The Sky is Falling On Exoplanets

Planet formation theories predict a relationship between planet mass and metallicity. Abundances measurements may be used to compare to these theoretical expectations if it is assumed that planetary atmospheres are a “closed box” whose elemental abundances reflect the time of formation. However, if there is ongoing accretion of heavy elements then the abundances may instead partially reflect those of the heavy element reservoir as well as those of the primordial planet. Accretion of interplanetary dust is of interest, as it may act as a steady source of heavy elements in the upper atmosphere over long timescales. If the accretion rate is large enough, this accreted dust and ablated gas-phase atoms may generate significant opacity, possibly to the point of affecting the transmission spectrum. In this talk I will discuss observational constraints on interplanetary dust orbiting near the parent star as well as theoretical estimates for the efficiency of accretion of this dust by extrasolar planets. Dust particles inspiraling toward the star due to Poynting-Robertson drag will encounter mean-motion resonances with the star-planet binary, and will suffer one of three fates when they exit resonance: hitting the planet, hitting the star, or being ejected from the system. Results will be presented that show the fraction of dust hitting the planet can be surprisingly high (10s of percent), hence much of the inspiraling dust may end up polluting the planetary upper atmosphere. Results for model transmission spectra including accreted dust will be presented.