Abstract
During the past two years I have written two articles explaining why a planet almost exactly the mass of Jupiter is essential for the survival of life (at least advanced life) on Earth. [1, 2] As you may recall, I described how a planet any bigger would pull the earth's orbit out of the life-support zone and a planet any smaller would inadequately shield us from comet and asteroid collisions. I also described George Wetherill's theoretical studies demonstrating the extreme rarity of Jupiter-sized planets anywhere.