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![The M-R diagram of planets with robust mass measurements with relative uncertainties smaller than 25% for mass and smaller than 8% for radius. The red triangles and blue circles correspond to data with mass determination from TTVs and RVs, respectively. Also shown are composition lines of pure-iron (brown), Earth-like planets (light-brown) and water ice (blue), and the distribution of exoplanet mass (top) and radius (right). We indicate the planets that are expected to be “terrestrial” “gaseous” or “intermediate” in terms of composition (from [111])](publication/351763038/figure/fig1/AS:1163071485681664@1654309259663/The-M-R-diagram-of-planets-with-robust-mass-measurements-with-relative-uncertainties.png)
The M-R diagram of planets with robust mass measurements with relative uncertainties smaller than 25% for mass and smaller than 8% for radius. The red triangles and blue circles correspond to data with mass determination from TTVs and RVs, respectively. Also shown are composition lines of pure-iron (brown), Earth-like planets (light-brown) and water ice (blue), and the distribution of exoplanet mass (top) and radius (right). We indicate the planets that are expected to be “terrestrial” “gaseous” or “intermediate” in terms of composition (from [111])
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The recently adopted Ariel ESA mission will measure the atmospheric composition of a large number of exoplanets. This information will then be used to better constrain planetary bulk compositions. While the connection between the composition of a planetary atmosphere and the bulk interior is still being investigated, the combination of the atmosphe...
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Gravitational microlensing is currently the only technique that helps study the Galactic distribution of planets as a function of distance from the Galactic center. The Galactic location of a lens system can be uniquely determined only when at least two of the three quantities that determine the mass--distance relations are measured. However, even...
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... The bulk densities for each planet are color coded and the markers are sized according to their mass. mation, evolution, and interior (e.g., Burrows 2014; Thorngren & Fortney 2019;Helled et al. 2022a). ...
We report the discovery of two transiting planets detected by the Transiting Exoplanet Survey Satellite (TESS), TOI-2374 b and TOI-3071 b, orbiting a K5V and an F8V star, respectively, with periods of 4.31 and 1.27 days, respectively. We confirm and characterize these two planets with a variety of ground-based and follow-up observations, including photometry, precise radial velocity monitoring and high-resolution imaging. The planetary and orbital parameters were derived from a joint analysis of the radial velocities and photometric data. We found that the two planets have masses of $(57 \pm 4)$ $M_\oplus$ or $(0.18 \pm 0.01)$ $M_J$, and $(68 \pm 4)$ $M_\oplus$ or $(0.21 \pm 0.01)$ $M_J$, respectively, and they have radii of $(6.8 \pm 0.3)$ $R_\oplus$ or $(0.61 \pm 0.03)$ $R_J$ and $(7.2 \pm 0.5)$ $R_\oplus$ or $(0.64 \pm 0.05)$ $R_J$, respectively. These parameters correspond to sub-Saturns within the Neptunian desert, both planets being hot and highly irradiated, with $T_{\rm eq} \approx 745$ $K$ and $T_{\rm eq} \approx 1812$ $K$, respectively, assuming a Bond albedo of 0.5. TOI-3071 b has the hottest equilibrium temperature of all known planets with masses between $10$ and $300$ $M_\oplus$ and radii less than $1.5$ $R_J$. By applying gas giant evolution models we found that both planets, especially TOI-3071 b, are very metal-rich. This challenges standard formation models which generally predict lower heavy-element masses for planets with similar characteristics. We studied the evolution of the planets' atmospheres under photoevaporation and concluded that both are stable against evaporation due to their large masses and likely high metallicities in their gaseous envelopes.
... Finally, a Saturn probe would allow us to do a comparative analysis of Jupiter's and Saturn's atmospheres and identify whether it is also the case for Saturn that there is tension between the atmospheric composition and interior models. Similarly, accurate measurements of the atmospheric composition of a large number of giant exoplanets, together with estimates of the planetary bulk composition, would provide a more global view of the relation between the atmospheric and bulk compositions of giant planets (Helled et al. 2022c;Müller & Helled 2023). ...
