Abstract
Terrestrial planets in the solar system, such as the Earth, are oxygen-rich, with silicates and iron being the most common minerals in their interiors. However, the true chemical diversity of rocky planets orbiting other stars is yet unknown. Mass and radius measurements are used to constrain the interior compositions of super-Earths (exoplanets with masses of 1-10 M ⊕), and are typically interpreted with planetary interior models that assume Earth-centric oxygen-rich compositions. Using such models, the super-Earth 55 Cancri e (mass 8 M ⊕, radius 2 R ⊕) has been suggested to bear an interior composition consisting of Fe, silicates, and an envelope (
10% by mass) of supercritical water. We report that the mass and radius of 55 Cancri e can also be explained by a carbon-rich solid interior made of Fe, C, SiC, and/or silicates and without a volatile envelope. While the data allow Fe mass fractions of up to 40%, a wide range of C, SiC, and/or silicate mass fractions are possible. A carbon-rich 55 Cancri e is also plausible if its protoplanetary disk bore the same composition as its host star, which has been reported to be carbon-rich. However, more precise estimates of the stellar elemental abundances and observations of the planetary atmosphere are required to further constrain its interior composition. The possibility of a C-rich interior in 55 Cancri e opens a new regime of geochemistry and geophysics in extraterrestrial rocky planets, compared to terrestrial planets in the solar system.
Export citation and abstract BibTeX RIS
1. INTRODUCTION
The recently discovered transiting super-Earth 55 Cancri e orbiting a nearby (naked eye) G8V star every 18 hours is one of the most favorable super-Earths for detailed characterization. The planet was originally discovered in a five-planet system by the radial velocity method which gave its minimum mass (McArthur et al. 2004; Fischer et al. 2008). However, the recent discovery of its transits across the host star (Winn et al. 2011; Demory et al. 2011) has made possible accurate measurements of its mass (8.37 ± 0.38 M⊕; Endl et al. 2012) and radius (2.04 ± 0.15 R⊕; Gillon et al. 2012), and hence constraints on its interior composition.
The interior of 55 Cancri e, inferred from its mass and radius, has been suggested to bear an interior composition made of iron, silicates, and an envelope (
10% by mass) of supercritical water (Winn et al. 2011; Demory et al. 2011; Gillon et al. 2012). A water envelope is required to explain the mass and radius with an oxygen-rich interior composition. Given its mass, even a purely silicate interior with no iron content could only barely explain the observed radius. Consequently, a massive water envelope (
10% by mass) over a rocky Earth-like interior has been required in the above studies to explain the radius of this highly irradiated super-Earth. Moreover, given the extreme stellar irradiation (T ~ 2500 K; Demory et al. 2012), the water has been suggested to be in a supercritical state in the planetary envelope.
The silicate-rich and water-rich interior of 55 Cancri e as suggested by previous studies is based on the assumption of an oxygen-rich interior, motivated by terrestrial planets in the solar system. However, several recent studies have suggested the possibility of carbon-rich extrasolar planets, both theoretically (Lodders 2004; Kuchner & Seager 2005; Bond et al. 2010; Madhusudhan et al. 2011b; Oberg et al. 2011; Mousis et al. 2012) and observationally (Madhusudhan et al. 2011a; Madhusudhan 2012). Motivated by these studies, in the present work we investigate if the observed mass and radius of 55 Cancri e may be explained by a carbon-rich interior.
The possibility of a carbon-rich interior in 55 Cancri e is also motivated by the composition of its host star. The host star 55 Cancri has been reported to be carbon-rich, with C/O =1.12 ± 0.19 (Delgado Mena et al. 2010; E. Delgado Mena 2012, private communication) and metal-rich ([Fe/H] = 0.31 ± 0.04; Valenti & Fischer 2005; Mena et al. 2010), and has an age of 10.2 ± 2.5 Gyr (von Braun et al. 2011). However, the stellar C/O is less than 2σ above the C/O of 0.8 required to form abundant carbon-rich condensates in protoplanetary environments. Furthermore, the C/O ratio could be overestimated due to systematic errors in estimating the C and O abundances (Fortney 2012). However, if the central value of C/O = 1.12 is taken at face value (see, e.g., Carter-Bond et al. 2012) and the protoplanetary disk is assumed to mimic the stellar abundances, then the super-Earth 55 Cancri e would indeed be expected to have accreted substantial amounts of carbon-rich material, such as SiC and C, and be depleted in H2O ice (e.g., Larimer 1975; Bond et al. 2010; Johnson et al. 2012).
