Accretion in the Early Kuiper Belt. I. Coagulation and Velocity Evolution
Abstract
We describe planetesimal accretion calculations in the Kuiper Belt. Our evolution code simulates planetesimal growth in a single annulus and includes velocity evolution but not fragmentation. Test results match analytic solutions and duplicate previous simulations at 1 AU. In the Kuiper Belt, simulations without velocity evolution produce a single runaway body with a radius r_i >~ 1000 km on a timscale tau_r~M^1_0e^x_0, where M_0 is the initial mass in the annulus, e_0 is the initial eccentricity of the planetesimals, and x ~ 12. Runaway growth occurs in 100 Myr for M_0 ~ 10M_E and e_0 ~ 10^3 in a 6 AU annulus centered at 35 AU. This mass is close to the amount of dusty material expected in a minimummass solar nebula extrapolated into the Kuiper Belt. Simulations with velocity evolution produce runaway growth on a wide range of timescales. Dynamical friction and viscous stirring increase particle velocities in models with large (8 km radius) initial bodies. This velocity increase delays runaway growth by a factor of 2 compared with models without velocity evolution. In contrast, collisional damping dominates over dynamical friction and viscous stirring in models with small (80800 m) initial bodies. Collisional damping decreases the timescale to runaway growth by factors of 410 relative to constantvelocity calculations. Simulations with minimummass solar nebulae, M_0 ~ 10M_E, and small eccentricities, e ~ 10^3, reach runaway growth on timescales of 2040 Myr with 80 m initial bodies, 50100 Myr with 800 m bodies, and 75250 Myr for 8 km initial bodies. These growth times vary linearly with the mass of the annulus, tau_r~M^1_0, but are less sensitive to the initial eccentricity than constantvelocity models. In both sets of models, the timescales to produce 1000+ km objects are comparable to estimated formation timescales for Neptune. Thus, Plutosized objects can form in the outer solar system in parallel with the condensation of the outermost large planets.
 Publication:

The Astronomical Journal
 Pub Date:
 May 1998
 DOI:
 10.1086/300331
 arXiv:
 arXiv:astroph/9804185
 Bibcode:
 1998AJ....115.2136K
 Keywords:

 KUIPER BELT OBJECTS;
 Astrophysics
 EPrint:
 45 pages of text (including 5 tables), 31 pages of figure