Detection of a southern peak in Mercury's sodium exosphere with the TNG in 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.01.016 Byline: V. Mangano (a), F. Leblanc (b), C. Barbieri (c), S. Massetti (a), A. Milillo (a), G. Cremonese (d), C. Grava (c) Keywords: Mercury; atmosphere; Spectroscopy Abstract: A long term plan of observations of the sodium exosphere of Mercury began in 2002 by using the high resolution echelle spectrograph SARG and a devoted sodium filter at the 3.5 m Galileo National Telescope (TNG) located in La Palma, Canary Islands. This program is meant to investigate the variations of the sodium exosphere appearance under different conditions of observations, namely Mercury's position along its orbit, phase angle and different solar conditions, as reported by previous observations in August 2002 and August 2003 [Barbieri, C., Verani, S., Cremonese, G., Sprague, A., Mendillo, M., Cosentino, R., Hunten, D., 2004. Planet. Space Sci. 52, 1169-1175; Leblanc, F., Barbieri, C., Cremonese, G., Verani, S., Cosentino, R., Mendillo, M., Sprague, A., Hunten, D., 2006. Icarus 185 (2), 395-402]. Here we present the analysis of data taken in June 29th and 30th and in July 1st 2005, when Mercury's true anomaly angle (TAA) was in the range 124-130[degrees]. The spectra show particularly intense sodium lines with a distinctive peak in emission localized in the southern hemisphere at mid-latitudes. This seems to be a persistent feature related to consecutive favorable IMF conditions inducing localized enhancements of surface sodium density. The comparison with previous data taken by Potter et al. [Potter, A.E., Killen, R.M., Morgan, T.H., 2002. Meteorit. Planet. Sci. 37 (9), 1165-1172] evidences a surprising consistency of the anti-sunward component, which appears to remain constant regardless of the changing illumination and space weather conditions at Mercury. Author Affiliation: (a) INAF-Istituto di Fisica dello Spazio Interplanetario, via Fosso del Cavaliere 100, 00133 Roma, Italy (b) Service d'Aeronomie, IPSL/CNRS, Universite Versailles Saint Quentin, Paris, France (c) Department of Astronomy, University of Padova, vicolo Osservatorio 2, 35122 Padova, Italy (d) INAF-Osservatorio Astronomico di Padova, 35122 Padova, Italy Article History: Received 18 November 2008; Revised 27 January 2009; Accepted 29 January 2009