air suspension system, car was driven and caused problem

Drove thw car about 2 miles and noticed the ride was rough, stopped the car
and the back end was low, turned around and drove back home.  Noticed
some smoke under car. started car and pulled forward to the driveway.  
Noticed a small round wheel part where car was parked. car runs and will
move , but I am worried about the part that was under the car.  Could you
you let me know what could have happened? I know the air suspension
needs repair , however that metal wheel part (about 5" in diameter) ia a
mystery to me.  what type of repair am I in for?   The Car is a 2006 Mercury
Gran Marquis, LS, Ultimate Edition