Where did Earth's water come from?

The atom on the left is a normal hydrogen atom. On the other hand, the atom on the right is hydrogen that contains a neutron known as deuterium. Deuterium is, in fact, a heavier which creates ice that sinks to the bottom. Water on Earth contains a certain percentage of deuterium. Thus, to determine if the water is similar or identical to Earth, it is possible to just measure the percentage of deuterium. If the deuterium percentage is too high, it indicates that the water is from elsewhere. In total. the scientists tried to match a certain sample with one from Earth to determine if they both came from the same environment, potentially from the same source.

This technique was used in order to determine if the water from the asteroid sample were similar or identical to water on Earth. The results came out to be surprising: the water contained just as much deuterium as the water on Earth. Moreover, the percentage was almost identical that it is believed that both of the water came from the same source. Scientists were also able to calculate the amount of water the asteroids account for on Earth and it turns out that at least half of the water came from these asteroids.

Although this is only one sample that scientists are currently using, there are two other missions that are trying to get more samples for the scientists to study in the near future. The first mission is the Hayabusa 2 mission from JAXA (Japan Aerospace Exploration Agency). The samples of the asteroid that scientists used were from the Hayabusa 1 mission which was greatly successful. This asteroid sample-return probe will return to Earth at around 2022 since it has recently finished collecting the samples. While the Hayabusa 1 mission took samples from an asteroid called Itokawa, this new mission targeted another asteroid called Ryugu. The aim of the mission is to test if the water on Ryugu is the same from Itokawa and Earth. The other mission is the Osiris-Rex mission by NASA (National Aeronautics and Space Administration), which is scheduled to return back to Earth in the next two to three years. With these missions, we will finally be able to understand if, just like this study, at least half of the Earth’s water came from asteroids.

It is, however, very possible that despite the water that came from outer space, at least half or possibly more came from within Earth from the upper and lower mantle. It is proven that there is still a lot of water in planet Earth, stored underneath the crust; most of the water has not still been released. In fact, the water will only be released in the next billion years. There are also other planets such as Venus and Mars that also contain water inside the planet. Therefore, one day, we can use the water to terraform these planets to make them more habitable.

All in all, it is very very likely that at least half of the water on our planet came from these wonderful rocks that used to orbit in the same region as Earth, eventually colliding with our planet. There is even a way for us to calculate how many asteroids it took to create half of our planet’s ocean. From a perspective, we are likely made out of asteroids that once upon a time collided with our planet, created a large explosion and then created an abundance of liquid water that eventually turned into life. The two missions in the future will conclude all of this discussion once and for all.