In what follows, we first present, in Section 2, internal structure models of 55 Cancri e and constraints on its interior composition based on its observed mass and radius. In Section 3, we present thermochemical calculations exploring the possible compositions of planetesimals that may have formed 55 Cancri e. We discuss the implications of our results and future work in Section 4.
2. INTERIOR COMPOSITION
2.1. Internal Structure Model
We model the internal structure of the super-Earth 55 Cancri e, and use its observed mass and radius to constrain the chemical composition of its interior. Our model solves the three canonical equations of internal structure for solid planets, namely, (1) mass conservation, (2) hydrostatic equilibrium, and (3) the equation of state (EOS; e.g., Fortney et al. 2007; Seager et al. 2007; Sotin et al. 2007; Valencia et al. 2007; Rogers & Seager 2010). In each spherical shell of the planet, the equations for mass and pressure balance form a system of two coupled differential equations, given by


Here, we have adopted the mass interior to each spherical shell (Mr) as the independent variable, and we numerically solve for the radius (r) and pressure (P). The density (ρ) is related to the pressure (P) and temperature (T) via the EOS of the material, P = P(ρ, T). We adopt room-temperature EOSs for the species considered in this work, since mass–radius relations of solid exoplanets are known to be insensitive to temperature dependence in the EOS (see, e.g., Seager et al. 2007). For H2O, MgSiO3 (perovskite), Fe, and SiC, we use the Birch–Murnaghan (Birch 1952) EOSs compiled in Seager et al. (2007). Our Birch–Murnaghan EOS for carbon comprises the graphite EOS (Wang et al. 2012) at low pressures, incorporates the phase transition (Bundy et al. 1996) from graphite to diamond at 10 GPa, and asymptotes to the Thomas–Fermi–Dirac EOS (Salpeter & Zapolsky 1967) for P > 1000 GPa. For diamond, we adopt the EOS from Dewaele et al. (2008). We assume that the planet is spherically symmetric, but is vertically differentiated into up to three chemically distinct regions, depending on the species under consideration. The mass fractions of the three regions are given as xi = Mi/Mp; i = [1–3], such that x1 + x2 + x3 = 1. Mp is the total mass of the planet and Mi is the mass of each of the three layers.
We solve the system of equations simultaneously using a fourth-order Runge–Kutta scheme. The inputs to the model are the total mass of the planet (Mp) and the mass fractions of two of the three different regions, i.e., x1 and x2. x3 is obtained from mass conservation, x3 = 1 − x1 − x2. We start with the upper boundary (Mr = Mp) and integrate downward in mass until Mr = 0. The upper boundary conditions, which serve as initial conditions, are


and the lower boundary condition is

We use our model in two ways. First, we study mass–radius relations for planets with homogeneous compositions. In such cases, x1 = 1 and x2 = x3 = 0. We choose a grid in Mp, and for each Mp we compute the corresponding Rp for the given composition. Since Rp is required for the initial conditions but is not known a priori, we use a bisection root finder to solve for Rp iteratively, such that the lower boundary condition is satisfied. Second, we also use our model to determine constraints on the heterogeneous interior composition of 55 Cancri e given its observed Mp and Rp. Here, we explore a fine grid in x1–x2 space to constrain the regions that match Mp and Rp within their observational uncertainties.
2.2. Mass–Radius Relations
Figure 1 shows mass–radius relations for homogeneous planets of different compositions (i.e., x1 = 1, x2 = x3 = 0) along with data for several super-Earths. Super-Earths with radii above the H2O curve likely host gaseous envelopes, since even purely ice compositions will not be able to explain their radii. However, those below the H2O curve can be explained by various combinations of minerals, depending on whether an O-rich or C-rich composition is assumed. An important exception is noticed for planets such as 55 Cancri e, with radii between the silicate and carbon curves. In such cases, assuming O-rich compositions would mean that the planet possesses a volatile (e.g., H2O) layer, since even a purely silicate composition would not explain the radius, as suggested in previous studies (e.g., Gillon et al. 2012). Whereas, if one allows for C-rich compositions, the same mass and radius could also be explained by purely solid planets with SiC and C based interiors without a volatile layer, as can be seen in Figure 1.
