Composition and fate of short-period super-Earths: The case of CoRoT-7b

By D. Valencia, M. Ikoma, T. Guillot, N. Nettelmann. 2009

202 citations recorded by the source corpus.

The discovery of CoRoT-7b, a planet of radius 1.68 +/- 0.09 R_E, mass 4.8 +/- 0.8 M_E and orbital period of 0.854 days demonstrates that small planets can orbit extremely close to their star. We use knowledge of hot Jupiters, mass loss estimates and models for the interior structure and evolution of planets to understand its composition, structure and evolution. The inferred mass and radius of CoRoT-7b are consistent with a rocky planet that would be depleted in iron relative to Earth. However, a one sigma increase in mass (5.6 M_E) and decrease in size (1.59 R_E) are compatible with an Earth-like composition (33% iron, 67% silicates). Alternatively, it is possible that CoRoT-7b contains a significant amount of volatiles. An equally good fit to the data is found for a vapor envelope equal to 3% (and up to 10%) by mass above an Earth-like nucleus. Because of its intense irradiation and small size, the planet cannot possess an envelope of H and He of more than 1/10,000 of its total mass. We show that the mass loss is significant (~ 10^11 g/s) and independent of planetary composition. This is because the hydrodynamical escape rate is independent of the atmosphere's mean molecular mass, and owing to the intense irradiation, even a bare rocky planet would possess an equilibrium vapor atmosphere thick enough to capture stellar UV photons. This escape rate rules out the possibility of a H-He envelope as it would escape in only ~1 Ma. A water vapor atmosphere would escape in ~ 1 Ga, and thus it is a plausible scenario. The origin of CoRoT-7b cannot be inferred from present observations: It may have formed rocky; or be the remnant of a Uranus-like ice giant, or a gas giant with a small core that was stripped of its gaseous envelope.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9808ee55e2bcf7caf0c790509ac3500414425444

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. C. Mordasini
2. Jon Fortney
3. J. Owen
4. N. Madhusudhan
5. Sheng Jin
6. Yanqin Wu
7. Th. Henning
8. E. Lopez

Citations in the corpus

• Characterization of exoplanets from their formation - I. Models of combined planet formation and evolution (2012, background): “…the minimal allowed semimajor axis for model planets is 0.1 AU at the moment, so that no simulated planets are exposed to the intense radiation field occurring on very tight orbits as, for example, CoRoT-7b (a = 0.017 AU), where atmospheric mass loss may be very important (Valencia et al. 2010).”
• MOST 1.6 EARTH-RADIUS PLANETS ARE NOT ROCKY (2014, background): “Close-in sub-Neptunes lose volatiles over time to photo-evaporation (e.g., Lecavelier Des Etangs 2007; Valencia et al. 2010; Rogers et al. 2011; Boué et al. 2012; Lopez et al. 2012).”
• Characterization of exoplanets from their formation - II. The planetary mass-radius relationship (2012, methodology): “This is a well know effect (e.g. Valencia et al. 2010; Sect.”
• AN ANCIENT EXTRASOLAR SYSTEM WITH FIVE SUB-EARTH-SIZE PLANETS (2015, background): “In particular, α elements comprise the bulk of the material that constitutes rocky, Earth-size planets (Valencia et al. 2007, 2010).”
• SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs - I. New atmospheric parameters and masses for 48 stars with planets (2013, methodology): “In addition, a combination of different techniques and methods is also giving the possibility to explorethe planetary properties, including the study of their atmospheres and internal structure (e.g. Valencia et al. 2010; Cowan & Agol 2011; Demory et al. 2012).”
• Disentangling between stellar activity and planetary signals (2010, background): “…higher than the published value, and its refined measurement of radius, slightly smaller RP = 1.58±0.10 REarth, derived by Bruntt et al. (2010) using improved stellar parameters, Valencia et al. (2010) predicted that is a planet compatible with an Earth-like composition (33% iron, 66% silicate).”
• HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, methodology): “We assume a core heat capacity of cv = 0.5–1.0 J K−1 g−1 (Alfè et al. 2002; Guillot et al. 1995; Valencia et al. 2010) as in Nettelmann et al. (2011).”
• FORMATION AND STRUCTURE OF LOW-DENSITY EXO-NEPTUNES (2011, methodology): “We consider energy-limited mass loss, (e.g., Lammer et al. 2003; Lecavelier Des Etangs 2007; Valencia et al. 2010), Ṁ = − ǫπFXUV R 2 XUV Rp GMpKtide .”
• Detection of a transit of the super-Earth 55 Cancri e with warm Spitzer (2011, methodology): “We used the internal structure model described in Valencia et al. (2010) suitable for rocky and gaseous planets.”
• Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, background): “Following the discovery of the first close-in rocky exoplanet (CoRoT-7b, Léger et al. 2009), Jackson et al. (2010) and Valencia et al. (2010) studied its possible evolutionary histories, arguing that even though it contained a negligible Hydrogen/Helium atmosphere today, its short orbital period…”
• 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).”
• SUPER-EARTH ATMOSPHERES: SELF-CONSISTENT GAS ACCRETION AND RETENTION (2015, background): “Mass lass by photo-ionization has been studied extensively, both in the context of hot Jupiters and super Earths (Baraffe et al. 2004, 2005, 2006; Hubbard et al. 2007a,b; Murray-Clay et al. 2009; Jackson et al. 2010; Valencia et al. 2010; Lopez et al. 2012; Owen & Jackson 2012; Owen & Wu 2013).”
• BULK COMPOSITION OF GJ 1214b AND OTHER SUB-NEPTUNE EXOPLANETS (2013, background): “…of discovered planets: the rocky exoplanets including the high-density ones CoRoT-7b and Kepler-10b, with a composition similar to that of Mercury (Valencia et al. 2010; Wagner et al. 2012), and Kepler-36b with an Earth-like composition, and the ”volatile” planets GJ 1214b, the Kepler-11 system,…”
• Can we constrain the interior structure of rocky exoplanets from mass and radius measurements (2015, background): “Many authors have shown that the variations due to temperature for rocky planets are small compared to uncertainties of material properties of silicate or iron compositions (e.g., Sotin et al. 2007; Seager et al. 2007; Grasset et al. 2009; Valencia et al. 2010).”