Which atmospheric layer is the outermost and where most man-made satellites orbit?

• A. Mesosphere
• B. Stratosphere
• C. Troposphere
• D. Thermosphere

Answer: (D)

The outermost layer where most satellites orbit is the thermosphere. In this region the air is incredibly thin, so objects in orbit experience very little drag, which is crucial for maintaining stable, long-lasting orbits. As you move upward from the lower layers—troposphere and stratosphere, then into the mesosphere—the atmosphere becomes progressively thinner, and temperatures behave differently, increasing with altitude in the thermosphere due to absorption of high-energy solar radiation. That heating, despite the sparse gas, is why the thermosphere is described as very hot, even though there isn’t enough air to feel warmth in the usual sense. Most low Earth orbit satellites operate within this layer, typically a few hundred to a couple thousand kilometers up, where the drag is small enough to keep them in orbit for extended periods. Beyond the thermosphere lies the exosphere, the transition zone toward space, but the layer where satellites commonly reside is the thermosphere.