MIGRATION THEN ASSEMBLY: FORMATION OF NEPTUNE-MASS PLANETS INSIDE 1 AU

By Brad M. S. Hansen, N. Murray. 2011

207 citations recorded by the source corpus.

We demonstrate that the observed distribution of “hot Neptune”/“super-Earth” systems is well reproduced by a model in which planet assembly occurs in situ, with no significant migration post-assembly. This is achieved only if the amount of mass in rocky material is ∼50–100 M⊕ interior to 1 AU. Such a reservoir of material implies that significant radial migration of solid material takes place, and that it occurs before the stage of final planet assembly. The model not only reproduces the general distribution of mass versus period but also the detailed statistics of multiple planet systems in the sample. We furthermore demonstrate that cores of this size are also likely to meet the criterion to gravitationally capture gas from the nebula, although accretion is rapidly limited by the opening of gaps in the gas disk. If the mass growth is limited by this tidal truncation, then the scenario sketched here naturally produces Neptune-mass objects with substantial components of both rock and gas, as is observed. The quantitative expectations of this scenario are that most planets in the “hot Neptune/super-Earth” class inhabit multiple-planet systems, with characteristic orbital spacings. The model also provides a natural division into gas-rich (hot Neptune) and gas-poor (super-Earth) classes at fixed period. The dividing mass ranges from ∼3 M⊕ at 10 day orbital periods to ∼10 M⊕ at 100 day orbital periods. For orbital periods <10 days, the division is less clear because a gas atmosphere may be significantly eroded by stellar radiation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/99c3fe382d6c08ef82f8a5029e5688879c811101

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In Astronomy and Astrophysics

1. Jon Fortney
2. J. Owen
3. C. Mordasini
4. Timothy Morton
5. Yanqin Wu
6. J. Johnson
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8. J. Winn

Citations in the corpus

• Spacing of Kepler Planets: Sculpting by Dynamical Instability (2015, background): “Dynamical Scuplting The formation of Kepler planets themselves is not yet understood and different theories have been proposed (Terquem & Papaloizou 2007; Ida & Lin 2010; Hansen & Murray 2012; Chiang & Laughlin 2013; Chatterjee & Tan 2014).”
• IN SITU FORMATION AND DYNAMICAL EVOLUTION OF HOT JUPITER SYSTEMS (2015, background): “The origins of the Super-Earth population are widely debated, and both migration-based models (Terquem and Papaloizou 2007; Cresswell and Nelson 2008) as well as in situ accretion scenarios (Hansen and Murray 2012; Chiang and Laughlin 2013) have been proposed to explain the data.”
• The California-Kepler Survey. I. High-resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets (2017, background): “These iconic Kepler systems present opportunities to determine planet masses and orbital properties through dynamical effects (Ford et al. 2011; Lissauer et al. 2011b) and have inspired new classes of planet formation models (Hansen & Murray 2012; Chiang & Laughlin 2013).”
• HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, background): “If these planets only contain rock, iron, and hydrogen/helium, then it is possible that they formed close to their current orbits (Hansen & Murray 2012).”
• A FRAMEWORK FOR CHARACTERIZING THE ATMOSPHERES OF LOW-MASS LOW-DENSITY TRANSITING PLANETS (2013, background): “Formation models are now aiming to understand the frequency of such planets, their formation timescale, and how often they end up in compact orbital configurations (Hansen & Murray 2012; Rogers et al. 2011; Ikoma & Hori 2012; Chiang & Laughlin 2013).”
• TESTING IN SITU ASSEMBLY WITH THE KEPLER PLANET CANDIDATE SAMPLE (2013, background): “Instead, Hansen & Murray (2012) propose that this population is the result of in situ assembly of rocky planets, which may capture substantial, but not dominant, gaseous envelopes if they grow to sufficient size before the gaseous disk disperses.”
• A STELLAR-MASS-DEPENDENT DROP IN PLANET OCCURRENCE RATES (2014, background): “Only a hybrid scenario (e.g., Hansen & Murray 2012; Cossou et al. 2014), in which building blocks (that are sufficiently large to resist sublimation) migrate inward and get trapped at the co-rotation and farther out, can explain the truncation at the co-rotation radius.”
• 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).”
• HUBBLE SPACE TELESCOPE NEAR-IR TRANSMISSION SPECTROSCOPY OF THE SUPER-EARTH HD 97658B (2014, background): “…tightly packed multiple planet systems (e.g., Lissauer et al. 2011; Fabrycky et al. 2012; Steffen et al. 2013), and there is an ongoing debate as to whether these systems formed in place or migrated in from more distant orbits (Hansen & Murray 2012; Chiang & Laughlin 2013; Raymond & Cossou 2014).”
• THE RADIUS DISTRIBUTION OF PLANETS AROUND COOL STARS (2013, background): “…of planetary mass seen close to host stars is evidence that protoplanetary disks may have much higher surface densities than previously thought (Hansen & Murray 2012; Chiang & Laughlin 2012) or that the observed planets migrated from regions further from their host star where more mass was…”
• Breaking the chains: hot super-Earth systems from migration and disruption of compact resonant chains (2017, background): “…standard in situ accretion models that invoke high-mass discs from the beginning to allow multi-Earth masses planets to form in the inner regions (Hansen & Murray 2012, 2013); and (b) drift-then-assembly model which proposes that these planets form in the innermost regions of the disc in…”
• 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).”
• MAKE SUPER-EARTHS, NOT JUPITERS: ACCRETING NEBULAR GAS ONTO SOLID CORES AT 0.1 AU AND BEYOND (2014, background): “But closer to the star, the universe of possibilities narrows considerably, assuming that planets form in-situ (Hansen & Murray 2012, 2013; Chiang & Laughlin 2013).”
• 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…”
• A dynamically-packed planetary system around GJ 667C with three super-Earths in its habitable zone (2013, background): “Therefore, the planets either formed at larger orbital distances and migrated in (e.g. Lin et al. 1996), or additional dust and ice flowed inward during the protoplanetry disk phase and accumulated into the planets Hansen & Murray (2012, 2013).”
• CHARACTERIZING THE COOL KOIs. IV. KEPLER-32 AS A PROTOTYPE FOR THE FORMATION OF COMPACT PLANETARY SYSTEMS THROUGHOUT THE GALAXY (2012, background): “The migration of planetesimals from outside this region also offers a possibility for late time growth of the Kepler-32 planets (Hansen & Murray 2012).”