Nasa just spotted a planet that they didn’t think could exist. The world, known as Wasp-18b, is wrapped in a stratosphere full of carbon monoxide and with no water at all. That suggests that it might have formed in an entirely different way from the gas giants we have known before.

“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 paper published in the Astrophysical Journal Letters. “We don’t know of any other extra solar planet where carbon monoxide so completely dominates the upper atmosphere.”

On Earth, the stratosphere keeps us safe from dangerous rays from the Sun. Ozone absorbs UV, which means that much of the otherwise harmful radiation is kept out and doesn’t land on us. Other planets tend to have a different molecule like titanium oxide, which is used for a variety of different purposes on Earth.

Nasa scientists examined the surface of the planet by looking at the light that comes to us from it, which is found 325 lightyears away. From that light they can work out the “spectral fingerprints” of the makeup of the planet — looking out for signatures that could suggest the planet has water or other important molecules.

But they didn’t find any water on the planet, even after repeated looks at it from the Hubble space telescope. The fingerprints they got back didn’t match any of the materials they expected to see there — and challenge their current understanding of how planets can form.

“The only consistent explanation for the data is an overabundance of carbon monoxide and very little water vapour in the atmosphere of WASP-18b, in addition to the presence of a stratosphere,” said Nikku Madhusudhan a co-author of the study from the University of Cambridge. “This rare combination of factors opens a new window into our understanding of physicochemical processes in exoplanetary atmospheres.”

Scientists now hope that they can find out yet more about WASP-18b and other planets like it. If they can understand more about the make-up of the strange world, then it might change their understanding of how gas giants can form.

The Independent