A Space Ocean

Comet Hartley 2 has been thrust into the limelight during the last couple of weeks after a report on it published by Nature. The comet has caused a bit of a problem for NASA scientists. And the problem .... Well, the water it contains is more like Earth's water than water on other comets. The problem is deuterium, the heavier isotope of hydrogen. The handful (six or so) of comets that have had their water content analysed seem to have twice as much deuterium. ...