The sun cannot illuminate its interior: What is hidden in the dark craters of the polar regions of the moon? AI technology now enables clearer images of the dark areas: Using self-learning algorithms, an international team of researchers succeeded in sharpening previously blurred images and thus making small structures visible. The method is now to be applied to other craters in order to uncover geological features that could be of importance for future lunar missions. The dark craters are particularly in focus, as they likely contain frozen water supplies.
As is well known, there are extremely detailed images of the lunar surface. But so far certain places have literally remained in the dark: “Since the sunlight falls very flat near the north and south poles, it never reaches the bottom of some craters and depressions,” explains first author Valentin Bickel from the Max Planck Institute for Solar System Research in Göttingen . Only the shimmer of the stars and scattered light ensure weak lighting there. Long exposure times allowed NASA’s Lunar Reconnaissance Orbiter (LRO) to deliver images from the shadow craters – but they were largely unusable: “Since the spacecraft is in motion, the images are completely smeared,” explains co-author Ben Moseley from Oxford University. So far, it has hardly been possible to differentiate between real geological structures and noise.
Possible water reservoirs
So the darkness is a problem – but at the same time it is the cause of an exciting aspect of the crater: in the eternal night the temperatures are extremely low, so that frozen water could probably hold up there. The existence of such deposits was already proven by an action in which a probe from space fired a projectile at the shadowed south polar crater Cabeus. As confirmed by analyzes, the dust that was thrown up contained water. The substance is interesting not only from a scientific, but also from a practical point of view: For manned lunar missions, the water resources would be a valuable resource and the dark craters an important target.
In order to gain more detailed information about the topography and geology of the shadow craters, Bickel and his colleagues have now devoted themselves to the task of bringing more clarity into the existing LRO images. To do this, they have developed a self-learning computer algorithm that can sharpen the noisy recordings. In order to train the system to differentiate between actual structures and shake effects in images of the moon, the scientists used more than 70,000 LRO calibration images as well as information about the camera temperature and the trajectory of the space probe.
Boulders and mini-craters stand out
The training was successful: the system finally gave the LRO images a resolution of around one to two meters per pixel. The scientists have thus ensured five to ten times more detail than before. So far, they have sharpened the images of 17 shaded areas with areas between 0.18 and 54 square kilometers in the south pole region of the moon with their method. As a result, geological structures only a few meters in size emerged there. These include boulders or mini-craters in the shaded areas.
“With the help of the new images, it is now possible to understand the geology of the dark areas better than before,” says Moseley. The number and shape of the mini-craters allow conclusions to be drawn about the age of the surface structures. For example, the scientists discovered an unusually bright specimen in one of the investigated craters on the Leibnitz Plateau. “This coloration could indicate that this mini-crater is quite young,” says Bickel. Since such a fresh impact scar enables comparatively unadulterated insights into deeper layers of the subsurface, this point could be an interesting target for future missions, the researchers suggest. In addition, the insights into the topography could also have a practical use: Potential obstacles for a rover or astronauts become visible.
However, the new views were unable to provide any direct evidence of frozen water near the surface, say the scientists. As they explain, the moon water is unlikely to appear as a clearly visible light deposit on the surface. Presumably it is heavily mixed with rock and dust or slumbers hidden underground. In order to collect more information on the geological structures, the researchers now want to use their new method to investigate as many other shaded craters as possible. “In the current publication we wanted to show what our algorithm can do. Now we want to apply it as widely as possible, ”Bickel concludes.
Source: Max Planck Institute for Solar System Research, specialist article: Nature Communications, doi: 10.1038 / s41467-021-25882-z