They are much older than our planet but have taken up residence there ... Dust from stars formed 7 billion years ago, brought by a meteorite which fell in Australia in 1969 but dated very recently, becomes solid matter the oldest discovery on Earth. Their formation is well before the birth of the Sun, 4.6 billion years old, and therefore in the solar system.
Researchers, largely working for the universities of Chicago or Zurich, analyzed some forty tiny grains taken from the meteorite and delivered their results in an article published Monday by the journal Proceedings of the National Academy of Sciences (PNAS ).
On its long journey through space, the Murchison meteorite captured dust left behind by dead stars and then brought it to Earth. To date the samples, no larger than 0.03 mm, the scientists were interested in their composition: the more time these grains have spent in space, the more the omnipresent cosmic rays have modified the matter.
Stellar baby boom
The age of one of these grains has thus been evaluated at 7 billion years. But a majority of them are more recent and are "only" 4.6 to 4.9 billion years old. The abundance of dust dating from this period suggests that there was then a peak of astral mortality in The Milky Way!
If we consider that a star begins to produce dust when it reaches two and a half billion years, we can conclude that the stellar baby boom occurred about 7 billion years ago. What the calculations of another researcher, the Brazilian Helio Jaques Rocha-Pinto, had already suggested.
In 1987, scientists had found grains of a new kind in the Murchison meteorite, but it is a completely new dating technique which today makes it possible to isolate the oldest micrograins, by reducing the samples in dust and passing everything in acid.
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Could we find even older dust on our planet? Possible, but according to Philipp Heck, who directed the latest work, there are less than five meteorites massive enough to harbor such nuggets today. As a reminder, the age of the universe is today estimated at 13.7 billion years.