BULK COMPOSITION OF GJ 1214b AND OTHER SUB-NEPTUNE EXOPLANETS

By D. Valencia, T. Guillot, V. Parmentier, R. Freedman. 2013

108 citations recorded by the source corpus.

GJ 1214b stands out among the detected low-mass exoplanets, because it is, so far, the only one amenable to transmission spectroscopy. Up to date there is no consensus about the composition of its envelope although most studies suggest a high molecular weight atmosphere. In particular, it is unclear if hydrogen and helium are present or if the atmosphere is water dominated. Here, we present results on the composition of the envelope obtained by using an internal structure and evolutionary model to fit the mass and radius data. By examining all possible mixtures of water and H/He, with the corresponding opacities, we find that the bulk amount of H/He of GJ 1214b is at most 7% by mass. In general, we find the radius of warm sub-Neptunes to be most sensitive to the amount of H/He. We note that all (Kepler-11b,c,d,f, Kepler-18b, Kepler-20b, 55Cnc-e, Kepler-36c, and Kepler-68b) but two (Kepler-11e and Kepler-30b) of the discovered low-mass planets so far have less than 10% H/He. In fact, Kepler-11e and Kepler-30b have 10%–18% and 5%–15% bulk H/He. Conversely, little can be determined about the H2O or rocky content of sub-Neptune planets. We find that although a 100% water composition fits the data for GJ 1214b, based on formation constraints the presence of heavier refractory material on this planet is expected, and hence, so is a component lighter than water required. The same is true for Kepler-11f. A robust determination by transmission spectroscopy of the composition of the upper atmosphere of GJ 1214b will help determine the extent of compositional segregation between the atmosphere and the envelope.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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Citations in the corpus

GASEOUS MEAN OPACITIES FOR GIANT PLANET AND ULTRACOOL DWARF ATMOSPHERES OVER A RANGE OF METALLICITIES AND TEMPERATURES (2014, methodology): “Analytic Opacity Fit Recently Valencia et al. (2013) used an older version of these tabulated mean opacities at metallicities from solar, 30× solar ([M/H]=+1.5), and 50× solar ([M/H]=+1.7) to derive analytic fits to the RM opacities as a function of pressure, temperature, and metallicity.”
Characterization of the K2-18 multi-planetary system with HARPS: A habitable zone super-Earth and discovery of a second, warm super-Earth on a non-coplanar orbit (2017, background): “The measured radius of 2.38 R⊕ is suggestive of an extended H/He envelope (Valencia et al. 2013; Rogers 2015; Fulton et al. 2017) that may contain additional molecular species such as water and/or methane that could be detectable with the James Webb Space Telescope (JWST; Beichman et al. 2014).”
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).”
UNDERSTANDING THE MASS–RADIUS RELATION FOR SUB-NEPTUNES: RADIUS AS A PROXY FOR COMPOSITION (2013, unknown): “…rare, such systems are incredibly valuable because with both a mass and a radius we can estimate a planet’s bulk composition using models of interior structure and thermal evolution (e.g. Rogers & Seager 2010a; Nettelmann et al. 2011; Miller & Fortney 2011; Lopez et al. 2012; Valencia et al. 2013).”
Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation (2017, background): “…relationship (Seager et al. 2007; Valencia et al. 2010), especially for low-mass planets with a gaseous H/He envelope (Rogers & Seager 2010b; Valencia et al. 2013; Howe et al. 2014): a silicate-iron core combined with a (potentially tenuous) H/He envelope can have the same mass-radius…”
DETECTION OF AN ATMOSPHERE AROUND THE SUPER-EARTH 55 CANCRI E (2015, background): “Even basic information about their density seems to suggest that there is a variety of cases (e.g. Sotin et al. 2007; Grasset et al. 2009; Valencia et al. 2007, 2013; Zeng & Sasselov 2014).”
HOW ROCKY ARE THEY? THE COMPOSITION DISTRIBUTION OF KEPLER’S SUB-NEPTUNE PLANET CANDIDATES WITHIN 0.15 AU (2014, background): “…CoRoT-7b (e.g. Léger et al. 2009; Valencia et al. 2010; Jackson et al. 2010), GJ1214b (e.g. Charbonneau et al. 2009; Rogers & Seager 2010; Nettelmann et al. 2011; Valencia et al. 2013), and the Kepler-11 system (Lopez et al. 2012), to provide constraints on what their bulk compositions could be.”
A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS (2013, methodology): “In particular, only Nettelmann et al. (2011) and Valencia et al. (2013) have investigated detailed thermal evolution including different values of Zenv.”