Here , we study the dichotomy of the escaping atmosphere of the newly discovered close-in exoplanet AU Mic b .
On one hand , the high EUV stellar flux is expected to cause a strong atmospheric escape in AU Mic b .
On the other hand , the wind of this young star is believed to be very strong , which could reduce or even inhibit the planet ’ s atmospheric escape .
AU Mic is thought to have a wind mass-loss rate that is up to 1000 times larger than the solar wind mass-loss rate ( \dot { M } _ { \odot } ) .
To investigate this dichotomy , we perform 3D hydrodynamics simulations of the stellar wind–planetary atmosphere interactions in the AU Mic system and predict the synthetic Ly- \alpha transits of AU Mic b .
We systematically vary the stellar wind mass-loss rate from a ‘ no wind ’ scenario to up to a stellar wind with a mass-loss rate of 1000 ~ { } \dot { M } _ { \odot } .
We find that , as the stellar wind becomes stronger , the planetary evaporation rate decreases from 6.5 \times 10 ^ { 10 } g/s to half this value .
With a stronger stellar wind , the atmosphere is forced to occupy a smaller volume , affecting transit signatures .
Our predicted Ly- \alpha absorption drops from \sim 20 \% , in the case of ‘ no wind ’ to barely any Ly- \alpha absorption in the extreme stellar wind scenario .
Future Ly- \alpha transits could therefore place constraints not only on the evaporation rate of AU Mic b , but also on the mass-loss rate of its host star .