Figure 1. Mass–radius relations of solid planets with homogeneous composition. The colored curves show mass–radius relations predicted by internal structure models of solid planets of uniform composition made of the different species shown in the legend. The black circles with error bars show measured masses and radii of known transiting super Earths (Mp = 1–10 M⊕), adopted from the exoplanet orbit database (Wright et al. 2011). Two values of radii are shown for 55 Cancri e. The red data point shows the radius measured in the visible, and the blue data point shows a gray radius obtained by combining visible and infrared measurements (see Section 2.3).
Download figure:
Standard image High-resolution image Export PowerPoint slide2.3. Constraints on Interior Composition
In what follows, we determine the constraints placed by the mass and radius of 55 Cancri e on the composition space of carbon-rich models of its interior. Interiors of carbon-rich planets are expected to be composed of iron (Fe), carbon (C), SiC, and/or silicates, depending on the thermal conditions where the planetesimals originated (Kuchner & Seager 2005; Bond et al. 2010; Carter-Bond et al. 2012; also see Section 3). Consequently, we consider two model families with distinct compositions: Fe–SiC–C and Fe–MgSiO3–C. Our planetary interior model in each case is comprised of three regions ordered by bulk density, an Fe core, overlaid by a layer of SiC or MgSiO3 (perovskite), and an uppermost layer of carbon. In each case, Fe–SiC–C or Fe–MgSiO3–C, we constrain the mass fractions of the three regions that explain the observed mass and radius of 55 Cancri e.
Figure 2 shows a ternary diagram of the possible compositions of 55 Cancri e which explain its observed mass and radius within their observational uncertainties. We adopt the latest estimate of its mass, M = 8.37 ± 0.38 M⊕ (Endl et al. 2012), and two values for its radius, Rp = 2.04 ± 0.15 R⊕ in the visible (Winn et al. 2011; Gillon et al. 2012), and Rp = 2.20 ± 0.12 R⊕ for a gray radius obtained by combining the visible and infrared (4.5 μm) radii (Demory et al. 2011; Gillon et al. 2012). The red region (which includes the blue region) in Figure 2 shows constraints from the visible radius, and the blue region which is a subset of the red region shows the constraints from the gray radius.
Figure 2. Ternary diagrams showing the range of interior compositions allowed by the mass and radii of 55 Cancri e. Two classes of interior models were considered, based on the planetesimal compositions predicted by the stellar abundances. Left: models composed of Fe, SiC, and C. Right: models composed of Fe, MgSiO3, and C. In each case, the red (blue) contours show the constraints from the visible (gray) radius. The blue contours are subsets of the red contours. The three axes in each case show the mass fractions of the corresponding species.
Download figure:
Standard image High-resolution image Export PowerPoint slideFigure 3(a) shows the constraints on the mass fractions for the Fe–SiC–C class of solutions. A wide range of carbon-rich interior compositions can explain the observed mass and radius of 55 Cancri e. The visible radius places an upper limit of 41% on the Fe mass fraction, but allows a wide range of (SiC, C) combinations. If an Earth-like Fe core mass (33%) or less is assumed, then the visible radius allows a differentiated mantle comprising of all possible proportions of SiC and C, constrained only by mass conservation (x1 + x2 + x3 = 1, see Section 2.1). For example, extreme combinations of (Fe, SiC, C) = (33%, 67%, 0%) and (33%, 0%, 67%) are both possible. However, intermediate compositions such as (33%, 33%, 34%) may be more representative of the true composition, since over the long planet formation timescales (Gyr) all the three species are likely to be abundant enough to contribute to planetesimal compositions in the inner nebular (a
1.2 AU) where the Fe–SiC–C type of planets are more likely to be formed (see, e.g., Section 3 and Bond et al. 2010).
Figure 3. Chemical composition of refractory condensates expected in the protoplanetary disk of the 55 Cancri system. The colored curves show molar mixing ratios of the major species, shown in the legend, in thermochemical equilibrium as a function of temperature in the protoplanetary disk mid-plane. A representative pressure of 10−4 bar is assumed. The elemental abundances of the host star (Mena et al. 2010; Carter-Bond et al. 2012) are assumed as initial conditions, and the equilibrium computations were performed using the HSC Chemistry software. The black filled circles at the top of the figure show the temperatures of the disk at different orbital separations and ages.
