The stratosphere atmospheric layer contains molecules which absorb ultraviolet and visible light, and acts as a sort of ‘sunscreen’ for the planet it envelops. Up until now, scientists were not certain whether these molecules would ever be found in the atmospheres of large, extremely hot planets in other star systems.
These findings appear in the Astrophysical Journal.
The researchers also reported the first evidence that WASP-33b’s atmosphere contains titanium oxide, which is one of only a handful of compounds that are strong absorbers of visible and ultraviolet radiation as weel as being capable of staying stable in a gaseous form around a planet as hot as this one.
The presence of a stratosphere provides hints about the composition of a planet and how it formed. Study co-author Avi Mandell, a planetary scientist at NASA’s Goddard Space Flight Center, explained:
“Some of these planets are so hot in their upper atmospheres, they’re essentially boiling off into space. At these temperatures, we don’t necessarily expect to find an atmosphere that has molecules that can lead to these multilayered structures.”
Our stratosphere in the Earth’s atmosphere, is located just on top of the troposphere, a turbulent, active-weather region that reaches from the ground to the altitude where nearly all clouds top out. Temperatures are warmer at the ground level in the troposphere, and cool down at higher altitudes.
Temperatures i the stratosphere are just the opposite. In that layer, the temperature increases with altitude, a phenomenon known as temperature inversion.
On the Earth, temperature inversion happens because ozone in the stratosphere absorbs much of the sun’s ultraviolet radiation, blocking it from reaching the surface, This protects the biosphere, and warms up the stratosphere instead.
‘Understanding the links between stratospheres and chemical compositions is critical to studying atmospheric processes in exoplanets,’ said co-author Nikku Madhusudhan of the University of Cambridge. ‘Our finding marks a key breakthrough in this direction.’
The researchers analyzed images from Hubble’s Wide Field Camera 3, which can capture a spectrum of the near-infrared region where the signature for water appears. Scientists can utilize the spectrum to detect water and other gases in a distant planet’s atmosphere and thus identify its temperature.