Nearby Exoplanet's Hellish Atmosphere Measured

NASA, ESA, L. Calçada. Artist's impression of HD 189733b as it passes in front of its parent star

Scientists from the University of Geneva have managed to measure the temperature of a nearby exoplanet’s scorching atmosphere with immense precision. Alongside documenting temperatures of close to 3000oC, the scientists also observed incredible wind speeds of more than 600 miles per hour (1,000 kph), painting a picture of a truly turbulent and infernal atmosphere. These findings have been published in Astronomy & Astrophysics and Astrophysical Journal Letters.

Located just 63 light-years from us, the exoplanet HD 189733b is the closest hot Jupiter to Earth, making it an ideal target for scientists who want to learn more about this kind of world. As the name suggests, this type of planet is similar in size to Jupiter, but orbits very close to its host star, making it hellishly hot.

A couple of years ago, scientists started to reveal details about this planet’s atmosphere after it passed in front of its parent star. Using Chandra and XMM Newton data, astronomers revealed that it likely possesses extended layers that are transparent to optical light but opaque to X-rays. Furthermore, NASA’s Kepler and Hubble Space Telescopes were able to confirm it has a deep blue color due to the presence of silicate (glass) rain that preferentially scatters blue light. Now, using two approaches, astronomers have managed to reveal details about both the temperature and the winds occurring in the planet’s atmosphere.

For their investigation, researchers made use of previous observations taken by the HARPS spectrometer, which is a ground-based instrument located on one of the European Southern Observatory’s telescopes. In particular, they wanted to scrutinize the signals coming from atmospheric sodium over time. The intensity of this distinctive signal varies when planets pass in front of their host star, an event known as transit.

By scouring through years of data, the scientists were able to observe changes in these so called sodium lines during several of HD 189733b’s transits. To their surprise, they found that HARPS could pick up these signals just as well as Hubble, but actually provided superior spectral resolution, which is why the researchers claim their new analysis is more precise than previous investigations. In combination with this new set of data, researchers from Bern University developed a novel technique for the interpretation of sodium line variations, which allowed researchers to produce more reliable atmospheric temperature measurements.

While Hubble data suggested that the planet’s atmosphere was 1000oC, the new analysis indicated temperatures of up to close to 3000oC (3270 K). Furthermore, Hubble observations led to wind speed estimates of 4,350 mph (7,000 kph), but the new measurements are a more modest, but still incredibly fast, 600 mph (1,000 kph), painting a picture of a truly turbulent atmosphere.   

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