The lunar dust samples collected by Apollo 11 have different shapes at the nanoscale, and they absorb and scatter light very differently.
The Moon constantly changes its appearance in the night sky, and in addition to the different phases of the Moon, it also looks different colors from Earth. This is known to be caused by the moon’s different positions in its orbit, as well as by the smog in the Earth’s atmosphere. A new study has found that the shape and size of the dust on the moon also affects its color.
The National Institute of Standards and Technology (NIST) has invented a new technique to measure the tiny, previously unmeasurable lunar dust on the moon, learning the shape and size of those particles on only the nanometer scale. This study accurately measured the shape of 25 small particles within a sample of lunar dust collected by Apollo 11 in 1969.
Scientists have been studying dust for many years, but this study is the first to measure small particles as small as 400 nanometers in diameter. It turned out that the different shapes of the particles absorbed and scattered light very differently.
The study says the method of measuring lunar nano-dust is complex, first to mix them with other media material, like making an omelet first to mix the ingredients evenly, and then thread it on a stick like baking a chicken. The process even uses straws and tailor’s pins.
NIST researcher Ed Garboczi says, “The process is complicated because they are randomly distributed, vary in size and shape, so you can’t measure one small particle alone, you have to measure many particles together and get statistics.”
They mixed the dust sample with an epoxy (Epoxy) material and dropped it on the outside of a thin pipette, in order to pick up a thin layer. The thin layer is then removed, threaded onto a large-headed needle used for tailoring, and embedded inside an X-ray nano-computed tomography (XCT) instrument for imaging. This process takes several hours.
The researchers first get the layered scan data, use software to superimpose the layers into a three-dimensional image, and then convert the image into a form with spatial voxel (voxel) coordinates that can distinguish whether each voxel is located inside or outside the particle. In a two-dimensional image, the computer uses a pixel to piece together the image. In a three-dimensional image, a small spatial point is called a voxel, which is like a new word for volume – pixel union.
By analyzing a voxel, the image of each particle is gradually pieced together, and after computer calculations, the shape of each particle is finally obtained. These voxels were in turn sent to computer software in separate files to analyze the scattering of light from visible to infrared wavelengths by these particles.
The results show that different shapes of lunar nanoparticles absorb different colors of light, such as spherical and ellipsoidal particles, even if they are the same size, the light absorbed varies greatly.
The researchers say the finding not only better explains the moon’s color and brightness, but also helps improve satellite systems that track weather changes. The satellite cameras used by these systems use the moon as a calibration source. Follow-up studies, which will measure more small particles, will find a clearer link between the shape of the moon’s nano-dust and light scattering.
The study was published April 27 in the Institute of Electrical and Electronics Engineers (IEEE) Geoscience and Remote Sensing Letters.
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