Spreading life …

… The Green Universe: A Vision by Freeman Dyson | The New York Review of Books. (Hat tip, Dave Lull.)

Almost all the current discussion of life in the universe assumes that life can exist only on worlds like our Earth, with air and water and strong gravity. This means that life is confined to planets and their moons. The sun and the planets and moons contain most of the mass of our solar system. But for life, surface area is more important than mass. The room available for life is measured by surface area and not by mass. In our solar system and in the universe, the available area is mostly on small objects, on comets and asteroids and dust grains, not on planets and moons.

When life has reached the small objects, it will have achieved mobility. It is easy then for life to hop from one small world to another and spread all over the universe. Life can survive anywhere in the universe where there is starlight as a source of energy and a solid surface with ice and minerals as a source of food. Planets and moons are the worst places for life from the point of view of mobility. Because Earth’s gravity is strong, it is almost impossible for life to escape from Earth without our help. Life has been stuck here, waiting for our arrival, for three billion years, immobile in its planetary cage.