IIt covers three quarters of the Earth’s surface and gives our planet its distinctive blue complexion when viewed from space. But the source of the liquid water that sustains our seas and has nurtured life on our world for eons is a subject of major scientific debate.
Some researchers argue that water, in one form or another, has been present on our world since it emerged from swirling clouds of dust and gas 4.5 billion years ago. The Earth has always been provided with a reservoir, in short.
However, other scientists have a different point of view. They say that at first the Earth was parched and waterless, and our oceans did not appear until much later – when ice and water rained on our world from extraterrestrial sources. These were responsible for most of the 332,500,000 cubic miles of water that now covers our planet, it is claimed.
And now a group of British scientists have given key support to the idea that the origins of our seas were out of this world. They studied grains of matter – found on an asteroid called 25143 Itokawa and brought back to Earth by a Japanese robotic probe – and concluded that these support the idea that we got our oceans from outer space.
“The dust we studied provides good evidence that our oceans were created from water from other parts of the solar system,” said Luke Daly, of the University of Glasgow. “This suggests that at least half of the water we have on Earth is filtered by interplanetary dust.”
Daly and his colleagues used atomic probe tomography to study the dust grains that were returned from 25143 Itokawa. This remarkable technique allows scientists to count the atoms in a sample one by one. In this way, it was revealed that the grains brought back from the asteroid contained significant amounts of water, the scientists say in an article published in the journal. Nature astronomy.
This water was most likely created by the solar wind, a flow of particles coming out of the Sun, Daly added. These particles would have interacted with the oxygen atoms in dust clouds that float through the solar system to create water molecules that would have accumulated in clouds over the history of the solar system.
Then, as the Earth circled around the Sun, it would have swept away those clouds and cleaned up the dust grains – and their water. In this way, water – “the driving force of all nature”, as Leonardo da Vinci once said – would have filtered from the sky to our planet, it is argued.
Above all, other bodies orbiting the Sun would also have swept these aquifer grains. On Earth, these small silicate fragments disintegrated a long time ago, but on the airless asteroid 25143 Itokawa, they will have remained motionless on its surface, probably for billions of years, until the Japanese probe Hayabusa picks up a sample and brings it back to Earth where its contents were revealed.
The group, which also included Professor Martin Lee of the University of Glasgow, points out that they don’t think all of the water in our seas comes from grains of solar dust. An equally large supply would have been provided by ice from comets and asteroids that crashed into Earth. “Together, solar dust and icy comets have provided us with the oceans in which life has evolved,” Lee said.
This latter point is supported by the fact that the ice of comets and asteroids contains relatively high amounts of the hydrogen isotope deuterium compared to water on Earth, while solar dust contains relatively low levels of deuterium. In combination, the two sources balanced each other to provide an isotopic signature that matches that 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 other worlds in the solar system could have water, possibly in the form of ice, on their surface with key implications for future space exploration and the search for life elsewhere in the galaxy.
“Any kind of moon should house a reservoir of renewable water produced by the solar wind,” Daly said. “And that would be important for the exploration of inhabited space. We need drinking water to run our bodies and we could use it as well, by breaking down water molecules into their hydrogen components and oxygen, to make rocket fuel. In the years to come, as we establish a base on the Moon, such water sources are likely to be invaluable. We will not have to take water with us when we will cross the solar system.
An ice deposit is now believed to have formed in Shackleton Crater near the Moon’s south pole and it is the primary target of NASA’s upcoming Artemis program, which aims to establish a colony there and exploit its water resources.
And the observation that the interplanetary dust within our own solar system contains water also has implications for the search for life elsewhere in the galaxy, Daly added. “Across our galaxy, we can observe dust clouds in other star systems where planets are forming. This suggests that these worlds will have a water supply that will allow them to develop seas and oceans, and then eventually life form. “