Formation of Hot Planets by a Combination of Planet Scattering, Tidal Circularization, and the Kozai Mechanism

By M. Nagasawa, Shigeru Ida, T. Bessho. 2008

392 citations recorded by the source corpus.

We have investigated the formation of close-in extrasolar giant planets through a coupling effect of mutual scattering, the Kozai mechanism, and tidal circularization, by orbital integrations. Close-in gas giants would have been originally formed at several AU beyond the ice lines in protoplanetary disks and migrated close to their host stars. Although type II migration due to planet-disk interactions may be a major channel for the migration, we show that this scattering process would also give a nonnegligible contribution. We carried out orbital integrations of three planets with Jupiter mass, directly including the effect of tidal circularization. We have found that in about 30% of the runs close-in planets are formed, which is much higher than suggested by previous studies. Three-planet orbit crossing usually results in the ejection of one or two planets. Tidal circularization often occurs during three-planet orbit crossing, but previous studies have monitored only the final stage after the ejection, significantly underestimating the formation probability. We have found that the Kozai mechanism in outer planets is responsible for the formation of close-in planets. During three-planet orbital crossing, Kozai excitation is repeated and the eccentricity is often increased secularly to values close enough to unity for tidal circularization to transform the inner planet to a close-in planet. Since a moderate eccentricity can retain for the close-in planet, this mechanism may account for the observed close-in planets with moderate eccentricities and without nearby secondary planets. Since these planets also remain a broad range of orbital inclinations (even retrograde ones), the contribution of this process would be clarified by more observations of Rossiter-McLaughlin effects for transiting planets.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/d23ddb1ac93a66d3b268d3daa9db7e200310d661

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Citations in the corpus

• EXOPLANETARY SPIN–ORBIT ALIGNMENT: RESULTS FROM THE ENSEMBLE OF ROSSITER–MCLAUGHLIN OBSERVATIONS (2009, background): “…occasionally large misalignments (Ford et al. 2001; Yu & Tremaine 2001; Papaloizou & Terquem 2001; Terquem & Papaloizou 2002; Marzari & Weidenschilling 2002; Thommes & Lissauer 2003; Wu et al. 2007; Fabrycky & Tremaine 2007; Chatterjee et al. 2008; Jurić & Tremaine 2008; Nagasawa et al. 2008).”
• MULTIPLE-PLANET SCATTERING AND THE ORIGIN OF HOT JUPITERS (2011, methodology): “For the tidal effects, Nagasawa et al. (2008) adopted the dynamic tide model by Ivanov & Papaloizou (2004), which is applicable for fully convective planets with near-parabolic orbits, but is not well suited for low-to-moderate eccentricities.”
• Tidal dissipation in planet-hosting stars: damping of spin-orbit misalignment and survival of hot Jupiters (2011, background): “…through secular interactions between multiple planets or Kozai effect induced by a distant companion (e.g., Wu & Murray 2003; Fabrycky & Tremaine 2007; Nagasawa et al. 2008; Naoz et al. 2011a,b; Wu & Lithwick 2011; Katz et al. 2011), although other effects involving star-disc interactions (Lai et…”
• FRIENDS OF HOT JUPITERS. I. A RADIAL VELOCITY SEARCH FOR MASSIVE, LONG-PERIOD COMPANIONS TO CLOSE-IN GAS GIANT PLANETS (2013, background): “…Naoz et al. 2012; Teyssandier et al. 2013b), which requires a distant stellar companion, planet-planet scattering (e.g., Chatterjee et al. 2008; Nagasawa et al. 2008), and secular chaotic excursions (Wu & Lithwick 2011; Lithwick & Wu 2013) frequently produce close-in planets with misaligned…”
• STARSPOTS, SPIN–ORBIT MISALIGNMENT, AND ACTIVE LATITUDES IN THE HAT-P-11 EXOPLANETARY SYSTEM (2011, background): “…a recent resurgence of the theory that close-in planets are emplaced by few-body gravitational interactions followed by tidal capture, rather than by gradual inspiral due to interactions with a protoplanetary disk (see, e.g., Fabrycky & Tremaine 2007, Nagasawa et al. 2008, Matsumura et al. 2010).”
• The Eccentric Kozai-Lidov Effect and Its Applications (2016, background): “The first is to consider a scattering, short time scale, event, which has been discussed in length in the literature (e.g., Hut and Bahcall 1983; Rasio and Ford 1996b; Chatterjee et al. 2008; Nagasawa et al. 2008; Antognini and Thompson 2015).”
• OBSERVATIONAL EVIDENCE FOR TIDAL DESTRUCTION OF EXOPLANETS (2009, background): “Other studies have invoked a combination of gravitational scattering and tidal evolution to move planets inward to the “pile-up” (Rasio & Ford 1996; Weidenschilling & Marzari 1996; Ford & Rasio 2006; Nagasawa et al. 2008).”
• Secular Dynamics in Hierarchical Three-Body Systems (2011, background): “2012) or if there is an episode of planet-planet scattering following planet formation (Chatterjee et al. 2008; Nagasawa et al. 2008) see also Merritt et al.”
• ZODIACAL EXOPLANETS IN TIME (ZEIT). III. A SHORT-PERIOD PLANET ORBITING A PRE-MAIN-SEQUENCE STAR IN THE UPPER SCORPIUS OB ASSOCIATION (2016, background): “…either migrated inwards via disk migration or formed in-situ, as planetstar and planet-planet interactions work on much longer timescales (Fabrycky & Tremaine 2007; Nagasawa et al. 2008), and the conditions for Kozai-Lidov evolution only begin after the disk dissipates (e.g., Martin et al. 2016).”
• The GAPS Programme with HARPS-N at TNG - XIV. Investigating giant planet migration history via improved eccentricity and mass determination for 231 transiting planets (2017, neutral): “…mutual inclinations: i. Young giant planets such as V830 Tau b (Donati et al. 2016) with an age of ∼ 2 Myr likely migrated through interactions with the protoplanetary disc because HEM would usually require longer times (e.g. Nagasawa et al. 2008; Petrovich 2015; Petrovich & Tremaine 2016). ii.”
• 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).”
• OBLIQUITIES OF HOT JUPITER HOST STARS: EVIDENCE FOR TIDAL INTERACTIONS AND PRIMORDIAL MISALIGNMENTS (2012, background): “…is that some of them would alter the planet’s orbital orientation and thereby change the relative orientation between the stellar and orbital spin (Nagasawa et al. 2008; Fabrycky & Tremaine 2007; Naoz et al. 2011), while others would preserve the relative orientation 1 Department of Physics, and…”
• SECULAR CHAOS AND THE PRODUCTION OF HOT JUPITERS (2010, background): “The noteworthy simulations of Nagasawa et al. (2008) combine planet scattering with Kozai oscillations.”
• PLANET OCCURRENCE WITHIN 0.25 AU OF SOLAR-TYPE STARS FROM KEPLER (2011, background): “Thus, standard planet formation theory probably requires additional planet–planet gravitational interactions to explain these noncircular and non-coplanar orbits (e.g., Chatterjee et al. 2011; Wu & Lithwick 2011; Nagasawa et al. 2008).”