Water is one of the most abundant molecules in the Universe. It is found on planets, moons, stars, and in stellar nurseries, in the Milky Way or beyond.
It is made up of an oxygen atom bonded to two hydrogen atoms, and it has incredible properties that make it the basis of the life we know. It seems that the water reached Earth through the impact of comets and asteroids, or perhaps when volcanoes released it from the interior, and that it would have an age of about 4.6 billion years.
But where did those molecules come from? How were they formed? It’s known that hydrogen was born after the Big Bang, and that oxygen comes from dead stars, but that does not explain how or when the water appeared. When did these atoms come together? How old are the molecules that are part of our body or that fall with the rain?
60 years ago, astronomers detected water in the nurseries of stars, regions of the Universe where interstellar gas is concentrated and allows the birth of these impressive bodies.
But as the European Space Agency (ESA) is recalling this week to recover the legacy of the mission, the data collected by the Herschel Space Observatory (whose “life” ended in 2013), made it possible to trace the origin of the water.
They managed to follow the journey of molecules from comets and asteroids to the planets of the Solar System and, for the first time, to detect the presence of water in a pre-stellar core, a cold accumulation of matter which can later become a star and a planetary system. Throughout its mission, this observatory managed to find water in all stages of the life of stars.
This core where the water was found is called Lynds 1544 and is located in the Taurus Molecular Cloud, a vast region of gas and dust located 430 light-years from Earth that is incubating the seed of stars and planets. There, Herschel detected enough water to fill all of Earth’s oceans 2,000 times.
The journey of water between the stars
Over time, this core will accumulate matter from the molecular cloud of gas and dust that has generated it and will separate from it. It will become a protostar and collapse in on itself due to gravity.
A rotating cloud of dust and gas, called the protoplanetary disk, will accumulate around it, and which will then be the raw material for the possible “manufacturing” of planets. Finally, the protostar will activate nuclear fusion reactions in its interior that will counteract the gravitational collapse. Then a star will be born.
Herschel was able to detect, for the first time, cold water vapor (at a temperature of about -173 degrees) in the intermediate region of one of these protoplanetary disks. In that same ring, the hottest vapor gathers in the vicinity of the stars and also accumulates further away, on the periphery, in a large reservoir of ice in the form of small particles.
The bombardment of the origins of the Universe
How does it get from the disks to the planets of the Universe? The answer is not clear, but here on Earth some clues can be found. Although water covers 70 percent of the surface, this molecule only makes up a small part of the total mass of the planet.
For this reason, among other things, it is believed that at the birth of the Solar System, around 4.6 billion years ago, the areas closest to the Sun were populated by dry, solid and very hot planets, and that later the bombardment of icy objects from the periphery brought the water to the center.
Herschel and other observatories have analyzed the water present on comets to try to clarify this question. He could not answer, because the water captured in these bodies is not always the same type as that present on Earth.
Why is this happening? The water on our planet is characterized by having a certain ratio of hydrogen and deuterium, a hydrogen atom with an extra neutron. If the planet’s water came from comets, the comets’ water should have the same ratio of deuterium to hydrogen.
But the reality is that this is not always the case. The mystery of the water remains unsolved. One of the difficulties in studying it is that if you want to observe the water in comets or distant stars, this cannot be done from Earth. Earth’s atmosphere is laden with moisture and makes it impossible to see the water beyond.
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