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
The Songs of Distant Earth would have to carry to first accelerate to the speeds required to travel such great distances within an acceptable time, and then decelerate upon approaching the destination. This limitation is overcome however with the development of the Quantum Drive less than a hundred years before the Sun is set to become a nova. This scientific break-through allows the construction of a fleet of manned interstellar vehicles, including the Starship "Magellan". The "Magellan" escapes the Earth three years before the Sun explodes, an event that is witnessed by the "Magellan"'s crew. In the intervening years the colony on Thalassa loses contact