Atmospheric boundaries

popular defined boundary of outer space

thumb|right|300px|The tropopause extends to high altitudes in the tropical latitudes and extends to low altitudes in the polar latitudes. The tropopause is the atmospheric boundary that demarcates the lowest two layers of the atmosphere of Earth – the troposphere and stratosphere – which occurs approximately above the equatorial regions, and approximately above the polar regions.

thumb | right The stratopause (formerly mesopeak) is the level of the atmosphere which is the boundary between two layers: the stratosphere and the mesosphere. In the stratosphere, the temperature increases with altitude, and the stratopause is the region where a maximum in the temperature occurs. This atmospheric feature is not exclusive to Earth, but also occurs on any other planet or moon with an atmosphere. According to James Kasting, planets whose atmospheres do not absorb shortwave sunlight, such as Venus and Mars, do not have a stratosphere and thus have no stratopause.

The mesopause is the point of minimum temperature 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 mesosphere is the coldest region on Earth with temperatures as low as -100 °C (-148 °F or 173 K). The altitude of the mesopause for many years was assumed to be at around 85 km (53 mi), but observations to higher altitudes and modeling studies in the last 10 years have shown that in fact there are two mesopauses - one at about 85 km and a stronger on

The thermopause is the atmospheric boundary of Earth's energy system, located at the top of the thermosphere. The temperature of the thermopause could range from nearly absolute zero to .

The turbopause, also called the homopause, marks the altitude in an atmosphere below which turbulent mixing dominates. Mathematically, it is defined as the point where the coefficient of Eddy diffusion is equal to the coefficient of molecular diffusion. Because the molecular diffusion coefficient is dependent on both the composition of the diffusing molecule and the background gas, the turbopause altitude will be different for the different molecular species in an atmosphere. For example, in hydrogen (H2) dominated atmospheres, the helium (He) and methane (CH4) turbopause altitudes are differe