TIDAL EVOLUTION OF CLOSE-IN PLANETS

By S. Matsumura, S. Peale, F. Rasio. 2010

141 citations recorded by the source corpus.

Recent discoveries of several transiting planets with clearly non-zero eccentricities and some large obliquities started changing the simple picture of close-in planets having circular and well-aligned orbits. The two major scenarios that form such close-in planets are planet migration in a disk and planet–planet interactions combined with tidal dissipation. The former scenario can naturally produce a circular and low-obliquity orbit, while the latter implicitly assumes an initially highly eccentric and possibly high-obliquity orbit, which are then circularized and aligned via tidal dissipation. Most of these close-in planets experience orbital decay all the way to the Roche limit as previous studies showed. We investigate the tidal evolution of transiting planets on eccentric orbits, and find that there are two characteristic evolution paths for them, depending on the relative efficiency of tidal dissipation inside the star and the planet. Our study shows that each of these paths may correspond to migration and scattering scenarios. We further point out that the current observations may be consistent with the scattering scenario, where the circularization of an initially eccentric orbit occurs before the orbital decay primarily due to tidal dissipation in the planet, while the alignment of the stellar spin and orbit normal occurs on a similar timescale to the orbital decay largely due to dissipation in the star. We also find that even when the stellar spin–orbit misalignment is observed to be small at present, some systems could have had a highly misaligned orbit in the past, if their evolution is dominated by tidal dissipation in the star. Finally, we also re-examine the recent claim by Levrard et al. that all orbital and spin parameters, including eccentricity and stellar obliquity, evolve on a similar timescale to orbital decay. This counterintuitive result turns out to have been caused by a typo in their numerical code. Solving the correct set of tidal equations, we find that the eccentricity behaves as expected, with orbits usually circularizing rapidly compared to the orbital decay rate.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f9eab3ed3b55be09fbcaed014e317f95e8acd698

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Citations in the corpus

• ON THE FORMATION OF HOT JUPITERS IN STELLAR BINARIES (2012, unknown): “Following Matsumura et al. (2010) we define RL = R2 0.6 ( m2 m2 +m1 )−1/3 , (2) where R2 = 1RJ .”
• FORETELLINGS OF RAGNARÖK: WORLD-ENGULFING ASYMPTOTIC GIANTS AND THE INHERITANCE OF WHITE DWARFS (2012, methodology): “In light of this uncertainty, we adopt the standardQ formalism and a constant time lag of the tidal bulge (Matsumura et al. 2010).”
• Tidal dissipation in planet-hosting stars: damping of spin-orbit misalignment and survival of hot Jupiters (2011, background): “Many previous works on tidal evolution in hot Jupiter systems (e.g., Rasio et al. 1996; Sasselov 2003; Dobbs-Dixon et al. 2004; Barker & Ogilvie 2009; Jackson et al. 2009; Levrard et al. 2009; Hansen 2010; Matsumura et al. 2010) were based on the weak friction theory of equilibrium tides.”
• Tidal Dissipation in Stars and Giant Planets (2014, background): “A few short-period systems with very massive planets are estimated to have L > Lc (Levrard et al. 2009; Matsumura et al. 2010).”
• 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, unknown): “(6) in Matsumura et al. (2008; hereafter M08) which also applies to the case of high eccentricities and assumes that tides in the planet are mainly responsible for circularising its orbit (e.g. Matsumura et al. 2010).”
• MIGRATION THEN ASSEMBLY: FORMATION OF NEPTUNE-MASS PLANETS INSIDE 1 AU (2011, methodology): “For planets with orbital periods of a few days, tidal capture from eccentric orbits might be an alternative model (Rasio & Ford 1996; Matsumura et al. 2010).”
• Tidal locking of habitable exoplanets (2017, background): “2013), rotational braking by stellar winds (Matsumura et al. 2010; Reiners et al. 2014), etc.”
• 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).”
• ECCENTRICITY GROWTH AND ORBIT FLIP IN NEAR-COPLANAR HIERARCHICAL THREE-BODY SYSTEMS (2013, background): “Tidal dissipation shrinks the orbit separation and circularizes it (Matsumura et al. 2010).”
• WASP-121 b: a hot Jupiter close to tidal disruption transiting an active F star (2015, background): “However, Matsumura et al. (2010) showed that these extreme orbits can still result from the scattering model, assuming first a scattering into an eccentric orbit beyond 2 aR, followed by a slow inward migration and circularization through tidal dissipation inside the planet mainly until reaching ∼2…”