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Synthetic detection PDF is shown in orange contours for bestfitting parameters from MODEL III. CKS planets from Fulton et al. (2017) are also shown to demonstrate the goodness of fit of model and data.
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The radius distribution of small, close-in exoplanets has recently been shown to be bimodal. The photoevaporation model predicted this bimodality. In the photoevaporation scenario, some planets are completely stripped of their primordial H/He atmospheres, whereas others retain them. Comparisons between the photoevaporation model and observed planet...
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... additionally choose to infer the index of photoevaporation efficiency scaling α η (equation 7) assuming a uniform prior, as well as the core composition distribution with a Gaussian function (also assuming uniform prior on mean and standard deviation). We show the detection PDF λ(P, R) for best-fitting parameters alongside the real CKS planets in Fig. 7, which demonstrates that our adopted likelihood is effective in capturing the shape of the planet distribution. As before, the bestfitting radius distribution for MODEL III is shown in the left-hand panel of Fig. 8. Similar to MODEL II, we get an excellent agreement of model and data. As well as a mean number of planets per star of f * ...
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... The two atmospheric mass loss models we compare occurrence to are a photoevaporation model from Rogers & Owen (2021) and a core-powered mass-loss model from Gupta & Schlichting (2020). We independently replicated the models of both of theories and validated our code with public benchmarks in their papers. ...
... Our photoevaporation model is based on the theoretical model presented in Rogers & Owen (2021). We build our code based on the code of Owen & Campos Estrada (2020). ...
... Next, we build a core-powered mass-loss model of based on the model of Gupta & Schlichting (2020). For the input Rogers & Owen (2021). Bottom: Model II, corepowered mass-loss model from Gupta & Schlichting (2020). ...
The Kepler mission enabled us to look at the intrinsic population of exoplanets within our galaxy. In period-radius space, the distribution of the intrinsic population of planets contains structure that can trace planet formation and evolution history. The most distinctive feature in period-radius space is the radius cliff, a steep drop-off in occurrence between 2.5 and 4 R ⊕ across all period ranges, separating the sub-Neptune population from the rarer Neptunes orbiting within 1 au. Following our earlier work to measure the occurrence rate of the Kepler population, we characterize the shape of the radius cliff as a function of orbital period (10–300 days) as well as insolation flux (9500 S ⊕ –10 S ⊕ ). The shape of the cliff flattens at longer orbital periods, tracking the rising population of Neptune-sized planets. In insolation, however, the radius cliff is both less dramatic and the slope is more uniform. The difference in this feature between period space and insolation space can be linked to the effect of EUV/X-ray versus bolometric flux in the planet’s evolution. Models of atmospheric mass loss processes that predict the location and shape of the radius valley also predict the radius cliff. We compare our measured occurrence rate distribution to population synthesis models of photoevaporation and core-powered mass loss in order to constrain formation and evolution pathways. We find that the models do not statistically agree with our occurrence distributions of the radius cliff in period space or insolation space. Atmospheric mass loss that shapes the radius valley cannot fully explain the shape of the radius cliff.
... Along with core-powered mass loss (Ginzburg et al. 2018;Gupta & Schlichting 2019), photoionization-driven atmospheric escape is thought to play a significant role in shaping the observed properties of the Kepler planet population (Fulton et al. 2017), likely contributing to carving the observed radius valley by stripping sub-Neptune-sized planets of their primordial envelopes and turning them into rocky cores (e.g., Owen & Wu 2013Rogers & Owen 2021;Affolter et al. 2023;Owen & Schlichting 2024). ...
