Evoking images of the Sun shouldn’t normally make you think of water. After all, it’s a giant hot ball of plasma; it’s so hot that there exists only a small window of distance from the Sun wherein water can exist as a liquid. It’s called the habitable zone of a star, and lucky for us, our planet’s sitting in it.
Of course, before any water could exist as liquid on any given planet, it must first get the water from somewhere. And that’s where the unknown lies for Earth’s history with water: we don’t know for sure where all our water came from.
Several candidate water sources have been put up for debate, including just having them lying around when our planet was forming, and another case where all the water was brought to us by meteorites crashing into an early Earth billions of years ago.
However, there appears to be a source for Earthly water that remains unaccounted for up until now, and it’s from the unlikeliest of places in space: our own Sun. The novel study, published in the journal Nature Astronomy, posits this radical new way of thinking where our oceans and rivers came from.
The key, according to the authors, lies with the fact that solar wind, which is a stream of charged particles frequently released from the upper atmosphere of the Sun, contains hydrogen (H) ions. These ions are then capable of hitting the surfaces of space objects with no atmosphere—like meteorites and space dust.
The ions are capable of penetrating a few nanometers from the outer surface of the space rock, and are then capable of reacting with whatever minerals are present within bare pieces of rock—a process called “space weathering.”
Once enough oxygen (O) atoms have been ejected from the surface of the rock via space weathering, they are then made available to react with the hydrogen ions from solar wind, creating water (H2O) that’s now trapped within the rock’s minerals.
“This phenomenon could explain why the [rocks] of airless worlds such as the Moon, which were once thought to be anhydrous, contain several percent H2O,” the authors explained within their study.
Dr. Luke Daly, lead author and from the University of Glasgow’s School of Geographical and Earth Sciences, continued: “That strongly suggests that fine-grained dust, buffeted by the solar wind and drawn into the forming Earth billions of years ago, could be the source of the missing reservoir of the planet’s water.”
The authors arrived at this conclusion with the help of data obtained from a surface study of the asteroid 25143 Itokawa. There, the team found enough water on its surface to account for an estimated 20 L of water for every cubic meter of Itokawa rock, despite the asteroid having no atmosphere to speak of. According to the authors, this gives credence to their conclusions.
“By showing for the first time that water is produced in-situ on the surface of an asteroid, our study builds on the accumulating body of evidence that the interaction of the solar wind with oxygen-rich dust grains does indeed produce water,” said co-author Prof. John Bradley, of the University of Hawaii. “Since dust that was abundant throughout the solar nebula prior to the onset of planetesimal accretion was inevitably irradiated, water produced by this mechanism is directly relevant to the origin of water in planetary systems and possibly the isotopic composition of Earth’s oceans.”
Dr. Daly and team believe that their findings may provide opportunities for future manned missions to find sources of water, like the upcoming Artemis missions to the Moon. “If the lunar surface has a similar water reservoir sourced by the solar wind this research uncovered on Itokawa, it would represent an enormous and valuable resource to aid in achieving that goal.”
(For more odd things found inside rocks, check out our recent coverage of carbon attributed to ancient life that was found inside a ruby. Next, check out more news of water on other worlds by reading about a newly-discovered form of it in superionic ice.)
References
- Cassella, C. (2021, November 30). The sun could be the mystery source of earth’s unexplained water, scientists say. ScienceAlert. https://www.sciencealert.com/scientists-identify-an-overlooked-source-for-some-of-our-planet-s-water-the-sun
- Daly, L., Lee, M. R., Hallis, L. J., Ishii, H. A., Bradley, J. P., Bland, P. A., Saxey, D. W., Fougerouse, D., Rickard, W. D. A., Forman, L. V., Timms, N. E., Jourdan, F., Reddy, S. M., Salge, T., Quadir, Z., Christou, E., Cox, M. A., Aguiar, J. A., Hattar, K., … Thompson, M. S. (2021). Solar wind contributions to Earth’s oceans. Nature Astronomy, 1–11. https://doi.org/10.1038/s41550-021-01487-w
- Space dust analysis could solve mystery of the origins of Earth’s water. (2021, November 29). University of Glasgow. https://www.gla.ac.uk/news/headline_822735_en.html
