Energetic Neutral Atom (ENA) Imaging
The co-existence of an energetic charged particle population (solar
wind, magnetospheric plasma) and a planetary neutral gas leads to
interaction, e.g., through charge-exchange:
A+(energetic) + P(cold) => A(energetic) + P+(cold)
In contrast to charged particles, ENAs are no longer influenced by
electromagnetic fields and propagate on straight paths from the source
to the observer. Directional detection of ENAs yields a global image
of the interaction and by complex inversion techniques properties of
the source populations can be deduced.
ENA production mechanisms in space plasmas comprise:
Charge - exchange reaction with atmospheric / exospheric gases
Sputtering of planetary atmospheres
Backscattering from the planetary atmospheres (ENA albedo)
Sputtering from planetary surfaces
Ion neutralization / sputtering on dust particles
ENA Imaging Applications
The IMAGE mission successfully proved that ENA imaging can provide global views of plasma processes (substorm particle injections, ring current distribution and dynamics) in the Earth's Magnetosphere.
The MIMI instrument on Cassini provided ENA images of the Jupiter - Io Torus system.
The simulated ASPERA-3 ENA response shows that the solar wind - exosphere interaction processes at Mars can be globally imaged in ENA.