Exosphere
Topic: Atmosphere: Composition, Structure and Elements of Weather · NCERT: Class 11, Ch 7 "Composition and Structure of Atmosphere"
Meaning
The exosphere is the topmost layer of the atmosphere, above the thermosphere. Its air is extremely thin and is made mostly of light gases, hydrogen and helium. Gravity is weak this far up, so some of these gases escape into space. The layer has no sharp top. It slowly merges into outer space, and very little is known about it.
Example
High above any place on Earth, including India, the last thin traces of hydrogen and helium drift in the exosphere. Some of these atoms move fast enough to escape Earth's pull, so the Earth slowly loses these light gases to space.
Don't confuse with
- Thermosphere: this is the layer just below. It holds the ionosphere, auroras and the International Space Station, and its temperature rises sharply with height. The exosphere is the outer fringe, where gases leak into space.