The movements of some comets and asteroids in our solar system still bear the mark of a stellar encounter that occurred 70,000 years ago -- when humans were already on Earth, says a study.
A small reddish star approached our solar system and gravitationally disturbed comets and asteroids, according to the study published in the journal Monthly Notices of the Royal Astronomical Society: Letters.
The close fly-by of this star 70,000 years ago did not disturb all the hyperbolic objects (with very open V-shaped, not the typical elliptical orbit) of the solar system, only those that were closest to it at that time, the researchers found.
At a time when modern humans were beginning to leave Africa and the Neanderthals were living on our planet, the Scholz's star -- named after the German astronomer who discovered it -- approached less than a light-year from the Sun.
Nowadays it is almost 20 light-years away, but 70,000 years ago it entered the Oort cloud, a reservoir of trans-Neptunian objects located at the confines of the solar system.
This discovery was first made public in 2015 by a team of astronomers led by Professor Eric Mamajek of the University of Rochester in the US.
The details of that stellar flyby, the closest documented so far, were presented in The Astrophysical Journal Letters.
Now, astronomers from the Complutense University of Madrid in Spain and the University of Cambridge analysed for the first time the nearly 340 objects of the solar system with hyperbolic orbits, and in doing so they detected that the trajectory of some of them is influenced by the passage of Scholz's star.
"Using numerical simulations we have calculated the radiants or positions in the sky from which all these hyperbolic objects seem to come," said study co-author Carlos de la Fuente Marcos from Complutense University of Madrid.
"In principle, one would expect those positions to be evenly distributed in the sky, particularly if these objects come from the Oort cloud; however, what we find is very different: a statistically significant accumulation of radiants," he added.
"The pronounced over-density appears projected in the direction of the constellation of Gemini, which fits the close encounter with Scholz's star," De la Fuente Marcos said.
Scholz's star is a binary system formed by a small red dwarf, with about 9% of the mass of the Sun, around which a much less bright and smaller brown dwarf orbits.
It is likely that our ancestors saw its faint reddish light in the nights of prehistory, according to the researchers.
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