Why should we go into space? What is the justification for spending all that effort and money on getting a few lumps of Moon rock? Aren’t there better causes here on Earth?In a way, the situation is like that in Europe before 1492. People might well have argued that it was a waste of money to send Columbus on a wild goose chase. Yet the discovery of the New World made a profound difference to the old. If nothing else, we wouldn’t have had a Big Mac or KFC.Spreading out into space will have an even greater effect. It will completely change the future of the human race and maybe determine whether we have any future at all. It won’t solve any of our immediate problems on planet Earth, but it will give us a new perspective on them, and cause us to look outwards rather than inwards. Hopefully it would unite us to face a common challenge. This would be a long-term strategy, and by long-term I mean hundreds or thousands of years. We could have a base on the Moon within 30 years, reach Mars in 50 years, and explore the moons of the outer planets in 200 years. By “reach” I mean with manned, or should I say “personed,” space flight. We have already driven rovers on Mars and landed a probe on Titan, a moon of Saturn, but if one is considering the future of the human race we have to go there ourselves.Going into space won’t be cheap, but it would take only a small proportion of world resources. NASA’s budget has remained roughly constant in real terms since the time of the Apollo landings, but it has decreased from 0.3% of US GDP in 1970 to 0.12% now. Even if we were to increase the international budget 20 times to make a serious effort to go into space it would only be a small fraction of world GDP.There will be those who argue that it would be better to spend our money solving the problems of this planet like climate change and pollution rather than wasting it on a possibly fruitless search for a new planet. I am not denying the importance of fighting climate change and global warming, but we can do that and still spare a quarter of a percent of world GDP for space. Isn’t our future worth a quarter of a percent?A new manned spaceflight program would do a lot to restore public enthusiasm for space and for science generally. Robotic missions are much cheaper and may provide more scientific information but they don’t catch the public imagination in the same way, and they don’t spread the human race into space, which I am arguing should be our long-term strategy....A goal of a base on the Moon by 2020 and of a manned landing on Mars by 2025 would re-ignite the space program and give it a sense of purpose in the same way that President Kennedy’s Moon target did in the 1960s.... It is not clear that intelligence confers a long-term survival advantage. Bacteria and insects will survive quite happily even if our so-called intelligence leads us to destroy ourselves...What about beyond the solar system? Our observations indicate that a significant fraction of stars have planets around them. So far, we can detect only giant planets like Jupiter and Saturn but it is reasonable to assume that they will be accompanied by smaller, Earth-like planets. Some of these will lie in the “Goldilocks” zone where the distance from the star is in the right region for liquid water to exist on their surface. There are around a thousand stars within 30 light years of Earth. If one percent of these have Earth-sized planets in the Goldilocks zone, we have 10 candidate new worlds. We can’t envisage visiting them with current technology, but we should make interstellar travel a long-term aim. By long-term, I mean over the next 200 to 500 years. The human race has existed as a separate species for about 2 million years. Civilization began about 10,000 years ago, and the rate of development has been steadily increasing. If the human race is to continue for another million years, we will have to boldly go where no one has gone before.