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23 April 2024 |
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Article overview
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Deflating Super-Puffs: Impact of Photochemical Hazes on the Observed Mass-Radius Relationship of Low Mass Planets | | Peter Gao
; Xi Zhang
; | | Date: |
31 Dec 2019 | | Abstract: | The observed mass-radius relationship of low-mass planets informs our
understanding of their composition and evolution. Recent discoveries of low
mass, large radii objects ("super-puffs") have challenged theories of planet
formation and atmospheric loss, as their high inferred gas masses make them
vulnerable to runaway accretion and hydrodynamic escape. Here we propose that
high altitude photochemical hazes could enhance the observed radii of low-mass
planets and explain the nature of super-puffs. We construct model atmospheres
in radiative-convective equilibrium and compute rates of atmospheric escape and
haze distributions, taking into account haze coagulation, sedimentation,
diffusion, and advection by an outflow wind. We develop mass-radius diagrams
that include atmospheric lifetimes and haze opacity, which is enhanced by the
outflow, such that young (~0.1-1 Gyr), warm (T$_{eq}$ $geq$ 500 K), low mass
objects ($M_c$ < 4M$_{
m Earth}$) should experience the most apparent radius
enhancement due to hazes, reaching factors of three. This reconciles the
densities and ages of the most extreme super-puffs. For Kepler-51b, the
inclusion of hazes reduces its inferred gas mass fraction to <10%, similar to
that of planets on the large radius side of the sub-Neptune radius gap. This
suggests that Kepler-51b may be evolving towards that population, and that some
warm sub-Neptunes may have evolved from super-puffs. Hazes also render
transmission spectra of super-puffs and sub-Neptunes featureless, consistent
with recent measurements. Our hypothesis can be tested by future observations
of super-puffs’ transmission spectra at mid-infrared wavelengths, where we
predict that the planet radius will be half of that observed in the
near-infrared. | | Source: | arXiv, 2001.0055 | | Services: | Forum | Review | PDF | Favorites | |
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