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Energetic neutral atom

"Neutral Atom Imaging" redirects here. For other uses, see Atom (disambiguation).
ENA images of the fluctuation of Earth's ring current during a geomagnetic storm that occurred during July 15–16, 2000. The images were generated by the High Energy Neutral Atom (HENA) instrument present on the IMAGE spacecraft.

Energetic Neutral Atom (ENA) imaging is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere.[1]

Charged particles— protons, electrons, and various nuclei— emitted from solar wind are the basis of the interstellar medium. These charged particles have the ability to be redirected by magnetic fields such as the magnetic field surrounding the Earth. Occasionally charged particles within the plasma of the solar wind will collide with neutral atoms. This collision results in the previously charged particle becoming a neutrally charged atom. Due to the loss of charge, the atom no longer experiences magnetic attraction while maintaining its gravitational attraction and velocity. These atoms are Energetic Neutral Atoms and the detection of these atoms can be reconstructed to build ENA images.[2]

Earth's magnetosphere preserves its atmosphere and protects life on Earth from cell-damaging radiation. 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. Geomagnetic weather systems have been late to benefit from the satellite imagery taken for granted in weather forecasting and space physics because their origins in magnetospheric plasma frequency present the added problem of invisibility.[1]

The heliosphere shields the Solar System from the majority of cosmic rays, but is so remote that only an imaging technique such as ENA imaging will reveal its properties. The heliosphere's structure is due to the interaction between the solar wind and cold gas from the local interstellar medium.[2]

The creation of ENAs by space plasma was predicted, but their discovery was both deliberate and serendipitous. While some early efforts were made at detection, their signatures also explained inconsistent findings by ion detectors in regions of expected low-ion populations. Ion detectors were co-opted for further ENA detection experiments in other low-ion regions.[2] However, the development of dedicated ENA detectors entailed overcoming significant obstacles in both skepticism and technology.[1][3]

Although ENAs were observed in space from the 1960s through the 1980s,[2] the first dedicated ENA camera was not flown until 1995 on the Swedish Astrid-1 satellite,[4] to study Earth's magnetosphere wind.

Today, dedicated ENA instruments have provided detailed magnetospheric images from Venus, Mars, Jupiter, and Saturn. Cassini's ENA images of Saturn revealed a unique magnetosphere with complex interactions that have yet to be fully explained.[1] The IMAGE mission's three dedicated ENA cameras observed Earth's magnetosphere from 2000–2005[5] while the TWINS Mission, launched in 2008, provides stereo ENA imaging of Earth's magnetosphere using simultaneous imaging from two satellites.[6]

The first ever images of the heliosphere boundary, published in October 2009, were made by the ENA instruments aboard the IBEX and Cassini spacecraft, and challenge existing theories about the heliosphere region.[5][7]

  1. ^ a b c d Brandt, P.C.; Mitchell, D.G.; Roelof, E.C.; Krimigis, S.M.; Paranicas, C.P.; Mauk, B.H.; Saur, J.; DeMajistre, R. (2005). "ENA Imaging: Seeing the Invisible" (PDF). Johns Hopkins APL Technical Digest. 26 (2): 143–155. Archived (PDF) from the original on 2023-09-29. Retrieved 2024-01-13.
  2. ^ a b c d Mike Gruntman (1997). "Energetic neutral atom imaging of space plasmas" (PDF). Review of Scientific Instruments. 68 (10): 3617–3656. Bibcode:1997RScI...68.3617G. doi:10.1063/1.1148389. Retrieved 2009-10-22.
  3. ^ Gruntman, Mike (2022). My fifteen years at IKI, the Space Research Institute : position-sensitive detectors and energetic neutral atoms behind the Iron Curtain. Rolling Hill Estates, Calif. ISBN 9798985668704.{{cite book}}: CS1 maint: location missing publisher (link)
  4. ^ P. C:son Brandt; S. Barabash; E. C. Roelof; C. J. Chase (2001). "Energetic neutral atom imaging at low altitudes from the Swedish microsatellite Astrid: Extraction of the equatorial ion distribution". Journal of Geophysical Research. 106 (A11): 25731–25744. Bibcode:2001JGR...10625731B. doi:10.1029/2000JA900023.
  5. ^ a b Sten Odenwald (2005). "IMAGE Scientific Discoveries". NASA IMAGE Education Center. Archived from the original on 2008-10-10. Retrieved 2009-10-27.
  6. ^ NASA. "TWINS Mission". Southwest Research Institute. Archived from the original on 2009-06-04. Retrieved 2009-10-27.
  7. ^ K. Munsell, ed. (2009-10-15). "Cassini Data Help Redraw Shape of Solar System". Jet Propulsion Laboratory. Archived from the original on 2009-10-19. Retrieved 2009-10-22.

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