A team led by NASA has found evidence that the large planet WASP-18b is enveloped in a suffocating stratosphere charged with carbon monoxide and devoid of water. The findings come from a new analysis of observations made by the Hubble and Spitzer space telescopes.
The formation of a stratosphere layer in a planet's atmosphere is attributed to "sun-protective" molecules, which absorb UV and visible radiation from the star and then release that energy in the form of heat. The new study suggests that the "hot Jupiter" WASP-18b, a massive planet orbiting very close to its host star, has an unusual composition, and the formation of this world could have been quite different from that of Jupiter, as well as the gas. giants in other planetary systems.
"The composition of WASP-18b defies all expectations," said Kyle Sheppard of NASA's Goddard Space Flight Center in Greenbelt, Maryland, lead author of the article published in Astrophysical Journal Letters . "We do not know of any other extrasolar planet where carbon monoxide completely dominates the upper atmosphere."
On Earth, ozone absorbs UV rays in the stratosphere, protecting our world from much of the sun's harmful radiation. For the handful of exoplanets with stratospheres, it is believed that the absorber is a molecule like rust of titanium, a close relative of titanium dioxide, used on Earth as a paint pigment and sunscreen ingredient.
The researchers analyzed the data collected for WASP-18b, located 325 light-years from Earth, as part of a survey to find exoplanets with stratospheres. The heavyweight planet, which has a mass of 10 Jupiter, has been observed repeatedly, allowing astronomers to accumulate a large number of data. This study analyzed five eclipses of Hubble data archived and two of Spitzer.
From the light emitted by the planet's atmosphere at infrared wavelengths, beyond the visible region, it is possible to identify the spectral fingerprints of water and some other important molecules. The analysis revealed the unique fingerprint of WASP-18b, which does not resemble any exoplanet examined so far. To determine which molecules were most likely to match, the team conducted extensive computer modeling.
"The only consistent explanation for the data is an overabundance of carbon monoxide and very little water vapor in the atmosphere of WASP-18b, in addition to the presence of a stratosphere," said Nikku Madhusudhan, co-author of the study. the University of Cambridge. "This rare combination of factors opens a new window in our understanding of physicochemical processes in exoplanetary atmospheres."
The findings indicate that WASP-18b has hot carbon monoxide in the stratosphere and cooler carbon monoxide in the layer of the atmosphere below, called the troposphere. The team determined this by detecting two types of carbon monoxide signatures, an absorption signature at a wavelength of approximately 1.6 micrometers and an emission signature of approximately 4.5 micrometers. This is the first time that researchers detect both types of fingerprints for a single type of molecule in the atmosphere of an exoplanet.
In theory, another possible adjustment for observations is carbon dioxide, which has a similar fingerprint. The researchers ruled this out because if there were enough oxygen available to form carbon dioxide, the atmosphere should also have some water vapor.
To produce the spectral fingerprints seen by the equipment, the upper atmosphere of WASP-18b would have to be charged with carbon monoxide. In comparison with other hot Jupiters, the atmosphere of this planet would probably contain 300 times more "metals", or elements heavier than hydrogen and helium. This extremely high metallicity would indicate that WASP-18b could have accumulated a greater amount of solid ice during its formation than Jupiter, suggesting that it did not form as other hot Jupiters did.
"The expected launch of the James Webb Space Telescope and other future space-based observatories will give us the opportunity to continue with even more powerful instruments and continue to explore the amazing variety of exoplanets that exist," said Avi Mandell, Goddard's exoplanet scientist and the second author of the article.  Source of the story:
Materials provided by NASA / Goddard Space Flight Center . Original written by Elizabeth Zubritsky. Note: Content can be edited by style and duration.