Harold Spencer Jones, M.A., Sc.D., F.R.S., is England's Astronomer Royal. A hardheaded, straight-thinking scientist, who refers to writings of Eddington and Jeans as "romance," he is, ex officio, director of Greenwich Observatory and responsible for Greenwich time's astronomical integrity.* The question he has heard most often in his 50-year career is: Does life exist on other worlds? Astronomer Jones set out to assemble the evidence in the case, published his conclusions last week in Life on Other Worlds (Macmillan; $3).
The same 92 standard elements from some of which earth's life is formed appear to be universal. No one, even with the most powerful microscope, has ever seen an atom. But modern astronomy, by splitting starlight in spectroscopes where atoms leave their signatures in parallel lines, has identified chemical elements in stars trillions and quadrillions of miles away. There is no reason to suppose that life cannot exist in worlds beyond earth for lack of suitable materials.
But in living organisms the elements are grouped in complex molecules. Living structures are broken up by even mild heat. They cannot stand temperatures of 150° F. and over. The sun's surface temperature is about 10,000°, and no known star is cooler than 2,000 or 3,000°. Thus the stars are instantly ruled out as possible abodes of life. That leaves the planets.
Planetary life, whatever its forms, must be built of cells or some other organic units comparable to the cells of earth's plants and animals. Such cells must have access to water, as a medium of nourishment and energy exchange, and to oxygen or carbon dioxide for metabolism. An atmosphere would also be desirable, 1) as a storehouse of oxygen and carbon dioxide; 2) as a shield against the ultraviolet radiation of the parent sun; 3) as a muffler against sharp day & night temperature changes. Any conceivable kind of living cell would be killed or paralyzed by extreme cold.
The temperature of Jupiter is about 220° below zero F., and the outer planets—Saturn, Uranus, Neptune, Pluto—are even colder, which eliminates them as harborers of life. Moreover the atmospheres of the big planets contain great quantities of ammonia and methane, which are poisonous to earthly organisms. These substances are rich in hydrogen, lightest of gases and hence the most likely to escape from a planet's gravitational pull. The big planets are massive enough still to retain most of their original hydrogen, hence the ammonia and methane. The young earth locked up some useful hydrogen in water vapor and fortunately lost most of the rest.
There can be no life on Mercury or on the earth's moon, says Astronomer Jones. These bodies are too small to have held their atmospheres. The telescope and spectroscope both clearly show the moon to be a dead world, without air or water. Having no atmospheric muffler, the moon swings through a temperature change of several hundred degrees between the lunar day and night. Mercury, innermost of the planets, keeps one face turned always toward the sun. That side is extremely hot—about 750°—and the perpetually dark side must be correspondingly cold.