NASA's Hubble finds 'sunscreen' layer on distant exoplanet

Researchers, including one of Indian-origin, have used NASA's Hubble Space Telescope to detect an atmospheric layer on a blazing-hot exoplanet that absorbs ultraviolet and visible light, acting as a kind of "sunscreen".
Scientists have detected a stratosphere, one of the primary layers of Earth's atmosphere, on the exoplanet known as WASP-33b.
This atmospheric layer includes molecules that absorb ultraviolet and visible light, acting as a kind of "sunscreen" for the planet it surrounds, researchers said.
Until now, scientists were uncertain whether these molecules would be found in the atmospheres of large, extremely hot planets in other star systems.
"Some of these planets are so hot in their upper atmospheres, they're essentially boiling off into space," said Avi Mandell, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and a co-author of the study.

"At these temperatures, we don't necessarily expect to find an atmosphere that has molecules that can lead to these multilayered structures," Mandell said.

In Earth's atmosphere, the stratosphere sits above the troposphere - the turbulent, active-weather region that reaches from the ground to the altitude where nearly all clouds top out.
In the troposphere, the temperature is warmer at the bottom - ground level - and cools down at higher altitudes.
The stratosphere is just the opposite. In this layer, the temperature increases with altitude, a phenomenon called temperature inversion.
On Earth, temperature inversion occurs because ozone in the stratosphere absorbs much of the Sun's ultraviolet radiation, preventing it from reaching the surface, protecting the biosphere, and therefore warming the stratosphere instead.

Similar temperature inversions occur in the stratospheres of other planets in our solar system, such as Jupiter and Saturn. In these cases, a different group of molecules called hydrocarbons is responsible.
Neither ozone nor hydrocarbons, however, could survive at the high temperatures of most known exoplanets, which are planets outside our solar system. This leads to a debate as to whether stratospheres would exist on them at all.
Using Hubble, the researchers have settled this debate by identifying a temperature inversion in the atmosphere of WASP-33b, which has about four-and-a-half times the mass of Jupiter.
Team members also believe they know which molecule in WASP-33b's atmosphere caused the inversion - titanium oxide.

"Understanding the links between stratospheres and chemical compositions is critical to studying atmospheric processes in exoplanets. Our finding marks a key breakthrough in this direction," said co-author Nikku Madhusudhan of the University of Cambridge, UK.