To try and be more useful.... that looks like part of the exhaust system of your car that has rotten and fallen off.
I think that the part exists because your cat convertor on the exhaust gets very very hot under the car as you drive, and if you park in a nice field where the grass is too long the exhaust can set fire to that grass underneath, and therefore your car too in the process!
I would like to hear more opinions on here, but I would easily still drive the car with that part missing. Just no parking over long grass!
Tangent time - didn't early MX5s used to set fire themselves on long grass due to cat shielding issues?