Origins of Eccentric Extrasolar Planets: Testing the Planet-Planet Scattering Model

By Eric B. Ford, F. Rasio. 2007

350 citations recorded by the source corpus.

In planetary systems with two or more giant planets, dynamical instabilities can lead to collisions or ejections through strong planet-planet scattering. Previous studies for initial conditions with two equal-mass planets revealed two discrepancies between the results of simulations and the observed orbits of exoplanets: potentially frequent collisions between giant planets and a narrow distribution of final eccentricities. We show that simulations with two unequal-mass planets starting on nearly circular orbits predict fewer collisions and a broader range of final eccentricities. Thus, the two-planet scattering model can reproduce the observed eccentricities with a plausible distribution of planet mass ratios. The model also predicts a maximum eccentricity of ≃0.8, independent of the distribution of planet mass ratios, provided that both planets are initially placed on nearly circular orbits. This compares favorably with observations and will be tested by future planet discoveries. Moreover, the combination of planet-planet scattering and tidal circularization may explain the existence of some giant planets with very short period orbits. Orbital migration due to planet scattering could play an important role in explaining the distribution of orbital periods found by radial velocity surveys. We also reexamine and discuss various possible correlations between eccentricities and other properties of exoplanets. We find that radial velocity observations are consistent with planet eccentricities being correlated with the ratio of the escape velocity from the planet's surface relative to the escape velocity from the host star at the planet's location. We demonstrate that the observed distribution of planet masses, periods, and eccentricities can provide constraints for models of planet formation and evolution.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/8a171d8b653dc15e8cdd31ac3b033d939db97048

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Citations in the corpus

• HOW ROCKY ARE THEY? THE COMPOSITION DISTRIBUTION OF KEPLER’S SUB-NEPTUNE PLANET CANDIDATES WITHIN 0.15 AU (2014, methodology): “The eccentricity distribution of RV planets were studied by Jurić & Tremaine (2008) and Ford & Rasio (2008), among others, who performed K-S tests to compare the eccentricity distributions of their planet-planet scattering simulations to various subpopulations of RV planets to illuminate their…”
• PLANET OCCURRENCE WITHIN 0.25 AU OF SOLAR-TYPE STARS FROM KEPLER (2011, background): “…observed planets may be strongly shaped by processes that take place after the gas clears, namely, planet–planet scattering (e.g., Ford et al. 2005; Ford & Rasio 2008; Chatterjee et al. 2008; Raymond et al. 2009), secular and resonant migration (e.g., Lithwick & Wu 2011; Wu & Lithwick 2011), and…”
• The Occurrence and Architecture of Exoplanetary Systems (2014, background): “When a closely-packed system suffers from dynamical instability, massive planets are more likely to eject one another, whereas smaller planets are more likely to collide until the system stabilizes (Ford & Rasio 2008).”
• Populating the asteroid belt from two parent source regions due to the migration of giant planets—“The Grand Tack” (2012, background): “The scattering of giant planets in a violent instability is thought to have occurred in the majority of known systems of giant extra-solar planets (Chatterjee et al. 2008; Ford and Rasio 2008; Juric and Tremaine 2008; Raymond et al. 2010).”
• On the tidal evolution of Hot Jupiters on inclined orbits (2009, background): “Recent studies of stage 2 (Jurić & Tremaine 2008; Chatterjee et al. 2008; Ford & Rasio 2008) have shown that this is a chaotic era, in which planet–planet scatterings force the ejection of all but a few (∼ 2−3) planets from the system, in a period of large–scale dynamical instability lasting .”
• TEN NEW AND UPDATED MULTIPLANET SYSTEMS AND A SURVEY OF EXOPLANETARY SYSTEMS (2008, background): “Consistent with Ford & Rasio (2008), Figure 23 shows that planets that scatter planets and planetesimals efficiently (i.e. those with θ >> 1) have a wider range of eccentricities than inefficient scatterers.”
• SECULAR CHAOS AND THE PRODUCTION OF HOT JUPITERS (2010, background): “First proposed by Rasio & Ford (1996), it asserts that close encounters between planets can induce extreme eccentricity in one of the planets (Ford et al. 2001; Papaloizou & Terquem 2001; Ford & Rasio 2008), which may then be tidally circularized to form a hot Jupiter.”
• ECCENTRICITY FROM TRANSIT PHOTOMETRY: SMALL PLANETS IN KEPLER MULTI-PLANET SYSTEMS HAVE LOW ECCENTRICITIES (2015, background): “Planet-planet interactions have been brought forward as a mechanism to explain the observed eccentricities in massive planets (Fabrycky & Tremaine 2007; Chatterjee et al. 2008; Nagasawa et al. 2008; Ford & Rasio 2008; Jurić & Tremaine 2008).”
• THE CALIFORNIA PLANET SURVEY. I. FOUR NEW GIANT EXOPLANETS (2010, background): “Moreover, planet-planet interactions among giant planets must be predicted and compared with the distributions of orbital elements (especially eccentricity) for systems containing multiple giant planets, e.g. Wright et al. (2009); Ford & Chiang (2007); Ford & Rasio (2008); Jurić & Tremaine (2008).”
• SOAR TESS Survey. I. Sculpting of TESS Planetary Systems by Stellar Companions (2019, background): “Planet–planet scattering has been shown to largely reproduce the observed distribution of eccentricities in transiting planets (e.g., Ford & Rasio 2008; Jurić & Tremaine 2008; Raymond et al. 2011).”
• THE sdB+M ECLIPSING SYSTEM HW VIRGINIS AND ITS CIRCUMBINARY PLANETS (2008, result): “This fact and the relatively high eccentricities are in line with theoretical results on planet–planet interaction and stability (Kley et al. 2004; Ford & Rasio 2008; Pierens & Nelson 2008a) and support a two-planet explanation.”
• The effects of fly‐bys on planetary systems (2010, background): “If the planets are too tightly packed, such systems may become unstable on time-scales of a few to several 10 Myr (e.g. Chatterjee et al. 2008; Ford & Rasio 2008; Jurić & Tremaine 2008; Raymond et al. 2009).”
• ECCENTRICITY GROWTH AND ORBIT FLIP IN NEAR-COPLANAR HIERARCHICAL THREE-BODY SYSTEMS (2013, background): “Eccentricity may be excited by planet-planet scattering or interactions with the protoplanetary disk (Ford & Rasio 2008; Nagasawa & Ida 2011).”
• RETIRED A STARS AND THEIR COMPANIONS. III. COMPARING THE MASS–PERIOD DISTRIBUTIONS OF PLANETS AROUND A-TYPE STARS AND SUN-LIKE STARS (2009, background): “…a posteriori in terms of orbital migration (Papaloizou et al. 2007) and planet-planet scattering (Nagasawa et al. 2008; Marchi et al. 2009; Ford & Rasio 2008), with the dearth of planets with periods between ∼ 10-100 days (the “period valley”) possibly resulting from differential…”