Planets that orbit other stars outside our solar system, known as exoplanets, come in all sizes and chemical flavors, but NASA has found one that's rewriting the rulebook of what's possible.

Classified as WASP-18b and located some 325 light-years from Earth, this gas giant is unique in that its atmosphere is devoid of water vapor and rich in "smothering" carbon monoxide. The unusual concentrations of this gas, toxic in high concentrations to all animal life on Earth, has led to some redundant labeling of WASP-18b as a "death planet."

According to Kyle Sheppard of NASA’s Goddard Space Flight Center, the discovery is exciting because it expands the possibilities of the types of exoplanets that are possible throughout the universe.

"The composition of WASP-18b defies all expectations," he said. "We don’t know of any other extrasolar planet where carbon monoxide so completely dominates the upper atmosphere."

In a study published in The Astrophysical Journal Letters, Sheppard and his team explained how they detected WASP-18b's chemical signature using data captured from both the Hubble and Spitzer space telescopes. Light emitted at infrared wavelengths by the planet's atmosphere during "secondary eclipses" (when the planet passes behind its host star) was analyzed, revealing a spectral fingerprint unlike any other ever recorded.

"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 study co-author from the University of Cambridge, explained in a statement. "This rare combination of factors opens a new window into our understanding of physicochemical processes in exoplanetary atmospheres."

The researchers add that the launch of the $10 billion James Webb Space Telescope in 2019 will allow for an even more detailed understanding of exoplanets like WASP-18b. Over the 10 years of the telescope's planned mission lifetime, NASA expects to aim its lens at a broad range of targets throughout the cosmos.

"From the very first galaxies after the Big Bang, to searching for chemical fingerprints of life on Enceladus, Europa, and exoplanets like Trappist-1e, Webb will be looking at some incredible things in our universe," Eric Smith, James Webb Space Telescope Director, said in a statement. "With over 2100 initial observations planned, there is no limit to what we might discover with this incredible telescope."

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.

NASA discovers unique exoplanet with 'smothering' atmosphere
Located over 300 light-years from Earth, exoplanet WASP-18b is defying expectations for how alien worlds are formed.