Updated formation and structure models of Jupiter predict a metal-poor envelope. This is at odds with the two to three times solar metallicity measured by the Galileo probe. Additionally, Juno data imply that water and ammonia are enriched. Here, we explore whether Jupiter could have a deep radiative layer separating the atmosphere from the deeper interior. The radiative layer could be caused by a hydrogen-transparency window or depletion of alkali metals. We show that heavy-element accretion during Jupiter’s evolution could lead to the desired atmospheric enrichment and that this configuration would be stable over billions of years. The origin of the heavy elements could be cumulative small impacts or one large impact. The preferred scenario requires a deep radiative zone, due to a local reduction of the opacity at ∼2000 K by ∼90%, which is supported by Juno data, and vertical mixing through the boundary with an efficiency similar to that of molecular diffusion ( D ≲ 10 ⁻² cm ² s ⁻¹ ). Therefore, most of Jupiter’s molecular envelope could have solar composition while its uppermost atmosphere is enriched with heavier elements. The enrichment likely originates from the accretion of solid objects. This possibility resolves the long-standing mismatch between Jupiter’s interior models and atmospheric composition measurements. Furthermore, our results imply that the measured atmospheric composition of exoplanets does not necessarily reflect their bulk compositions. We also investigate whether the enrichment could be due to the erosion of a dilute core and show that this is highly unlikely. The core-erosion scenario is inconsistent with evolution calculations, the deep radiative layer, and published interior models.
... Measuring the chemical composition of giant planets' atmospheres promises a new dawn in giant exoplanets characterisation: Knowledge of the atmospheric composition can reveal information on the planetary interior and origin (Burrows, 2014;Teske et al., 2019;Turrini et al., 2021;Helled et al., 2022). Although the connection between FIGURE 2 (A) Radius evolution for different bulk metallicites shown together with three exoplanets (Kepler 16b, Kepler 167e, K2 114b). ...
... the atmospheric composition and that of the planetary bulk is challenging and is yet to be determined (e.g., Helled et al., 2022), in the case of warm Jupiters the planets can be better characterised. In particular, it was clearly shown that atmospheric measurements can break the degeneracy in determining the planetary bulk composition and it is expected that measurements of warm Jupiter atmospheres can reduce the uncertainty of the bulk composition by at least a factor of four (Müller and Helled, 2023). ...
The characterisation of giant exoplanets is crucial to constrain giant planet formation and evolution theory and for putting the solar-system’s giant planets in perspective. Typically, mass-radius (M-R) measurements of moderately irradiated warm Jupiters are used to estimate the planetary bulk composition, which is an essential quantity for constraining giant planet formation, evolution and structure models. The successful launch of the James Webb Space Telescope (JWST) and the upcoming ARIEL mission open a new era in giant exoplanet characterisation as atmospheric measurements provide key information on the composition and internal structure of giant exoplanets. In this review, we discuss how giant planet evolution models are used to infer the planetary bulk composition, and the connection between the compositions of the interior and atmosphere. We identify the important theoretical uncertainties in evolution models including the equations of state, atmospheric models, chemical composition, interior structure and main energy transport processes. Nevertheless, we show that atmospheric measurements by JWST and ARIEL and the accurate determination of stellar ages by PLATO can significantly reduce the degeneracy in the inferred bulk composition. Furthermore, we discuss the importance of evolution models for the characterisation of direct-imaged planets. We conclude that giant planet theory has a critical role in the interpretation of observation and emphasise the importance of advancing giant planet theory.
... Measuring the chemical composition of giant planets' atmospheres promises a new dawn in giant exoplanets characterisation: Knowledge of the atmospheric composition can reveal information on the planetary interior and origin Teske et al., 2019;Turrini et al., 2021;. Although the connection between the atmospheric composition and that of the planetary bulk is challenging and is yet to be determined (e.g., Helled et al., 2022), in the case of warm Jupiters the planets can be better characterised. In particular, it was clearly shown that atmospheric measurements can break the degeneracy in determining the planetary bulk composition and it is expected that measurements of warm Jupiter atmospheres can reduce the uncertainty on the bulk composition by at least a factor of four (Müller and Helled, 2023). ...
