Here's a new game. Identify what in the heck caused this kind of damage. It's weird because the top portion turned silver...
Actually it looks like it may have been sitting in a wishing well / fountain or something similar. As if something else was on top that corroded it and the tiny holes are just more metal eaten away from corrosion. Put it in a metal box labeled "Mars Space Capsule" and bury it, then put the coordinates up on a geo-cache site. See if you make the news some day.
First of all it's a fake coin. It first suffered corrosion, and then somebody (one they'd found it) scraped, filed, or ground away the plating to reveal the base metal underneath and confirm that it was a fake coin.