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EARTH GROUND-BASED OBSERVATIONS OF MERCURY
EXOSPHERE — MAGNETOSPHERE — SURFACE
RELATIONS
LEBLANC FRAN ¸OIS
Service d'Aeronomie du CNRS/IPSL, France
francois.leblanc@aerov.jussieu.fr
Mariner-10 flybys of Mercury were the main sources of information on Mer-
cury's exosphere up to the discovery of the exospheric sodium emission from
ground based observatories (Potter and Morgan, Science 229 (1985) 651-653).
These later observations were followed by the discovery of potassium (Potter
and Morgan, Icarus 67 (1986) 336-340) and calcium emissions in Mercury's
exosphere (Bida et al. , Nature 404 (2000) 159-161). Several ground-based
observations have underlined the significant spatial and temporal variations
of Mercury's exosphere. Such observations lead to the suggestion of a large
number of potential sources of ejection of volatiles from Mercury's surface, but
also to the suggestions of strong relations between Mercury's exosphere and its
magnetosphere as well as between Mercury's exosphere and upper surface.
1. Introduction
Since the Mariner-10 flybys of Mercury, most of the studies and obser-
vations of Mercury's neutral exosphere have concerned the bright sodium
exospheric emissions. 1 - 3 Since its first observation, 4 several observations
underlined the significant spatial and temporal variabilities of Mercury's
sodium exosphere. 5 , 6 Such observations lead to the suggestion of a large
number of potential sources of ejection of the sodium atoms from Mer-
cury's surface. They also suggest strong relations between Mercury's exo-
sphere and its magnetosphere 7 as well as between Mercury's exosphere and
upper surface. 8 - 10
This paper is focused on the different sources of variation of the known
exospheric abundances and does not intend to be a complete review on
Mercury's exosphere already done in several recent papers. 1 - 3 Most of
these variations derived from the strong links between Mercury's exosphere,
its magnetosphere, and its upper surface. These exospheric variations can
therefore, be also interpreted as indirect observations of the characteristics
of the magnetosphere and of the upper surface. This paper emphasizes the
5
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