NASA's Hubble Space Telescope has detected an exoplanet with a built-in "sunscreen," similar to what is seen on Earth.
The telescope picked up signs of a stratosphere, one of the primary layers in Earth's atmosphere that protects it from the Sun, on the blazing-hot exoplanet WASP-33b, NASA's Goddard Space Flight Center reported. Until now, researchers were unsure if stratospheric molecules, which absorb ultraviolet and visible light, would be present on large, hot planets.
"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, 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."
On Earth, the stratosphere is located above the troposphere, which reaches the ground and contains surface weather. Earth's troposphere is characterized by warmer temperatures at the bottom and cooler temperatures at higher altitudes. In the stratosphere, the opposite is true because ozone absorbs the Sun's radiation, blocking it from reaching the surface and warming the stratosphere instead. The temperature disparities in the stratosphere are linked to hydrocarbons, but neither ozone nor hydrocarbons could survive the heat of most exoplanets, leading to debates as to whether temperature inversion exists on these objects at all.
The new observations identify a temperature inversion in the atmosphere of WASP-33b, potentially settling the debate once and for all. The team believes the Earth-like phenomenon is caused by titanium oxide molecules, as opposed to hydrocarbons.
"These two lines of evidence together make a very convincing case that we have detected a stratosphere on an exoplanet," said Korey Haynes, lead author of the study.
The findings were made using Hubble's Wide Field Camera 3, which uses the spectrum of the near-infrared region where the signature for water appears to identify water and other gases in the planet's atmosphere and determine temperature. The researchers determined water was produced in the planet's stratosphere at about 6,000 degrees Fahrenheit, and emissions lower in the atmosphere were at about 3,000 degrees Fahrenheit. The observations also offer the first observational evidence that WASP-33b's atmosphere contains titanium oxide, which is a strong absorber visible and ultraviolet radiation and has the ability to remain in a gaseous state in extreme heat.
"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, United Kingdom. "Our finding marks a key breakthrough in this direction."
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