Astronomers have studied in detail the chemical composition of two dozen planetary systems and have not found significant differences between them and the Earth. This increases the chances of the discovery of extraterrestrial intelligence, said scientists who spoke at the Goldschmidt geochemical conference in Boston.
“All the 'bricks' that make up planets in other star systems look the same as their counterparts on Earth. All critical elements are present there, and their shares are approximately equal to that of the earth. This means that planets similar to Earth must exist in the Milky Way,”says Siyi Xu of the Jiminy Observatory in Hawaii (USA).
More than half a century ago, American astronomer Frank Drake, trying to estimate the chances of detecting extraterrestrial intelligence and life, developed a formula to calculate the number of civilizations in the Galaxy with which contact is possible.
Physicist Enrico Fermi, in response to a rather high assessment of the chances of interplanetary contact using Drake's formula, formulated the thesis, which is now known as the Fermi paradox: if there are so many alien civilizations, then why does humanity not observe any traces of them?
Scientists have tried to solve this paradox in many ways, the most popular of which is the "unique Earth" hypothesis. She says that for the emergence of intelligent beings, unique conditions are necessary, in fact, a complete copy of our planet.
According to Xu, testing this theory is now complicated by the fact that modern telescopes do not have sufficient sensitivity for direct observation of Earth-like exoplanets and study of their chemical composition.
For this reason, astrogeologists are forced to go in a roundabout way, calculating their composition by what impurities their stars contain and how their atmospheres are arranged. Xu and his colleagues found an ingenious way to solve this problem using one recently discovered feature of white dwarfs, "dead" stars.
All white dwarfs and subdwarfs have one curious property - any matter they absorb is distributed over their surface not by chance, but in the form of a kind of flaky cake. Heavy elements like oxygen or silicon will gradually "sink", while hydrogen and helium will "float".
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Due to this, traces of heavy elements, even if they are present on the surface of the dwarf in large quantities, can be seen almost only at the initial stage of absorption of debris from planets, asteroids and comets. At this time, heavy elements have not yet had time to "drown", and their presence in the atmosphere and on the surface of the dwarf can be seen from the characteristic absorption and emission lines in its spectrum.
In total, Xu and his team managed to discover 18 such luminaries located relatively close to Earth, at a distance of 458 light years or closer. Having studied their spectrum with the Keck telescope, the scientists calculated the amount of matter "eaten" by the dwarfs and studied its composition.
As it turned out, all the planets, ground by their former stars, contained completely "terrestrial" portions of calcium, magnesium, silicon, iron and other rock-forming elements. In one case, Xu said his team even managed to find traces of water and other volatiles, but failed to measure their relative mass.
This suggests that the planets, similar to Earth in composition, are by no means unique and are found quite often in the Milky Way. This significantly increases our chances of discovering a twin of the Earth and representatives of extraterrestrial civilizations, scientists conclude.
