More than 70 percent of the surface of our “blue planet” is covered by oceans. But where does the water come from? Previous theories assumed that asteroids that struck our planet in the earliest times brought the water with them. New analyzes now indicate that the sun also contributed to the formation of water on earth. According to this, charged hydrogen particles from solar winds can dissolve oxygen from dust grains in space and thus form water molecules. They could then have reached young earth with space dust.
The origins of our earthly water lie in space – this much has long been clear to scientists. But where exactly the water comes from has so far been a mystery, at least in parts. According to the previous theory, in the final phase of the earth’s formation 4.6 billion years ago it came to earth with so-called type C asteroids, which contain water as well as carbon. But studies show that the water on earth has a slightly different composition than that of the type C asteroids: The asteroid water contains a little more of the heavy hydrogen isotope deuterium than the water on earth. According to this, some of our water actually comes from type C asteroids, but there must be another source.
Investigations of an asteroid
A team led by Luke Daly from the University of Glasgow has now possibly identified this source. “Our research suggests that the solar wind created water on the surface of tiny grains of dust and that this isotopically lighter water likely supplied the rest of the water on Earth,” says co-author Phillip Bland of Curtin University in Perth, Australia. The space dust fell on the earth shortly after the formation of our planet and brought the water it contained with it.
Daly and his colleagues examined samples of a different type of asteroid, called an S-type asteroid, which orbits closer to the Sun than C-type asteroids and which contains primarily the mineral silicate. The samples were collected by a Japanese spacecraft from the asteroid Itokawa and brought to Earth in 2010. Using a technique called atom probe tomography, the researchers were able to measure the atomic structure of the sample atom by atom and thus track down individual water molecules. “Atom probe tomography gives us an incredibly detailed look into the first 50 nanometers of the surface of the dust grains on Itokawa. So we could see that this fragment of the space-weathered rim contains enough water. If you extrapolate it, the water would amount to around 20 liters per cubic meter of rock. “
How solar winds create water
Daly explains, “The solar winds are streams of hydrogen and helium ions that flow continuously from the sun into space. When these hydrogen ions hit an airless surface such as an asteroid or a speck of dust in space, they penetrate a few tens of nanometers into the surface, where they can influence the chemical composition of the rock. Over time, the weathering of space by the hydrogen ions can dissolve enough oxygen atoms from the materials of the rock to form water, which is trapped in the minerals of the asteroid. “
A crucial finding of the researchers is that this water from the solar wind from the early solar system is isotopically light. “This strongly suggests that fine-grained dust thrown up by the solar wind and drawn into the forming earth billions of years ago could be the source of the planet’s missing water reservoir,” said Daly.
Water source on space missions?
The results of Daly and his colleagues not only give an insight into the early days of our earth, but could also possibly be of importance for future space missions. “One of the problems with human exploration of space in the future is how the astronauts can find enough water to stay alive and do their jobs without having to carry it with them on their journey,” says Co -Author Hope Ishii from the University of Hawaii at Mānoa, Honolulu.
“We think it is reasonable to assume that the same weathering process that produced the water on Itokawa also took place to a certain extent on many airless worlds such as the moon or the asteroid Vesta. That could mean that space explorers may well be able to extract fresh water supplies directly from the dust on the planet’s surface. It is exciting to think that the processes that have shaped the planets could help support human life beyond Earth. “
Source: Luke Daly (University of Glasgow, UK) et al., Nature Astronomy, doi: 10.1038 / s41550-021-01487-w