How did water get to Earth? A new theory suggests that our planet was able to capture the precious element in a steam bath, shortly after the formation of the Solar System, according to a study published Tuesday in Astronomy & Astrophysics.
According to the dominant theory, water arrived on Earth mainly via asteroids and comets, coming from outside the Solar System, in the first hundred million years.
When it was formed, located too close to its star, our planet would have been too hot to retain water.
A bombing that resembles a “gravitational billiards game”, described to AFP by Quentin Kral, first author of thestudy: complex dynamic mechanisms would thus have sent icy objects towards the Earth, at a precise time and in sufficient quantity.
The astrophysicist proposes a process that is “a little more natural and a little simpler to implement”. Less random and, above all, applicable to other rocky planets in the Solar System, such as Mars or Mercury, which are known to contain water, just like the Moon.
For him, it all starts from the asteroid belt, a ring of small celestial bodies, located between Mars and Jupiter, which was much more massive at the time of the formation of the Solar System, 4.6 billion years ago years.
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“We know that initially the asteroids were icy,” explains the researcher at the laboratory LESIA of the Paris-Meudon PSL Observatory. These ices, “we don’t see them too much” today, except on Ceres, the most massive asteroid (read box).
The idea of the LESIA team, with an astronomer from the Institute of Globe Physics in Paris, is that the Earth has indeed recovered water from asteroids, but without the latter bringing it directly to it.
In this scenario, the Sun has just formed and heats the asteroid belt, peaking around 25 million years ago. This heating “sublimates the water ices” and then forms a “disk of water vapor at the level of the asteroid belt”, describes Quentin Kral.
The water cycle
From there, this disk spreads out in the Solar System, up to the internal planets of the Solar System, of which the Earth is a part: the latter will gradually capture this resource as it cools. Once accreted – or captured under the effect of gravitation – on the planet, this “water vapor lives its life as water”, and is found there in liquid form, thus forming the oceans.
The model developed by Quentin Kral and his colleagues works just as well with a massive asteroid belt, as they assume our system’s belt did, as with a thinner belt, but over a longer period of time.
This is the first time that such a hypothesis has been put forward. But it “does not come out of nowhere”, specifies the astrophysicist. It owes a lot to radio telescope observations ALMAa great specialist in the detection of clouds of gas and dust in the Universe: “For ten years we have known that there are discs of carbon and oxygen gas in planetesimal belts”, in other words asteroids and miniplanets, “extra-solar systems”.
Before that we only saw dust, where now we see the presence of gas. Or water ice in the asteroid belt of HD 69830, a solar system with at least three planets.
To test this potentially universal theory, the research team will try to find slightly younger systems that still have their water gas disk.
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