Earth is the only planet in our solar system with a significant amount of water. There are different theories of how it got here, but one that has been around for quite a while is that it came from comets. But comets come from different sources. The Herschel telescope’s recent observations of comet Hartley 2 are the first in-depth look at water in a comet from the Kuiper Belt in the outer reached of our solar system.
Using a highly sensitive infrared spectrometer, Herschel looked at the comet’s coma (the thin, gaseous atmosphere around the comet ) and found that the deuterium/light water ratio in Hartley 2 is different from other comets analyzed to date, which were all non-Kuiper comets. Furthermore Herschel found that the deuterium/light water ratio in Hartley 2 is the same as the water on the Earth’s surface.
The five comets besides Hartley 2 whose heavy-water-to-regular-water ratios have been obtained all came from the Oort Cloud, an even more distant region in the solar system.
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