In 1972, astronauts from the Apollo 17 mission brought home more than 200 pounds of lunar rocks and soil.
Now researchers from the University of Chicago are using just a tiny bit of the sample to answer big questions about the Moon's composition and the formation of precious resources like water and helium.
From a single grain of dust, the scientists analyzed the chemistry of the Moon’s soil.
The team's understanding of the lunar environment, published in Meteoritics & Planetary Science , will support the efforts of future astronauts as they prepare for longer-duration explorations to the Moon.
“We’re analyzing rocks from space, atom by atom,” said Jennika Greer , the paper’s first author and a PhD student at the Field Museum and University of Chicago. “ It’s the first time a space-weathered sample has been studied like this. We’re using a technique many geologists haven’t even heard of."
That technique, known as atom probe tomography (APT), is one most commonly used in the manufacturing and analysis of steel and nanowires.
The APT system combines a mass spectrometer and a microscope. Electric pulses remove ions from a sample surface, allowing the atoms to then be imaged and identified.
To study the tiny grain, Greer used a focused beam of charged atoms to carve a very sharp, very tiny tip — only a few hundred atoms wide — into its surface.
As Greer zapped atoms off of the sample one by one, the particles struck a detector plate — at different speeds depending on the weight of the element. Lighter elements like hydrogen reached the detector first; heavier elements like iron reached the detector later.
By measuring the times between the laser firing and the atom striking the detector, Greer's instrument determined the atom type and its charge. Using a color-coded point for each atom and molecule, Greer reconstructed the data in three dimensions and made a nanoscale 3D map of the Moon dust.
In the tiny grain, Greer identified pure iron, water, and helium, which formed through the interactions of the lunar soil with the space environment. Such resources could help future astronauts sustain their activities on the Moon.
Greer also discovered evidence of space weathering, a change in the lunar materials due to the harsh, atmosphere-less environment.
“Because of something like this, we understand what the environment is like on the Moon. It goes way beyond what astronauts are able to tell us as they walk on the Moon," said Greer. "This little grain preserves millions of years of history."
In an edited interview below, Greer tells Tech Briefs about her team's findings, and the discovery that surprised her the most.
Tech Briefs: What inspired you to use APT – a method most commonly used in steel and nanowire manufacturing?
Jennika Greer: Our group started working with APT in the study of presolar nanodiamonds. These nanodiamonds, found in meteorites, are only a few nanometers across, and there are very few instruments that can analyze something that small. After using the atom probe, it’s very easy to be inspired by how you can use it to work on other projects, like these space-weathered grains.
Tech Briefs: What can be learned from a single grain of dust?
Jennika Greer: In a single grain, we can see the full suite of space weathering products. There is a rim that is made up partly from other lunar rocks that have been vaporized and redeposited on this grain; there are pure iron particles that change how the surface looks to remote sensing techniques; and there is solar wind implanted in the outermost surface. We can get a holistic view of a process that affects all airless bodies in the solar system from a tiny volume.
Tech Briefs: What was the most surprising or unexpected finding?
Jennika Greer: There is actually quite a bit of water in these samples! The water isn’t in bubbles, but exists as single molecules within the rock. This, and other hydrogen species, could be a valuable resource for a future lunar base.
Tech Briefs: Why is it so important to the study the lunar surface?
Jennika Greer: Astronauts specifically collected these soils, and through them we can learn about space weathering. Space weathering is a process that affects all airless bodies, including asteroids, and alters the surface so that the spectra we see with telescopes is different from that in the lab. Through laboratory studies of space-weathered samples, we are better able to interpret the data from telescopes and other remote sensing techniques.
Tech Briefs: What’s next regarding this work?
Jennika Greer: APT is a great technique for precious samples, as very little is consumed during analysis. There are several sample return missions active right now (Chang'e-4 to the moon, Hayabusa 2, and Osiris-REX to asteroids), and this would be a great technique to apply to these samples once they come back to Earth.
What do you think? Share your questions and comments below.