Here's why:

* Exosphere: The outermost layer of the atmosphere, extending from about 700 km (435 miles) to 10,000 km (6,214 miles) above Earth. It's extremely thin, with very few air molecules. This allows satellites to orbit without significant air resistance.

* Other layers: The lower layers of the atmosphere (troposphere, stratosphere, mesosphere, thermosphere) are too dense for satellites to orbit stably.

While the exosphere is considered the outermost layer, it's important to note that the boundary between the exosphere and outer space isn't precisely defined.