Water On Earth Did Not Come From Comets, Rosetta Probe Studies Say

While the Philae lander that landed atop Comet 67/P might have run out battery power, the data that it managed to send to the Rosetta probe orbiting the comet is already changing our views regarding the source of water on Earth, reports BBC News.

In a study published in the journal Science, a group of researchers have opined that it is unlikely that the water on Earth could have come from a comet like 67/P, as was previously thought. Billions of years ago, a nascent Earth was bombarded by thousands of comets, which according to many scientists, were the "carriers" of water to the Earth from space. This theory was gradually gaining wider acceptance -- until this new piece of evidence came from comet 67/P, which suggests that this could not possibly be true.

The researchers say it is possible that the source of water on Earth could more likely be from asteroids. The researchers, however, added that at this stage, the possibility water did indeed come from comets cannot be entirely ruled out owing to the fact comets have not been studied in detail yet. Also, it is possible that other comets which orbit our solar system could have entirely different properties.

Nevertheless, this new piece of news came a few weeks after the Philae lander, a part of the Rosetta Mission, became the first man-made object to land on the surface of something that is not a planet or a moon. Prior to the landing, the Rosetta probe circled comet 67/P for nearly three months, taking in as much data as it could do possible. Finally, on November 12, the Philae lander managed to land on the surface of comet 67P after traveling over 300 million miles.

Following the landing, instruments aboard the Rosetta probe were able to analyze in detail the components that comprised the comet. Two mass spectrometers aboard Rosetta have managed to find that there indeed is water on Comet 67/P -- but it's composition and signature is different to the water found on Earth. The water found on Earth too has a distinctive signature.

Wondering what the difference is?

On Earth, it is common to notice the prevalence of deuterium (an isotope of hydrogen) in a ratio that is around three atoms of deuterium per 10,000 molecules of water. This is quite typical, and according to researchers, stays constant all across the Earth. It is not easy to change this ratio. This water, consisting of deuterium atoms, has the same properties as normal water -- but is heavier in mass. In case of comet 67/P, however, the prevalence of deuterium atoms is on a much higher scale.

Prof Kathrin Altwegg, from the University of Bern in Switzerland, explains as follows.

"This ratio between heavy and light water is very characteristic. You cannot easily change it and it stays for a long time. If we compare the water in comets with the water we have on Earth, we can definitely say if the water on Earth is compatible with the water on comets" - But there was far more heavy water on Comet 67/P than on our planet. In fact, the prevalence of deuterium atoms in the water on comet 67/P is more than three times the ratio of the same found on Earth. It is the highest-ever measured ratio of heavy water relative to light water in the Solar System. It is more than three times higher than on the Earth, which means that this kind of comet could not have brought water to the Earth."

Previous research has found that the type of water on comets originating from a region in the far reaches of the solar system known as the Oort Cloud also have different properties. Comet 67/P, however, originates from the Kuiper belt. This new piece of evidence proves the water on Earth did not come from comets from the Kuiper belt -- which also forms the vast majority of comets in the solar system.

"The conclusion here is that in the reservoir of the Kuiper Belt we have very diverse comets that probably came from different regions of the early Solar System. We have light water in some comets and very heavy water in other comets. We have to assume the mixture of all these comets is something that is heavier than what we have on Earth, so this probably rules out Kuiper Belt comets as the source of terrestrial water," says Altwegg.

With comets sort of out of the way, researchers believe that the source of water on Earth could be asteroids -- objects that is believed to have formed closer to our Sun than comets.

She said, "We know already something about the characteristic of asteroids by studying meteorites, which are pieces of asteroids - and the characteristics of asteroids are very much like our water. They are also much closer to the Earth so it is more likely that they hit the Earth than the very distant comets, which are beyond Neptune."

All said, there are people from the scientific community who are of the belief that the team could be "jumping the gun a bit," and that it is too early to draw conclusions.

According to Prof Monica Grady, "The measurements that have been made by Rosina are of the gas that has come from the surface of the comet. The amount of hydrogen relative to deuterium changes as the gas escapes from the surface This is why other instruments on the lander were going to make complementary measurements of the ice on the surface. We are going to have to wait to see what comes from COSAC and Ptolemy [Rosetta instruments] before we can say any more."

[Image Via Pixabay]