A NASA-led team of scientists have come across WASP-18b -- a 'hot Jupiter' located 325 light-years from Earth that has a smothering stratosphere and is loaded with carbon monoxide with no signs of water.
The findings, published in the Astrophysical Journal Letters, come from a new analysis of observations made by the Hubble and Spitzer space telescopes.
“The composition of WASP-18b defies all expectations,” Kyle Sheppard of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said.
“We don't know of any other extrasolar planet where carbon monoxide so completely dominates the upper atmosphere,” Sheppard added.
The new study suggests that the planet -- that orbits very close to its host star, has an unusual composition. The researchers looked at data collected for WASP-18b as part of a survey to find exoplanets with stratospheres.
The formation of a stratosphere layer in a planet's atmosphere is attributed to "sunscreen"-like molecules, which absorb ultra violet (UV) and visible radiation coming from the star and then release that energy as heat. On Earth, ozone absorbs UV in the stratosphere, protecting our world from a lot of the Sun's harmful radiation.
The heavyweight planet that contains the mass of 10 Jupiters, has been observed repeatedly, allowing astronomers to accumulate a relatively large trove of data.
The analysis revealed WASP-18b's peculiar fingerprint, which does not resemble any exoplanet examined so far. To determine which molecules were most likely to match it, the team carried out 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,” Nikku Madhusudhan, a co-author of the study from the University of Cambridge, said.
“This rare combination of factors opens a new window into our understanding of physicochemical processes in exoplanetary atmospheres,” Madhusudhan said.
'Hot Jupiters' are gas giants like Jupiter but much hotter, with orbits that take them feverishly close to their stars.