At this point it is worth recalling that, according to estimates, our Sun is "only" 4.6 billion years old. The dust found inside the meteorite is therefore older than the Sun, and it was formed during the final stage of life of another star. this, dying, she finally threw her guts into space, which have become a component of new stars, planets, moons and asteroids, just like the one that fell into the Earth's atmosphere.
"This is one of the most exciting studies I have participated in."Said cosmochemist Philipp Heck from the Natural History Museum in Chicago and the University of Chicago.
Interestingly, although the universe is full of stardust, so far no stardust on the Earth has been found to be older than the sun. This is because plate tectonics, volcanism and other planetary processes led to the heating and transformation of all "solar" dust that could have accumulated on Earth when it was formed.
Star dust can also accumulate on cosmic rocks like the Murchison meteorite. However, unlike Earth, the meteorite was in space "Almost an indifferent piece of rock that formed in the star nebula and has not changed much since then". That is why stardust found in it has not become another type of material.
How was the age of dust determined? In brief, researchers used a scanning electron microscope and secondary ion mass spectrometry (SIMS) and noble gas mass spectrometry methods to detect effects on particles in the cosmic radiation meteorite. This radiation penetrates objects such as asteroids and leaves a trail on their stardust particles.
"Some of these cosmic rays interact with matter to form new elements. The longer this matter is exposed to them, the more new elements are formed. "
Researchers analyzed 43 grains of solar dust found in the Murchison meteorite. Among them, these elements were found that formed under the influence of cosmic rays – helium-3 and neon-21. On their basis, it was estimated that some dust grains are very old and are more than 5.5 billion years old (up to 7 billion years old), but most were from 4.6 to 4.9 billion years old.
It is worth adding that the presence of so many younger grains in the stardust can confirm that 7 billion years ago in our galaxy there was a period of frequent and intense star formation. About 2 to 2.5 billion years later, the larger stars of this period ended their lives, sending dust into space, which is now between 4.6 and 4.9 billion years old.
"These are the oldest solid materials found. They tell us how stars formed in our galaxy. ", added Heck.