A group of researchers from the Arizona State University, USA, found water in samples from the surface of the Itokawa asteroid, collected by the Japanese space probe Hayabusa, according to a study published today in the journal Science Advances.
This finding, according to the authors, suggests that the first impacts on the history of the Earth by similar asteroids may have generated "up to half the water of the oceans of our planet".
"We found that the samples we examined were enriched in water compared to the average of the objects in the inner solar system," said Ziliang Jin, a researcher at the university.
In two of the five samples of the celestial object, the team led by Jin identified the mineral pyroxene, which in the terrestrial samples has water in its crystalline structure.
The researchers suspected that the Itokawa particles could also have traces of water, but they wanted to know exactly how much.
To study the samples, each about half the thickness of a human hair, the team used the nanometer-scale secondary ion mass spectrometer (NanoSIMS) from Arizona State University, which can measure these minute mineral grains with great sensitivity.
NanoSIMS measurements revealed that the samples were unexpectedly water-rich and also found that even "nominally dry" asteroids such as Itokawa can, in fact, accommodate more water than scientists thought.
Itokawa, a peanut-shaped asteroid about 550 meters long and about 300 wide, orbits the Sun every 18 months at an average distance of 1.3 times the distance between the Earth and the Sun.
Part of Itokawa's path, which is an S-type asteroid, takes him inside the earth's orbit and extends slightly beyond Mars.
Type S asteroids are one of the most common objects in the asteroid belt and were originally formed at a distance from the Sun of one third to three times the distance from the Earth.
The researchers pointed out that the current Itokawa is the remnant of a body at least 19 kilometers wide that once warmed up between 537 and 815 degrees Celsius.
The primitive body underwent several shocks of great impact, with a final event that broke it and, consequently, two of the fragments merged and formed the Itokawa of today, which has reached the current size and shape around 8 million years ago.
"Although the samples were collected on the surface, we do not know where these grains were in the original body, but our best estimate is that they were buried more than 100 meters deep," Jin concluded.
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