Energetic neutral atom

This region of "space weather" is the site of geomagnetic storms that disrupt communications systems and pose radiation hazards to humans traveling in airplanes (at high altitude and latitude) or in orbiting spacecraft.

While some early efforts were made at detection, their signatures also explained inconsistent findings by ion detectors in regions of expected low-ion populations.

Today, dedicated ENA instruments have provided detailed magnetospheric images from Venus, Mars, Jupiter, and Saturn.

[2] Some ENAs are lost in further charge-exchange, electron collisions and photoionization and polarization, but a great many travel very long distances in space completely undisturbed.

[8] Although plasma recombination and neutral atom acceleration by the solar gravitation may also contribute to an ENA population under certain conditions, the main exception to this creation scenario is the flux of interstellar gas, where neutral particles from the local interstellar medium penetrate the heliosphere with considerable velocity, which classifies them as ENAs as well.

[8] Solar flares and coronal mass ejections (CMEs) are the result of eruptions on the surface of the Sun, which may provide another source of ENAs.

The resulting ENAs propagated through space without being bound to follow the Parker Spiral, so were observed near the Earth before the helium ions that were created in this reaction.

This experiment was followed by the launch of a similar instrument on a Javelin sounding rocket in 1970 to an altitude of 840 kilometres (520 mi) at Wallops Island off the coast of Virginia.

[2] ENA data from the NASA/ESA ISEE 1 satellite enabled the construction of the first global image of the storm time ring current in 1982.

A more sophisticated high energy particle instrument was launched on the 1992 NASA/ISAS GEOTAIL spacecraft dedicated to observing Earth's magnetosphere astronomy.

Extensive and detailed observations of the Earth's magnetosphere were made with three ENA instruments aboard the NASA IMAGE Mission from 2000 – 2005.

By imaging ENAs over a broad energy range (~1–100 KeV) using identical instruments on two widely spaced high-altitude, high-inclination spacecraft, TWINS enables 3-dimensional visualization and the resolution of large-scale structures and dynamics within the magnetosphere.

[2] In February 2009, the ESA SARA LENA instrument aboard India's Chandrayaan-1 detected hydrogen ENAs sputtered from the lunar surface by solar wind protons.

Predictions had been that all impacting protons would be absorbed by the lunar regolith but, for an as yet unknown reason, 20% of them are bounced back as low energy hydrogen ENAs.

Launched in 2018, the ESA BepiColombo mission includes ENA instruments to further its objective to study the origin, structure and dynamics of Mercury's magnetic field.

Launched in 2005, the ESA VEX (Venus Express) mission's ASPERA (Energetic Neutral Atoms Analyser) consists of two dedicated ENA detectors.

[1] In 2006 ENA images were obtained of the interaction between the solar wind and the Venusian upper atmosphere, showing massive escape of planetary oxygen ions.

[18] Launched in 2003, the ESA MEX (Mars Express) mission's ASPERA instrument has obtained images of the solar wind interacting with the upper Martian atmosphere.

[19] The GAS[20] instrument on the ESA/NASA Ulysses, launched in 1990, produced unique data on interstellar helium characteristics and ENAs emitted from Jupiter's Io torus.

[2] The first glimpse of this view was announced in October, 2009, when the NASA's IBEX Mission returned its first image of the unexpected ENA ribbon at the edge of the heliosphere.

Furthermore, it is worth noting that for large distances to the object, high energy (velocity) and slower ENAs emitted simultaneously would be detected at different times.

[2] Although the study of ENAs promised improvements in the understanding of global magnetospheric and heliosphere processes, its progress was hindered due to initially enormous experimental difficulties.

A set of electrostatic plates deflect charged particles away from the instrument and collimates the beam of incoming neutral atoms to a few degrees.

The ENA arriving at its solid state detector (SSD) creates the end pulse and its impact position yields its trajectory and therefore path length.

ENAs pass through the grating and the film to impact a solid state detector (SSD), scattering electrons and allowing path length and TOF determinations as for the HENA above.

[2] Results from the TWINS Mission are eagerly awaited, as two viewing points will provide substantially more information about the 3-D nature of Earth's magnetosphere.

Although the angular resolution has now decreased to a few degrees and different species can be separated, one challenge is to expand the energy range upwards to about 500 Kev.

This high energy range covers most of the plasma pressure of Earth's inner magnetosphere as well as some of the higher-energy radiation belts so is desirable for terrestrial ENA imaging.

Similarly, the heliosphere protects the Solar System from the majority of otherwise damaging cosmic rays, with the remainder being deflected by the Earth's magnetosphere.

Although most orbiting satellites are protected by the magnetosphere, geomagnetic storms induce currents in conductors that disrupt communications both in space and in cables on the ground.