One of the first papers released post Rosetta landing states “the Rosetta mission found that the comet’s water contains more of a hydrogen isotope called deuterium than water on Earth does”.
I have always thought that the source of water on earth was more likely long period Comets coming in from the Oort Cloud – or even in fact comets sling-shot in from an adjacent star.
To me this is no surprise. Just like Halley, 67P is a short period comet. But could its water have been ejected from MARS or VENUS? I must check the Rosetta paper and the hydrogen isotope ratio compared to that of water measured on other bodies such as on Mars.
The hydrogen isotope measure could be thoughts of as a fingerprint of the water’s source : ie from
- another solar system planet
- Asteroid (usually rock with minimal water)
- Kuiper Belt Comet
- Oort Cloud Comet
- Adjacent Solar Systems
We still seem to be looking at evidence from an “earth centric” point of view. I expect one day we might discover the hydrogen isotope fingerprint ratio is ideal to determine the source star. I think though this will not be as useful a fingerprint as the DNA/Protein Fingerprint of the Viruses and Bacteria.