A single grain of Apollo Moon dust opens up a world of lunar science
A team of scientists set out to find a way to analyse Moon dust based on only a single grain of the material. The researchers reported their results in a new study that analyses a single grain of Moon dust gathered in 1972 by astronauts on the Apollo 17 mission. “We’re analysing rocks from space, atom by atom,” revealed Jennika Greer, a doctoral student in geophysical sciences at the University of Chicago. “It’s the first time a lunar sample has been studied like this. We’re using a technique many geologists haven’t even heard of.”
“We can apply this technique to samples no one has studied,” Philipp Heck, a curator at the Field Museum, said. “You’re almost guaranteed to find something new or unexpected. This technique has such high sensitivity and resolution, you find things you wouldn’t find otherwise and only use up a small bit of the sample.”
Researchers use the technique, called atom probe tomography, to learn more about the Moon’s history. For example, scientists can analyse samples to figure out how water and helium formed on the Moon. Both compounds could be useful resources for future landing missions, the first of which NASA is planning for 2024. In the sample of Moon dust – or regolith – that she analysed, Greer found water, helium, iron and even traces of weathering caused by the exposure of the regolith to harsh phenomena in space, including micrometeoroids and radiation.
To find those features she shaved a layer of a few hundred atoms of material from the surface – a sample much thinner than a sheet of paper, which is hundreds of thousands of atoms thick. Then she placed the sample inside an atom probe at Northwestern University in Illinois and used a laser to carefully peel individual atoms off the sample and crash them into a detector plate for analysis.
Coronal mass ejections (CMEs) aren’t known for being subtle: each event can fling huge amounts of the soup of charged particles called plasma off the Sun and out into the Solar System. In November 2018, as seen from Earth and certain spacecraft, the Sun seemed to be calm… but it wasn’t. It was experiencing what scientists call a ‘stealth’ coronal mass ejection. Conveniently, NASA’s Parker Solar Probe was completing its first close pass behind the Sun at the time, putting its instruments in a perfect position to see what was happening on 11 and 12 November during this usually cryptic event.
“If you’ve ever seen a CME image, you normally see a lot of activity in these images,” Kelly Korreck, a solar physicist at the Smithsonian Astrophysical Observatory, said. “You would see a large blowout; you would probably see one of these exploding. But there wasn’t much there.”
Even in some of the Parker Solar Probe data, it wasn’t obvious at first what was happening during the incident, Korreck said. “When we looked at this initially – just the thermal data – we didn’t necessarily think that there was a coronal mass ejection there.” But other observations targeting energetic particles did include the fingerprint of a shock, a phenomenon that usually accompanies a coronal mass ejection. Scientists could also confirm the probe was flying through a coronal mass ejection based on data its instruments were gathering about the magnetic field.
Seeing a stealth coronal mass ejection is a step in the right direction. “They’re something that we’re not traditionally able to see in the ways that we’ve previously detected coronal mass ejections,” Korreck said. “We’re starting to see hints of them with better and better telescope resolution.”