Collision Enhancement due to Planetesimal Binary Formation Planetesimal Binary Formation Junko Kominami Jun Makino (Earth-Life-Science Institute, Tokyo Institute of Technology) 1/15

Solar System Focus on TNO region 2/15

Mystery in TNO Region TNO Binaries Semimajor Axis from Sun ～ 44.5AU Total mass ～ Binary’s period ～ 570days Binary’s eccentricity ～ 0.8 Binary’s separation ～ 22300km （ several 100s x ） Number of TNO binaries observed is 65 ~10% of observed TNOs are binaries (Veillet et al. 2002) 1998WW31 Difference from quasi-satellites in asteroid belt ： Equal-mass, large eccentricity, long distance between the components 3/15

Difference in TNO region and Asteroid Belt TNO region （ Beyond 30AU ） Asteroid Belt Terrestrial Planets Gas GiantsIce Giants Difference in ratio of Hill radius/Physical radius Quasi-satellites : Large mass difference, small eccentricity TNO binaries : Small mass difference, large eccentricity 4/15

Planetesimal accretion in Terrestrial Planet Region ~1AU~1.5AU Planetesimals (e.g. Makino et al. 1997, Kokubo and Ida 1998) Protoplanets Runaway and Origarchic Growth (e.g. Kokubo and Ida 2002)Isolation mass (Kokubo and Ida 2002) We assume that this can be extrapolated to outer region 5/15

Problems Growth scenario considering planetesimal binaries has not been clarified yet To clarify the effect of planetesimal binary formation on collision process Aim of the Work Method 4 th order Hermite Scheme N-body simulation Perfect accretion Equation of Motion 6/15

Model Runaway growth is assumed Large mass has small eccentricity Small mass has large eccentricity Eccentricity of Assumed equallibrium state : 7/15

Binary formation example 8/15

Binary formation example 9/15 How many of planetesimals are the binaries?

Time Evolution of Binaries’ Number Binaries’ number increases as distance from the Sun increases 10/15

Mass Distribution Large planetesimals tend to form binaries total particles Binary particles t=1000 years (binary formation peak) 11/15

Collision after Binary Formation 20 % of the collision was binary induced collision Some of the binaries ended up colliding 3 body encounter 1 get ejected 2 get collided 12/15

Binary Induced Collision Cumulative number of Binary induced collision When binaries are disrupted, most of the binary induced collisions take place Binaries increase the collision probability 13/15

Collision Probability Increase Analysis When m is large, and eventually all the binaries collide,, Binary formation probability Probability that 3 rd body encounters the binary 14/15

Summary and Discussion Timescale of ice giant’s’ core may be shortened Formation of large size TNOs may be explained Outer region of the disk : planetesimal binaries are formed Large planetesimals tend to form binaries Binaries increase the collision probability Collision probability can increase by factor of ~10 15/15