Geoscience Reference
In-Depth Information
NEUTRAL ATOM EMISSION FROM MERCURY
A. MURA
†,∗
,S.ORSINI
†
,A.MILILLO
†
,D.DELCOURT
§
,A.M.DILELLIS
‡
,
E. DE ANGELIS
†
and S. MASSETTI
†
†
INAF-IFSI, Roma, Italy
‡
AMDL Srl., Roma, Italy
§
CETP-CNRS, Saint Maurice des Fosses, France
∗
mura@ifsi.rm.cnr.it
Neutral Atom emission from Mercury Magnetosphere is discussed in this study.
In particular, we consider those neutrals whose emission is directly related to
the circulation of energetic ion of solar wind origin, via both charge-exchange
and ion-sputtering. The environment of Mercury, in fact, is characterized by a
weak magnetic field; thus, cusp regions are extremely large if compared to the
Earth's ones, and intense ion fluxes are expected there. Spatial and energy dis-
tributions of ions and neutrals, and energy-integrated simulated ENA images,
are obtained by means of a single-particle 3D simulation. The feasibility of neu-
tral atom detection and imaging in the Hermean environment is also discussed
here: simulated neutral atom images are investigated in the frame of the Neutral
Particle Analyser-Ion Spectrometer (SERENA NPA-IS) experiment, on board
the ESA mission BepiColombo/MPO.
1. Introduction
Since Mariner-10 observations of Mercury revealed an intrinsic magnetic
field,
1
several studies have been focused on the solar wind/magnetosphere/
exosphere/surface interaction at Mercury.
2
-
4
In particular, numerical
simulations
5
-
7
and theoretical studies
8
suggest that the solar wind may
directly have access to the inner regions through magnetospheric cusps and
reach the surface of Mercury. This may results both in charge-exchange
(CE) between solar wind ions and planetary neutrals, and in surface ion-
sputtering process, which is one of the sources of the exospheric populations.
The CE occurs when an energetic ion collides with an exospheric neu-
tral. The ion may grab an electron and become an energetic neutral atom
(ENA), which retains both the energy and the direction of the incoming
ion. No more affected by electro-magnetic forces, these ENAs travel on
straight lines just like photons; ENA imaging is hence a common way to
indicate the detection and analysis of ENA fluxes. The ENA detection not
only gives information about the effectiveness of CE as a loss process of
37
