On the Origins of Eccentric Close-In Planets

Strong tidal interaction with the central star can circularize the orbits of close-in planets. With the standard tidal quality factor Q of our solar system, estimated circularization times for close-in extrasolar planets are typically shorter than the ages of the host stars. While most extrasolar planets with orbital radii -->a 0.1 AU indeed have circular orbits, some close-in planets with substantial orbital eccentricities have recently been discovered. This new class of eccentric close-in planets implies that either their tidal Q factor is considerably higher, or circularization is prevented by an external perturbation. Here we constrain the tidal Q factor for transiting extrasolar planets by comparing their circularization times with accurately determined stellar ages. Using estimated secular perturbation timescales, we also provide constraints on the properties of hypothetical second planets exterior to the known ones.

[1]  Yanqin Wu.  Origin of Tidal Dissipation in Jupiter. II. The Value of Q , 2004, astro-ph/0407628.

[2]  G. M. Clemence,et al.  Methods of Celestial Mechanics , 1962 .

[3]  S. Barnes.  An Assessment of the Rotation Rates of the Host Stars of Extrasolar Planets , 2001, astro-ph/0107350.

[4]  Steven Soter,et al.  Q in the solar system , 1966 .

[5]  D. Hamilton,et al.  Orbital resonances in the inner neptunian system. II. Resonant history of Proteus, Larissa, Galatea, and Despina , 2008 .

[6]  M. Nagasawa,et al.  Formation of Hot Planets by a Combination of Planet Scattering, Tidal Circularization, and the Kozai Mechanism , 2008, 0801.1368.

[7]  F. Rasio,et al.  submitted to ApJ Preprint typeset using L ATEX style emulateapj v. 10/09/06 PLANETARY SYSTEMS IN BINARIES. I. DYNAMICAL CLASSIFICATION , 2022 .

[8]  D. N. C. Lin,et al.  Tidal Dissipation in Rotating Giant Planets , 2004 .

[9]  T. E. Sterne.  Apsidal motion in binary stars , 1939 .

[10]  D. Lin,et al.  Calculating the Tidal, Spin, and Dynamical Evolution of Extrasolar Planetary Systems , 2002 .

[11]  S. Peale,et al.  The tides of Io , 1981 .

[12]  C. Murray,et al.  Solar System Dynamics: Expansion of the Disturbing Function , 1999 .

[13]  Martin Pätzold,et al.  Constraints on the tidal dissipation factor of a main sequence star: The case of OGLE-TR-56b , 2007 .

[14]  Structure and Evolution of Nearby Stars with Planets. II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog , 2006, astro-ph/0607235.

[15]  Yoshihide Kozai,et al.  Secular perturbations of asteroids with high inclination and eccentricity , 1962 .

[16]  S. Tremaine,et al.  Submitted to ApJ Preprint typeset using L ATEX style emulateapj v. 10/09/06 SHRINKING BINARY AND PLANETARY ORBITS BY KOZAI CYCLES WITH TIDAL FRICTION , 2022 .

[17]  Gregory Laughlin,et al.  Effects of Secular Interactions in Extrasolar Planetary Systems , 2006, astro-ph/0606346.

[18]  J. Winn,et al.  A Possible Spin-Orbit Misalignment in the Transiting Eccentric Planet HD 17156b , 2007, 0712.2569.

[19]  R. Paul Butler,et al.  The Planet around 51 Pegasi , 1997 .

[20]  Seppo Mikkola,et al.  Tidal friction in triple stars , 1998 .

[21]  Secular Evolution of Hierarchical Triple Star Systems , 2000 .

[22]  S. Tremaine,et al.  Chaotic variations in the eccentricity of the planet orbiting 16 Cygni B , 1997, Nature.

[23]  Tidal decay of close planetary orbits , 1996, astro-ph/9605059.

[24]  D. Lin,et al.  Spin-Orbit Evolution of Short-Period Planets , 2004, astro-ph/0408191.

[25]  E. Ford,et al.  On the Relation between Hot Jupiters and the Roche Limit , 2005, astro-ph/0510198.

[26]  J. Bean,et al.  Observational consequences of the recently proposed Super-Earth orbiting GJ 436 , 2008, 0806.3270.

[27]  Ignasi Ribas,et al.  A ~5 M⊕ Super-Earth Orbiting GJ 436? The Power of Near-Grazing Transits , 2008, 0801.3230.

[28]  Peter P. Eggleton,et al.  The Equilibrium Tide Model for Tidal Friction , 1998, astro-ph/9801246.