When stars and planets are born from a cloud of gas and dust, it is possible, and perhaps even probable, that the planets end up being swallowed by the stars around which they orbit; and if this did not happen to the Earth too, it is fortunate, and not a foregone conclusion. This was revealed by a research conducted by a group of astronomers led by the Italian National Institute of Astrophysics (INAF). The study was conducted on binary stars, not because they are more inclined to eat planets, but because sharing the origin from the same cloud they had the same chemical composition at the start, and if in our survey they show two different ones, it means that in the meantime they have devoured something. Research published in the journal Nature Astronomy revealed that a significant fraction of binary systems with Sun-like stars hide a very troubled past, culminating in the fall of some of the planetary material into the reference star. If this has not happened in the Solar System that hosts the Earth it is because the planets around the Sun have well-ordered and almost circular orbits, which has favored the flourishing of life on our planet.
The astronomers performed a statistical study of 107 composite binary systems using data produced by the HARPS spectrograph mounted on ESO’s 3.6-meter telescope. To these spectra they then added other data already present in the databases and which were acquired by high resolution spectrographs similar to HARPS. As we said at the beginning, the two stellar components of a binary system are formed by the same gas and therefore should be chemically identical. However, if a planet falls into one of the two stars it dissolves in the outer stellar layer changing the chemical composition of the cannibal star, with heavier elements (such as lithium and iron) being more abundant than expected. The chemical composition of the other star, on the other hand, will remain unchanged. By comparing the chemical elements of the two components of a large number of binary systems, the researchers were able to identify which stars had an anomalous composition, then showing that the chemical anomalies can only be caused by the fall of planets towards the central star. .
The team was able to determine how often Sun-like stars engulf their planets: as many as a quarter of these stars host planetary systems so chaotic that they have led to dramatic planetary cannibalization events. This occurs with a probability of between 20 and 35%. Says Lorenzo Spina, first format of the article and research fellow at the INAF of Padua: «It would be as if Jupiter or Saturn fell towards the Sun, destroying even the orbits of the innermost planets. It is unlikely that such dynamic planetary systems are suitable for hosting complex life forms such as those present on Earth ». And he continues: «One of the main scientific challenges of the twenty-first century is undoubtedly the search for planets that are as close to Earth as possible. However, the Milky Way contains millions of stars similar to our Sun and the hunt for Earth 2.0 is likely to become very similar to the search for the proverbial ‘needle in a haystack’. Our study opens up the possibility of using information on the chemical composition of stars to identify those that are more or less likely to host twins from our solar system. “