Definition - What does Thermosphere mean?
The earth’s atmosphere consists of several layers, and the thermosphere is one of these. The thermosphere begins at a height of approximately 55 miles above the earth’s surface and extends to a height of between 311 and 621 miles above ground-level.
Safeopedia explains Thermosphere
The temperatures of the gases in the thermosphere fluctuate by up to 360 F between day and night and are extremely high during the day, reaching temperatures of up to 3,632 F in the upper portion of the thermosphere down to 932 F closer to the earth. However a thermometer would read temperatures below freezing because the super-heated gas molecules are so far apart. In fact, the molecules in the thermosphere are so far apart, that sound cannot be transmitted through them. The most common gases in the thermosphere are oxygen and nitrogen.