Giant Exo Planets

Giant Exo Planets

The recent discovery of 2012 VP113, a Sedna-like body and a potential additional member of the inner Oort cloud, prompted Trujillo & Sheppard (2014) to note that a set of Kuiper belt objects (KBOs) in the distant solar system exhibits unexplained clustering in orbital elements. Specifically, objects with perihelion distance larger than the orbit of Neptune and semi-major axis greater than 150 AU – including 2012 VP113 and Sedna – have arguments of perihelia, ω, clustered approximately around zero. A value of ω = 0 requires that the object’s perihelion lies precisely at the ecliptic, and during ecliptic-crossing the object moves from south to north (i.e. intersects the ascending node). While observational bias does preferentially select for objects with perihelia (where they are closest and brightest) at the heavily observed ecliptic, no possible bias could select only for objects moving from south to north. Recent simulations (de la Fuente Marcos & de la Fuente Marcos 2014) confirmed this lack of bias in the observational data. The clustering in ω therefore appears to be real. Orbital grouping in ω is surprising because gravitational torques exerted by the giant planets are expected to randomize this parameter over the multi-Gyr age of the solar system. In other words, the values of ω will not stay clustered unless some dynamical mechanism is currently forcing the alignment. To date, two explanations have been proposed to explain the data.