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Fifty years after NASA’s Apollo mission, moon rocks still have secrets to uncover


The moon and meteorite samples consist of a variety of rocks, some of which look like pebbles and some that look like lava rocks found in Hawaii. The samples have different chemical compositions and represent different geological and astronomical events throughout the history of the Moon. A better understanding of the atoms in the samples provides a better understanding of how the solar system formed and what mineral resources are available to fuel space travel to Mars. Credit: Genevieve Martin/ORNL, US Department of Energy

How did we get from stardust to where we are today? This is the question that NASA scientist Andrew Needham has pondered throughout his career.

In 1969, Apollo 11 astronauts were the first to set foot on the moon and study its surface. During the next several Apollo missions, which ended in 1972, they returned moon rocks for scientific research to unlock the secrets of the universe.

Scientists knew that the rocks contained clues to the origins of the solar system as well as minerals that could be important in driving space travel beyond the moon. But at that time, in-depth analysis was hampered by the low stock of rock samples and the lack of advanced research technology.

Now, nearly 50 years later, Needham is studying those same rocks using characterization tools and techniques light years ahead of their predecessors. One such technique is neutron scattering.

At the Department of Energy’s High Flux Isotope Reactor, or HFIR — located at Oak Ridge National Laboratory — Needham studied a small group of moon and asteroid samples using the newly renamed MARS, short for Advanced Multimodal Imaging Neutron Imaging Station (MARS). At the time of the experiments, Needham worked with Jacobs as Contractor Division Manager for Astromaterials Curation at NASA’s Johnson Space Center in Houston.

Neutrons, like X-rays, are used to search within materials to identify and measure elements and their atomic arrangement. Neutrons can also provide insights into how materials can be harnessed to improve technology. In Needham’s case, he’s using them to study the mineral content inside Apollo samples and meteorites, looking for evidence of early planetary formations and where water was stored on the Moon.

“In the past decade, there has really been a renewed interest in looking for water in places like the moon,” he said. “We used to think that the moon was very dry, but now we know that water is trapped within the mineral content of these rocks. Studies have shown that water may accumulate near the poles of the moon through the collision events that are evidenced in these samples. .

“If humans are going to explore the Moon further, and Mars one day, we need to figure out ways to fuel ourselves and survive off Earth, rather than constantly supplying everything from the surface of the Earth, which is very difficult and very expensive.

“Understanding the composition of these rocks, where the hydrogen atoms are located, and how they are stored and transported, really helps us understand the Moon throughout its history and up to the present day, and how we can use this information to travel even further.”

Fifty years after NASA's Apollo mission, moon rocks still have secrets to uncover

At left, neutron imaging data from moon rocks collected during the NASA Apollo missions highlight differences in color based on how different parts of the sample, including different minerals, absorb neutrons. On the right, more details of the sample’s interior can be seen, including areas shaded in purple, which can help researchers determine where the material slices were made to extract only elements of interest and preserve rare moon rocks for further studies. Credit: Yuxuan Zhang/ORNL, US Department of Energy

The Apollo mission samples Needham is studying include impact breccias, which consist of dust, rock fragments and melted particles mixed together after meteorites were drawn into gravity wells and bombarded the lunar surface. Needham explained that when meteorites struck nearly 4 billion years ago, the impacts combined and stirred up a mixture of material from the moon’s surface as well as its deep inner layers. In essence, he said, even a single moon rock can contain a large number of information from multiple astronomical events.

Neutrons are ideally suited to study the chemical composition of Apollo moon rocks: they can pass through almost any material, but light elements like hydrogen will block or deflect them on contact.

Using the MARS instrument, which specializes in creating radiological images similar to clinical X-rays, Needham loaded the samples into containers positioned on a rotating platform that allowed 360-degree measurements of the rock to be taken. Regions where hydrogen atoms are likely to be present are marked within the rock as the neutron beam passes through the sample.

In the neutron images, the hydrogen atoms appear as brightly colored spots in contrast to the rest of the sample. The harder it is for a neutron to pass through an element, the brighter that element appears, creating a color scale that corresponds to different elements. The 360-degree measurements can then be used to create 3D models of the rocks that can in turn be compared to the results of other research techniques, such as X-rays and electron microscopy.

Additional neutron measurements of the moon rocks were taken at HFIR’s sister facility, the Spallation Neutron Source, or SNS, which is powered by a world-leading 1.55-megawatt pulsating beam accelerator. The SNS’s SNAP instrument is specialized in studying materials under high pressures, but is also currently serving as a testbed for VENUS, a state-of-the-art SNS imaging instrument that will finish construction in 2024. Together, MARS and VENUS will provide researchers with the most complete set of imaging capabilities available in an enterprise. one in the world.

“These are precious specimens, so we can’t slice and cube them as much as we want,” Needham said. “Neutrons help us see inside samples so we can make the most accurate slices to expose just the regions of interest. And only neutron imaging makes the hydrogen atoms visually pop, letting you know, ‘Oh!’ This is something I want to consider. ”

A month after his experiments with the MARS instrument, Needham started a new position: a research scientist at NASA’s Goddard Space Flight Center as a pollution control scientist for the agency’s Artemis program. Artemis represents the next step in human space exploration. Its goal is to establish a sustainable presence on the Moon as a step toward sending the first astronauts to Mars.

“Apollo only landed on a few select regions of the Moon,” Needham said. “The Artemis missions will be bringing back samples from many different regions, samples that are likely to be rich in hydrogen and other important minerals. Part of my job will be to ensure that these samples are preserved as perfectly as possible for future research, just like scientists who have the foresight of 50 years To do the same for the samples we are examining today.

“The types of analyzes available at Oak Ridge are going to be really important to Artemis. It’s part of a long-term plan to bring next-generation technologies to the next generation of samples that we’ll be returning.”

Provided by Oak Ridge National Laboratory

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