Science: Moon Mirror

Life does not exist on Mars or any other solar planet except Earth, in the opinion of Dr. Walter Sydney Adams, director of Mt. Wilson Observatory. Mars, most propitious of Earth's neighbors, is not only inhospitably cold and scantily watered, but also almost devoid of oxygen. Some months ago Dr. Adams and Dr. Theodore Dunham Jr. trained spectroscopes on the red planet, computed that it has under 1% as much free oxygen as Earth has.

Dr. Adams wondered whether the lack of oxygen lines in his spectrum was due to interference by light from other gases in the Martian atmosphere.

Possibly a spectroscope, placed far out in space and trained on Earth, would show a similar lack of oxygen lines. Dr. Adams last week told how he finessed this physical difficulty by using earthshine.

Earthshine is what makes the dark part of the moon faintly visible. It is light that has passed through Earth's air once on its way here from the sun, again on its reflected journey to the moon, a third time on its trip back to Earth. Light from the moon's bright side, directly reflected from the sun, traverses Earth's atmosphere only once. Drs. Adams & Dunham found that the spectrum of earthshine showed three times as much oxygen as that of the moon's bright light.

Said Dr. Dunham: "This shows quite definitely that if the atmosphere of a planet should contain oxygen the presence of that gas would be revealed to an outside observer."