1) Atmosphere of Earth 
The mesopause is the temperature minimum at the boundary between the mesosphere and the thermosphere atmospheric regions. Due to the lack of solar heating and very strong radiative cooling from carbon dioxide, the mesopause is the coldest region on Earth with temperatures as low as -100°C (-146°F or 173 K). The altitude of the mesopause for many...
Top of the mesosphere situated at about 80-85 km.
(from the article `Earth`) Above the relatively warm stratopause is the even more tenuous mesosphere, in which temperatures again decline with altitude to 80–90 km (50–56 ...
A level in the ionosphere, at an altitude of about 85 km, above which temperatures rise as altitude increases instead of falling as they do in the lower ionosphere.
the upper boundary of the mesosphere
Thin boundary layer found between the mesosphere and the thermosphere. It is usually found at an average altitude of 80 kilometers. Coldest temperatures in the atmosphere are found at the mesopause.
top of the mesosphere , situated at about 80-85 kilometers (50-53 miles).