Carbonatites from Ol Doinyo Lengai, Tanzania — An unusual rock as analog for Mercury as potential species for hollow formation

In this work, we propose a new potential mechanism for the formation of the so-called hollows on Mercury, hypothesizing that they are composed of carbonatites—volcanic rocks that are exceedingly rare on Earth. To evaluate this hypothesis, mid-infrared spectroscopic measurements were performed on a rare, unaltered terrestrial carbonatite sample from Mount Ol Doinyo Lengai, Tanzania, composed primarily of the carbonate minerals nyerereite and gregoryite. For comparison, spectra of several common terrestrial carbonate minerals were also acquired. The collected spectra display characteristic features of carbonate minerals. Our analysis suggests that carbonatite rocks should be taken into account for several physical properties required for the formation of hollows on Mercury’s surface. These include appropriate thermal stability, chemical composition, and surface coloration. In particular, the eruption temperatures of terrestrial carbonatite lavas are less than 100 °C below Mercury’s estimated daytime surface temperatures. This thermal similarity makes the measured spectra relevant for the MERTIS instrument onboard the BepiColombo spacecraft, which will investigate Mercury’s surface mineralogy in near future. • New formation hypothesis of hollows on Mercury. • Infrared spectroscopy of a natrocarbonatite. • Infrared spectroscopy of different carbonate minerals.