Motivated by the recent surge in interest concerning white dwarf (WD) planets, this work presents the first numerical exploration of WD-driven atmospheric escape, whereby the high-energy radiation from a hot/young WD can trigger the outflow of the hydrogen–helium envelope for close-in planets. As a pilot investigation, we focus on two specific cases: a gas giant and a sub-Neptune-sized planet, both orbiting a rapidly cooling WD with mass M * = 0.6 M ⊙ and separation a = 0.02 au. In both cases, the ensuing mass outflow rates exceed 10 ¹⁴ g s ⁻¹ for WD temperatures greater than T WD ≳ 50,000 K. At T WD ≃ 18,000 K (22,000 K), the sub-Neptune (gas giant) mass outflow rate approaches 10 ¹² g s ⁻¹ , i.e., comparable to the strongest outflows expected from close-in planets around late main-sequence stars. Whereas the gas giant remains virtually unaffected from an evolutionary standpoint, atmospheric escape may have sizable effects for the sub-Neptune, depending on its dynamical history, e.g., assuming that the hydrogen–helium envelope makes up 1% (4%) of the planet mass, the entire envelope would be evaporated away so long as the planet reaches 0.02 au within the first 230 Myr (130 Myr) of the WD formation. We discuss how these results can be generalized to eccentric orbits with effective semimajor axis a ′ = a / ( 1 − e 2 ) 1 / 4 , which receive the same orbit-averaged irradiation. Extended to a much broader parameter space, this approach can be exploited to model the expected demographics of WD planets as a function of their initial mass, composition, and migration history, as well as their potential for habitability.
... Each unconfirmed planet candidate is included, or excluded, based on a random draw as per their false-positive probability (see Section 4.4). 10 Figure 7. Number of combined confirmed planets (dark) and planet candidates (light) detected in our SPOC (left) and QLP (right) planet surveys compared to the expected yield (light yellow) from our forward model calculations using the Kepler occurrence rates (Kunimoto & Matthews 2020) and the expected yield from evolution models for hydrogen-dominated (dark yellow) planets (Rogers & Owen 2021) as a function of orbital period (top) and planet radius (bottom). We find a significant excess in planets with orbital periods between 6.2 and 12 days around young stars. ...
... To test these predictions, we perform a forward modeling exercise using the models presented in Rogers & Owen (2021) and Rogers et al. (2023). These models consider the thermal contraction and photoevaporative mass loss for small, close-in exoplanets hosting hydrogen-helium atmospheres. ...
... For each star in the underlying SPOC and QLP stellar samples presented in Table 1, we forward model 100 planets, assuming the underlying core mass, initial atmospheric mass fraction, core composition, and orbital period distributions inferred in Rogers & Owen (2021). The synthesized planets have ages corresponding to that estimated for each respective association as listed in Table 1. ...
Within the first few hundreds of millions of years, many physical processes sculpt the eventual properties of young planets. NASA’s Transiting Exoplanet Survey Satellite (TESS) mission has surveyed young stellar associations across the entire sky for transiting planets, providing glimpses into the various stages of planetary evolution. Using our own detection pipeline, we search a magnitude-limited sample of 7219 young stars (≲200 Myr) observed in the first 4 yr of TESS for small (2–8 R ⊕ ), short period (1.6–20 days) transiting planets. The completeness of our survey is characterized by a series of injection and recovery simulations. Our analysis of TESS 2 minute cadence and Full Frame Image (FFI) light curves recover all known TESS Objects of Interest (TOIs), as well as four new planet candidates not previously identified as TOIs. We derive an occurrence rate of 35 − 10 + 13 % for mini-Neptunes and 27 − 8 + 10 % for super-Neptunes from the 2 minute cadence data, and 22 − 6.8 + 8.6 % for mini-Neptunes and 13 − 4.9 + 3.9 % for super-Neptunes from the FFI data. To independently validate our results, we compare our survey yield with the predicted planet yield assuming Kepler planet statistics. We consistently find a mild increase in the occurrence of super-Neptunes and a significant increase in the occurrence of Neptune-sized planets with orbital periods of 6.2–12 days when compared to their mature counterparts. The young planet distribution from our study is most consistent with evolution models describing the early contraction of hydrogen-dominated atmospheres undergoing atmospheric escape and inconsistent with heavier atmosphere models offering only mild radial contraction early on.
... largely rocky cores with an H 2 -rich atmosphere (e.g. Lopez, F ortne y & Miller 2012 ;Owen & Wu 2013 ;Gupta & Schlichting 2019 ;Rogers & Owen 2021 ). Two methods of mass-loss are generally considered, photoe v aporation (e.g. ...
... Mechanisms of atmospheric mass loss, including both photoe v aporative (e.g. Owen & Wu 2013Rogers & Owen 2021 ) and core-MNRAS 529, 409-424 (2024) powered (e.g. Gupta & Schlichting 2019, make predictions for permitted envelope mass fractions for sub-Neptunes. ...
