Constraints on formation DH ratio

As the presolar cloud collapsed into a circumstellar disk incoming material arriving from the presolar cloud would have been subjected to appreciable reprocessing both through the collapse process itself, and also through shocking as the material entered the dense nebula. Both these effects are likely to have been more substantial near the Sun and less important at greater distances. Some models suggest that the water molecules in the ices were completely dissociated by this process and then recom-bined. This theory may be tested by examining the D/H ratio of the various bodies currently in the solar system. As we mentioned earlier, deuterium is a truly primordial isotope, which was created just after the Big Bang and has not been produced since. After H2 and He, the most abundant molecule in the ISM, and thus the presolar cloud, is H2O, either in the gaseous or condensed phases. In dense, neutral media such as the solar nebula, fractionation of D and H in water occurs though reactions between the gas phases

At higher temperatures the D/H ratio in molecular hydrogen and water is the same, but at lower temperatures (T < 500 K), deuterium becomes concentrated in water (Drouart et al., 1999). While the equilibrium D/H ratio in water molecules and other molecules increases rapidly as the temperature drops, the rate of

Table 2.3. Solar system D/H ratios.

Molecule

Species

Value (x10—5)

Reference

Proto-solar

Was this article helpful?

0 0
Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment