Starship Asterisk*

Artistic impression of exoplanet KELT-9b orbiting its star. (c) NASA/JPL-Caltech

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An international team of researchers, led by astronomers from the University of Amsterdam, has directly demonstrated the presence of iron in the atmosphere of an exoplanet for the first time. The researchers discovered emission lines of uncharged iron atoms in the light spectrum of KELT-9b. The observation was complicated as the exoplanet is outshined by its bright host star.

The exoplanet KELT-9b orbits around its star KELT-9 in 36 hours. The star and planet are located at a distance of approximately 620 light-years from Earth in the Cygnus constellation. The star has a temperature of over 10,000 degrees, almost twice as hot as the sun. The planet KELT-9b is bigger than Jupiter. It is close to its star, around thirty times closer than the Earth to the sun.

The researchers already knew there had to be iron in the planetary atmosphere. A few years ago, they already saw signs of this when studying the starlight while the planet passed in front of its star.

In the new observations, the researchers looked directly at the light of the planet. This is complicated, as the planet is outshined by the light of its star. Furthermore, due to its proximity to its host star, one year on the planet lasts about one day and a half. During half of this very short “year", the planet’s night side is facing Earth, but that is too dark to be seen. Thus, the researchers picked up the light during a narrow 8 hours just before the planet disappeared behind the star, to observe its hotter, brighter day-side. ...

• Astrophysical Journal Letters 894(2):L27 (2020 May 10) DOI: 10.3847/2041-8213/ab8c44
• arXiv.org > astro-ph > arXiv:2004.11335 > 23 Apr 2020