Geoscience Reference
In-Depth Information
which is orbiting from 30 to 60
◦
N at 12:00 MLT (the virtual periherm is
at 0
◦
, 12:00 MLT). The intense proton precipitation in the dayside, north-
ern hemisphere results in an intense O-ENA production in the center of
the global 2D image. In general, it is possible to have a global view of pro-
ton precipitation by means of ion-sputtered directional ENAs, with surface
spatial resolution between 15 and 50 km, depending on s/c altitude. Some
studies
7
,
8
have estimated that, under different IMF conditions, the config-
uration of the Hermean magnetosphere changes so that the area of high
proton precipitation (and subsequent neutral release) moves.
According to our simulations, the ion-sputtering ENA signal from day-
side is high enough to be detected by ELENA; the spatial and time
resolution is good enough to monitor instantaneous changes of the mag-
netospheric configuration; the spatial resolution permits to discriminate
surface emissivity variations. Those considerations apply to an accumula-
tion time of 30 s, which is a compromise between time resolution, count
rates and downlink data-rate.
6. Summary and Conclusions
In this study, we have used a Monte-Carlo model of proton circulation in
Mercury's dayside as an input for the simulation of neutral particle emis-
sion from both the surface (via ion-sputtering) and the exosphere (via CE).
Monitoring the product of such interactions gives important information
about Mercury's magnetosphere and exosphere
30
such as effectiveness of
CE as a loss process of magnetospheric ions; effectiveness of ion-sputtering
as a release process of exospheric neutrals; instantaneous and global mon-
itoring of spatial distribution (via ENA deconvolution) and energy distri-
bution of the magnetospheric plasma. Simulated ENA images, for realistic
MPO/SERENA/ELENA vantage points and FoV, have been obtained and
discussed; the results show the feasibility of neutral atom remote sensing
made by the SERENA/ELENA sensor.
A first result of this study is that ENA fluxes coming from both CE
and ion-sputtering, at Mercury, could be high enough to allow using this
technique. Moreover, we have show that these neutral fluxes are extremely
sensible to the external conditions, thus leading to a “neutral imaging”
investigation technique for Mercury's magnetosphere and surface, through
directional neutral atoms detection. In this way, it is possible to obtain basic
information about plasma circulation, as it happens at the Earth,
9
,
10
,
31
and to study surface release processes.
11
According to our model, solar
