ASPERA-3

Energetic Neutral Atom (ENA) Imaging

Basic Concept

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:

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
• Recombination (CMI)

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.