Sorry but no picture. I was crawling through a wrecking yard today and found what was left of what appears to be a 2004 S class with the trunk gone. In the back, on the right hand side of the trunk, was a coffee can sized silver colored metal can. What is this thing?

This is not a pressing question. I have just never seen one of these an wonder if anyone knew what it was or was for? It is located in the fender just in front to the right side tail light and is tilted towards the front.

Thanks!