Download figure:
Standard image High-resolution image Export PowerPoint slideOn the other hand, considering the gray radius narrows down the solution space, requiring a maximum of 18% Fe by mass, the SiC and C fractions allowed depend on the Fe mass fraction. Considering Fe = 10%, for example, a minimum of ~70% C is required, with SiC < 20%. For Fe < 5%, however, all possible combinations of SiC and C are allowed, such that SiC + C < 95%. We note, however, that the Fe content derived from the gray radius may only be a lower limit. The infrared radius may contain atmospheric molecular absorption, making it slightly larger than the visible radius. Such absorption may be caused by an atmosphere (~1000 km) of varied compositions, between just ~2 scale heights (RH) of a metal-rich H2-dominated atmosphere and ~30 RH of a CO-dominated atmosphere (see, e.g., Figure 7 of Gillon et al. 2012). New spectral data would be required to precisely constrain this possibility.
Figure 3(b) shows the constraints on the mass fractions for the Fe–MgSiO3–C class of solutions. Considering an Earth-like Fe content of 33%, the visible radius allows for a maximum of 20% MgSiO3, requiring over 47% C, which is expected given the dominance of C in the planetesimal composition in a carbon-rich environment. In principle, allowing for lower Fe allows higher MgSiO3. For example, an Fe = 20% (10%) allows for MgSiO3 up to ~60% (80%) and C as low as 20% (10%). Such Fe contents are considerably low (compared to Earth's Fe fraction of 33 %), and are likely extreme, if not unphysical, (also see Gillon et al. 2012), particularly considering that the host star has a supersolar metallicity ([Fe/H] = 0.31 ± 0.04; Valenti & Fischer 2005). However, even a C mass fraction of 10% is two orders of magnitude higher than that in the Earth, which has less than 0.1% C by mass (McDonough & Sun 1995).
3. FORMATION CONDITIONS AND PLANETESIMAL COMPOSITIONS
A carbon-rich 55 Cancri e may also be tentatively consistent with the composition of the host star. We investigate the possible formation conditions of 55 Cancri e assuming that the reported stellar abundances represent those of its primordial disk (see Sections 1 and 4 for challenges in this assumption). We adopt the abundances of the host star reported by Delgado Mena et al. (2010), following Carter-Bond et al. (2012). Given the thermodynamic conditions in the disk mid-plane, we compute the condensate chemistry in multi-phase chemical equilibrium using the commercial software HSC Chemistry.
We model the protoplanetary disk using a thin disk model based on the prescription of Shakura & Sunyaev (1973), with a turbulent viscosity given by νt = αC2S/Ω, where CS is the local sound velocity, Ω is the Keplerian rotation frequency, and α is the dimensionless viscosity parameter. Our model incorporates the opacity law developed by Ruden & Pollack (1991) (see, e.g., Drouart et al. 1999 for details). The temporal evolution of the disk temperature, pressure, and surface density profiles depends upon the evolution of the accretion rate,
, which we define (following Makalkin & Dorofeeva 1991) to be
, where
is the initial accretion rate, and t0 is the accretion timescale. We adopt S = 1.5, a value that is consistent with the evolution of accretion rates in circumstellar disks (Hartmann et al. 1998). The accretion timescale t0 is calculated based on Makalkin & Dorofeeva (1991) as t0 = R2D/3νD, where νD is the turbulent viscosity at the initial radius of the sub-disk, RD. Three parameters constrain
and t0: the initial mass of the disk MD0, the coefficient of turbulent viscosity α, and the radius of the sub-nebula RD. In the present case, we have adopted the parameters used by Kavelaars et al. (2011) for their nominal solar nebula model, i.e., α = 0.003, RD0 = 15 AU, and MD0 = 0.06 M☉.
