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Solar System
Earth's Geocorona
Very close to home, Chandra has detected evidence of X-rays from Earth's geocorona (extended outer atmosphere) through which Chandra moves. The geocoronal X-rays are caused by collisions between hydrogen atoms in the geocorona with carbon, oxygen and neon ions that are streaming away from the Sun in the solar wind.
This process, called "charge exchange" because an electron is exchanged between a neutral atom in the atmosphere and an ion, typically carbon, nitrogen, or oxygen, in the solar wind. After such collisions, X-rays are emitted as the captured electrons move into tighter orbits. These X-rays have an energy that is equal to the difference in energy states for the electron orbits. The spectrum, or overall distribution of X-rays with energy from charge-exchange collisions can be distinguished from other processes with a sensitive X-ray spectrometer, and provide evidence that the charge-exchange collision is occurring.
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