  The discovery of a planet around the closest star to our Sun, Proxima
Centauri, represents a quantum leap in the testability of exoplanetary models.
Unlike any other discovered exoplanet, models of Proxima b could be contrasted
against near future telescopic observations and far future in-situ
measurements. In this paper we aim at predicting the planetary radius and the
magnetic properties (dynamo lifetime and magnetic dipole moment) of Proxima b
analogues (solid planets with masses of $\sim 1-3\,M_\oplus$, rotation periods
of several days and habitable conditions). For this purpose we build a grid of
planetary models with a wide range of compositions and masses. For each point
in the grid we run the planetary evolution model developed in
\citet{Zuluaga2013}. Our model assumes small orbital eccentricity, negligible
tidal heating and earth-like radiogenic mantle elements abundances. We devise a
statistical methodology to estimate the posterior distribution of the desired
planetary properties assuming simple prior distributions for the orbital
inclination and bulk composition. Our model predicts that Proxima b would have
a mass $1.3\leq M_{\rm p}\leq 2.3\,M_{\oplus}$ and a radius $R_{\rm
p}=1.4^{+0.3}_{-0.2}\,R_{\oplus}$. In our simulations, most Proxima b analogues
develop intrinsic dynamos that last for $\geq$4 Gyr (the estimated age of the
host star). If alive, the dynamo of Proxima b have a dipole moment ${\cal
M}_{\rm dip}>0.32^{\times 2.3}_{\div 2.9}{\cal M}_{\rm dip,\oplus}$. These
results are not restricted to Proxima b but they also apply to earth-like
planets having similar observed properties.
