Development of an H₂O atmosphere around Comet kohoutek (1973f) and its Possible detection

ALTHOUGH chemically stable "parent molecules" like H ₂O, CH₄, NH₃ and C₂N₂, for the observed radicals in comets, have been suspected for more than thirty years¹ none of them has yet been observed spectroscopically. But the indirect evidence both for the existence, as well as perhaps the preponderance, of H₂O in the nucleus has been growing steadily during the past ten years^2-4. In particular the recent observations of two bright long period comets Tago-Sato-Kosaka (1969g) and Bennett (1969i) (as well as P/Encke) both in the vacuum ultraviolet and in the near violet with detectors on orbiters^5-8 and rockets⁹ (which have shown extensive hydrogen and hydroxyl halos) as well as associated numerical models of the neutral atmospheres^10-13 strongly suggest H₂O as the common parent of both these species.