Recent studies have suggested the possibility of Hycean worlds, characterized by deep liquid water oceans beneath H2-rich atmospheres. These planets significantly widen the range of planetary properties over which habitable conditions could exist. We conduct internal structure modelling of Hycean worlds to investigate the range of interior compositions, ocean depths and atmospheric mass fractions possible. Our investigation explicitly considers habitable oceans, where the surface conditions are limited to those that can support potential life. The ocean depths depend on the surface gravity and temperature, confirming previous studies, and span 10s to ∼1000 km for Hycean conditions, reaching ocean base pressures up to ∼6 × 104 bar before transitioning to high-pressure ice. We explore in detail test cases of five Hycean candidates, placing constraints on their possible ocean depths and interior compositions based on their bulk properties. We report limits on their atmospheric mass fractions admissible for Hycean conditions, as well as those allowed for other possible interior compositions. For the Hycean conditions considered, across these candidates we find the admissible mass fractions of the H/He envelopes to be ≲10−3. At the other extreme, the maximum H/He mass fractions allowed for these planets can be up to ∼4–8 per cent, representing purely rocky interiors with no H2O layer. These results highlight the diverse conditions possible among these planets and demonstrate their potential to host habitable conditions under vastly different circumstances to the Earth. Upcoming JWST observations of candidate Hycean worlds will allow for improved constraints on the nature of their atmospheres and interiors.
... The final mass and radii of these planets were shown to be inconsistent with current observational data, with the models producing a higher atmospheric mass fraction than is observed. Then, in Rogers & Owen (2021) and Rogers et al. (2023a), XUV photoevaporation was exploited to rewind the clock for Kepler planet evolution. To be consistent with the present-day demographics, they showed that the initial atmospheric mass fraction of planets, once their discs had dispersed, must scale positively with core mass, consistent with the analytic findings of Ginzburg et al. (2016). ...
... The onset of disc dispersal then triggers boil-off, in which planets typically lose ≳ 90% of their accreted atmospheres. This mechanism provides a possible solution to the documented discrepancy between predicted accreted masses and the initial conditions inferred from Kepler data with XUV photoevaporation, as shown in Jankovic et al. (2019); Rogers & Owen (2021). ...
The atmospheres of small, close-in exoplanets are vulnerable to rapid mass-loss during protoplanetary disc dispersal via a process referred to as ‘boil-off’, in which confining pressure from the local gas disc reduces, inducing atmospheric loss and contraction. We construct self-consistent models of planet evolution during gaseous core accretion and boil-off. As the surrounding disc gas dissipates, we find that planets lose mass via subsonic breeze outflows which allow causal contact to exist between disc and planet. Planets initially accrete of order |$\sim 10~{{\%}}$| in atmospheric mass, however, boil-off can remove |$\gtrsim 90~{{\%}}$| of this mass during disc dispersal. We show that a planet’s final atmospheric mass fraction is strongly dictated by the ratio of cooling timescale to disc dispersal timescale, as well as the planet’s core mass and equilibrium temperature. With contributions from core cooling and radioactivity, we show that core luminosity eventually leads to the transition from boil-off to core-powered mass-loss. We find that smaller mass planets closest to their host star may have their atmospheres completely stripped through a combination of boil-off and core-powered mass-loss during disc dispersal, implying the existence of a population-level radius gap emerging as the disc disperses. We additionally consider the transition from boil-off/core-powered mass-loss to X-ray/EUV (XUV) photoevaporation by considering the penetration of stellar XUV photons below the planet’s sonic surface. Finally, we show that planets may open gaps in their protoplanetary discs during the late stages of boil-off, which may enhance mass-loss rates.
... For more massive stars, the smaller observational signal often impedes precise planetary mass determination. In that case, a clear picture of density does not emerge with present-day data, and the different theoretical models cannot easily be falsified 18 unless the planetary masses are constrained using theoretical arguments, such as the output of a planet formation model 15,19,20 . ...
