  Understanding convection in red supergiants and the mechanisms that trigger
the mass loss from these evolved stars are the general goals of most
observations of Betelgeuse and its inner circumstellar environment. Linear
spectropolarimetry of the atomic lines of the spectrum of Betelgeuse reveals
information about the three-dimensional (3D) distribution of brightness in its
atmosphere. We model the distribution of plasma and its velocities and use
inversion algorithms to fit the observed linear polarization. We obtain the
first 3D images of the photosphere of Betelgeuse. Within the limits of the used
approximations, we recover vertical convective flows and measure the velocity
of the rising plasma at different heights in the photosphere. In several cases,
we find this velocity to be constant with height, indicating the presence of
forces other than gravity acting on the plasma and counteracting it. In some
cases, these forces are sufficient to maintain plasma rising at 60\,\kms to
heights where this velocity is comparable to the escape velocity. Forces are
present in the photosphere of Betelgeuse that allow plasma to reach velocities
close to the escape velocity. These mechanisms may suffice to trigger mass loss
and sustain the observed large stellar winds of these evolved stars.