The characterisation of giant exoplanets is crucial to constrain giant planet formation and evolution theory and for putting the solar-system's giant planets in perspective. Typically, mass-radius (M-R) measurements of moderately irradiated warm Jupiters are used to estimate the planetary bulk composition, which is an essential quantity for constraining giant planet formation, evolution and structure models. The successful launch of the James Webb Space Telescope (JWST) and the upcoming ARIEL mission open a new era in giant exoplanet characterisation as atmospheric measurements provide key information on the composition and internal structure of giant exoplanets. In this review, we discuss how giant planet evolution models are used to infer the planetary bulk composition, and the connection between the compositions of the interior and atmosphere. We identify the important theoretical uncertainties in evolution models including the equations of state, atmospheric models, chemical composition, interior structure and main energy transport processes. Nevertheless, we show that that atmospheric measurements by JWST and ARIEL and the accurate determination of stellar ages by PLATO can significantly reduce the degeneracy in the inferred bulk composition. Furthermore, we discuss the importance of evolution models for the characterisation of direct-imaged planets. We conclude that giant planet theory has a critical role in the interpretation of observation and emphasise the importance of advancing giant planet theory.
... Studying the bulk atmospheric enrichment of exoplanets, mostly based on water detections in HST WFC3 spectra, has also been attempted, but the community would clearly benefit from data with higher signal-to-noise and larger spectral coverage to improve abundance constraints, break degeneracies with clouds, and probe additional atmospheric absorbers (e.g., Kreidberg et al. 2014;Fisher & Heng 2018;Wakeford et al. 2018;Pinhas et al. 2019;Welbanks et al. 2019). We note here, and discuss later, that a connection between atmosphere and bulk planet composition is far from trivial (also see, e.g., the recent discussion in Helled et al. 2021, and the references therein). ...
... If refractory atomic species are relatively abundant, this may point to a dominant accretion of solids which are mostly locked into the planet's interior. An interesting recent discussion of how to constrain planet formation in the case where the atmospheric and planetary bulk compositions differ can be found in Helled et al. (2021), who come to similar conclusions. We note again that these avenues for analyzing the origin of the metals in a planet's atmosphere will be further complicated if volatile-rich gas from evaporated pebbles was accreted by the planet. ...
Constraining planet formation based on the atmospheric composition of exoplanets is a fundamental goal of the exoplanet community. Existing studies commonly try to constrain atmospheric abundances, or to analyze what abundance patterns a given description of planet formation predicts. However, there is also a pressing need to develop methodologies that investigate how to transform atmospheric compositions into planetary formation inferences. In this study we summarize the complexities and uncertainties of state-of-the-art planet formation models and how they influence planetary atmospheric compositions. We introduce a methodology that explores the effect of different formation model assumptions when interpreting atmospheric compositions. We apply this framework to the directly imaged planet HR 8799e. Based on its atmospheric composition, this planet may have migrated significantly during its formation. We show that including the chemical evolution of the protoplanetary disk leads to a reduced need for migration. Moreover, we find that pebble accretion can reproduce the planet's composition, but some of our tested setups lead to too low atmospheric metallicities, even when considering that evaporating pebbles may enrich the disk gas. We conclude that the definitive inversion from atmospheric abundances to planet formation for a given planet may be challenging, but a qualitative understanding of the effects of different formation models is possible, opening up pathways for new investigations.
... With the increased precision of mass and radius measurements of planets, it become possible to characterize the interiors and bulk composition of low-mass exoplanets (Helled et al., 2021, Nettelmann & Valencia, 2021. Several attempts have been made in the last years trying to link the composition of low-mass planets and their host stars. ...
Because of their common origin, it was assumed that the composition of planet building blocks should, to a first order, correlate with stellar atmospheric composition, especially for refractory elements. In fact, information on the relative abundance of refractory and major rock-forming elements such as Fe, Mg, Si has been commonly used to improve interior estimates for terrestrial planets. Recently Adibekyan et al. (2021) presented evidence of a tight chemical link between rocky planets and their host stars. In this study we add six recently discovered exoplanets to the sample of Adibekyan et al and re-evaluate their findings in light of these new data. We confirm that i) iron-mass fraction of rocky exoplanets correlates (but not a 1:1 relationship) with the composition of their host stars, ii) on average the iron-mass fraction of planets is higher than that of the primordial iron-mass fraction of the protoplanetary disk, iii) super-Mercuries are formed in disks with high iron content. Based on these results we conclude that disk-chemistry and planet formation processes play an important role in the composition, formation, and evolution of super-Earths and super-Mercuries.
