Escape of hydrogen from venus.

Recombination of O(2)(+) represents a source of fast oxygen atoms in Venus' exosphere, and subsequent collisions of oxygen atoms with hydrogen atoms lead to escape of about 10(7) hydrogen atoms per square centimeter per second. Escape of deuterium atoms is negligible, and the ratio of deuterium to hydrogen should increase with time. It is suggested that the mass-2 ion observed by Pioneer Venus is D(+), which implies a ratio of deuterium to hydrogen in the contemporary atmosphere of about 10(-2), an initial ratio of 5 x 10(-5) and an original H(2)O abundance not less than 800 grams per square centimeter.