Thermosphere gas and the ionospheric plasma. The International Space Station orbits the Earth within the middle of the thermosphere, between . It is convenient to separate the atmospheric regions according to the two temperature minima at about 12 km altitude (the tropopause) and at about 85 km (the mesopause) (Figure 1). The thermosphere (or the upper atmosphere) is the height region above 85 km, while the region between the tropopause and the mesopause is the middle atmosphere (stratosphere and mesosphere) where absorption of solar UV radiation generates the temperature maximum near 45 km altitude and causes the ozone layer. The density
S/2004 S 6 dissipate on a timescale of years or months. Notably, an imaging sequence covering an entire orbital period at 4 km resolution taken on November 15, 2004 (soon after 's discovery) failed to recover the object, while it has been seen again later. The lighting conditions in 's part of the orbit were different during these two observations, however, with the discovery being made when the region was strongly backlit by the sun. A suggested resolution of the absence in November is that 's visibility is primarily due to a diffuse cloud of fine dust that is much brighter in forward