Hello Internet, I'm looking for some advice regarding interplanetary relations. 
About 2 years ago I left Earth hoping to see the galaxy and joined the Intex voidfleet corporation. I've fairly enjoyed my stay aboard the IVC Zantha (Good pay, dental plan, fellow crewmen are nice, etc). 

The Intex Void Fleet mainly operates massive fabrication ships that systematically strip planets and astroids of raw materials to convert to alloys to sell. It Is quite the sight if I say so myself. 

Anyway, yesterday I bumped into the ship's captain, Captain Tung, and he commented on how he had never met a "Terran" before. He then jokingly said they should send a survey ship to see if anything of worth was in "your" system. I laughed and said us Terrans probably wouldn't like their system being harvested, then he said "It's only theirs if they can stop us" before slapping me on the shoulder and walking off. 

I'm not sure whether he was just joking or if that's something he was actually considering, but either way this brings up the issue of space politics. No Earth nation I know of claims territory in space, so if an alien nation show up is there anything we can do? I know the conspiracies about advanced government technology but are we capable of defending ourselves?

Ps: I'm not concerned about the Intex messing with earth. There are laws about harvesting planets with life, but I'm just wondering what/if anything can be done if we just showed up and started to eat Jupiter in like a month.

Looking for some advice on interplanetary relations.