  We present a study of four different formation scenarios that may be able to
explain the origin of the recently announced planet (`Proxima b') orbiting
Proxima Centauri. The aim is to examine how the formation scenarios differ in
their predictions for the multiplicity of the Proxima system, the
water/volatile content of Proxima b and its orbital eccentricity, so that these
can be tested by future observations. A scenario of in situ formation via giant
impacts from a locally enhanced disc of planetary embryos/planetesimals
predicts that Proxima b will be in a multiplanet system with a measurably
finite eccentricity. Assuming that the local solid enhancement needed to form a
Proxima b analogue arises because of the inwards drift of solids in the form of
small planetesimals/boulders, this scenario also results in Proxima b analogues
being only moderately endowed with water/volatiles. A scenario in which
multiple embryos form, migrate and mutually collide within a gas disc results
in Proxima b being a member of a multiple system, possibly displaying mean
motion resonances, but where the constituent members are Ocean planets due to
accretion occurring mainly outside of the snowline. A scenario in which a
single accreting embryo forms outside the snowline, and migrates inwards while
accreting planetesimals/pebbles results in Proxima b being an isolated Ocean
planet on a circular orbit. A scenario in which Proxima b formed via pebble
accretion interior to the snowline produces a dry planet on a circular orbit.
Future observations that characterise the physical and orbital properties of
Proxima b, and any additional planets in the system, will provide valuable
insights into the formation history of this neighbouring planetary system.
