Our moon was born too small to harbor life. It came from the collision of a Mars-sized world into the primordial Earth. From that colossal crunch spun a disk of rocks that condensed into a satellite.

It turns out that if you optimize the performance of a car and of an airplane, they are very far away in terms of mechanical features. So you can make a flying car. But they are not very good planes, and they are not very good cars.

The moon's closeness is a huge advantage: To make it habitable, we would first have to bombard it with water-ice comets, a tricky endeavor best attempted with the many resources waiting on and near Earth.

Gregory Benford Quotes