Carl Sagan said that we are star dust and he was not mistaken. The reflection that the American scientist made in the 80s has become an iconic appointment that, in addition to poetics, is based on science, as it could not be otherwise coming from a great popularizer.
It is believed that all the matter that exists on our planet, including ourselves and the oxygen we breathe, comes from the remains of ancient stars of the Universe. When they run out of fuel and die, all that star dust travels through the cosmos, forming new stars, planets, moons and meteorites. It is thought that life on Earth should have originated from all the chemical elements of those ancient stars, which were transformed.
Meteors that continually reach Earth retain some of that primal material and, analyzing one of these rocks, scientists have come across a big surprise: the oldest star dust that had been found on Earth on date. The rock, which fell in 1969 in the Astralian town of Murchison , contains stellar dust grains that formed over 5,000 million years ago, according to a study published Monday in the Proceedings of the National Academy of Sciences (PNAS) .
For Philipp Heck, curator of the Field Museum and professor at the University of Chicago, discovering that the fragment of this meteorite found half a century ago and that they keep in his collection contains this astronomical treasure has been very exciting: « They are the oldest solid materials found, and they give us information about how the stars formed in our galaxy, ”explains Heck, co-author of the study.
Older than the Sun
These cosmic dust grains are so old that they originated before the sun was born. They were trapped in meteorites, where they have remained unchanged for billions of years, as if they were a time capsule.
Stardust grains prior to the Solar System - which was formed about 4.6 billion years ago - are very rare , as it is estimated that only 5% of the meteorites that have reached Earth contain them.
Thirty years ago, scientists from the University of Chicago isolated those grains of dust from the fragment that they kept from the Murchison meteorite, a carbonaceous condrite in which they found frequent amino acids such as glycine and glutamic acid, and other rarer ones such as isovaline.
To date the grains, they calculate the exposure that the rock has had to cosmic rays that, when interacting with the material, forms new chemical elements. The longer you have been exposed to cosmic rays, the more elements are formed.
Most of the stellar dust grains analyzed were between 4,600 and 4,900 million years old, but there were also 5,500 million years old. "Our hypothesis is that most of these grains were formed in a phase of great stellar activity, greater than normal and prior to the Solar System," he says.
At present, there is a scientific debate about whether stars are generated at a stable rate or if there are peaks of star formation and other periods in which they are born less. According to Heck, one of the main findings of his study is precisely that, "thanks to these grains, we have direct evidence of a stage of accelerated star formation in our galaxy 7,000 million years ago."
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