In a first, Mercury's missing lithium found through invisible magnetic fingerprints

Yahoo

4 days ago

For decades, scientists believed lithium might be hiding in Mercury's ultra-thin atmosphere, or exosphere, but every attempt to find it came up empty.
Now, in a groundbreaking study, researchers have finally confirmed its presence, but not by spotting the lithium atoms directly. Instead, they detected its electromagnetic fingerprint. Using a trick involving magnetic waves, scientists have managed to pick up the unmistakable signature of lithium ions as they were swept up by the solar wind.
"During our survey, we identified signatures of pick-up ion cyclotron waves that could be attributed to freshly ionized lithium," said Daniel Schmid, first author of the study and a researcher at the Austrian Academy of Sciences.
This is the first time lithium has been identified on Mercury, and the discovery provides crucial evidence that Mercury's surface is still chemically active and shaped by constant meteoroid bombardment.
Meteorites bring out Mercury's hidden lithium
Mercury's exosphere is not like Earth's atmosphere. It is incredibly thin and fragile, with atoms so far apart they rarely interact. Over the years, missions like Mariner 10 and MESSENGER have confirmed the presence of elements like hydrogen, sodium, potassium, and iron.Since potassium and sodium belong to the same family of alkali metals as lithium, scientists had long assumed the possibility of lithium. However, there was a catch. It was conjectured that lithium is likely present in extremely low concentrations, making it nearly impossible to detect with traditional instruments such as particle detectors or ground-based telescopes.
Hence, Schmid and his team decided to look at the problem from a different angle. Rather than searching for the lithium atoms themselves, they studied how lithium ions interact with the solar wind. When meteoroids crash into Mercury's surface, they vaporize parts of the crust, releasing neutral lithium atoms.
These atoms quickly lose electrons when exposed to intense ultraviolet radiation from the sun, becoming positively charged lithium ions. This is where things get interesting. As the solar wind captures fresh lithium ions, it triggers a kind of electromagnetic disturbance known as ion cyclotron waves (ICWs).
Data from MESSENGER mission helped detect ICWs
These waves have a very specific frequency that depends on the mass and charge of the ion involved, almost like a radio station tuned specifically to lithium. By digging through four years' worth of magnetic field data collected by the MESSENGER spacecraft, the study authors found 12 separate events where these lithium-tuned waves appeared.
Each event lasted just tens of minutes, revealing brief windows when lithium was being ejected into the exosphere. These weren't random occurrences. The team ruled out slow processes like solar heating and focused instead on sudden, violent events—meteoroid impacts.When meteoroids measuring between 13 to 21 centimeters in radius, and weighing 28 to 120 kilograms, slam into Mercury at speeds of up to 110 kilometers per second, they create mini-explosions. These impacts can heat material to temperatures as high as 2,500–5,000 Kelvin, launching lithium atoms into space. Surprisingly, a single impact can vaporize 150 times more material than the mass of the meteoroid itself."The detection of lithium and its association with impact events strongly supports the hypothesis. It demonstrates that meteoroids not only deliver new material but also vaporize existing surface deposits, releasing volatiles into the exosphere and sustaining a dynamic cycle of supply," Schmid explained, while speaking to Phys.org.
The wave method can reveal more secrets
Previous theories assumed that because Mercury is so close to the sun, most of its volatile elements, including lithium, should have been lost long ago. However, MESSENGER has already shown that Mercury still retains many volatiles.The current study strengthens a new idea that meteoroid bombardments have been continuously enriching the planet's surface, acting like a delivery service for elements and releasing them into space through high-energy impacts.
The implications reach far beyond Mercury. The same wave-based detection method could be used to study other airless or thin-atmosphere bodies like the moon, mars, and even asteroids, where direct detection of rare elements is difficult.
'This has important implications for understanding surface chemistry and long-term space weathering across the inner solar system," Schmid added. He and his team hope that future missions with more sensitive instruments will help verify and expand on these findings.
The study is published in the journal Nature Communications.
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