Dust and rocks residing on the surface of the moon take a beating in space. Without a protective magnetosphere and atmosphere like Earth’s, the lunar surface faces continual particle bombardment from solar wind, cosmic rays, and micrometeoroids. This constant assault leads to space weathering.
New NASA-funded research by Georgia Tech offers fresh insights into the phenomenon of space weathering. Examining Apollo lunar samples at the nanoscale, Tech researchers have revealed risks to human space missions and the possible role of space weathering in forming some of the water on the moon.
Most previous studies of the moon involved instruments mapping it from orbit. In contrast, this study allowed researchers to spatially map a nanoscale sample while simultaneously analyzing optical signatures of Apollo lunar samples from different regions of the lunar surface — and to extract information about the chemical composition of the lunar surface and radiation history.
The researchers recently published their findings in Scientific Reports.
“The presence of water on the moon is critical for the Artemis program. It’s necessary for sustaining any human presence and it’s a particularly important source for oxygen and hydrogen, the molecules derived from splitting water,” said Thomas Orlando, Regents’ Professor in the School of Chemistry and Biochemistry, co-founder and former director of the Georgia Tech Center for Space Technology and Research, and principal investigator of Georgia Tech’s Center for Lunar Environment and Volatile Exploration Research (CLEVER).
Building on a Decade of Lunar Science Research
As a NASA SSERVI (Solar System Exploration Research Virtual Institute), CLEVER is an approved NASA laboratory for analysis of lunar samples and includes investigators from multiple institutes and universities across the U.S. and Europe. Research areas include how solar wind and micrometeorites produce volatiles, such as water, molecular oxygen, methane, and hydrogen, which are all crucial to supporting human activity on the moon.
Georgia Tech has built a large portfolio in human exploration and lunar science over the last decade with two NASA Solar System Exploration Research Virtual Institutes: CLEVER and its predecessor, REVEALS (Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces).
Studying Moon Samples at the Nanoscale Level
Georgia Tech’s labs are world-renowned, particularly for analyzing surfaces and semiconductor materials. For this work, the Georgia Tech team also tapped the University of Georgia (UGA) Nano-Optics Laboratory run by Professor Yohannes Abate in the Department of Physics and Astronomy. While UGA is a member of CLEVER, its nano-FTIR spectroscopy and nanoscale imaging equipment was historically used for semiconductor physics, not space science.
“This is the first time these tools have been applied to space-weathered lunar samples, and it’s the first we’ve been able to see good signatures of space weathering at the nanoscale,” says Orlando.
Normal spectrometers are at a much larger scale, with the ability to see more bulk properties of the soil, explains Phillip Stancil, professor and head of the UGA physics department.
The UGA equipment enabled the study of samples “in tens of nanometers.” To illustrate how small nanoscale is, Stancil says a hydrogen atom is .05 nanometers, so 1 nm is the size of 20 atoms if placed side by side. The spectrometers provide high-resolution details of the lunar grains down to hundreds of atoms.
“We can look at an almost atomistic level to understand how this rock was formed, its history, and how it was processed in space,” Stancil says.
“You can learn a lot about how the atom positions change and how they are disrupted due to radiation by looking at the tiny sample at an atomistic level,” says Orlando, noting that a lot of damage is done at the nanoscale level. They can determine if the culprit is space weathering or from a process left over during the rock’s formation and crystallization.
Finding Radioactive Damage, Evidence of Water
The researchers found damage on the rock samples, including changes in the optical signatures. That insight helped them understand how the lunar surface formed and evolved but also provided “a really good idea of the rocks’ chemical composition and how they changed when irradiated,” says Orlando.
Some of the optical signatures also showed trapped electron states, which are typically missing atoms and vacancies in the atomic lattice. When the grains are irradiated, some atoms are removed, and the electrons get trapped. The types of traps and how deep they are, in terms of energy, can help determine the radiation history of the moon. The trapped electrons can also lead to charging, which can generate an electrostatic spark. On the moon, this could be a problem for astronauts, exploration vehicles, and equipment.
“There is also a difference in the chemical signatures. Certain areas had more neodymium (a chemical element also found in the Earth’s crust) or chromium (an essential trace mineral), which are made by radioactive decay,” Orlando says. The relative amounts and locations of these atoms imply an external source like micrometeorites.
Translating Research to Human Risks on the Moon
Radiation and its effects on the dust and lunar surface pose dangers to people, and the main protection is the spacesuit.
Orlando sees three key risks. First, the dust could interfere with spacesuits’ seals. Second, micrometeorites could puncture a spacesuit. These high-velocity particles form after breaking off from larger chunks of debris. Like solar storms, they are hard to predict, and they’re dangerous because they come in at high-impact velocities of 5 kilometers per second or higher. “Those are bullets, so they will penetrate the spacesuits,” Orlando says. Third, astronauts could breathe in dust left on the suits, causing respiratory issues. NASA is studying many approaches for dust removal and mitigation.
Mapping the Moon: Going from Nanoscale to Macroscale
The next research phase will involve combining the UGA analysis tools with a new tool from Georgia Tech that will be used to analyze Apollo lunar samples that have been in storage for over 50 years.
“We will combine two very sophisticated analysis tools to look at these samples in a level of detail that I don’t think has been done before,” Orlando says.
The goal is to build models that can feed into orbital maps of the moon. To get there, the Georgia Tech and UGA team will need to go from nanoscale to the full macro scale to show what’s happening on the lunar surface and the location of water and other key resources, including methane, needed to support humanity’s moon and deep-space exploration goals.
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