The refractory condensate composition as a function of the temperature (T) is shown in Figure 3. At high temperatures (T > 1100 K), SiC and Fe are the most dominant condensates. As the temperatures cool to between 700 and 1100 K, pure carbon (as graphite) becomes the most dominant condensate, followed by Fe and silicates, e.g., Mg2SiO4. However, at low temperatures, T below 700 K, Mg2SiO4 dominates the condensate composition, despite the high C/O ratio (also see Bond et al. 2010; Carter-Bond et al. 2012). Figure 1 also shows representative orbital separations (a) in the protoplanetary disk and their corresponding temperatures at different epochs in the disks evolution. For a
1.2 AU in the disk, SiC, Fe, and C condense early in the disks lifetime, and hence dominate the planetesimal composition. For a ~ 1.2–1.6 AU, graphite far dominates the planetesimal composition, followed by Fe and Mg2SiO4. At lower temperatures, however, for a
1.6 AU, Mg2SiO4 dominates the planetesimal composition.
Depending on whether the planetesimals that formed 55 Cancri e originated primarily within or beyond ~1.2 AU, its interior can bear end-member compositions of Fe–SiC–C or Fe–silicates–C, respectively, or an intermediate composition. Since the protoplanet likely formed farther than the planet's current orbital separation (0.015 AU) and migrated in, it likely accreted substantial amounts of Fe-rich and C-rich condensates irrespective of its original location. On the other hand, it is unlikely that the planet formed in situ because the disk temperatures at this location prevent the condensation of dominant refractory condensates.
4. DISCUSSION
We show that the sum total of available data, including the planetary mass and radius, and the stellar abundances, supports the possibility of a carbon-rich interior in 55 Cancri e. Numerous studies have suggested the possibility of carbon-rich exoplanets, both theoretically (e.g., Kuchner & Seager 2005; Bond et al. 2010; Madhusudhan et al. 2011b) and observationally (Madhusudhan et al. 2011a; Madhusudhan 2012). However, the prevalent practice is to assume Earth-centric compositions, comprising Fe, silicates, and H2O, in explaining super-Earth observations. A carbon-rich 55 Cancri e would represent a departure from Earth-centric mineralogies in rocky exoplanets. Nevertheless, follow-up efforts are required to confirm a carbon-rich 55 Cancri e.
High confidence elemental abundances of the host star can help refine the constraints on the formation conditions of 55 Cancri e. Given currently reported abundances, a C/O ≥ 0.8, required to form C-rich refractories (Larimer 1975), holds only at ~2σ and the C/O ratio may also have been overestimated (Fortney 2012). Furthermore, we assume that the protoplanetary disk bears the same composition as the host star. While this may be a reasonable assumption for deriving refractory compositions of planetesimals forming rocky planets (see, e.g., Bond et al. 2010; Carter-Bond et al. 2012; Johnson et al. 2012), the possibility of local perturbations in the C/O ratio of the disk may not be entirely ruled out; i.e., the possibility that carbon-rich planets may form around oxygen-rich stars and vice versa (Kuchner & Seager 2005; Madhusudhan et al. 2011b; Oberg et al. 2011). In particular, carbon-rich gas giant planets may form by predominantly accreting effectively carbon-rich gas in regions beyond the water-ice condensation line in an oxygen-rich disk (Oberg et al. 2011).
High-precision spectroscopy in the future may also be able to constrain the presence of an atmosphere in 55 Cancri e and its composition. Currently, both reported radii, visible and infrared, are consistent at the 1σ uncertainties, though the latter is slightly larger (Gillon et al. 2012). Excess infrared absorption may be caused by molecular species and/or collision-induced absorption (Miller-Ricci et al. 2009), which could be constrained by future observations.
A carbon-rich interior in 55 Cancri e has far-reaching implications for geophysical processes in its interior. Earth's interior is oxygen-rich, with carbon less than 0.1% by mass (McDonough & Sun 1995), in contrast to a carbon-rich interior of 55 Cancri e. Both carbon and SiC have over two orders of magnitude higher thermal conductivities than the silicates and oxides that dominate Earth's mantle (Goldberg et al. 2001), implying that the thermal evolution of 55 Cancri e may be different from that of oxygen-rich planets. The high thermal conductivities, compounded with the paucity of water, may influence the likelihood of plate tectonics in carbon-rich super-Earths (Valencia et al. 2007; Korenaga 2010), though new measurements of viscosity of carbon-rich materials at high pressures and high temperatures are required to constrain this possibility. A carbon-rich 55 Cancri e bolsters the idea that rocky exoplanets may be diverse in their chemical compositions and, hence, in their geophysical conditions.
