The Moon’s Hidden Side Is No Longer a Mystery. NASA’s Camera Is to Blame

Last June, China successfully completed a historic mission. It became the first country to bring back samples from the far side of the moon. We call it that because it is the part of the moon’s hemisphere that we cannot see from Earth (because the moon takes as much time to rotate as it does to move forward around the Earth). In any case, this is the most inhospitable region of the moon, and until recently, its “darkness” was the moon’s greatest mystery. That is now a thing of the past.

The need to discover the unknown. Since 2009, NASA’s Lunar Reconnaissance Orbiter has been taking detailed photographs of almost the entire surface of the Moon, but there was a problem: the camera wasn’t sensitive enough to see anything in the permanently shadowed craters.

Sometimes it’s not pitch black. Sometimes sunlight reflects off the ground and hits a crater, then bounces up, like onto South Korea’s Danuri orbiter as it passes overhead. Other images are also lit by groundshine: sunlight reflecting off the Earth toward the moon. That’s enough to light up the shadowed craters a bit.

But something more was needed.

ShadowCam. Behind that name lies the secret to NASA’s success in revealing to us what this kind of molten blackness has been like up until now. In essence, we’re looking at a kind of “night vision goggles,” a tool NASA gave Danuri when he arrived on the moon. The camera uses advanced technology to detect detail in areas that don’t receive direct sunlight, like polar craters.

Its ability to take high-resolution images in the lunar penumbra allows us to study the geology of these dark regions and search for possible ice deposits, which will significantly contribute to our understanding of the lunar environment and future exploration and colonization efforts. In fact, as we can see, the images it has provided us with are an unprecedented view of our neighboring satellite.

Unheard of sensitivity. This may be the device’s key feature. ShadowCam is more than 200 times more sensitive to light in shadowed regions than other lunar cameras. It takes images of the dark surface based on “Earthshine,” which is the reflection of light from our planet shining on the moon. The camera also uses sunlight reflected off the moon’s own mountains and ridges.

Saturation. This was their main problem, especially in bright regions. Last year, for example, NASA tried using a camera to photograph Shackleton Crater, which has only three spots that receive sunlight about 90% of the year. Those sunlit parts eventually turned white. The solution? Mosaics.

When the oversaturated, sunlit areas of ShadowCam are replaced with images from other orbiting lunar cameras, the entire scene can be captured in stunning detail like never before.

The invisible becomes visible. Prasoon Mahanti, ShadowCam’s deputy principal investigator, told the New York Times this week that when scientists saw the first images, their reaction was relief that the instrument was working as intended. “Then the emotion immediately took over,” he explains.

In fact, it was announced in March that in some places and at certain times, the shadows aren’t even that dark. At a conference, researchers working on the camera reported that the indirect light could be compared to “comfortable indoor lighting levels.” In other words, astronauts visiting these regions might not need to carry flashlights to see where they’re going, though bright lights and long shadows could still be a problem.

The mystery of water. Of course, behind all this effort is the big question that ShadowCam and the other instruments are trying to answer: Where is the water on the moon? A key element for future astronauts who spend long days on the satellite. Although the camera’s images show white patches, none of them yet look like ice.

Most of the bright spots are rocks, exposed rock, or recent craters. Other possibilities include water being covered in dust or trapped in minerals in the rocks. Whatever the case, with ShadowCam, it seems the final mystery is close to being solved.

Image | Dan Meinek, NASA/KARI/Arizona State University

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