Earth is a unique blue world in the entire solar system. About 71% of its surface is covered with water, thus making it the only planet far richer in water content than any other in the entire solar system. However, the most vexing mystery is where Earth got such large amounts of water.
The popular theory goes that large chunks of asteroids delivered it to the Earth during the early history of the planet, billions of years ago. This theory has garnered potential evidence to back it. But, the water on Earth is of such high volume compared to other rocky planets in the solar system that it would have been impossible for the space rocks alone to deliver it.
And that’s why scientists have been in constant pursuit to unravel the missing extra sources that might have gone unnoticed so far. And their curiosity was spot on, and surprisingly, our majestic Sun has a role to play!
A new study puts together a chain of reactions that may have combined to result in such large volumes of water on Earth during its infant years. This added insight about water on Earth comes out of the research from an international team of scientists from the UK, Australia and America.
How can the Sun provide water?
Sun can contribute to water content across the solar system thanks to the Sun’s super energised solar wind, which sweeps across the entire solar system! The solar wind is a constant stream of plasma that carries along with it charged particles gushing in an outward direction. The wind speed is as high as 900 km/s, with temperatures scorching up to 1 million degree Celsius. And the wind interacts with a large chunk of space rocks.
The lead of the study, Dr Luke Daly, explains the interplay of solar wind and dust grain of asteroids: “The solar winds are streams of mostly hydrogen and helium ions which constantly flow from the Sun out into space. When those hydrogen ions hit an airless surface like an asteroid or a spaceborne dust particle, they penetrate a few tens of nanometres below the surface, where they can affect the chemical composition of the rock. Over time, the ‘space weathering’ effect of the hydrogen ions can eject enough oxygen atoms from materials in the rock to create H2O– water–trapped within minerals on the asteroid.”
Scientists hope that this complex mechanism could be the missing link that explains the presence of an abundant amount of water on Earth.
So, how did the water reach Earth?
Going with the popular theory, the various types of water-carrying asteroids delivered it to the Earth about billions of years ago.
The present study was conducted on an S-type asteroid, which smashed along with other majorly known water carrying C-types during the forming years of the Earth. The latter mostly holds the credit for bringing water to Earth.
The team conducted atom probe tomography to scrutinise samples of an S-type asteroid called Itokawa—the samples were retrieved back to the planet in 2010 by the Japanese space probe Hayabusa. Using this technique, the researchers examined the atomic structure of the dust grains to detect individual water molecules.
This cutting edge technique gave an incredibly detailed look at the surface of Itokawa dust grains that produced large amounts of water. The results indicated the presence of enough water equivalent to 20 litres for every cubic metre of rock. The study estimates that other types of water-rich meteorites might also hold the credit of bringing some share of water to the Earth.
Scientists agree with the findings as most water isotypes examined so far reveal the carbonaceous chondrites, while a fraction of them don’t match. The experts deemed the other sources for the unmatched percentage as Sun or the solar nebula.
Interestingly, the revelations obtained from this study could also help future space exploration missions. The team suggests that astronauts can get sufficient water supply from these sources during long human space missions.
The results have been published in the journal Nature Astronomy last week and can be accessed here.