Magnetic Wave Study Detects Lithium in Mercury’s Exosphere for First Time Ever

Using a new technique based on magnetic-wave analysis, scientists have, for the first time, discovered lithium in the atmosphere of Mercury. Published in Nature Communications, the study constitutes the first detection of lithium around the smallest planet in our solar system. The exosphere of Mercury, Unlike thickened atmospheres, the thin shell of particles that constitutes Mercury's exosphere can render direct searching methods inadequate. Instead of searching for atoms, scientists analysed pick-up ion cyclotron waves—an electromagnetic fingerprint left behind when solar wind interacts with freshly ionised lithium. These faint signals finally confirmed lithium's long-speculated presence.

MESSENGER Data Reveals Lithium Traces from Meteoroid Impacts in Mercury's Exosphere

As per the Austrian Academy of Sciences, the research team led by Daniel Schmid reviewed four years of magnetic field data collected by NASA's MESSENGER spacecraft. Twelve short-lived events—each lasting mere minutes—revealed these lithium-specific wave signatures.

The waves are generated when solar ultraviolet radiation ionises lithium atoms, and temporary lithium wind blows the ionised atoms into space, which increases the speed of the formation of electromagnetic instabilities. These perturbations induce oscillations at a single cyclotron frequency, determined by the mass and charge of lithium (such that it is identified as lithium indirectly by magnetic measurements).

Lithium has been difficult to find, as the rare alkali metal is thinly scattered. The traditional particle detectors on Mariner 10 and MESSENGER couldn't directly capture it. The most likely candidate is meteoroid impacts, which would cause heated vapour clouds in the collision and throw lithium into the exosphere.

Mercury's surface is continuously replenished by extraterrestrial bombardment, according to a study linking detected events to meteoroid strikes by objects 13-21 centimetres in radius. These high-speed collisions can vaporise up to 150 times their own mass, endowing the atmosphere with volatiles such as lithium.

Schmid's study reveals that such processes could also account for the retention or acquisition of volatile elements in other airless bodies, which would transform our understanding of the geochemical story of Mercury and open up new steps in exosphere exploration.