Asteroids and fallen smaller meteorites are responsible for a lot of different things in our solar system. For instance, moondust. Space rocks striking the surface of the Moon have pulverized their surface into sharp dust that ranges in size down to nano-particles capable of irritating skin and damaging lungs. 

When not irritating astronauts, these tiny fragments are also responsible for giving the Moon its colors and defining how much light it reflects. In a new journal article in IEEE Xplore with first author Somen Baidya, researchers discuss how they used tiny X-ray wavelengths of light to examine the shape of particles just 400 nanometers across. Several hundred of these particles could fit across the diameter of a human hair! 

Just measuring these grains is remarkable. According to researcher Ed Garboczi: Since they are so tiny and because they only come in powders, a single particle needs to be separated from all the others.  They are too small to do that by hand, at least not in any quantity, so they must be carefully dispersed in a medium. The medium must also freeze their mechanical motion, in order to be able to get good XCT images. If there is any movement of the particles during the several hours of the XCT scan, then the images will be badly blurred and generally not usable. The final form of the sample must also be compatible with getting the X-ray source and camera close to the sample while it rotates, so a narrow, straight cylinder is best. 

Basically, they made fancy moondust popsicles, looked at them with X-rays, and got remarkable images of the dust grains’ shapes. Those shapes, depending on how round or elongated they are, give the Moon its colors. This final “what does each shape mean” work is ongoing. Today, we just want to celebrate that they measured the shapes. And if you’re into fancy high-tech imaging setups, now we are celebrating the spirit of the tinkerer. 

According to the release: The procedure involved stirring the Apollo 11 material into epoxy, which was then dripped over the outside of a tiny straw to get a thin layer. Small pieces of this layer were then removed from the straw and mounted on dressmakers’ pins, which were inserted into the XCT instrument.

More Information

NIST press release

“Optical Scattering Characteristics of 3-D Lunar Regolith Particles Measured Using X-Ray Nano Computed Tomography,” Somen Baidya et al., 2021 April 27, IEEE Geoscience and Remote Sensing Letters