Right. There isn't a stream of Donner parties headed into the middle of the Sahara, or north into Greenland, or for that matter onto the seafloor. Many of the h

Right. There isn't a stream of Donner parties headed into the middle of the Sahara, or north into Greenland, or for that matter onto the seafloor. Many of the heroes of the Age of Exploration were economically motivated, and certainly almost all historical colonists have been. If there's a Gold Rush waiting for us on Mars we haven't seen any indication of it yet.