Which layer of the atmosphere is considered outer space?

The exosphere is recognized as the outermost layer of Earth's atmosphere, transitioning into outer space. In this layer, atmospheric particles are extremely sparse, and it extends from approximately 600 kilometers (about 370 miles) above sea level to around 10,000 kilometers (approximately 6,200 miles) where it merges with the vastness of outer space.

One of the defining characteristics of the exosphere is that it does not contain a uniform composition of gases; instead, it predominantly consists of lighter elements like hydrogen and helium. The exosphere is significant because it is the region where satellites orbit the Earth, and the low density of particles allows spacecraft to travel with minimal atmospheric drag.

Understanding the structure of the atmosphere is crucial, as it helps to clarify the distinctions between the layers. The troposphere, which is the lowest layer, contains the majority of the atmosphere’s mass and is where weather phenomena occur. The stratosphere and mesosphere are further up but do not extend into outer space. These layers, while incredibly important for atmospheric processes, are still firmly part of Earth's atmosphere rather than the realm of outer space.