When NASA launched its Submillimeter Wave Astronomy Satellite (SWAS) little more than two years ago, astronomers expected it to collect data confirming certain key ideas about interstellar clouds, the pools of gas and dust from which stars are born. In particular, they believed that the radio astronomy observatory would find relatively ample amounts of water vapor and molecular oxygen. But according to new results, that isn't the case: water seems to be 10,000 times less abundant than was previously thought; molecular oxygen is at least 100 times less abundant than predicted and perhaps 1,000 times more scarce. "There's not much to drink there, and it's hard to breathe," says Cornell University astronomer Paul Goldsmith, one of 12 members of the satellite science team.
The astronomers struggle to explain this lack of water and oxygen. Because the interstellar clouds are as cold as 30 degrees above absolute zero (or minus 240 degrees Celsius), they say, water may be frozen on dust grains in the clouds and thus are not detectable by radio astronomy. The missing oxygen, however, is much harder to account for. "Since oxygen is the third most abundant atom in the universe, after hydrogen and helium, we ought to be able to understand where the oxygen atoms are and in what form. And they certainly don't seem to be in molecular oxygen in the gas phase as predictions would have it," Goldsmith says. "It really is a dilemma for interstellar chemistry, but it might be a hint that something is wrong with our picture of the structure of these giant clouds." Because these findings are so far off from what was expected, the scientists hope that NASA will extend SWAS's planned three-year mission into a fourth year or more.