This is the innermost of the two structures treated by Lineberry's layering modifications to the Jacchia model.
This is the innermost of the two structures treated by Lineberry's layering modifications to the Jacchia model. Scientists never figured out the cause of a 2009 "collapse" of this structure that was much larger than sunspot cycles could explain. This region receives most of its energy from solar EUV rays, which is why its size changes so much seasonally. Air molecules in this region become sufficiently far apart that humans cannot hear sound past where its anacoustic zone begins. Astronautics begins at this region's Karman Line. The International Space Station orbits within this layer, which extends up to about 700 kilometers. For 10 points, identify this second-outermost layer of earth's atmosphere, named for the high temperatures reached within.
This is the innermost of the two structures treated by Lineberry's layering modifications to the Jacchia model.
thermosphere [prompt on ionosphere, I guess, but none of the clues are specifically about that, prompt on outer atmosphere]