There isn't a single person credited with "discovering" the exosphere. It's more accurate to say that the concept of the exosphere evolved over time through the contributions of many scientists.

Here's why:

* Early Theories: Early astronomers like Edmund Halley (17th century) and others observed the aurora borealis and theorized about a "gaseous envelope" surrounding Earth. This was before the scientific understanding of atmospheric layers.

* Early Space Exploration: During the early space age (1950s-1960s), rocket and satellite data provided the first direct evidence of a very thin, outermost layer of the atmosphere extending far into space.

* Defining the Exosphere: Through the work of atmospheric scientists, like Sydney Chapman, and later, the development of advanced instruments and space probes, the exosphere was more clearly defined as a region where the atmosphere gradually fades into the vacuum of space.

So, while no single person can be credited with discovering the exosphere, the work of numerous scientists and advancements in technology contributed to our understanding of this outermost layer of Earth's atmosphere.