Observations from NASA's Hubble and Spitzer telescopes have allowed a team of researchers to find evidence that the exoplanet WASP-18b has a stratosphere rich in carbon monoxide, and without any water. The planet belongs to a class of bodies known as "Hot Jupiters", and the researchers have found that the planet which is unusually close to its host star may have emerged as a different planetary evolution process as compared to gas giants in other planetary systems, as well as our solar system.
The planet, which is around 325 light years away from Earth was being observed as part of a survey to identify exoplanets with stratospheres. Typically, the stratosphere of a planet contains molecules that absorb the radiation from the host star and releases the stored energy as heat. The spectral fingerprint of the star, which allows researchers to identify its composition by looking carefully at the light emitted by the atmosphere of the planet, was unlike anything seen before.
Kyle Sheppard of NASA’s Goddard Space Flight Center says, "The composition of WASP-18b defies all expectations. We don’t know of any other extrasolar planet where carbon monoxide so completely dominates the upper atmosphere."
The researchers had to use computer simulations to arrive at the conclusion that the planet was cloaked by a thick layer of carbon monoxide. Carbon monoxide has a similar spectral fingerprint to carbon dioxide, but the presence of the latter molecule was ruled out considering that the spectral lines did not indicate the presence of water at all, and the stratosphere was expected to have more water if there was enough oxygen to form carbon dioxide.
The researchers pointed out that the launch of the James Webb Space Telescopes and other follow up missions would provide a deeper understanding of the variety of exoplanets.