... We obtained the mass distribution, shown in Extended Data Fig. 3, by modelling planet growth from the embryo stage onward via solid and gas accretion followed by long-term evolution. This forward modelling approach differs from (and allows for contrasting insights compared to) using an educated guess for the planetary masses 35 or retrieving mass distributions by solving the inverse problem and starting with radii found by the Kepler satellite 18,35 . We obtain a trend in mass from low-mass, rocky planets over more massive, migrated, steamy water worlds to the H/He-rich (sub)giants. ...
The radius valley (or gap) in the observed distribution of exoplanet radii, which separates smaller super-Earths from larger sub-Neptunes, is a key feature that theoretical models must explain. Conventionally, it is interpreted as the result of the loss of primordial hydrogen and helium (H/He) envelopes atop rocky cores. However, planet formation models predict that water-rich planets migrate from cold regions outside the snowline towards the star. Assuming water to be in the form of solid ice in their interior, many of these planets would be located in the radius gap contradicting observations. Here we use an advanced coupled formation and evolution model that describes the planets’ growth and evolution starting from solid, moon-sized bodies in the protoplanetary disk to mature Gyr-old planetary systems. Employing new equations of state and interior structure models to treat water as vapour mixed with H/He, we naturally reproduce the valley at the observed location. The model results demonstrate that the observed radius valley can be interpreted as the separation of less massive, rocky super-Earths formed in situ from more massive, ex situ, water-rich sub-Neptunes. Furthermore, the occurrence drop at larger radii, the so-called radius cliff, is matched by planets with water-dominated envelopes. Our statistical approach shows that the synthetic distribution of radii quantitatively agrees with observations for close-in planets, but only if low-mass planets initially containing H/He lose their atmosphere due to photoevaporation, which populates the super-Earth peak with evaporated rocky cores. Therefore, we provide a hybrid theoretical explanation of the radius gap and cliff caused by both planet formation (orbital migration) as well as evolution (atmospheric escape).
... The photoe v aporation models used to match the observed location of the radius valley have not included magnetic fields (e.g. Owen & Wu 2017 ;Wu 2019 ;Rogers & Owen 2021 ;Rogers et al. 2023a , b ). Photoe v aporati ve outflo ws are highly ionized, so they should be influenced by any planetary magnetic fields. ...
Planetary magnetic fields can affect the predicted mass loss rate for close-in planets that experience large amounts of UV irradiation. In this work, we present a method to detect the magnetic fields of close-in exoplanets undergoing atmospheric escape using transit spectroscopy at the 10830 Å line of helium. Motivated by previous work on hydrodynamic and magneto-hydrodynamic photoevaporation, we suggest that planets with magnetic fields that are too weak to control the outflow’s topology lead to blue-shifted transits due to day-to-night-side flows. In contrast, strong magnetic fields prevent this day-to-night flow, as the gas is forced to follow the magnetic field’s roughly dipolar topology. We post-process existing 2D photoevaporation simulations, computing synthetic transit profiles in helium to test this concept. As expected, we find that hydrodynamically dominated outflows lead to blue-shifted transits on the order of the sound speed of the gas. Strong surface magnetic fields lead to unshifted or slightly red-shifted transit profiles. High-resolution observations can distinguish between these profiles; however, eccentricity uncertainties generally mean that we cannot conclusively say velocity shifts are due to the outflow for individual planets. The majority of helium observations are blue-shifted, which could be a tentative indication that close-in planets generally have surface dipole magnetic field strengths ≲ 0.3 Gauss. More 3D hydrodynamic and magneto-hydrodynamic simulations are needed to confirm this conclusion robustly.
... We modelled the internal structure of LTT 9779 b assuming a silicateiron (rocky) core surrounded by a large H/He-rich atmosphere, following Rogers & Owen ( 2021 ). This description entails a total of four model parameters: the core radius R core , core mass M core , envelope radius R env , and envelope mass fraction f env (see Table 4 ). ...
The Neptunian desert is a region in period-radius parameter space with very few Neptune-sized planets at short orbital periods. Amongst these, LTT 9779 b is the only known Neptune with a period shorter than one day to retain a significant H-He atmosphere. If the Neptune desert is the result of X-ray/EUV-driven photoevaporation, it is surprising that the atmosphere of LTT 9779 b survived the intense bombardment of high energy photons from its young host star. However, the star has low measured rotational broadening, which points to the possibility of an anomalously slow spin period and hence a faint X-ray emission history that may have failed to evaporate the planet’s atmosphere. We observed LTT 9779 with XMM-Newton and measured an upper limit for its X-ray luminosity that is a factor of fifteen lower than expected for its age. We also simulated the evaporation past of LTT 9779 b and found that the survival of its atmosphere to the present day is consistent with an unusually faint XUV irradiation history that matches both the X-ray and rotation velocity measurements. We conclude that the anomalously low X-ray irradiation of the one Neptune seen to survive in Neptunian desert supports the interpretation of the desert as primarily a result of photoevaporation.
