The observations, from NASA’s James Webb Space Telescope, provide new insights into the formation of the planet, a hot gas giant called Wasp-39b located 700 light-years away in the constellation Virgo. They also provide the first clear evidence for carbon dioxide in the atmosphere of a planet orbiting a distant star. “We want to know how unique we are and what the chances are of life elsewhere in the universe,” said Dr Vivien Parmentier, associate professor of physics at the University of Oxford and part of the collaboration behind the project. “CO2 detection is usually one of the things we will look for. This shows that we have the potential, which is extremely exciting for all of us.” A central goal of James Webb is to analyze the atmospheres of distant planets and search for biosignature gases that could indicate the presence of life on the planet below. Wasp-39b itself is not seen as a promising candidate for life. The gas giant planet is about 1.3 times the size of Jupiter, with an average temperature of about 900C. It is so close to its host star — about one-eighth the distance between the Sun and Mercury — that it takes only four Earth days to make a complete circuit. Its proximity to the star means it is likely to be tidally locked, with one side constantly facing its star and the other side shrouded in endless darkness. The planet was discovered in 2011 after astronomers detected a subtle, periodic dimming of light from its host star caused by the planet’s in-front passage. The latest work goes further by measuring starlight filtering through the planet’s atmosphere. Because different gases absorb different wavelengths of light, analyzing the rainbow of starlight can show exactly which gases are present. Previous results from the Hubble and Spitzer telescopes had hinted at the presence of carbon dioxide, but the latest observations, to be published in the journal Nature, provide the first convincing evidence. Wasp-39b’s massive size and unattainable atmosphere made it an ideal first target. Astronomers now plan to apply the same techniques to analyze the atmospheres of smaller, rocky planets thought to be potentially habitable, such as those in the Trappist-1 star system. They will look for Earth-like atmospheres dominated by nitrogen, carbon dioxide and water vapor and an overall gas balance that suggests the contribution of biological processes. “We’re looking for a combination of gases that we can’t easily explain with our understanding of chemistry, could suggest that something is producing it,” said Dr Jo Barstow, an astronomer at The Open University and a member of the JWST collaboration behind the paper. Subscribe to Global Dispatch Get a different view of the world with a collection of the best news, features and images, curated by our global development team Privacy Notice: Newsletters may contain information about charities, online advertising and content sponsored by external parties. For more information, see our Privacy Policy. We use Google reCaptcha to protect our website and Google’s Privacy Policy and Terms of Service apply. Observing planetary atmospheres will also help astronomers distinguish between small, rocky planets that are more like Earth and those closer to Venus, which is sometimes referred to as Earth’s evil twin because of its surface temperature of 470° C and its dense, toxic atmosphere. “It was probably a bit of luck of the draw that Venus ended up being so inhospitable and Earth ended up with life,” Barstow said. “It may have been a very small turning point that took them in such different directions.”
