Free Astronomy Magazine March-April 2015

29 MARCH-APRIL 2015 SOLAR SYSTEM A rtist’s repre- sentation of Scholz's Star with its dark companion, dur- ing its close pass near the Sun (visible in the far left) occurred 70,000 years ago. [Michael Osadciw, Univer- sity of Roch- ester] kilometre, could dis- rupt the orbits of several of them and drive some of these towards the inner planets, with consider- able risks for life on Earth. Astronomers are particularly attentive to these issues and for decades have been evaluating the possible correlations between mass extinctions and flybys of stars. A supposed periodicity of extinctions has led to presume (in the ‘80s) the existence of a dark star companion of the Sun, a dim dwarf located on an extreme- ly wide orbit, which every 26 million years, when returning to the perihelion, would have inject- ed cometary nuclei in the inner solar system. The ascertained inexistence of that companion star has not, however, eliminat- ed the problem, as in the long-term other stars may have perturbed (or could perturb) the Oort Cloud and their effects are neither predictable nor immediate. Hence the need to know more about the stars that in the past transited at “short” distance from the Sun. Recognizing them among the myriad of other stars that populate the sky is not years ago, Oort Cloud