Space Research Scientists Detect Water Ice in Moon Simulation

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Researchers tested measuring instruments and robots with the Polar Explorer campaign that can detect water ice on the Moon—under realistic conditions in the LUNA facility in Cologne (Germany), which is filled with moon dust simulant.

That there is water ice on the Moon is very likely. For example, in the South Pole region, where some craters have never seen sunlight. In these "cold traps," water ice may have been hiding for billions of years. Can humans use the water when they return to the Moon? Is the water solidly frozen in the lunar dust, chemically bound, or are there even layers of ice in the shadowed craters, on the surface, or underground?

There are many open questions. To get closer to the answers, the German Aerospace Center (DLR), together with several universities, tested how water on the Moon can be detected. The setting was the LUNA facility in Cologne (Germnay), where robotic and astronaut lunar missions can be prepared under realistic conditions.

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What Exactly is LUNA?

LUNA offers researchers a 7,500 sq ft area filled with lunar dust simulant. The material is strikingly similar to the regolith on the Moon, making it suitable for testing measuring tools and robots. "If we want to find and map water ice on the Moon, we need to be very mobile on the surface. That’s why we used two rovers equipped with special instruments. The combination of different methods offers advantages and proved to be particularly reliable here as well," explains Nicole Schmitz from the DLR Institute for Space Research. She co-led the Polar Explorer campaign with the LUNA team. The first results are already in: the researchers were successful—they found and mapped the simulated water ice in the LUNA Hall. The collected data is now being analyzed in detail.

How Did Water Get to the Moon?

"Scientists used to agree that the Moon was bone-dry," explains planetary researcher Nicole Schmitz. "Now we have many indications that there is water ice on the Moon—and at the same time, we have many unanswered questions. That’s extremely exciting." The ice could have arrived with impacts from comets or icy micrometeorites. Or it could originate from an interaction between solar wind and lunar dust. Perhaps it is a remnant of early lunar volcanism. "If we solve this mystery, we will also learn more about the evolutionary history of the solar system," says Nicole Schmitz.

How Do You Detect Water Ice in A Moon Simulation?

The Deep-Floor-Area in the LUNA Hall is three meters deep and filled to the brim with regolith. It not only hides a lava cave but also countless acrylic glass elements. For the radar instruments used, these appear as pure water ice hidden beneath the surface: the contrast between pure ice and lunar regolith is very similar to that between acrylic glass and LUNA regolith. This is precisely what radar detects. A seismic source (PASS—Portable Active Seismic Source) also generated measurable vibrations during the Polar Explorer campaign, making the simulated water ice in the ground visible. For this purpose, a fiber optic cable was laid beforehand, which could also be deployed on the Moon. The structure formed its own geophysical network for so-called Distributed Acoustic Sensing (DAS). Tiny deformations of the fiber optic cable indicate ground movements that provide insights into the structure of the subsurface.

How Did the Search Proceed?

Water has already been detected in lunar rock, for example, trapped in the crystal lattice of mineral grains or in volcanic glass. To detect the hydrogen in rock samples, researchers used a so-called LIBS (Laser-Induced Breakdown Spectroscopy).

• LIBS uses a pulsed laser to create a small plasma cloud from the sample material.
• The light from the plasma provides information about the elemental composition of the material.
• The LIBS is housed in a payload box, and a robotic arm positions it directly at the target.
• The robotic arm, in turn, belongs to LRU2 (Lightweight Rover Unit 2), a rover from the DLR Institute for Robotics and Mechatronics.

LRU2 can not only hold laser boxes with its equipment but also collect samples and execute and calculate its tasks autonomously. It forms a rover team with LRU1. For the Polar Explorer campaign, LRU1 pulled a trailer with ground-penetrating radar behind it, "scanning" the subsurface.

Linked with the camera data, researchers obtain a three-dimensional representation of the investigated area, both of the surface and the subsurface. During a lunar mission, the instruments would, of course, not be on a trailer but integrated within the rover itself.

Dress Rehearsal for A Complete Mission Concept

The campaign is based on a mission concept that researchers from DLR proposed to the European Space Agency (ESA). The mission concept could be selected to fly to the Moon in the future with the Argonaut lander. A model of the Argonaut lander is located in the LUNA Hall. It is a spacecraft designed to provide infrastructure systems, instruments, and resources. "As part of this mission concept, we have now brought all the elements together for the first time: the teams with the rovers and instruments tested the entire operational process. They demonstrated that all elements are ready and functioning," adds Nicole Schmitz.

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