Sedna and the cloud of comets surrounding the Solar System in Milgromian
  dynamics
  We reconsider the hypothesis of a vast cometary reservoir surrounding the
Solar System - the Oort cloud of comets - within the framework of Milgromian
Dynamics (MD or MOND). For this purpose we built a numerical model of the cloud
assuming QUMOND, a modified gravity theory of MD. In the modified gravity
versions of MD, the internal dynamics of a system is influenced by the external
gravitational field in which the system is embedded, even when this external
field is constant and uniform, a phenomenon dubbed the external field effect
(EFE). Adopting the popular pair $\nu(x)=[1-\exp(-x^{1/2})]^{-1}$ for the MD
interpolating function and $a_{0}=1.2\times10^{-10}$ m s$^{-2}$ for the MD
acceleration scale, we found that the observationally inferred Milgromian cloud
of comets is much more radially compact than its Newtonian counterpart. The
comets of the Milgromian cloud stay away from the zone where the Galactic tide
can torque their orbits significantly. However, this does not need to be an
obstacle for the injection of the comets into the inner solar system as the EFE
can induce significant change in perihelion distance during one revolution of a
comet around the Sun. Adopting constraints on different interpolating function
families and a revised value of $a_{0}$ (provided recently by the Cassini
spacecraft), the aforementioned qualitative results no longer hold, and, in
conclusion, the Milgromian cloud is very similar to the Newtonian in its
overall size, binding energies of comets and hence the operation of the
Jupiter-Saturn barrier. However, EFE torquing of perihelia still play a
significant role in the inner parts of the cloud. Consequently Sedna-like
orbits and orbits of large semi-major axis Centaurs are easily comprehensible
in MD. In MD, they both belong to the same population, just in different modes
of their evolution.
