A massive and blazing hot distant exoplanet has a stratosphere, a "sunscreen" layer that's one of the main layers of our own planet's atmosphere, astronomers say.
The atmosphere layer on the planet cataloged as WASP-33b was detected during observations using the Hubble Space Telescope, they report.
A stratosphere layer in an atmosphere includes molecules capable of absorbing both ultraviolet and visible light, serving as a kind of planetary "sunscreen," they explain.
There has been considerable debate about whether such molecules could exist or survive in the atmosphere of massive, extremely hot exoplanets like WASP-33b, whose gaseous surface has a temperature of 3,200 degrees Centigrade, almost 5,800 degrees Fahrenheit.
"Some of these planets are so hot in their upper atmospheres, they're essentially boiling off into space," says Avi Mandell, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.
"At these temperatures, we don't necessarily expect to find an atmosphere that has molecules that can lead to these multilayered structures," says Mandell, who co-authored a study on WASP-33B appearing in the Astrophysical Journal.
In the atmosphere of Earth, the stratosphere lies above our troposphere, a turbulent, weather-producing region extending from the surface to the altitude where most clouds top out.
The troposphere's temperature is warmest at ground level and gets cooler as altitude increases.
In the stratosphere, just the opposite is the case; the temperature rises the higher you go, in a phenomenon known as temperature inversion created by the stratosphere absorbing the sun's ultraviolet radiation, shielding the Earth - and us - from its harmful effects.
The high temperatures of most known exoplanets have raised debate about whether molecules that can absorb ultraviolet light - ozone on Earth and hydrocarbons on some planets in our solar system such as Saturn and Jupiter - could even exist above them, suggesting such planets might not have stratospheres at all.
However, the Hubble observations of WASP-33b have detected a temperature inversion in its atmosphere, proof of the existence there of a stratosphere.
And the researchers say they even have a candidate for the molecule responsible; not ozone or a hydrocarbon but titanium oxide, one of only a few light-absorbing compounds capable of existing in gaseous form in an atmosphere as hot as that of WASP-33b.
"These two lines of evidence together make a very convincing case that we have detected a stratosphere on an exoplanet," says study lead author Korey Haynes.
Finding a link between stratospheres and chemical compositions helps scientists understand atmospheric processes on exoplanets.
