Liquid water on Earth is what makes this planet so special: it is the forerunner of life as we know it and that is why scientists try tofind water on other planets, both within the Solar System and outside it. Like everything else, water on Earth also had a beginning, although the answer to the enigma of its origin is not without controversy.
For a long time, the most accepted theory to explain the origin of the water in our oceans was the one that involved comets: huge balls of ice and dust that orbit beyond Neptune and that sometimes visit the inner zones of the Solar System. This theory states that,When the Earth formed, about 4.6 billion years ago, it was too hot to hold liquid water on its surface.. We must think that in its beginning, the Solar System was a chaotic and violent place, where thousands of objects collided with each other. It was at this time that the planets formed. Probably, in that first stage, although there was no liquid water on the surface, the mantle, the region between the core and the surface of our planet, would be humid.But that moisture disappeared about 4.4 billion years agowhen Earth and Tea, a proto-planet the size of Mars, collided, causing the Moon to form and drastically drying up our planet.
Over time, the Earth recovered from such a catastrophe, the Solar System calmed down, and impacts became less frequent. In this stage, plate tectonics began and volcanism generatedgases that favored, along with some minor comet impacts, small seas on the surface.But it was about 3.9 billion years ago when a change in the orbits of Uranus and Neptune produced a phase known as “late bombardment”, a stage of great gravitational instability that radically affected comets and asteroids and caused their redistribution throughout the System. Solar.Millions of these bodies collided with the inner planets, producing on Earth the oceans that we see today.
However, when today we measure what type of water is in comets using a technique that determines the ratio of deuterium to hydrogen (deuterium being the same as hydrogen but heavier), we find no coincidences, and that ratio turns out to be the twice or even more in comets than in Earth’s oceans . This causes great confusion, and again raises the question: Where does the water in the Earth’s oceans come from? What if it did not come from comets? What if during that late violent bombardment other bodies were the ones? who brought the water?
The Main Asteroid Belt, a possible candidate?
Until a few years ago, we thought that only comets had ice, which volatilized as they approached the Sun and caused the startling dust tails that we observe to unfold. But one day, suddenly, an object that should not have a tail did. It was an asteroid: unlike comets, asteroids do not have ice and are made of rock and dust, so they do not activate, that is, they do not develop tails like comets.
Many of these asteroids are in an extremely stable region between Mars and Jupiter, in what is known asMain Asteroid Belt. It was thought that the activation of that object was due to a fortuitous impact with another asteroid, and the issue was closed. But a few years later, just as the body was passing through its perihelion (closest point to the Sun) it was activated again, again showing a tail of dust.
This could not be a coincidence, so impacts were ruled out as the cause of these activations. Several hypotheses were raised and it was concluded that the sublimation of water ice (passing from the solid state to the gaseous state without going through the liquid state when heated) was the most probable cause to explain these phenomena.It was therefore a hybrid between comet and asteroid, a unique object of its kind.. But shortly after another object of that Asteroid Belt was activated, and then another, and another, up to a total today of about 15 cataloged: this new class of objects are called “Main Belt KitesUnfortunately, these are very dim, they activate without warning and for a very short time, which makes it tremendouslydifficult to measure the ratio of deuterium and hydrogento determine if they are the cause that the surface of our planet is full of liquid water.
At the moment, there is still much to investigate, but this new family of objects could be the key to explain why our planet is, today, the source of life that it is.
FJ Pozuelos is a researcher at the Instituto de Astrofísica de Andalucía-CSIC
