There is much we can do to further space plans from the ground. Going out into space with current technology and no real fixed ideas is just wasting resources.

  1. A "space elevator". 50 years ago a sci-fi joke. True, still doesn't work, but Japan believes it can - and is putting its money where its mouth is.
  2. Novel materials. No need to go to the moon for these. They can be created and developed here.
  3. Laser technology. Might be useful for propulsion at a distance.
  4. Computer development
  5. Medical development


Delving into the sea is a short term project. But one we've not bothered with although we've managed to leave some junk on the Moon to vacuum evaporate.

An asteroid is a possibility. I fail to see how a colony on Mars helps this. Increasing surveillance around the earth or indeed on the earth helps here. And creating missiles to combat this threat is rather difficult to what space craft would require.

As has been said the sun going out gives us a few BILLION years to play around with. By then we'll have been extinct or long gone.

A nearby star that can sterilise the earth means we need to get far enough away to avoid that. The nearest star is a few light years off (excluding the sun, obviously). Assuming shielding here would be insufficient we'd need to be a long, long way away. Again, expending money on maths / physics is what is required as boosters / ion engines / solar sails wouldn't cut it - even an ark would be sterilised if it can do that to earth.