[rocqua]

What products would a martian colony produce that are worth transport costs? Even taking into account you only need to pay for the return trip, because the earth-mars leg is payed for by imports anyway.

Data has much more favorable transport costs, but there is only so much valuable data on Mars. Especially since astronomy isn't really a free market. There might be resources on Mars that are rare enough on Earth to be worth it. I'd be interested in hearing more on those.

It seems to me like the main value of a Mars colony (human exploration, achievement, and insurance against planetary wipe-out) are abstract, and can't be exported in any real sense.