The debate about the origin of Earth’s water just got deeper.
The European Space Agency’s (ESA) comet-chasing spacecraft Rosetta has sent back some interesting information regarding water vapor it detected and analyzed on its target, Comet 67P/Churyumov-Gerasimenko.
According to the ESA and an international group of scientists, the analysis shows that the chemical composition of the comet’s water vapor is very different from water found on Earth.
Scientists studying the origin of Earth’s water say Rosetta’s findings have added some fuel to the ongoing debate about where our water came from.
Some scientists believe Earth’s supply of life-sustaining water is the result of chemical reactions that took place as the Sun and solar system began forming some 4.6 billion years ago.
Others theorize that since the Earth was so hot after its formation, any water that had been here originally probably boiled off, therefore the water we have now had to have been delivered by large numbers of water-rich comets and asteroids that bombarded our planet after it had cooled down.
Asteroids, which are mostly made of rock and/or metals, can be found in the asteroid belt that lies between the orbits of Mars and Jupiter.
However a majority of comets, sometimes called ‘dirty snowballs’ since they’re made up of rock, dust, ice and frozen gases, are located in deep space in either the Kuiper Belt, an area of space that’s just outside the orbit of Pluto or even further out toward the edge of the solar system in the Oort cloud.
Scientists are still debating how much of Earth’s current water supply was delivered by asteroids or by comets.
One of key elements in the origin of Earth’s water involves the chemical structure of our water.
While most of us are familiar with the H20 composition of water, two atoms of hydrogen and one atom of oxygen, some of our water (mostly seawater) also contains a very tiny amount of 2H2O or D2O or heavy water that’s been enriched with deuterium, an isotope of hydrogen.
The data provided by the spacecraft’s Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument indicates that the water vapor sampled from Comet 67P/Churyumov-Gerasimenko has a much higher deuterium to hydrogen (D/H) ratio, meaning its water is more enriched with the deuterium than what can be found on Earth.
The scientific group studying ROSINA data says their findings seem to contradict the theory that most of Earth’s water originated in deep space and was delivered to us via comets.
Some of the scientists who believe most of our water came from asteroids have found that the lower ratio of deuterium enriched water to ordinary water here on Earth matches the same value found in water-rich asteroids.
This lower ratio of deuterium/hydrogen found in Earth’s water and in the water-rich asteroids is thought to be the result of time and more exposure to the Sun.
And, since comets originate so far away from the Sun, they may not be as exposed to solar radiation as asteroids which could explain the higher deuterium/hydrogen ratio ROSINA found in Comet 67P’s water vapor.
The Rosetta spacecraft, which arrived for its rendezvous with Comet 67P/Churyumov-Gerisimenko back in August, is expected to complete its mission in December 2015, about four months after the comet reaches its closest point to the Sun (August 2015). The comet will then begin its journey back out to the far reaches of the solar system.