Sun rids space of dangerous junk

摘要

Low Earth orbit just got a free spring clean, thanks to the sun. It turns out that increased solar activity in recent years has removed some of the satellite debris that clogs this region, making it temporarily safer for other satellites and astronauts. The sun will hit an 11-year peak in its activity - the solar maximum -in 2013. As this approaches, small increases in solar radiation warm the outer layer of Earth's atmosphere, called the thermosphere, forcing it to expand into space. This places atmospheric molecules in the path of low orbiting debris, which brake their orbital velocity and cause them to re-enter the atmosphere sooner than expected, where they usually burn up.