Earth is the blue planet by definition, but no one really knows where all this water comes from.
Dust from a nearby asteroid has now revealed a potentially overlooked, almost unsuspected source: the sun. The thesis: the water on our planet may have been created by a river of charged particles, "blown" by the Sun's upper atmosphere billions of years ago.
When the solar wind interacts with the tiny dust particles found on some asteroids it can create a small amount of water, and this could explain some of the liquid we find here on our planet.
Most modern models suggest that most of the water on Earth originally came from an extraterrestrial source. Probably from C-type asteroids in the Jupiter-Saturn region, possibly beyond: these distant asteroids are known to contain a significant amount of water-containing minerals.
Alone they are not enough
Carbonaceous chondrites (this is the name of the water-carrying asteroids on our planet) are probably not our only “source”. Other types of water-rich meteorites may also have done the same, not least because carbonaceous chondrites cannot represent the entire water balance of the planet.
There is an asteroid relatively close to Earth. Is called Itokawa, and an analysis of samples taken from this silicate-rich rock in 2010 found signs of water. The source? It could be the sun itself.
Water from the sun on our planet
Solar wind irradiation has also been proposed in the past as a possible way to form water on silicate-rich materials that travel through space. In laboratory tests, volatile hydrogen ions react with silicate minerals, giving water as a by-product. Electron microscopy and electron spectroscopy studies have found direct evidence of water even within extraterrestrial dust particles.
In theory, if water gets trapped in these dust particles, the element will be protected from the elements of space. And it can then be delivered via meteorites to another planet.
"This phenomenon could explain why the rules of airless celestial bodies such as the Moon, which were once thought to be anhydrous, contain oxygen and water, ”explain the authors of the new study.
Tell me how you are, and I'll tell you how much water you have
To explore this hypothesis further and in a slightly different way, the researchers looked at the asteroid Itokawa. The target? See if this object contains a "volatile reservoir" of isotypes similar to that of the solar wind.
Based on a meticulous atom-by-atom analysis, known as atomic probe tomography, the scientists have now measured the abundance of water found inside the dust of the asteroid Itokawa, brought to Earth by the Japanese Aerospace Exploration Agency (JAXA). in 2011. By measuring everything around these particles, including the parts hidden from the Sun, the team found hydroxide and water enriched in the edges on all sides. This suggests that the Sun's hydrogen ions have been "implanted" into the rock, storing water where it cannot be touched.
“Our research suggests that the solar wind created water on the surface of tiny specks of dust. This lighter 'isotopic' water probably provided the rest of Earth's water. And maybe that of any other planet in the same conditions ”, says the planetologist Phil Bland of Curtin University in Australia.
The study was published in Nature Astronomy .
Judging by how much water they found in these tiny dust particles, the team estimates that the S-type asteroids may contain 20 liters of water for every cubic meter of rock.
Wet planet, lucky planet
The findings suggest that isolated dust grains in space could represent an important source of water in our solar system, which we could potentially collect in the future if we collect enough.
"The way astronauts can get enough water, without carrying supplies, is one of the barriers to future space exploration," says the geoscientist. Luke Daly, who worked on the analysis.
“Our research shows that the same spatial alteration process that created water on Itokawa likely occurred on other airless planets, meaning astronauts may be able to process new supplies of water directly from dust. on the surface of a planet, or on the Moon ”.