The lower boundary of the exosphere is called the thermopause or exobase. It is also called the critical altitude, as this is the altitude where barometric conditions no longer apply. Atmospheric temperature becomes nearly a constant above this altitude.Bauer, Siegfried; Lammer, Helmut. Planetary Aeronomy: Atmosphere Environments in Planetary Systems, Springer Publishing, 2004. On Earth, the altitude of the exobase ranges from about depending on solar activity.
The lower boundary of the exosphere is called the thermopause or exobase. It is also called the critical altitude, as this is the altitude where barometric conditions no longer apply. Atmospheric temperature becomes nearly a constant above this altitude.Bauer, Siegfried; Lammer, Helmut. Planetary Aeronomy: Atmosphere Environments in Planetary Systems, Springer Publishing, 2004. On Earth, the altitude of the exobase ranges from about depending on solar activity.