Last updated January 11, 2018 at 10:28 am
NASA scientists have discovered a giant exoplanet has a type of atmosphere never seen before – and one unlikely to play home to any lifeforms we know of. Its stratosphere is loaded with carbon monoxide and there is no water at all.
A new study, based on observations from the Hubble and Spitzer space telescopes, shows that the plannet, dubbed WASP-18b, is a so-called “hot Jupiter” – a massive planet that orbits very close to its host star.
But its atmosphere suggests it was formed in a very different way from Jupiter.
“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 extrasolar planet where carbon monoxide so completely dominates the upper atmosphere.”
The scientists believe this layer of carbon monoxide was formed due to prevalence of titanium oxide, so called “sunscreen” molecules common to many exoplanets. These molecules absorb UV and visible radiation coming from the star and then release it energy as heat.
WASP-18b is located 325 light-years from Earth and was analysed as part of NASA’s mission to survey exoplanets with stratospheres. The planet has the mass of 10 Jupiters, and has been observed repeatedly.
The analysis light emitted by the planet’s atmosphere at infrared wavelengths revealed WASP-18b’s peculiar fingerprint, which doesn’t resemble any exoplanet examined so far.
To determine which molecules were most likely to match it, the team carried out extensive computer modelling.
“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.”
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.
In theory carbon dioxide would have a similar fingerprint but the researchers ruled this out because if there were enough oxygen available to form carbon dioxide, the atmosphere also should have some water vapour.