Why does the Earths atmosphere have a positive effect on space debris?
The Earth’s atmosphere causes air drag that extracts orbital energy and leads to a contraction and final re-entry of a space object. Upper layers of the atmosphere are supported by lower layers, which are compressed under the weight of the air column above them. The air density increases, and hence the increase in air drag with decreasing altitude is progressive. Changes in air density at a given orbital altitude are mainly driven by the Sun, which varies its activity in an 11-year cycle. Thus, every 11 years, lower parts of the atmosphere are heated and expand toward higher altitudes, where the air density increases, causing higher air drag on space objects. As a consequence, space debris are periodically cleaned from the lower orbital regions (but these are subsequently re-filled by objects descending from higher orbits). After sufficient exposure to air drag the orbit decays, and the object re-enters into the denser Earth atmosphere, where the air drag converts orbital energy into h
