Constraining the Bulk Composition of Disintegrating Exoplanets Using Combined Transmission Spectra from JWST and SPICA

Abstract

Disintegrating planets are ultra-short-period exoplanets that appear to have a comet-like dust tail. They are commonly interpreted as low-mass planets whose solid surface is evaporating and whose tail is made of recondensing minerals. Transmission spectroscopy of the dust tails could thus allow us to directly probe the elementary compositions of the planets. Previous work already investigated the feasibility of such observations using the JWST mid-infrared instrument. In this study, we explore if one can obtain a strong constrain on the tail composition by adding spectroscopy at longer wavelengths using SPICA mid-infrared instrument. We use a simple model for the spatial distribution of the dust tails and produce their synthetic transmission spectra assuming various dust compositions. We find that combined infrared spectra from JWST and SPICA will allow us to diagnose various components of the dust tails. JWST will be able to detect silicate and carbide absorption features with a feature-to-noise ratio of 3 in the tail transmission spectrum of a disintegrating planet located within 100 pc from the Earth with a transit depth deeper than 0.5%. SPICA can distinguish between Fe-and Mg-bearing crystalline silicates for planets at 100 pc with a transit depth of 2%. Transit searches with current and future space telescopes (e.g., TESS and PLATO) will provide ideal targets for such spectroscopic observations.

Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs

“…These planets undergo intense stellar irradiation that vaporizes rocky surfaces and drives the escape of mineral atmospheres entraining recondensed dust (Perez-Becker & Chiang 2013; Kang et al 2021). The dust tail offers clues to the rocky composition of planets through spectroscopy of future space-based telescopes (Bodman et al 2018;Okuya et al 2020), whereas the origin of the tail is still highly uncertain. Rappaport et al (2012) estimated the dust-to-gas mass ratio of order unity in the outflow.…”

“…Although meteoric dust has relatively minor impacts on observed radii, it is interesting to note that they produce silicate features at λ∼10 µm. The emergence of silicate feature has been anticipated for silicate clouds in hot Jupiters (Powell et al 2019;, mineral atmospheres on magma ocean planets (Ito et al 2015(Ito et al , 2021, and dust tails of ultra-short period disintegrating planets (Bodman et al 2018;Okuya et al 2020), but not expected for the temperature regimes of super-puffs. Though this is beyond the topic of this study, searching for silicate features in cool exoplanetary atmospheres may help to constrain how much meteoroids are infalling to the planet.…”

A Circumplanetary Dust Ring May Explain the Extreme Spectral Slope of the 10 Myr Young Exoplanet K2-33b

“…We note that a pure FeO composition is likely unrealistic, as the mass fraction of FeO is up to ∼20 wt% in solar system crustal rocks (McLennan 2020) and predicted to be ∼50 wt% (the remainders are mostly SiO 2 and MgO) even in a hypothetical coreless planet where the iron core did not form (Elkins-Tanton & Seager 2008). Thus, similar to the spectroscopy of dust tails of disintegrating rocky exoplanets (Bodman et al 2018;Okuya et al 2020), future observations of absorption features at the mid-infrared wavelength would also provide a unique opportunity to explore the origins of CPDRs and their possible parent bodies.…”