BREEDING SUPER-EARTHS AND BIRTHING SUPER-PUFFS IN TRANSITIONAL DISKS

By Eve J. Lee, E. Chiang. 2015

161 citations recorded by the source corpus.

The riddle posed by super-Earths (1–4R⊕, 2–20M⊕) is that they are not Jupiters: their core masses are large enough to trigger runaway gas accretion, yet somehow super-Earths accreted atmospheres that weigh only a few percent of their total mass. We show that this puzzle is solved if super-Earths formed late, as the last vestiges of their parent gas disks were about to clear. This scenario would seem to present fine-tuning problems, but we show that there are none. Ambient gas densities can span many (in one case up to 9) orders of magnitude, and super-Earths can still robustly emerge after ∼0.1–1 Myr with percent-by-weight atmospheres. Super-Earth cores are naturally bred in gas-poor environments where gas dynamical friction has weakened sufficiently to allow constituent protocores to gravitationally stir one another and merge. So little gas is present at the time of core assembly that cores hardly migrate by disk torques: formation of super-Earths can be in situ. The basic picture—that close-in super-Earths form in a gas-poor (but not gas-empty) inner disk, fed continuously by gas that bleeds inward from a more massive outer disk—recalls the largely evacuated but still accreting inner cavities of transitional protoplanetary disks. We also address the inverse problem presented by super-puffs: an uncommon class of short-period planets seemingly too voluminous for their small masses (4–10R⊕, 2–6M⊕). Super-puffs most easily acquire their thick atmospheres as dust-free, rapidly cooling worlds outside ∼1 AU where nebular gas is colder, less dense, and therefore less opaque. Unlike super-Earths, which can form in situ, super-puffs probably migrated in to their current orbits; they are expected to form the outer links of mean-motion resonant chains, and to exhibit greater water content. We close by confronting observations and itemizing remaining questions.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/9bc3d2392c59918804a23a4561ab1d1802a77210

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. J. Owen
2. T. Birnstiel
3. S. Andrews
4. D. Wilner
5. Jon Fortney
6. Timothy Morton
7. E. Petigura
8. E. Chiang

Citations in the corpus

• The Complete Transmission Spectrum of WASP-39b with a Precise Water Constraint (2017, result): “This is consistent with the envelope accretion models by Lee & Chiang (2016), which argue that most hot Neptunes accrete their envelopes insitu shortly before the disk dissipates resulting in lower heavy element contamination in the atmosphere.”
• The Disk Substructures at High Angular Resolution Project (DSHARP). II. Characteristics of Annular Substructures (2018, background): “These wide Corresponding author: Jane Huang jane.huang@cfa.harvard.edu variations in properties are thought to be closely tied to differences in where and when planets formed in the protoplanetary disks orbiting young stars (e.g., Öberg et al. 2011b; Mordasini et al. 2012; Lee & Chiang 2016).”
• An ALMA Survey of Protoplanetary Disks in the σ Orionis Cluster (2017, background): “In this scenario, super-Earths would result when giant planet cores form in gas-depleted disks, prohibiting the cores from rapidly accreting gaseous envelopes (e.g., Lee & Chiang 2016) as predicted by core accretion theory (e.g., Pollack et al. 1996; Ida & Lin 2004).”
• 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).”
• The California-Kepler Survey. VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap (2018, background): “…mechanisms have been proposed that could potentially produce a gap in the size distribution including delayed formation in a gas-poor disk (e.g., Lee et al. 2014; Lee & Chiang 2016), and sculpting by giant impacts (e.g., Liu et al. 2015; Schlichting et al. 2015; Inamdar & Schlichting 2016).”
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes (2016, background): “…for the lower boundary of the desert and for the existence of the super-Earth ridge, we mention the recent works that suggested in situ models for the formation of short-period super-Earths (Lee & Chiang (2016); see also Hansen & Murray (2012); Chiang & Laughlin (2013) and Lee et al. (2014)).”
• Kepler Planet Masses and Eccentricities from TTV Analysis (2016, background): “Explaining how such planets manage to accrete and retain such large gaseous envelopes while avoiding runaway gas accretion presents an interesting theoretical challenge (e.g., Lee & Chiang 2016).”
• Multiple Disk Gaps and Rings Generated by a Single Super-Earth (2017, background): “Their compositions, as inferred from their bulk densities, span a wide range; some are consistent with pure rock while others have 1–10% of their mass in voluminous H/He envelopes (e.g., Lopez & Fortney 2014; Rogers 2015; Lee & Chiang 2016).”
• IN SITU FORMATION AND DYNAMICAL EVOLUTION OF HOT JUPITER SYSTEMS (2015, background): “For instance, the paucity of close-in giant planets can be alternatively be explained by the relative timing of gas dispersal and core coagulation, as advocated by Lee et al. (2014); Lee and Chiang (2016).”
• SUPER-EARTH ATMOSPHERES: SELF-CONSISTENT GAS ACCRETION AND RETENTION (2015, background): “This logarithmic dependence 5 on the nebular density allows Lee & Chiang (2016) to accrete substantial gas envelopes even in highly depleted transitional disks.”
• Photoevaporation and high-eccentricity migration created the sub-Jovian desert (2018, background): “Many authors (e.g. Hansen & Murray 2012; Chatterjee & Tan 2014; Lee et al. 2014; Lee & Chiang 2016; Mohanty et al. 2017) suggested that low-mass super-Earths/mini-Neptunes formed in situ, close to their current orbital locations, while Boley et al. (2016); Batygin et al. (2016) suggested that…”