Energetic neutral atom
Energetic neutral atom (ENA) imaging, often described as ""seeing with atoms"", is a technology used to create global images of otherwise invisible phenomena in the magnetospheres of planets and throughout the heliosphere, even to its outer boundary.This constitutes the far-flung edge of the solar system.The solar wind consists of ripped-apart atoms (called plasma) flying out of the Sun. This is mostly hydrogen, that is, bare electrons and protons, with a little bit of other kinds of nuclei, mostly helium. The space between solar systems is similar, but they come from other stars in our galaxy. These charged particles can be redirected by magnetic fields; for instance, Earth's magnetic field shields us from these particles. But, every so often, a few of them steal electrons from neutral atoms they run into. At that point, they become neutral, although they're still moving very fast, and they travel in an exact straight line. These are called Energetic Neutral Atoms. ENA images are constructed from the detection of these energetic neutral atoms.Earth's magnetosphere preserves Earth's atmosphere and protects us 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 at high polar altitudes or in orbiting spacecraft. A deeper understanding of this region is vitally important. 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 plasmas present the added problem of invisibility.The heliosphere protects the entire 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 invisible interaction between the solar wind and cold gas from the local interstellar medium.The creation of ENAs by space plasmas 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. However, the development of dedicated ENA detectors entailed overcoming significant obstacles in both skepticism and technology.Although ENAs were observed in space from the 1960s through 1980s, the first dedicated ENA camera was not flown until 1995 on the Swedish Astrid-1 satellite, to study Earth's magnetosphere.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. The IMAGE mission's three dedicated ENA cameras observed Earth's magnetosphere from 2000–2005 while the TWINS Mission, launched in 2008, provides stereo ENA imaging of Earth's magnetosphere using simultaneous imaging from two satellites.The first ever images of the heliospheric boundary, published in October 2009, were made by the ENA instruments aboard the IBEX and Cassini spacecraft. These images are very exciting because they challenge existing theories about the region.