Commentary: Wonders - HOH and Life Elsewhere; May 1997; Scientific American Magazine; by Morrison; 2 Page(s)

For once, write the familiar H2O as HOH; it stands for the same molecular species, two hydrogen atoms linked to one oxygen. Although the symbol HOH is ramrod straight, the real molecule is a bent, symmetric clump of three near-spherical atoms. Nearly two thirds of all the atoms in an adult human are stacked in just this form. To be sure, water is but the stage and setting of life; life¿s actors are mainly carbonaceous molecules, more complex by far. We can now make out most of the molecular devices--those intricate electromechanical contrivances similar to ratchets, clamps, tubes and electrodes-- at work in every cell.

Destructive collisions, whether with overenergetic photons or with fast-moving atoms, can sever and dismember big molecules. Too high temperature is fully hostile. Too low temperature does not damage the molecules, but their reactions slow or even cease. And all that watery machinery has to work in its watery ambience. Wherever water cannot persist, biomolecules cannot function. So liquid water marks the regime we know as hospitable.