*Originally seen on Phys.org.*
Recently, the Rosetta space probe analyzed water from a Kuiper Belt comet theorized to have originally brought water to Earth billions of years ago. It was found to contain more of a hydrogen isotope called deuterium than water found on Earth, fueling the debate on the origin of our planet’s oceans.
About 97% of Earth’s surface water is found in our oceans, meaning that all of the water from lakes, rivers, mountains, glaciers, ice caps and groundwater only make up 3% of Earth’s surface water. But the Earth was once thought to be a dry planet some 4.5 billion years ago, as the oceans are thought to be only 3.8 billion years old.
The two current prevailing theories about the ocean’s formation state that 1) the Earth was formed with water and that this water came from the inside out, as well as 2) the Earth’s water was also brought here by other sources.
The current theory proposes that during the differentiation of Earth’s layers, (i.e., core, mantle, etc.), there were massive amounts of gases being released from volcanic activity, and while this was taking place the Earth was also thought to be bombarded by objects such as comets. These two processes are thought to have provided the Earth with its water.
But the comet aspect of this theory was recently displaced, according to water samples analyzed from the Rosetta comet 67P/C-G.
Different Type Of Water Found On Comets Compared To Earth Water
The measurements were made in the month following the spacecraft’s arrival at Comet 67P/Churyumov–Gerasimenko on 6 August. It is one of the most anticipated early results of the mission, because the origin of Earth’s water is still an open question, Phys reports.
One of the leading hypotheses on Earth’s formation is that it was so hot when it formed 4.6 billion years ago that any original water content should have boiled off. But, today, two thirds of the surface is covered in water, so where did it come from?
The key to determining where the water originated is in its ‘flavour,’ in this case the proportion of deuterium –a form of hydrogen with an additional neutron –to normal hydrogen. This proportion is an important indicator of the formation and early evolution of the Solar System, with theoretical simulations showing that it should change with distance from the Sun and with time in the first few million years.
But thanks to the dynamics of the early Solar System, this is not a straightforward process. Long-period comets that hail from the distant Oort cloud originally formed in Uranus–Neptune region, far enough from the Sun that water ice could survive.
They were later scattered to the Solar System’s far outer reaches as a result of gravitational interactions with the gas giant planets as they settled in their orbits.
Conversely, Jupiter-family comets like Rosetta’s comet were thought to have formed further out, in the Kuiper Belt beyond Neptune. Occasionally these bodies are disrupted from this location and sent towards the inner Solar System, where their orbits become controlled by the gravitational influence of Jupiter.
Previous measurements of the deuterium/hydrogen (D/H) ratio in other comets have shown a wide range of values. Of the 11 comets for which measurements have been made, it is only the Jupiter-family Comet 103P/Hartley 2 that was found to match the composition of Earth’s water, in observations made by ESA’s Herschel mission in 2011.
By contrast, meteorites originally hailing from asteroids in the Asteroid Belt also match the composition of Earth’s water. Thus, despite the fact that asteroids have a much lower overall water content, impacts by a large number of them could still have resulted in Earth’s oceans.
It is against this backdrop that Rosetta’s investigations are important. Interestingly, the D/H ratio measured by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, or ROSINA, is more than three times greater than for Earth’s oceans and for its Jupiter-family companion, Comet Hartley 2. Indeed, it is even higher than measured for any Oort cloud comet as well.
“This surprising finding could indicate a diverse origin for the Jupiter-family comets – perhaps they formed over a wider range of distances in the young Solar System than we previously thought,” says Kathrin Altwegg, principal investigator for ROSINA and lead author of the paper reporting the results in the journal Science this week.
“Our finding also rules out the idea that Jupiter-family comets contain solely Earth ocean-like water, and adds weight to models that place more emphasis on asteroids as the main delivery mechanism for Earth’s oceans.”
“We knew that Rosetta’s in situ analysis of this comet was always going to throw up surprises for the bigger picture of Solar System science, and this outstanding observation certainly adds fuel to the debate about the origin of Earth’s water,” says Matt Taylor, ESA’s Rosetta project scientist.
“As Rosetta continues to follow the comet on its orbit around the Sun throughout next year, we’ll be keeping a close watch on how it evolves and behaves, which will give us unique insight into the mysterious world of comets and their contribution to our understanding of the evolution of the Solar System.”
What are your thoughts on this discovery? Do you think extraplanetary sources helped to provide our planet’s oceans? Share with us below!
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Thank you for your article.
I think the water may have come from our own planet. We should consider several chemical reactions of the gasses that formed it after the slow cooling of the Earth when the sun blaze was slowly retreating.
Yet some water may have dropped on the planet as ice along with the comets but that would be too little, don’t you think? There is a low chance of hitting the planet let alone hitting the planet as small as the earth with enough projectiles to form as much water to form great oceans.
(Please, excuse my bad English – I’m not a native writer)
Water forms slowly but constantly on this planet because of the mixing of the hydrogen particles emitted by the sun and the oxygen in the atmosphere. Two hydrogen molecules bonded to one oxygen molecule makes water. This is why no other planets in our solar system has been discovered with water, because the other planets do not have an oxygen rich atmosphere like the Earth. Too simple yet possible, but scientists do not want to believe it for some reason. Go figure.
The same as when you burn logs, the moon is bombarded by firewood molecules, making dust.
Who says, there is no water in other planets? The two moons of planet Jupiter have water, icy form. There are distant planets from Sun, have more water, as the sunlight is not much falling on them, to receive sufficient heat for melting them, to rise water. Earth is one planet gets always heat from sunlight at all the time, at any part of its surface. So, ocean is formed and existed. Otherwise, our Earth also must be a chilled/full of icy crystals/snow rocks only. But still, the search of water existence on other planets, is the basic step for assumption that other life forms also do exists in it, by scientists. Our man made devices like probes on the satellites have their own limitations. In my opinion, the water formation in our Earth is influenced by the heat generated by Sun Light. The abandon availability of oxygen in the atmosphere is to be probed. Why our Earth alone has got so much rich in oxygen? why not hydrogen? The universe/space is full of hydrogen gas. Hence, we do learn that all other neighbor planets have toxic gases filled on its atmosphere. But I cann’t understand, why ESA, ISRO, NASA, Japanese agencies all are utilizing same kind of probes and methods aimed on only one planet? If NASA checks for water on mars, let ESA checks for oxygen on moon. They should have diversified aims but ofcourse with good, support from each others in terms of technology. It looks like scientists are not behaving matured way. I liked one thought/idea of ESA is, making satellite to sit on Comet, which is in its orbit. That is a very good idea, as like parasites living on host, without its knowledge. I like this concept. If it is so, then, we can use this technique to attach living satellite to sit on many asteroids too. These asteroids do travel everywhere in the cosmos, touching many galaxies. If you think in this angle, then, you realize that our technology is not superior at all. We are not developed to that level to gather continuous data gathered and transmitted from satellite on moving objects , beyond our solar system or milky way galaxy. I get such kind of thoughts as I am an engineer. May be others can criticize my sayings/thoughts here. However, i be open to accept my wrong intentions if any.
By mistake, I wrote two moons of Jupiter have icy water. It is one of them has icy water, another is full of volcano.