Temperature mystery of planetary atmospheres revealed
Washington – Researchers have said that they have solved the atmospheric peculiarity that Earth shares with Jupiter, Saturn, Uranus and Neptune, claiming that it is likely common to billions of planets.
In 1902 a scientist named Leon Teisserenc de Bort, used instrument-equipped balloons, found a point in Earth’s atmosphere at about 40,000 to 50,000 feet where the air stops cooling and begins growing warmer.
He called this invisible turnaround a “tropopause,” and coined the terms “stratosphere” for the atmosphere above, and “troposphere” for the layer below, where we live — terms still used today.
Then, in the 1980s, NASA spacecraft discovered that tropopauses are also present in the atmospheres of the planets Jupiter, Saturn, Uranus and Neptune, as well as Saturn’s largest moon, Titan, and this happen at the same level in the atmosphere of each of these different worlds — at a pressure of about 0.1 bar, or about one-tenth of the air pressure at Earth’s surface.
University of Washington astronomer Tyler Robinson said that the explanation lies in the physics of infrared radiation. Atmospheric gases gain energy by absorbing infrared light from the sunlit surface of a rocky planet or from the deeper parts of the atmosphere of a planet like Jupiter, which has no surface.
Using an analytic model, planetary scientist David Catling, professor of Earth and space sciences, and Robinson, a postdoctoral researcher in astronomy, show that at high altitudes atmospheres become transparent to thermal radiation due to the low pressure. Above the level where the pressure is about 0.1 bar, the absorption of visible, or ultraviolet, light causes the atmospheres of the giant planets — and Earth and Titan — to grow warmer as altitude increases.
The physics, they write, provides a rule of thumb which should apply to the vast number of planetary atmospheres with stratospheric gases that absorb ultraviolet or visible light.
The study has been published in the journal Nature Geoscience.