【惑星科学】系外惑星KELT-9bの大気中に鉄が検出された

Iron and titanium have been detected in the atmosphere of the exoplanet KELT-9b according to a study published in Nature.

KELT-9b belongs to a class of ultrahot Jupiter-like planets that straddle the transition between stars and gas-giant exoplanets, and is expected to have a cloud-free atmosphere. Although iron is the most abundant transition metal, it has never been directly detected in the atmosphere of an exoplanet because of its highly refractory nature. However, at high temperatures, iron and several other transition metals are not sequestered in molecules or cloud particles in atmospheres and exist solely in their atomic form. Therefore, it has been predicted that spectral lines of iron should be detectable in the visible range of wavelengths for KELT-9b.

Using the HARPS-N spectrograph on the Telescopio Nazionale Galileo located on the Canary Island of La Palma, Spain, Jens Hoeijmakers, Kevin Heng, and colleagues conducted a search for metal lines in the high-resolution transmission spectrum of KELT-9b on the night of 31 July to 1 August 2017. By analysing the data obtained while KELT-9b passed in front of its star, the authors detected atomic neutral and singly ionized iron (Fe and Fe+), and singly ionized titanium (Ti+). They also found that the lines of Fe+ showed up more prominently than those of Fe, which suggests that the atmospheric temperatures exceed approximately 4,000 kelvin.