Detection of lithium in the exosphere of Mercury

Mercury’s exosphere contains various neutral species, including hydrogen, helium, sodium, potassium, calcium, magnesium, aluminum, iron, and manganese. Although lithium has been predicted to exist, it had not been detected until now. Here, we demonstrate the presence of lithium in Mercury’s exosphere, using data from the Mercury Surface, Space ENvironment, GEochemistry, and Ranging spacecraft. The sporadic detection of lithium suggests its meteoritic origin, likely released through evaporation caused by sporadic meteoroid impacts. Our findings provide strong evidence supporting the hypothesis that (micro-)meteoroids and larger meteoroids, which have continuously and sporadically impacted Mercury’s surface over billions of years, are a significant source of volatile elements and contributed substantially to Mercury’s unexpectedly volatile-rich surface. This detection emphasizes the significant role of meteoroids in shaping Mercury’s exosphere and provides insights into the planet’s evolution and the history of volatile elements in the Solar System.