... Specifically, theories have been developed that attempt to recover the bimodal radius distribution of planets smaller than ∼4 R ⊕ , as well as dependencies of that distribution on additional variables such as orbital distance and stellar host type. Among these theories, both photoevaporation (Owen & Wu 2017;Rogers & Owen 2021) and core-powered mass loss (Ginzburg et al. 2018) explain the planet radius distribution of Keplerdiscovered planets orbiting F/G/K-type stars with mass loss from an accreted H 2 atmosphere overlying a rocky planetary core-giving support to the gas-dwarf hypothesis. When lowmass host stars are investigated separately, a different evolution of the radius gap with irradiation is uncovered (Cloutier & Menou 2020), potentially indicating an additional formation/ evolution mechanism for sub-Neptunes orbiting later-type stars. ...
It remains to be ascertained whether sub-Neptune exoplanets primarily possess hydrogen-rich atmospheres or whether a population of H 2 O-rich water worlds lurks in their midst. Addressing this question requires improved modeling of water-rich exoplanetary atmospheres, both to predict and interpret spectroscopic observations and to serve as upper boundary conditions on interior structure calculations. Here, we present new models of hydrogen-helium-water atmospheres with water abundances ranging from solar to 100% water vapor. We improve upon previous models of high-water-content atmospheres by incorporating updated prescriptions for water self-broadening and a nonideal gas equation of state. Our model grid ( https://umd.box.com/v/water-worlds ) includes temperature–pressure profiles in radiative-convective equilibrium, along with their associated transmission and thermal emission spectra. We find that our model updates primarily act at high pressures, significantly impacting bottom-of-atmosphere temperatures, with implications for the accuracy of interior structure calculations. Upper-atmosphere conditions and spectroscopic observables are less impacted by our model updates, and we find that, under most conditions, retrieval codes built for hot Jupiters should also perform well on water-rich planets. We additionally quantify the observational degeneracies among both thermal emission and transmission spectra. We recover standard degeneracies with clouds and mean molecular weight for transmission spectra, and we find thermal emission spectra to be more readily distinguishable from one another in the water-poor (i.e., near-solar) regime.
... One of the possible consequences of GCE for exoplanets is the resulting core mass fractions due to variations in lithophile/siderophile ratios. The mass fractions of iron-rich cores of rocky planets have been shown to be related to the iron mass fractions deduced from their host stars (e.g., Adibekyan et al. 2021;Rogers & Owen 2021 ...
A persistent question in exoplanet demographics is whether exoplanetary systems form from similar compositional building blocks to our own. Polluted white dwarf stars offer a unique way to address this question, as they provide measurements of the bulk compositions of exoplanetary material. We present a statistical analysis of the rocks polluting oxygen-bearing white dwarfs and compare their compositions to rocks in the solar system. We find that the majority of the extrasolar rocks are consistent with the composition of typical chondrites. Measurement uncertainties prevent distinguishing between chondrites and bulk Earth but do permit detecting the differences between chondritic compositions and basaltic or continental crust. We find no evidence of crust among the polluted white dwarfs. We show that the chondritic nature of extrasolar rocks is also supported by the compositions of local stars. While galactic chemical evolution results in variations in the relative abundances of rock-forming elements spatially and temporally on galaxy-wide scales, the current sample of polluted white dwarfs are sufficiently young and close to Earth that they are not affected by this process. We conclude that exotic compositions are not required to explain the majority of observed rock types around polluted white dwarfs and that variations between exoplanetary compositions in the stellar neighborhood are generally not due to significant differences in the initial composition of protoplanetary disks. Nonetheless, there is evidence from stellar observations that planets formed in the first several billion years in the Galaxy have lower metal core fractions compared with Earth on average.
