METALLIC SPECIES IN MERCURY'S EXOSPHERE: EMMI/NEW TECHNOLOGY TELESCOPE OBSERVATIONS

We performed high spectral resolution observations of Mercury's exosphere on 2005 October 30 and 31 using the European Southern Observatory-New Technology Telescope, La Silla, Chile. The large spectral range, 385-855 nm, of the spectrograph, ESO Multi-Mode Instrument, provides a unique opportunity to search for nonidentified species in Hermian's environment. In this paper, we report a tentative detection of atomic aluminum in the exosphere of Mercury. This detection should be confirmed by further observations and can be used as an upper limit for this element in Mercury's exosphere. We also estimate the upper limit for the column densities of Fe and Si exospheric atoms. Detection of Al, a refractory element, if confirmed, as well as its high exospheric abundance (between 2 and 18) with respect to Ca would suggest either an unexpected surface composition or a relation between exosphere and surface composition that is not well understood.