NM acknowledges support from the Yale Center for Astronomy and Astrophysics (YCAA) in the Department of Physics, Yale University, through the YCAA postdoctoral Fellowship. We thank Debra Fischer, Elisa Delgado Mena, Andrew Szymkowiak, and Dave Bercovici for helpful discussions. This research has made use of the Exoplanet Orbit Database and the Exoplanet Data Explorer at exoplanets.org.
References
- Bond, J. C., OBrien, D. P., & Lauretta, D. S. 2010, ApJ, 715, 1050
- Bundy, F. P., Bassett, W. A., & Weathers, M. S. et al. 1996, Carbon, 34, 141
- Carter-Bond, J. C., O’Brien, D. P., & Delgado Mena, E. et al. 2012, ApJ, 747, L2
- Delgado Mena, E., Israelian, G., & González Hernndez, J. I. et al. 2010, ApJ, 725, 2349
- Demory, B-O., Gillon, M., & Seager, S. et al. 2012, ApJ, 751, L28
- Endl, M. et al. 2012, ApJ, in press (arXiv:1208.5709)
- Fischer, D. A., Marcy, G. W., & Butler, R. P. et al. 2008, ApJ, 675, 790
- Fortney, J. J. 2012, ApJ, 747, L27
- Fortney, J. J., Marley, M. S., & Barnes, J. W. 2007, ApJ, 659, 1661
- Goldberg, Y., Levinshtein, M. E., & Rumyantsev, S. L., eds. 2001, Properties of Advanced Semiconductor Materials GaN, AlN, SiC, BN, SiC, SiGe (New York: Wiley), 93
- Hartmann, L., Calvet, N., Gullbring, E., & D’Alessio, P. 1998, ApJ, 495, 385
- Johnson, T. V., Mousis, O., Lunine, J. I., & Madhusudhan, N. 2012, ApJ, 757, 192
- Kavelaars, J. J., Mousis, O., Petit, J.-M., & Weaver, H. A. 2011, ApJ, 734, L30
- Korenaga, J. 2010, ApJ, 725, L43
- Kuchner, M. & Seager, S. 2005, arXiv:astro-ph/0504214
- Lodders, K. 2004, ApJ, 611, 587
- Madhusudhan, N. 2012, ApJ, in press (arXiv:1209.2412)
- Madhusudhan, N., Mousis, O., Johnson, T. V., & Lunine, J. I. 2011b, ApJ, 743, 191
- Makalkin, A. B. & Dorofeeva, V. A. 1991, Priroda, 9, 79
- McArthur, B. E., Endl, M., & Cochran, W. D. et al. 2004, ApJ, 614, L81
- McDonough, W. F. & Sun, S.-s. 1995, Chem. Geol., 120, 223
- Miller-Ricci, E., Seager, S., & Sasselov, D. 2009, ApJ, 690, 1056
- Mousis, O., Lunine, J. I., Madhusudhan, N., & Johnson, T. V. 2012, ApJ, 751, L7
- Oberg, K., Murray-Clay, R., & Bergin, E. A. 2011, ApJ, 743, 16
- Rogers, L. A. & Seager, S. 2010, ApJ, 712, 974
- Seager, S., Kuchner, M., Hier-Majumder, C. A., & Militzer, B. 2007, ApJ, 669, 1279
- Shakura, N. I. & Sunyaev, R. A. 1973, A&A, 24, 337
- Valencia, D., O’Connell, R. J., & Sasselov, D. D. 2007, ApJ, 670, L45
- Valenti, J. A. & Fischer, D. A. 2005, ApJS, 159, 141
- von Braun, K., Boyajian, T. S., & ten Brummelaar, T. A. et al. 2011, ApJ, 740, 49
- Wang, Y. P., Panzik, J. E., Kiefer, B., & Lee, K. K. M. 2012, Sci. Rep., 2, 520
- Winn, J. N., Matthews, J. M., & Dawson, R. I. et al. 2011, ApJ, 737, L18
- Wright, J. T., Fakhouri, O., & Marcy, G. W. et al. 2011, PASP, 123, 412
Citations
- Ian A. Crawford 2018 3413
- Caroline Dorn et al 2018 3111
- Patrick A. Young 2018 2959
- Debra A. Fischer 2018 2677
-
Equation of State of SiC at Extreme Conditions: New Insight Into the Interior of Carbon-Rich Exoplanets
F. Miozzi et al 2018 Journal of Geophysical Research: Planets -
A Review of Equation-of-State Models for Inertial Confinement Fusion Materials
J.A. Gaffney et al 2018 High Energy Density Physics 28 7 -
High-energy environment of super-Earth 55 Cancri e
V. Bourrier et al 2018 Astronomy & Astrophysics 615 A117 - Patrick A. Young 2018 1
- Chaitanya Giri 2018 127
-
