Discovery of Lithium on Mercury Revealed by Electromagnetic Waves

In a groundbreaking study published in the journal *Nature Communications* on July 20, 2025, researchers have confirmed the presence of lithium on Mercury, overturning decades of speculation about the elusive element in the planet's ultra-thin exosphere. This discovery is significant as it provides crucial evidence that Mercury's surface remains chemically active, continually shaped by meteoroid impacts.

For many years, scientists had theorized that lithium might exist in Mercury's atmosphere, but prior attempts to detect it directly yielded no results. Instead, the team, led by Daniel Schmid, a researcher at the Austrian Academy of Sciences, adopted a novel approach by detecting the electromagnetic signatures associated with lithium ions rather than the atoms themselves. According to Schmid, “During our survey, we identified signatures of pick-up ion cyclotron waves that could be attributed to freshly ionized lithium.” This method, which relies on magnetic wave analysis, allowed the researchers to identify 12 distinct events where these lithium-specific waves were recorded, suggesting that meteoroid impacts are a primary source of lithium ejection into the planet's exosphere.

Mercury's exosphere is a stark contrast to Earth's atmosphere; it is incredibly thin and composed of atoms that rarely interact due to their low density. Previous missions, including Mariner 10 and MESSENGER, confirmed the presence of other elements such as hydrogen and sodium, leading scientists to speculate about lithium's existence. However, the anticipated concentrations were so low that traditional detection methods proved ineffective.

The study reveals that when meteoroids impact Mercury—traveling at speeds of up to 110 kilometers per second—they can vaporize portions of the planet's crust. This process releases neutral lithium atoms, which subsequently lose electrons and become lithium ions when exposed to the sun’s ultraviolet radiation. This ionization triggers electromagnetic disturbances known as ion cyclotron waves (ICWs), which were detected using data collected by the MESSENGER spacecraft over a period of four years.

The research indicated that meteoroids measuring between 13 to 21 centimeters in radius can vaporize significant amounts of material, with one impact capable of ejecting 150 times the mass of the meteoroid itself. Schmid stated, “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.”

This finding challenges previous theories suggesting that Mercury had lost most of its volatile elements due to its proximity to the sun. Instead, it supports the notion that continuous meteoroid bombardment has contributed to the planet's volatile inventory, acting as a delivery system for elements. In extending the implications of their findings, the researchers highlighted that the same electromagnetic wave detection approach could be applied to other celestial bodies with thin atmospheres, including the Moon, Mars, and asteroids.

The study's results not only enhance understanding of Mercury's surface chemistry and its geological processes but also provide a framework for future research in planetary science. As Schmid noted, “This has important implications for understanding surface chemistry and long-term space weathering across the inner solar system.” The team advocates for upcoming missions equipped with more sensitive instruments to further explore these findings and their broader implications for planetary science across the solar system.