A FRAMEWORK FOR QUANTIFYING THE DEGENERACIES OF EXOPLANET INTERIOR COMPOSITIONS

By Leslie A. Rogers, Sara Seager. 2009

191 citations recorded by the source corpus.

Several transiting super-Earths are expected to be discovered in the coming few years. While tools to model the interior structure of transiting planets exist, inferences about the composition are fraught with ambiguities. We present a framework to quantify how much we can robustly infer about super-Earth and Neptune-size exoplanet interiors from radius and mass measurements. We introduce quaternary diagrams to illustrate the range of possible interior compositions for planets with four layers (iron core, silicate mantles, water layers, and H/He envelopes). We apply our model to CoRoT-7b, GJ 436b, and HAT-P-11b. Interpretation of planets with H/He envelopes is limited by the model uncertainty in the interior temperature, while for CoRoT-7b observational uncertainties dominate. We further find that our planet interior model sharpens the observational constraints on CoRoT-7b's mass and radius, assuming the planet does not contain significant amounts of water or gas. We show that the strength of the limits that can be placed on a super-Earth's composition depends on the planet's density; for similar observational uncertainties, high-density super-Mercuries allow the tightest composition constraints. Finally, we describe how techniques from Bayesian statistics can be used to take into account in a formal way the combined contributions of both theoretical and observational uncertainties to ambiguities in a planet's interior composition. On the whole, with only a mass and radius measurement an exact interior composition cannot be inferred for an exoplanet because the problem is highly underconstrained. Detailed quantitative ranges of plausible compositions, however, can be found.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/301df04b9e421cc752c4fe9070e13b713104d231

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

1. Jon Fortney
2. N. Madhusudhan
3. C. Mordasini
4. J. Owen
5. Sara Seager
6. V. Parmentier
7. Sheng Jin
8. E. Lopez

In Nuclear and High Energy Physics

1. Jon Fortney
2. E. Lopez
3. C. Mordasini
4. Sheng Jin
5. Leslie A. Rogers
6. J. Owen
7. Sara Seager
8. N. Madhusudhan

Citations in the corpus

• HOW ROCKY ARE THEY? THE COMPOSITION DISTRIBUTION OF KEPLER’S SUB-NEPTUNE PLANET CANDIDATES WITHIN 0.15 AU (2014, background): “Inferring more detailed composition parameters like an individual planet’s core, mantle, and envelope mass is of course a highly degenerate problem made worse by the possible choices for the number and type of layers in the planet’s interior (Valencia et al. 2007; Rogers & Seager 2010).”
• KEPLER PLANETS: A TALE OF EVAPORATION (2013, background): “Variations in the planetary structure Low-mass planets could contain volatile-rich atmospheres, they could also contain a significant amount of iron and/or ice in their cores, (Adams et al. 2008; Rogers & Seager 2010).”
• HOW TO DISTINGUISH BETWEEN CLOUDY MINI-NEPTUNES AND WATER/VOLATILE-DOMINATED SUPER-EARTHS (2013, background): “According to theoretical studies, (e.g., Seager et al. 2007; Rogers & Seager 2010a; Nettelmann et al. 2011) many super-Earth exoplanets show a bulk density that is high enough to require a larger ice or rock fraction than the solar system ice giants, but far too low to be explained by an entirely…”
• UNDERSTANDING THE MASS–RADIUS RELATION FOR SUB-NEPTUNES: RADIUS AS A PROXY FOR COMPOSITION (2013, methodology): “For 1- 2 R⊕ planets the densities of water, silicate rocks, and iron (i.e. ∼ 1-10 gcm−3) are similar enough that it is impossible to uniquely constrain the relative abundance of these components (Valencia et al. 2007; Rogers & Seager 2010a).”
• HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, background): “In general, there is a large degeneracy between the relative amounts of rock, iron, water, and hydrogen/helium (Rogers & Seager 2010a).”
• BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS (2015, background): “Yet super-Earths are not Jupiters; the gasto-core mass ratios (GCRs) of super-Earths are of order 1–10% (e.g., Lopez & Fortney 2014; Rogers & Seager 2010a,b).”
• HUBBLE SPACE TELESCOPE NEAR-IR TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH HD 97658B (2014, background): “…sample it is possible to match their measured densities with a broad range of compositions, including both waterrich and water-poor scenarios, simply by varying the amount of hydrogen in their atmospheres (Seager et al. 2007; Valencia et al. 2007, 2013; Rogers & Seager 2010a; Zeng & Sasselov 2013).”
• MOST 1.6 EARTH-RADIUS PLANETS ARE NOT ROCKY (2014, background): “For planets in this size range, a wide diversity of planet compositions are a priori plausible; rock, astrophysical ices (H2O, NH3, and CO), and H/He gas can all make significant contributions to both the planets’ mass and volume (e.g., Rogers & Seager 2010a,b).”
• Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation (2017, methodology): “Such combined measurements directly lead to the mean density of the planet which can be used as a first constraint on the bulk composition (e.g., Valencia et al. 2007, 2010; Rogers & Seager 2010b,a).”
• FORMATION AND STRUCTURE OF LOW-DENSITY EXO-NEPTUNES (2011, methodology): “We supplement the detailed core nucleated accretion calculations with equilibrium models of Neptunesize planets having H/He envelopes calculated following the approach of Rogers & Seager (2010a) and Rogers & Seager (2010b).”
• THREE POSSIBLE ORIGINS FOR THE GAS LAYER ON GJ 1214b (2009, methodology): “The model we use in this work is improved over Rogers & Seager (2010) by including a temperaturedependent water EOS and is different from most previous planet interior models by providing quantitative constraints on the range of plausible gas envelope masses for a given planet mass and radius.”
• THE OPTICAL AND NEAR-INFRARED TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ 1214b: FURTHER EVIDENCE FOR A METAL-RICH ATMOSPHERE (2011, background): “The only thing that can be said with a high degree of confidence based on just the mass and radius of the planet is that it must have a substantial atmosphere because it is too large to be composed solely of solid material (Rogers & Seager 2010b; Nettelmann et al. 2011).”
• MAKE SUPER-EARTHS, NOT JUPITERS: ACCRETING NEBULAR GAS ONTO SOLID CORES AT 0.1 AU AND BEYOND (2014, background): “E P] 4 N ov 2 01 4 2 super-Earths apparently retain only small amounts of gas: only ∼3–10% by mass (e.g., Lopez & Fortney 2014) or even less (e.g., Rogers & Seager 2010a,b), based on modeling of observed radius-mass data.”
• A POSSIBLE CARBON-RICH INTERIOR IN SUPER-EARTH 55 Cancri e (2012, methodology): “Our model solves the three canonical equations of internal structure for solid planets, namely, (a) mass conservation, (b) hydrostatic equilibrium, and (c) the equation of state (e.g. Fortney et al. 2007; Seager et al. 2007; Sotin et al. 2007; Valencia et al. 2007; Rogers & Seager 2010).”