Monetary-wise bitcoin's already surpassed gold.
Longevity speaking though, that is a little hard to discern. Gold's been the standard of money ever since we learned how to count. It has value that we have already agreed upon and while it doesn't rise as fast as bitcoin, it's on a steady increase as the supply here on Earth dwindles. A case could be made for mining precious metals on nearby asteroids or whatever but that's a farfetched tale the way things are looking right now, and besides, it's not as if that will immediately dilute the value of gold anyway.
Bitcoin however, while fairly valued, is a little volatile for most people's tastes. This could deter them from investing, and not to mention the immutable supply which will only make it harder to get a hold of a bitcoin in the future.
volatility of bitcoin will significantly be reduced once BTC is approved for strategic bitcoin reserve and then big corporation and institutional investor will put their money, which mostly made up of passive investor, who just holds, into bitcoin and as a result lesser supply in the market and greater stability of price.
although you say asteroid mining is farfetched tale, I don't think it's that far from happening, technology advancement happen at really fast rate, see the technology 100 year ago and compare it to now, then you'll realize maybe in just 30 year we already have the technology for asteroid mining.