... With the increased precision of mass and radius measurements of planets, it become possible to characterize the interiors and bulk composition of low-mass exoplanets (Helled et al., 2021, Nettelmann & Valencia, 2021. Several attempts have been made in the last years trying to link the composition of low-mass planets and their host stars. ...
Because of their common origin, it was assumed that the composition of planet building blocks should, to a first order, correlate with stellar atmospheric composition, especially for refractory elements. In fact, information on the relative abundance of refractory and major rock-forming elements such as Fe, Mg, Si has been commonly used to improve interior estimates for terrestrial planets. Recently Adibekyan et al. (2021) presented evidence of a tight chemical link between rocky planets and their host stars. In this study we add six recently discovered exoplanets to the sample of Adibekyan et al and re-evaluate their findings in light of these new data. We confirm that i) iron-mass fraction of rocky exoplanets correlates (but not a 1:1 relationship) with the composition of their host stars, ii) on average the iron-mass fraction of planets is higher than that of the primordial f star iron , iii) super-Mercuries are formed in disks with high iron content. Based on these results we conclude that disk-chemistry and planet formation processes play an important role in the composition, formation, and evolution of super-Earths and super-Mercuries.
... At the moment, the presence and speciation of atmospheres on hot rocky exoplanets is contentious (Swain et al. 2021;Mugnai et al. 2021) due to the limitations of current astronomical observatories. Detailed characterization of individual, close-by transiting rocky planets may be the most direct path to investigate this question (Trifonov et al. 2021), but population studies of atmospheric properties will be needed to address the statistical significance for planetary bulk compositions (Wang et al. 2019;Helled et al. 2021). From a formation perspective, finding evidence for or against steam atmospheres on close-in super-Earths can further constrain the accretion path and composition of the atmosphere-stripped part of the Kepler radius valley (Rogers & Owen 2021). ...
Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of primary envelope-stripped exoplanets may thus constrain magma ocean dynamics.
... At the moment, the presence and speciation of atmospheres on hot rocky exoplanets is contentious (Swain et al. 2021;Mugnai et al. 2021) due to the limitations of current astronomical observatories. Detailed characterization of individual, close-by transiting rocky planets may be the most direct path to investigate this question (Trifonov et al. 2021), but population studies of atmospheric properties will be needed to address the statistical significance for planetary bulk compositions (Wang et al. 2019;Helled et al. 2021). From a formation perspective, finding evidence for or against steam atmospheres on close-in super-Earths can further constrain the accretion path and composition of the atmosphere-stripped part of the Kepler radius valley (Rogers & Owen 2021). ...
Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of atmosphere-stripped exoplanets may thus constrain magma ocean dynamics.
The two prevailing planet formation scenarios, core accretion and disk instability, predict distinct planetary mass–metallicity relations. Yet, the detection of this trend remains challenging due to inadequate data on planet atmosphere abundance and inhomogeneities in both planet and host stellar abundance measurements. Here we analyze high-resolution spectra for the host stars of 19 transiting exoplanets to derive the C, O, Na, S, and K abundances, including planetary types from cool mini-Neptunes to hot Jupiters ( T eq ∼ 300–2700 K; planet radius ∼0.1–2 R J ). Our Monte Carlo simulations suggest that the current data set, updated based on Welbanks et al., is unable to distinguish between a linear relation and an independent distribution model for the abundance-mass correlation for water, Na, or K. To detect a trend with strong evidence (Bayes factor > 10) at the 2 σ confidence interval, we recommend a minimum sample of 58 planets with Hubble Space Telescope measurements of water abundances coupled with [O/H] of the host stars, or 45 planets at the JWST precision. Coupled with future JWST or ground-based high-resolution data, this well-characterized sample of planets with precise host-star abundances constitute an important ensemble of planets to further probe the abundance-mass correlation.
