  When an asteroid has a few observations over a short time span the
information contained in the observational arc could be so little that a full
orbit determination may be not possible. One of the methods developed in recent
years to overcome this problem is based on the systematic ranging and combined
with the Admissible Region theory to constrain the poorly-determined
topocentric range and range-rate. The result is a set of orbits compatible with
the observations, the Manifold Of Variations, a 2-dimensional compact manifold
parametrized over the Admissible Region. Such a set of orbits represents the
asteroid confidence region and is used for short-term hazard predictions. In
this paper we review the Manifold Of Variations method and make a detailed
analysis of the related probabilistic formalism.
