Though Mars is the best place for colonization in the solar system because it has by far the greatest potential for self-sufficiency, it will not have the labor power required to make it a fully self-sufficient until its population reaches in the millions. Therefore, for the first couple of centuries, it will be necessary for Mars to be able to import specialized manufactured goods from Earth, which can obviously be achieved; however, what can Mars export to Earth in return?
First of all, Mars, as we know, possesses metals with value, such as: silver, germanium, hafnium, lanthanum, gold, iridium, and a host of others. These metals could be transported back to Earth for a substantial profit; however, the existence of such precious metal ores is still hypothetical. But there is one commercial resource that we know exists on Mars in enormous amounts, deuterium. Deuterium is the key fuel not only for both first and second generation fusion reactors, but it is also an essential material for the nuclear power industry today. In addition, deuterium is very valuable; it's current market value on earth is about $10,000 per kilogram, roughly 50 times the price of silver. At current deuterium prices, Mars could possibly be able to gain an annual export income potential of $10 billion. Another option that Mars posseses to make a fortune is via trade in support of mining operations in the asteroid belt, the band of small, mineral rich bodies lying between the orbits of Mars and Jupiter. The asteroid belt enters into the picture because it is known to contain vast supplies of very high grade metal ore in a low-gravity environment that makes it potentially easy to export to Earth. Therefore, the asteroid belt is the third leg of Martian interplanetary commerce. In essence, the outline of future interplanetary commerce will be a "triangle trade," with Earth supplying high technology manufactured goods to Mars; Mars supplying low technology manufactured goods and food staples to the asteroid belt; and the asteroid belt sending metals back to the Earth.