  The space-weather conditions that result from stellar winds significantly
impact the habitability of exoplanets. The conditions can be calculated from
first principles if the necessary boundary conditions -- namely on the plasma
density in the outer corona and the radial distance at which the plasma forces
the closed magnetic field into an open geometry -- are specified. Low frequency
radio observations ($\nu \lesssim 200$ MHz) of plasma and cyclotron emission
from stars probe these magneto-ionic conditions. Here we report the detection
of low-frequency ($120-167\,{\rm MHz}$) radio emission associated with the dMe6
star WX UMa. If the emission originates in WX UMa's corona, we show that the
closed field regions extends to at least $\approx 10$ stellar radii, that is
about a factor of a few larger than the solar value, and possibly to $\gtrsim
20$ stellar radii. Our results suggest that the magnetic-field structure of M
dwarfs is in between Sun-like and planet-like configurations, where compact
over-dense coronal loops with X-ray emitting plasma co-exist with a large-scale
magnetosphere with lower plasma density and closed magnetic geometry.