Mass, Radius, and Composition of the Transiting Planet 55 Cnc e: Using Interferometry and Correlations
Aurélien Crida et al. 2018 The Astrophysical Journal 860 122 -
On the Impact Origin of Phobos and Deimos. III. Resulting Composition from Different Impactors
Francesco C. Pignatale et al. 2018 The Astrophysical Journal 853 118 -
Decomposition of silicon carbide at high pressures and temperatures
Kierstin Daviau and Kanani K. M. Lee 2017 Physical Review B 96 - Debra A. Fischer 2017 1
- Ian A. Crawford 2017 1
-
Born dry in the photoevaporation desert: Kepler's ultra-short-period planets formed water-poor
Eric D. Lopez 2017 Monthly Notices of the Royal Astronomical Society 472 245 -
Zinc-blende to rocksalt transition in SiC in a laser-heated diamond-anvil cell
Kierstin Daviau and Kanani K. M. Lee 2017 Physical Review B 95 -
Thermal expansion of SiC at high pressure-temperature and implications for thermal convection in the deep interiors of carbide exoplanets
C. Nisr et al 2017 Journal of Geophysical Research: Planets -
A Case for an Atmosphere on Super-Earth 55 Cancri e
Isabel Angelo and Renyu Hu 2017 The Astronomical Journal 154 232 -
A Search for Water in a Super-Earth Atmosphere: High-resolution Optical Spectroscopy of 55Cancri e
Lisa J. Esteves et al. 2017 The Astronomical Journal 153 268 -
Detection of the Atmosphere of the 1.6 M ⊕ Exoplanet GJ 1132 b
John Southworth et al. 2017 The Astronomical Journal 153 191 -
Constraints on Super-Earth Interiors from Stellar Abundances
B. Brugger et al. 2017 The Astrophysical Journal 850 93 -
Spectroscopic Evolution of Disintegrating Planetesimals: Minute to Month Variability in the Circumstellar Gas Associated with WD 1145+017
Seth Redfield et al. 2017 The Astrophysical Journal 839 42 -
Metal-silicate Partitioning and Its Role in Core Formation and Composition on Super-Earths
Laura Schaefer et al. 2017 The Astrophysical Journal 835 234 -
Whole planet coupling between climate, mantle, and core: Implications for rocky planet evolution
Bradford J. Foley and Peter E. Driscoll 2016 Geochemistry, Geophysics, Geosystems 17 1885 -
Free energy model for solid high-pressure phases of carbon
Manuel Schöttler et al 2016 Journal of Physics: Condensed Matter 28 145401 -
A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres
P. B. Rimmer and Ch Helling 2016 The Astrophysical Journal Supplement Series 224 9 -
The Imprint of Exoplanet Formation History on Observable Present-day Spectra of Hot Jupiters
C. Mordasini et al. 2016 The Astrophysical Journal 832 41 -
C/O and Mg/Si Ratios of Stars in the Solar Neighborhood
John M. Brewer and Debra A. Fischer 2016 The Astrophysical Journal 831 20 -
Effects of Dynamical Evolution of Giant Planets on the Delivery of Atmophile Elements during Terrestrial Planet Formation
Soko Matsumura et al. 2016 The Astrophysical Journal 818 15 -
Connecting the dots – II. Phase changes in the climate dynamics of tidally locked terrestrial exoplanets
L. Carone et al 2015 Monthly Notices of the Royal Astronomical Society 453 2413 - T. Duffy et al 2015 149
-
Investigation of the solid–liquid phase transition of carbon at 150 GPa with spectrally resolved X-ray scattering
J. Helfrich et al 2015 High Energy Density Physics -
The Chemical Composition of τ Ceti and Possible Effects on Terrestrial Planets
Michael Pagano et al. 2015 The Astrophysical Journal 803 90 -
