This week, Jacob Kloos, a PhD Student here at PVL discusses exciting new research he has just published in the Journal of Geophysical Research, Planets. In his work, Jake found that the famous permanently shadowed regions (PSRs) are surrounded by seasonally shadowed regions (SSRs) which turn out to have important implications for the lunar water exosphere and the amount of water available in different locations at different times of the year - they're not what you would expect! Above, one of the key findings of the research: maps of the lunar poles showing these SSRs.
By Jacob Kloos
Over the past few decades, the north and south polar regions of Earth’s moon have garnered much attention within the field of planetary science. In addition to becoming prime targets for robotic and human exploration, the lunar poles have also been the subject of an increasing number of scientific studies. What makes these areas so intriguing for science and exploration? The answer lies in their unique illumination environments.
Unlike the Earth which rotates on an axis tilted 23.5 degrees from the ecliptic normal, the spin axis of the Moon is tilted only 1.5 degrees, ensuring that the Sun is always near the horizon for an observer at one of the poles. The low axial tilt of the Moon, coupled with its heavily heavily cratered surface, produce complex illumination patterns at high latitudes, giving rise to extremes in both sunlight and shadow: areas that are high in elevation may experience near-continuous sunlight, while some low-lying basins are in permanent shadow. Although no regions on the Moon (or indeed in the solar system) have yet been discovered which can claim the ethereal title of “peaks of eternal light,” some regions, like the rim of Shackleton crater near the South Pole, remain bathed in sunlight for 80-90% of the year. Such areas are attractive sites to send a solar-powered rover.
The permanently shadowed regions (PSRs), which are in many cases directly adjacent to the near-continuously illuminated regions, are not only interesting from an exploration perspective, but also from a scientific perspective. As a direct consequence of not receiving direct sunlight, and because the Moon lacks a substantial atmosphere to sequester and transport heat, permanently shadowed regions are among the coldest places in the solar system, enabling them to trap and store volatiles such as water across geologic periods of time. These volatile deposits constitute a valuable resource for scientific study as they would be well preserved and largely protected from chemical weathering; as such they could provide valuable insight into the delivery of water to the inner solar system - in particular to the Earth-Moon system. As for exploration, water could be extracted in-situ by future explorers, and could provide a source of potable drinking water, breathable air or perhaps even rocket fuel if broken down into its constituent components.