Perhaps the best motivation for going to Mars is political. It is obvious that no single nation currently has either the will or the resources to do it alone, but a consortium of nations and space agencies could achieve it within 20 years.

The origin of life is one of the great outstanding mysteries of science.

General relativity is the cornerstone of cosmology and astrophysics. It has also provided the conceptual basis for string theory and other attempts to unify all the forces of nature in terms of geometrical structures.

If you get a drill and drill down 5km beneath the ground, it's teeming with life - millions of tiny living fossils. They resemble the earliest life forms and suggest that life started under the Ground. The bible talks of Eden as a sunny parkland with white fluffy clouds, but it probably ascended from the region that we now associate with Hell.

The laws of physics ... seem to be the product of exceedingly ingenious design... The universe must have a purpose.

In time, [a Martian] colony would grow to the point of being self- sustaining. When this stage was reached, humanity would have a precious insurance policy against catastrophe at home. During the next millennium there is a significant chance that civilization on Earth will be destroyed by an asteroid, a killer plague or a global war. A Martian colony could keep the flame of civilization and culture alive until Earth could be reverse-colonized from Mars.

Science can proceed only if the scientist adopts an essentially theological worldview. ..even the most atheistic scientist accepts as an act of faith the existence of a law-like order in nature that is at least in part comprehensible to us.