A DETERMINATION OF THE HDO H2O RATIO IN COMET C/1995 O1 (HALE-BOPP)/

Deuterated water (HDO) was detected in comet C/1995 O1 (Hale-Bopp) wit h the use of the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. T he inferred D/H ratio in Hale-Bopp's water is (3.3 +/- 0.8) x 10(-4). This result is consistent with in situ measurements of comet P/Halley and the value found in C/1996 B2 (Hyakutake). This D/H ratio, higher t han that in terrestrial water and more than 10 times the value for pro tosolar H-2,, implies that comets cannot be the only source for the oc eans on Earth.