact site. Shaded relief of the south pole region from LRO’s Lunar Orbiter Laser Altimeter [NASA/GSFC]; orange indicates extent of PSRs
In 2009, the Lunar Crater Observation and Sensing Satellite (LCROSS) intentionally impacted a PSR in Cabeus crater near the lunar south pole, and detected water-ice and other volatiles hiding in the dark and cold. The impact site occurred in the shadowed area below the bottom center of the image, which shows the northwest rim of Cabeus crater.
Mining the Moon for Water-Ice
Orbiter Laser Altimeter color-shaded digital terrain model from pole to 88°S with areas of low (safe) slopes (less than 10°) overlain in gray, and large PSRs shown in bright pink. An ideal location to explore on the surface would have high topography (and better illumination year-round), safe low slopes, and access to nearby PSRs. The red-orange colored ridge between Shackleton and de Gerlache craters has been identified as one possible site to land and operate on the surface.
Exploring the Moon’s south pole will require planning for the low-angle solar illumination as well as low surface temperatures. Water-ice is a key driver of future exploration, it can be used as consumables (air or water) or rocket propellant. We still need to know more about the form and distribution of the Moon’s water-ice reserves; maps of the illumination conditions, terrain, and PSR areas help to identify the best places on the surface to explore. In order to use polar water-ice, the lunar soil inside PSRs will need to be processed to extract water in the desired form, possibly mined by robotic rovers.
Exploring the Moon's South Pole
Malapert Mountain, located at the lunar south pole, is a potential site for future missions due to the nearly constant sunlight and the ideal conditions for line-of-sight communications with Earth. [NASA/GSFC/Arizona State University]
Dr. Julie Stopar, staff scientist, studies the places where water-ice could melt and interact with rocks and soil. When impacts occur in cold polar regions, water-ice can be exposed and melt. Near the lunar surface, the presence of water or water vapor can convert rocks to other mineral phases, for example, iron rusting. Finding the results of mineral alteration on the surface could help explorers identify buried water-ice. This is one of the ways the imagery and data gathered by the Lunar Reconnaissance Orbiter Camera (LROC) is preparing us to go back to the Moon to stay.
Dr. Julie Stopar
Staff Scientist
Dr. Julie Stopar, staff scientist, studies the places where water-ice could melt and interact with rocks and soil. When impacts occur in cold polar regions, water-ice can be exposed and melt. Near the lunar surface, the presence of water or water vapor can convert rocks to other mineral phases, for example, iron rusting. Finding the results of mineral alteration on the surface could help explorers identify buried water-ice. This is one of the ways the imagery and data gathered by the Lunar Reconnaissance Orbiter Camera (LROC) is preparing us to go back to the Moon to stay.
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