Unveiling the Faustini permanently shadowed region of the Moon
The Diviner instrument has played a significant role in characterizing the Permanently Shadowed Regions (PSRs) near the poles of the Moon. Areas near the poles can be permanently shadowed from the Sun and receive only scattered light from surrounding terrain. Temperatures of the ground within these regions can become frigid (less than -280° F/-170° C) with Diviner observing temperatures as low as -420° F (-250° C) in isolated areas, colder than the surface of Pluto and nearly 150° F (80° C) colder than the Earth's coldest recorded temperatures on the East Antarctic Plateau.
The ShadowCam instrument, aboard the Korea Pathfinder Lunar Orbiter (KPLO/Danuri), is a very sensitive camera designed to image the PSRs with a pixel resolution of about 1.7 meters (5 feet). ShadowCam completed its one year primary mission earlier this year and has continued operating in an extended mission. Diviner observations, along with LRO companion instruments Lunar Orbiter Laser Altimeter (LOLA) and Miniature Radio-Frequency (Mini-RF), have been contributing to understanding and interpreting the new images from ShadowCam. A new study, combining these datasets has been published in the Planetary Science Journal revealing the interior of the Faustini PSR. Using photo mosaics created from ShadowCam images, and elevation maps from LOLA data, the terrain within Faustini has been mapped and characterized.
Faustini crater near the Moon’s south pole hosts one of the largest PSRs on the Moon and is thought to have a high potential to host water ice and other types of ices. Radar remote sensing can be sensitive to the presence of ice; however, with the help of ShadowCam imagery, areas that are bright in radar on the floor of Faustini crater are seen to be areas where rocks have been excavated from the subsurface by impacts. While ShadowCam images suggest rocks (and not ice) dominate the radar bright signal in Faustini, Diviner shows that ice could still be stable there. Diviner also shows that the average and maximum temperatures are colder on the north half of the floor. The colder area has the potential to host a variety of ices such as ices formed from frozen hydrogen cyanide, sulfur dioxide, and ammonia. Isolated areas that receive extremely low levels of light are cold enough to contain carbon dioxide ice (“dry” ice). These colder areas are found to have smoother surfaces than the warm portion of the floor. This is mostly due to differences in how long impact craters are retained in these areas. Because crater retention is linked to the mechanical properties of the substrate, the observed surface texture variation could be due to differences in the distribution or concentration of ices.
For more details see: Williams, J.-P., P. Mahanti, M. S. Robinson, R. V. Wagner, M. Chertok, N. Schörghofer, E. Mazarico, B. W. Denevi, S. Li, and D. A. Paige (2024) The Fausini permanently shadowed region on the Moon, Planetary Sci. Journal, 5, 209,
Figure: (a) An image of the Faustini PSR created from a mosaic of multiple KPLO ShadowCam images. (b) The maximum temperatures of the floor of Faustini crater within the PSR observed by Diviner showing warmer temperatures in the southern half of the floor and colder temperatures in the northern half of the floor. The south pole is to the low left of the figures. Axes show distances in kilometers from the south pole
