Water on Mars

It is reported that the SNC meteorites are a factor of 2 richer in moderately volatile elements (Na, K, P, etc.) and some volatile elements (Cl, Br, I, S) compared to the Earth and Mars. It is proposed that Mars accreted homogeneously, with the result that all the water except trace amounts (on reaction with metallic Fe) was converted to H(sub 2) and escaped. This model predicts a total Mars H(sub 2)O inventory of 18 ppm (equivalent to an ocean 80 m deep on the planet), and a value for Earth of 300 ppm, close to the actual abundance.