This image from NASA’s Lunar Reconnaissance Orbiter (LRO) depicts lunar swirl Reiner Gamma, a bright patch amid the otherwise dark Oceanus Procellarum mare. While visible from a backyard telescope, LRO’s view from orbit reveals tendrils that extend for several hundred kilometers. (Image: NASA/Goddard Space Flight Center/Arizona State University)
ST. LOUIS — Have you ever looked at the Moon through a telescope and noticed strange, bright swirls on its surface? These mysterious patterns, known as lunar swirls, have puzzled scientists for years. Now, thanks to some clever lab experiments, scientists might have an answer to this lunar mystery — lava!
Lunar swirls are like nature’s abstract art gallery on the Moon. These light-colored, twisting patterns can stretch for hundreds of miles across the lunar landscape. They’re so striking that even backyard astronomers can spot them with a decent telescope. So, what causes these cosmic doodles, and why do they stay so bright when the rest of the Moon’s surface tends to darken over time?
Recent studies have shown that rocks in the swirls are magnetic, acting like tiny shields against the constant barrage of solar wind particles hitting the Moon. This protective effect keeps the swirls light-colored while surrounding areas darken due to chemical reactions caused by those particle impacts.
Here’s the catch: the Moon doesn’t have a magnetic field today. So, how did these rocks become magnetized in the first place? That’s the question that Michael J. Krawczynski, an associate professor at Washington University in St. Louis, set out to answer.
“Impacts could cause these types of magnetic anomalies,” Krawczynski explains in a media release, referring to the possibility that iron-rich meteorites striking the Moon might be responsible. “But there are some swirls where we’re just not sure how an impact could create that shape and that size of thing.”
Instead, in the Journal of Geophysical Research: Planets, Krawczynski and the team focused on another intriguing possibility: what if the magnetism comes from below the surface?
“Another theory is that you have lavas underground, cooling slowly in a magnetic field and creating the magnetic anomaly,” Krawczynski says.
Methodology: How Did Scientists Examine the Moon?
To test this idea, Krawczynski and lead author Yuanyuan Liang conducted experiments simulating conditions on the Moon. Their work centered on a mineral called ilmenite, which is common on the Moon but not particularly magnetic on its own. However, under the right conditions, ilmenite can react to form tiny particles of iron metal – and that’s where things get interesting.
On Earth, rocks often contain a highly magnetic mineral called magnetite, which makes them easy to magnetize. On the Moon, however, it’s a different story.
“A lot of the terrestrial studies that have focused on things with magnetite are not applicable to the Moon, where you don’t have this hyper-magnetic mineral,” Krawczynski points out.
Key Results
The team’s experiments showed that in a lunar-like environment, ilmenite could produce magnetizable iron particles. Interestingly, they found that smaller grains of the mineral were more effective at creating strong magnetic fields.
“The smaller grains that we were working with seemed to create stronger magnetic fields because the surface area to volume ratio is larger for the smaller grains compared to the larger grains. With more exposed surface area, it is easier for the smaller grains to undergo the reduction reaction,” Liang explains.
These findings support the idea that slowly cooling magma beneath the Moon’s surface could be responsible for creating the magnetic anomalies that produce lunar swirls.
“Our analog experiments showed that at lunar conditions, we could create the magnetizable material that we needed. So, it’s plausible that these swirls are caused by subsurface magma,” Krawczynski reports.
Discussion & Takeaways
Understanding the origin of lunar swirls is more than just satisfying our curiosity about pretty patterns. It could help scientists piece together the Moon’s history, including whether it once had a magnetic field like Earth’s. This knowledge could even shed light on how the surfaces of planets and moons interact with the space environment around them.
The research also has practical applications for future lunar exploration. NASA plans to send a rover to a famous lunar swirl called Reiner Gamma in 2025 as part of its Lunar Vertex mission. Krawczynski’s work could help interpret the data from that mission and others like it.
“If you’re going to make magnetic anomalies by the methods that we describe, then the underground magma needs to have high titanium,” Krawczynski notes. “We have seen hints of this reaction creating iron metal in lunar meteorites and in lunar samples from Apollo. But all of those samples are surface lava flows, and our study shows cooling underground should significantly enhance these metal-forming reactions.”
For now, lab experiments like these are our best window into the underground processes that might be creating lunar swirls.
“If we could just drill down, we could see if this reaction was happening. That would be great, but it’s not possible yet. Right now, we’re stuck with the surface,” Krawczynski concludes.
