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Will Misener @willmisener.bsky.social · 26/08/2026

The structural changes, both in the locations of non-convective regions and in the mean molecular weights, lead to different planetary radii. The transitions between regimes are sudden for small changes in base abundance, indicating you can constrain interiors using atmospheric abundances.

$A three panel plot indicating the variation in atmospheric properties as function of base Mg/Si ratio. Variations in gas number fractions at the base, at the 1 bar level, and transit radii are shown by colored lines.$

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Will Misener @willmisener.bsky.social · 26/08/2026

Different base abundances promote different condensates at equilibrium, which draw down Si and O at different rates and in different ratios. This feedback leads to entirely different atmospheric chemistry! We find Si-depleted envelopes rich in water and O-depleted endmembers with CH4 and SiH4.

Figure 2 from Misener et al. (2026), a six panel plot comparing the mixing ratios of gases, the condensate number densities, and temperatures as functions of pressure using colored lines for two base Mg:Si:O ratios.

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Will Misener @willmisener.bsky.social · 05/05/2026

We also model planetary evolution using these self-consistent escape rates. We find that incorporating all relevant mechanisms is vital for capturing the evolution: any missing piece produces inaccurate results! Excited to see what people think!

Three panels showing atmospheric mass, transit radius, and mass loss rates as functions of time. A solid line shows PE+CPML, while dashed lines of various colors compare other models missing various components. The other models produce less escape and different radius evolution compared to the self-consistent one.

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Will Misener @willmisener.bsky.social · 05/05/2026

We make easy-to-use scalings for the transition radius between CPML and PE as functions of planet mass and equilibrium temperature. We find that most sub-Neptunes transition into photoevaporation at late times, but core-powered escape is important early and dominates for low-mass, close-in planets.

Two panels plotting transition radius against planet mass and equilibrium temperature. Dots show the modeled transition radius, which increases with planet mass and decreases with temperature. Linear fit equations are shown.

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Will Misener @willmisener.bsky.social · 05/05/2026

We find escape rates self-consistently over a range of planet radii, masses, temperatures, and UV fluxes. We find that outflows are core-powered early on, and transition to photoevaporation as they shrink! Funky physics happens at the transition, when UV just barely penetrates

Three panels showing mass loss rate as a function of radius for three planet masses. Dots show aiolos hydrodynamic outputs, which are overlain with lines showing analytic scalings. The dots follow the core-powered scaling at large radii and switch to the energy limit at small radii, with some dots in the middle dipping below both models

Three panels showing atmospheric escape rates against XUV luminosity for three planet masses. The lines are color coded by radius. Large radii in light-colors have large mass loss rates that are independent of XUV, while small radii in dark colorsare linearly dependent on XUV. Intermediate radii can decrease in mass loss rate with increasing XUV as they transition from bolometric to XUV dominated escape.

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Will Misener @willmisener.bsky.social · 27/02/2025

That means that sub-Neptunes will evolve differently depending on the exact upper atmosphere composition, even if they're always hydrogen-dominated. We find that the opacity ratios can make a difference between very little atmosphere being retained under core-powered mass loss, or nearly all. 8/10

Three panel plot showing RCB radius, atmospheric mass, and mass loss rate as functions of time. Different color curves represent different values of gamma. High values of gamma lead to large escape rates. Therefore most of the initial atmosphere is stripped within 1 billion years. Conversely, if gamma is low, virtually no primordial atmosphere is lost. Adapted from Misener et al. (2025), Fig 4.

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Will Misener @willmisener.bsky.social · 27/02/2025

The difference in mass loss rates for different opacity ratios is biggest when the atmospheres are most contracted, with up to a factor of 10^10 in mass loss rate separating cold upper atmospheres from hot ones! We provide tabulated rates in case you'd like to use these numbers yourself. 7/10

A plot showing mass loss rate as a function of radiative-convective boundary (RCB) radius. Different colors show different values of the opacity ratio gamma. Mass loss rate increases as a function of radius for all gamma values. But lower values of gamma lead to escape rates lower by 10 orders of magnitude at small radii than do high values of gamma. The rates converge at larger radii. Adapted from Misener et al. (2025), Fig 3.

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Will Misener @willmisener.bsky.social · 27/02/2025

What we found is that the opacities have big implications for escape from sub-Neptunes: hotter temperature profiles lead to more mass loss! The most important reason why is that the density falls off more slowly if the temperatures are higher, leading to higher escape rates. 6/10

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Will Misener @willmisener.bsky.social · 27/02/2025

If the ratio (termed gamma) is near 1, then the atmosphere is roughly isothermal, but if it's not, you can get cool stratospheres or thermal inversions. This won't come as news to a lot of exoplaneteers, as we've long seen evidence for the phenomenon in atmospheric spectra! 4/10

Model P-T profiles of hot Jupiters from Fortney et al. (2008), showing prominent thermal inversions due to the presence of efficient optical absorbers (i.e., high gamma values in the upper atmosphere).

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Will Misener @willmisener.bsky.social · 27/02/2025

Core-powered mass loss, one of the mechanisms that can explain the radius valley separating the super-Earths and sub-Neptunes, has always been modeled using an analytic escape rate calculation, called a Parker wind, that assumed the outer atmosphere was isothermal at the equilibrium temperature 2/10

A two-panel plot showing the predictions of a core-powered mass loss model (left) against the observed planet demographics (right), showing good agreement. The mass loss rates in the models were calculated assuming an isothermal outer atmosphere. Adapted from Gupta+Schlichting 2019, Fig 2.

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Will Misener @willmisener.bsky.social · 07/01/2024

Excited for my first-ever (!) AAS this week. Look out for my thesis talk, conveniently on Monday morning to ease you back into conferencing: 133.05D “Coupled chemistry and structure of sub-Neptune atmospheres: a window into the interior” Mon, Jan 8 10:40-11:00am Room R04 #AAS243

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