Cold trap (astronomy)

On airless bodies, the ices trapped inside cold-traps can potentially remain there for geologic time periods, allowing us a glimpse into the primordial solar system.

Harold Urey first noted that depressions or craters located near the poles of these bodies will cast persistent shadows that can survive for geologic time periods (millions–billions of years).

This region is called a cold-trap, because it traps ascending gases with high boiling points, forcing them to drop back into Earth.

[citation needed] Some astronomers believe that the lack of a cold trap is why the planets Venus and Mars both lost most of their liquid water early in their histories.

[12] The Earth's cold trap is located about 12 km above sea level, well below the height in which water vapor would be permanently split apart into hydrogen and oxygen by solar UV rays and the former irreversibly being lost to space.

At that rate it would take trillions of years, far longer than Earth's life expectancy, for all of its water to disappear (this is also why, due to human-caused climate change, extreme weather events like hurricanes and floods will intensify in the near term, as a warmer atmosphere can hold more moisture, and therefore increase the amount of said water vapor returning as precipitation, as even then the cold trap will still prevent said water vapor from being lost to space, and therefore Earth's atmosphere is still too cold for such to happen), although the eventual warming of the Sun as it ages will only make the cold trap weaker over the next billion years by making the Earth's atmosphere even warmer, which pushes the cold trap even higher into the atmosphere, and therefore causing it to lose the ability to prevent any water vapor from being dissociated back into hydrogen and oxygen by the Sun's UV rays and the former escaping into space, leading to the Earth ultimately losing its oceans to space in about 1 billion years' time, long before the Sun finally expands into a red giant.