One of Earth’s greatest mysteries is where all that water on our planet comes from. But the sun may have a finger in the pie.

In 2005, the Japanese space probe Hayabusa paid a visit to the potato-shaped asteroid Itokawa. The mission didn’t quite go according to plan; an accompanying lander failed to land on the surface of Itokawa, and the return trip to Earth took several years longer than planned. The spacecraft did manage to descend to the surface to collect samples. And now, more than a decade later, those collected samples answer perhaps one of our planet’s greatest mysteries: What is the origin of all Earth’s water?

Water on Earth

Our earth is actually quite an odd one out. For example, Earth is the only planet in our solar system that is a real wet oasis. More than 70 percent of the surface is covered with liquid water. And that while the other rocky planets orbiting our sun are dry and arid worlds. Scientists have long puzzled over its origin. Because where does all this water come from? Asteroids and comets are believed to have played a role in this. They would have deposited water on the earth by hitting the young earth. But we may be overlooking another key candidate. And one from an unexpected quarter: the sun.

Monsters of Itokawa

In the study the researchers examined the samples of asteroid Itokawa brought by Hayabusa. Then they performed a meticulous atom-by-atom analysis. Using ingenious technology, they were able to get an incredibly detailed look into the first 50 nanometers of the surface of Itokawa dust grains. The team found that these contain a lot of water; when scaled up it would work out to about 20 liters for every cubic meter of rock. And that leads to a remarkable new insight and groundbreaking discovery about the mysterious source of the water on Earth. The researchers suspect that solar wind — a stream of charged particles (ions and electrons) that constantly escape from the sun — created water on the surface of tiny dust grains, which then found their way to Earth.

More about asteroid Itokawa
Itokawa is one of the S-type asteroids, one of the most common objects in the asteroid belt. Itokawa is about 550 meters long and between 200 and 300 meters wide. It is a fragment of a much larger asteroid that suffered several collisions. During one such collision, the asteroid disintegrated, after which two fragments fused together to form Itokawa. That would have happened about 8 million years ago. The samples Hayabusa brought to Earth have been thoroughly studied in multiple studies. And that led, among other things, to the discovery of water on the asteroid.

Researcher Nick Timms explains the process in more detail when asked. “Our sun exhales a continuous stream of mostly hydrogen and helium ions, known as solar wind,” he said in an interview with Scientias.nl. Celestial bodies that revolve around the sun – think of asteroids and space dust particles – are constantly exposed to this solar wind. The hydrogen ions can then penetrate the outer surface and start a certain reaction, creating water molecules that are trapped in dust particles and asteroids. Space dust and asteroids abounded in the early solar system. And so it may well be that some of the water on our planet that was previously unexplainable ended up here due to bombardments of aquatic dust on the young Earth.”

The sun, solar wind and asteroid Itokawa. Image: Curtin University

It means that it is very likely that our sun had a finger in the pie and is partly responsible for the creation of water on Earth. “This is a surprising discovery in many ways,” Timms says. “On the one hand, the composition of the deuterium/hydrogen isotope of Earth’s water has been puzzling for decades. While C-type asteroids may be suitable water carriers, they are misconfigured. The sun, on the other hand, has a suitable isotopic composition but, crucially, lacked a viable delivery mechanism. Our findings now complete the puzzle.”

Water on other celestial bodies

The findings from this study have important implications for future space missions, Timms said. For example, manned missions to the moon and Mars are planned, where astronauts may stay for a long time. One of the biggest challenges associated with colonizing other celestial bodies, however, is how to get oxygen or water, for example. Transport from Earth can be quite expensive. But, as this study shows, that may not be necessary at all. The research shows that the same process that created water on Itokawa probably also took place on other celestial bodies. “It’s reasonable to assume that the dusty surfaces of airless worlds contain a significant amount of solar wind implanted water,” Timms said. And that means astronauts will be able to extract fresh water supplies directly from the dust on the surface of a celestial body, such as the moon. “It’s exciting to think that future missions to other worlds could somehow extract water, or even hydrogen and oxygen as fuel, from water-rich dust on their surfaces,” Timms said.

The researcher emphasizes how incredibly important space missions like the one from Hayabusa to Itokawa are. “NASA’s Apollo missions, JAXA’s Hayabusa I mission and China’s Chang’e 5 moon mission have all led to an unparalleled understanding of the history of our solar system, the moon and planets,” he says. “Not only thanks to the samples returned to Earth, but also thanks to the sensory equipment and experiments performed that are part of such missions. I am very much looking forward to future sample return missions and hope to continue to be part of the great scientific teams making new discoveries. The possibilities are endless.”