The source of the liquid water that has sustained our seas and has nourished life in our world for centuries has been the subject of serious scientific debate.
Some researchers have argued that water has been present in our world in one form or another since it was formed from swirling clouds of dust and gas 4.5 billion years ago. In short, the Earth has always been equipped with a reservoir.
However, other scientists take a different point of view. They say that in the beginning the Earth was scorched and waterless, and our oceans appeared much later – when ice and water hit our world from extraterrestrial sources. They are said to be responsible for most of the 332.5 million cubic miles of water that now covers our planet.
And now a group of British scientists have provided key support for the idea that the origins of our seas were out of this world. They studied grains of material found on asteroid 25143 Itokawa and brought to Earth by a Japanese robot probe, and concluded that this supports the idea that we got our oceans from space.
“The dust we have studied is compelling evidence that our oceans were created from water that came from other parts of the solar system,” said Luke Daly of the University of Glasgow. “This suggests that at least half of the water on Earth has been filtered by interplanetary dust.”
Daly and his colleagues used atomic probe tomography to study dust particles that were returned from Itokawa 25143. This remarkable technique allows scientists to count the atoms in a sample one by one. Thus, it was discovered that the grains brought from the asteroid contain a significant amount of water, scientists say in an article published in the journal Nature Astronomy.
This water was most likely created by the solar wind, a stream of particles flowing from the sun, Daly added. These particles would interact with oxygen atoms in dust clouds that float across the solar system to create water molecules that would accumulate in clouds throughout the solar system’s history.
Then, as the Earth revolved around the Sun, it would sweep through these clouds and wash away the dust particles and their water. It is argued that in this way water – “the driving force of all nature”, as Leonardo da Vinci once put it, – would seep from heaven to our planet.
It is important to note that other bodies orbiting the Sun must have carried away these aquiferous grains as well. On Earth, these small fragments of silicate disintegrated long ago, but on airless asteroid 25143 Itokawa, they would lie undisturbed on its surface for probably billions of years, until the Japanese Hayabusa probe sighted the sample and brought it to Earth, where its contents were revealed.
The group, which also included Professor Martin Lee of the University of Glasgow, emphasizes that they do not think that all the water in our seas was formed from particles of sun dust. An equally important source could be provided by the ice of comets and asteroids that crashed on Earth. “When combined, sun dust and ice comets provided us with oceans in which life evolved,” Lee said.
This latter claim is supported by the fact that ice from comets and asteroids contains a relatively large amount of the hydrogen isotope deuterium compared to water on Earth, while solar dust contains relatively low levels of deuterium. When combined, the two sources balance each other to provide an isotopic signature that matches the signature of water on Earth.
And the discovery is important not only because it provides compelling evidence for the origin of water on Earth. It also suggests that there may be water on the surface of other worlds in the solar system, possibly in the form of ice, which is key for future space exploration and the search for life elsewhere in the galaxy.
“Any moon should be home to a renewable reservoir of water produced by the solar wind,” Daly said. “And this would be important for human space exploration. We need drinking water to support our bodies, and we can also use it by breaking down water molecules into hydrogen and oxygen components to make rocket fuel. In the coming years, when we establish a base on the Moon, such water sources are likely to be invaluable. We don’t have to carry water with us when we travel through the solar system. “
One ice deposit is currently believed to have formed in Shackleton Crater near the Moon’s south pole, and this is the main goal of NASA’s upcoming Artemis program, which aims to create a colony there and use its water resources.
And the observation that interplanetary dust in our solar system contains water also has implications for the search for life in other parts of the galaxy, Daly added. “Throughout our galaxy, we can observe dust clouds in other star systems where planets are forming. This suggests that these worlds will have a supply of water that will allow them to develop seas and oceans, and then, possibly, some kind of life. “
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