“Raindrops on me“, Translation of the title (original title” Raindrops Keep Fallin ‘on My Head “) of a very famous song written in 1969 by the great Bert Bacharach. But science assures us that rain is not the only thing that … from heaven … ends up on Our heads!
On the surface of the Earth, in fact, dust is constantly falling from space, a kind of “heavenly rain” that has not stopped falling on our planet since its inception, billions of years ago. We are all well aware of the more obvious manifestations of this phenomenon, which are the consistent fragments of rock and metal that cross the upper layer of the atmosphere on fire, take on the shape of bright stars, and sometimes reach the ground. Soils in the form of meteors. However, the material that ends up on Earth is usually much smaller in size, less than a millimeter (fine meteorites).
Of course, one of the questions for researchers in the field is to be able to first estimate the exact amount of meteorites that end up on Earth, certainly not an easy process on a planet already surrounded by a whirlwind of dust.
Recently, a research (published in “Earth and Planetary Sciences Letters”) conducted by an international group of scientists, coordinated by J. Duprat, cosmic chemist at the University of Paris-Saclay (Orsay, France), micro-meteorites accumulated in the pristine region. Snow is in Antarctica, while providing the most reliable estimate yet of extraterrestrial debris. calendar? On the basis of the data collected and processed, it was calculated that on Earth, every year, about 5,200 tons of fine meteorites precipitate (with a statistical range between 4000 and 6700)!
But what are the most appropriate geographical areas to conduct this type of survey? Certainly, polar regions like Greenland and Antarctica, which are covered in ice year-round, are distinct points for research into micro-meteorites, due to their geographical isolation and static nature. Moreover, very few terrestrial materials reach these remote areas and “pollute” the landscape. Thus, almost unchangeable continental ice is capable of absorbing space dust with very few pollutants. Permafrost also provides a means for researchers to age debris based on annual snow layers. Although both poles would be suitable for this type of research, Duprat says he prefers southern ice: “The South Pole is much better, because it is surrounded by oceans, completely isolated from other continents.” It is no coincidence that during three seasons in the field, Duprat and his colleagues visited the Franco-Italian station Concordia, located in the Antarctic region – called “Dom Sea” – several times to collect minute meteorites.
Indeed, Dome C is located 1,100 kilometers inland and more than three kilometers above sea level, and it is an ideal cosmic dust gathering site.. In particular, scientists began analyzing the debris deposited before 1995 (to avoid any human contamination due to construction work on the Concordia plant, which began in 1996), then extracting deeper and older layers. Indeed, during the years of research, Duprat noticed that even researchers were unwittingly importing small but significant amounts of ground dust to the site, eventually contaminating the samples. The problem was immediately solved by correcting the methods of collection and handling: each ice sample was sealed in a polyethylene drum and transferred to a pure room to be smelted and filtered. After filtering the dust from the snow, the researchers used electron microscopy, X-ray spectroscopy, and other techniques to analyze more than 2,000 particles ranging in size from 12 to 700 μm. Thus the various analytical methods applied allowed the group not only to identify cosmic dust, but also to track the most probable source of each extraterrestrial particle.
In this way, it was possible to ensure that more than 60% of cosmic dust likely comes from the Jupiter family of comets, guided by the gravitational effect of the giant planet in orbital periods of less than twenty years, while another 20% or so comes from The main asteroid belt.
“Meteors and cosmic dust – explains Mark Fries, a planetary scientist who was not involved in the study and curator on cosmic dust clusters on behalf of NASA – is kind of a sample copy of astronomical materials.” Moreover, in his opinion, the organic compounds present in cosmic dust may be of crucial importance to the origin of life on Earth. “Space dust deposits may have added a great deal of volatiles already present on Earth’s surface,” Fries adds. “A complete understanding of the formation of these particles is equivalent to getting a snapshot of the formation of the inner solar system, especially small objects.”
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