Characterization of exoplanets from their formation - II. The planetary mass-radius relationship

By C. Mordasini, Y. Alibert, C. Georgy, K. Dittkrist, H. Klahr, Th. Henning. 2012

216 citations recorded by the source corpus.

The research of exoplanets has entered an era in which we characterize extrasolar planets. This has become possible with measurements of radii and luminosities. Meanwhile, radial velocity surveys discover also very low-mass planets. Uniting all this observational data into one coherent picture to better understand planet formation is an important, but difficult undertaking. Our approach is to develop a model which can make testable predictions for all these observational methods. We continue to describe how we have extended our formation model into a self-consistently coupled formation and evolution model. We show how we calculate the internal structure of the solid core and radiogenic heating. We also improve the protoplanetary disk model. Finally, we conduct population synthesis calculations. We present how the planetary mass-radius relationship of planets with primordial H/He envelopes forms and evolves in time. The basic shape of the M-R relation can be understood from the core accretion model. Low-mass planets cannot bind massive envelopes, while super-critical cores necessarily trigger runway gas accretion, leading to "forbidden" zones in the M-R plane. For a given mass, there is a considerable diversity of radii. We compare the synthetic M-R relation with the observed one, finding good agreement for a>0.1 AU. The synthetic radius distribution is characterized by a strong increase towards small R, and a second, lower local maximum at ~1 Jovian radius. The increase towards small radii reflects the increase of the mass function towards low M. The second local maximum is due to the fact that radii are nearly independent of mass for giant planets. A comparison of the synthetic radius distribution with Kepler data shows agreement for R>2 Earth radii, but divergence for smaller radii. We predict that in the next few years, Kepler should find the second, local maximum at ~1 Jovian radius.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e0611e4e934b9ff1827abb8376e91892ba41e519

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In Astronomy and Astrophysics

1. J. Owen
2. Jon Fortney
3. C. Mordasini
4. Yanqin Wu
5. Timothy Morton
6. Sheng Jin
7. E. Lopez
8. B. Fulton

Citations in the corpus

• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets (2017, background): “Modern formation models are now able to reproduce the observed population of super-Earths (Hansen & Murray 2012; Mordasini et al. 2012; Alibert et al. 2013; Chiang & Laughlin 2013; Lee et al. 2014; Chatterjee & Tan 2014; Coleman & Nelson 2014; Raymond & Cossou 2014; Lee & Chiang 2016).”
• Origin and loss of nebula-captured hydrogen envelopes from ‘sub’- to ‘super-Earths’ in the habitable zone of Sun-like stars (2014, methodology): “One can see from Mordasini et al. (2012), that z0 and R0 move to higher distances if the protoplanets that are surrounded by a more massive hydrogen envelope.”
• THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS (2016, methodology): “The model has been described in detail in several previous works (Alibert et al. 2004, 2005, Mordasini et al. 2012c) with a recent overview in Mordasini et al. (2015).”
• UNDERSTANDING THE MASS–RADIUS RELATION FOR SUB-NEPTUNES: RADIUS AS A PROXY FOR COMPOSITION (2013, background): “At larger sizes, planets are limited by their ability to accrete a H/He envelope from the disk before the disk dissipates (Bodenheimer et al. 2000; Ikoma & Hori 2012; Mordasini et al. 2012).”
• PLANETARY POPULATION SYNTHESIS COUPLED WITH ATMOSPHERIC ESCAPE: A STATISTICAL VIEW OF EVAPORATION (2014, methodology): “We assume that the luminosity is constant with radius, which does not significantly affect the evolution as discussed in Mordasini et al. (2012a).”
• KEPLER PLANETS: A TALE OF EVAPORATION (2013, background): “It is at this point that we will begin to learn valuable information about the planet population at birth and make inferences about the planet formation process (e.g Ida & Lin 2005; Mordasini et al. 2012a,b; Hansen & Murray 2012, 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, methodology): “Such low-mass planets can have a large radius even with a tenuous envelope (Adams et al. 2008; Rogers et al. 2011; Mordasini et al. 2012b), and can be easily evaporated to bare cores at close-in orbits (Lopez & Fortney 2013; Jin et al. 2014).”
• SOPHIE velocimetry of Kepler transit candidates XVII. The physical properties of giant exoplanets within 400 days of period (2015, background): “Interestingly, we find that the radius distribution of EGPs with a moderate irradiation is significantly different from the one predicted by Mordasini et al. (2012b).”
• A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS (2013, methodology): “The planets are synthesized using an upgraded version (Mordasini et al. 2012b) of the planet formation model originally presented in Alibert et al. (2004).”