The Photoeccentric Effect and Proto-hot Jupiters. III. A Paucity of Proto-hot Jupiters on Super-eccentric Orbits
Rebekah I. Dawson et al. 2015 The Astrophysical Journal 798 66 -
Astrobiological Stoichiometry
Patrick A. Young et al 2014 Astrobiology 14 603 -
Disk Evolution, Element Abundances and Cloud Properties of Young Gas Giant Planets
Christiane Helling et al 2014 Life 4 142 -
Extrasolar Cosmochemistry
M. Jura and E.D. Young 2014 Annual Review of Earth and Planetary Sciences 42 45 -
From stellar nebula to planets: The refractory components
Amaury Thiabaud et al 2014 Astronomy & Astrophysics 562 A27 -
The Role of Carbon in Extrasolar Planetary Geodynamics and Habitability
Cayman T. Unterborn et al. 2014 The Astrophysical Journal 793 124 -
Interior Phase Transformations and Mass-Radius Relationships of Silicon-Carbon Planets
Hugh F. Wilson and Burkhard Militzer 2014 The Astrophysical Journal 793 34 -
Chemistry in an Evolving Protoplanetary Disk: Effects on Terrestrial Planet Composition
John Moriarty et al. 2014 The Astrophysical Journal 787 81 -
Photochemistry in Terrestrial Exoplanet Atmospheres. III. Photochemistry and Thermochemistry in Thick Atmospheres on Super Earths and Mini Neptunes
Renyu Hu and Sara Seager 2014 The Astrophysical Journal 784 63 -
Probing the Complex Ion Structure in Liquid Carbon at 100 GPa
D. Kraus et al 2013 Physical Review Letters 111 -
On the stability of thermal stratification of highly compressible fluids with depth-dependent physical properties: implications for the mantle convection of super-Earths
Masanori Kameyama and Yuya Kinoshita 2013 Geophysical Journal International 195 1443 -
Tidal dissipation and eccentricity pumping: Implications for the depth of the secondary eclipse of 55 Cancri e
Emeline Bolmont et al 2013 Astronomy & Astrophysics 556 A17 -
Dynamics of rotation of super-Earths
Nelson Callegari and Ádrian Rodríguez 2013 Celestial Mechanics and Dynamical Astronomy -
Molecular Dynamics Simulations of Shock Compressed Graphite
Nicolas Pineau 2013 The Journal of Physical Chemistry C 130607124743007 -
The carbon-to-oxygen ratio in stars with planets
P. E. Nissen 2013 Astronomy & Astrophysics 552 A73 -
Probing the blow-off criteria of hydrogen-rich 'super-Earths'
H. Lammer et al 2013 Monthly Notices of the Royal Astronomical Society -
Strange news from other stars
Raymond T. Pierrehumbert 2013 Nature Geoscience 6 81 -
Carbon and Oxygen Abundances in Cool Metal-rich Exoplanet Hosts: A Case Study of the C/O Ratio of 55 Cancri
Johanna K. Teske et al. 2013 The Astrophysical Journal 778 132 -
Planet Hunters. V. A Confirmed Jupiter-size Planet in the Habitable Zone and 42 Planet Candidates from the Kepler Archive Data
Ji Wang et al. 2013 The Astrophysical Journal 776 10 -
Ground-based Detections of Thermal Emission from the Dense Hot Jupiter WASP-43b in the H and K s Bands
W. Wang et al. 2013 The Astrophysical Journal 770 70 -
Resolving the Gap and AU-scale Asymmetries in the Pre-transitional Disk of V1247 Orionis
Stefan Kraus et al. 2013 The Astrophysical Journal 768 80 -
Kepler-68: Three Planets, One with a Density between that of Earth and Ice Giants
Ronald L. Gilliland et al. 2013 The Astrophysical Journal 766 40 -
Mass-Radius Relationships of Rocky Exoplanets
Frank Sohl et al 2012 Proceedings of the International Astronomical Union 8 350


