Dust and minerals in the HR 8799 atmospheres: JWST MIRI prediction

<p>We are learning rapidly about the gas composition of exoplanet atmospheres, but know almost nothing about their solid composition. The upcoming James Webb Space Telescope will radically change this! The HR8799 exoplanetary system is a perfect candidate because it provides us with a unique opportunity of simultaneously measuring mineral clouds and refractory element composition of its four gas giant atmospheres. The HR8799 system is very young and additionally contains two particle belts. The giant planets are predicted to be bombarded with material from the belts, analogous to the Late Heavy Bombardment. Signatures of this bombardment, such as mineral clouds and refractory element composition, might be observable in their atmospheres. JWST MIRI will allow to characterise these exoplanets in the mid-infrared thermal regime (5-28 μm) which is not possible from the ground. We use the ARtful modeling Code for exoplanet Science (ARCiS) to calculate the mid-infrared spectra of planets HR 8799 b, c, d and e, and we simulate MIRI spectroscopic observations. Besides the dust features, we also expect to identify narrower gas features from molecular species such as CO<sub>2</sub>, H<sub>2</sub>O, HCN, C<sub>2</sub>H<sub>2</sub> etc.</p>