  Two close-in planets have been recently found around the M-dwarf flare star
AU Microscopii (AU Mic). These Neptune-sized planets (AU Mic b and c) seem to
be located very close to the so-called "evaporation valley" in the exoplanet
population, making this system an important target for studying atmospheric
loss on exoplanets. This process, while mainly driven by the high-energy
stellar radiation, will be strongly mediated by the space environment
surrounding the planets. Here we present an investigation on this last area,
performing 3D numerical modeling of the quiescent stellar wind from AU Mic, as
well as time-dependent simulations describing the evolution of a highly
energetic Coronal Mass Ejection (CME) event in this system. Observational
constraints on the stellar magnetic field and properties of the eruption are
incorporated in our models. We carry out qualitative and quantitative
characterizations of the stellar wind, the emerging CMEs, as well as the
expected steady and transient conditions along the orbit of both exoplanets.
Our results predict an extreme space weather for AU Mic and its planets. This
includes sub-Alfv\'enic regions for the large majority of the exoplanet orbits,
very high dynamic and magnetic pressure values in quiescence (varying within
$10^{2} - 10^{5}$ times the dynamic pressure experienced by the Earth), and an
even harsher environment during the passage of any escaping CME associated with
the frequent flaring observed in AU Mic. These space weather conditions alone
pose an immense challenge for the survival of the exoplanetary atmospheres (if
any) in this system.
