MCQ Detailed View

The thermosphere is one of the upper layers of Earth’s atmosphere. It lies above the mesosphere and below the exosphere. The thermosphere extends approximately from 85 km to 690 km above Earth’s surface. This layer is characterized by a rapid increase in temperature with height. Solar activity, such as ultraviolet radiation and X-rays from the Sun, excites the few gas molecules in this region, causing temperatures to rise significantly, sometimes exceeding 1,500°C.

Although the thermosphere is extremely hot, the air density is very low, meaning there are very few gas molecules. This low density means it would not feel “hot” to a human because there are not enough particles to transfer significant heat. The thermosphere is also the layer where phenomena like auroras (Northern and Southern Lights) occur, due to the interaction of solar wind with the Earth’s magnetic field.

Satellites and the International Space Station orbit within the thermosphere because its low density provides minimal air resistance, allowing them to maintain high speeds without significant drag. The upper boundary of the thermosphere gradually transitions into the exosphere, the outermost layer of the atmosphere.

Understanding the height and characteristics of the thermosphere is essential for studies in atmospheric science, physics, and space exploration. Knowing the exact range, from about 85 km to 690 km, helps explain where satellites orbit, where auroras appear, and how energy from the Sun affects the upper atmosphere.

This makes 690 km the correct endpoint for the thermosphere in the Earth’s atmospheric structure.