Did you know? The thermosphere can reach temperatures over 2,000°C (3,600°F), yet it would feel freezing cold to you! This counterintuitive fact reveals an important distinction between temperature and heat.
The thermosphere is one of the upper layers of Earth's atmosphere, located approximately 80-700 km (50-440 miles) above Earth's surface. It sits above the mesosphere and below the exosphere.
In the thermosphere, intense ultraviolet and X-ray radiation from the Sun is absorbed by the sparse gas molecules, causing them to move at extremely high velocities. This is where the International Space Station orbits, and where auroras (Northern/Southern Lights) occur. Despite the extreme molecular speeds that create high temperature readings, the air is so thin that astronauts and spacecraft require heating systems—not cooling!
Watch the molecular activity in two different environments:
Temperature measures the average kinetic energy (speed) of individual molecules. In the thermosphere, intense solar radiation causes molecules to move extremely fast, resulting in very high temperatures.
Heat is the total thermal energy transferred between objects, which depends on both temperature AND the number of molecules (density/mass). The thermosphere has extremely low density—very few molecules per cubic meter.
The Result: While individual molecules in the thermosphere zoom around at incredibly high speeds, there are so few of them that they can't transfer much thermal energy to your body. You would feel cold because insufficient collisions occur to warm you up!
Temperature ≠ Heat