Solar System's near-miss revealed
Astronomers have logged a near-miss between our Solar System and a star that occurred 70,000 years ago.
The dim red-dwarf, known as "Scholz's star", came as close as 0.8 light years - or five trillion miles - from the Sun, scientists believe.
During the encounter the star may actually have brushed the edge of the Solar System, passing through the "Oort Cloud" - a distant region of icy bodies where comets are born.
Today, Scholz's star is safely located 20 light years away from the Earth in the constellation of Moneceros.
Scientists discovered that it is racing directly away from the Solar System at considerable speed.
When they traced its trajectory back they found that around 70,000 years ago it must have come incredibly close to the Sun's family of planets.
Dr Eric Mamajek, from the University of Rochester in the US, said: "The radial velocity measurements were consistent with it running away from the Sun's vicinity, and we realised it must have had a close flyby in the past."
Scholz's star would have come five times closer than our nearest current stellar neighbour, Proxima Centauri, which is 4.2 light years away.
At its closest point it would have been about 50 times fainter than any star visible with the naked eye at night.
However, it is a magnetically active star prone to "flares" that temporarily boost its brightness thousands of times over.
During these rare flaring events, Scholz's star may have been visible by our ancient ancestors for minutes or hours at a time, said the scientists.
Homo sapiens was in the process of migrating out of Africa into Europe and Asia when the near-miss occurred.
The star is part of a binary system consisting of a low-mass red dwarf with about 8% the mass of the Sun, and an even dimmer "brown dwarf" companion.
Brown dwarfs are considered to be "failed stars" much more massive than gas giant planets such as Jupiter but still too small to ignite a nuclear reaction in their cores.
The scientists, who report their findings in Astrophysical Journal Letters, carried out computer simulations that showed a 98% probability of the star passing through the outer Oort Cloud. One simulation brought the star within the inner Oort Cloud, which could have the effect of triggering comet showers.
Dr Mamajek added: "Other dynamically important Oort Cloud perturbers may be lurking among nearby stars."
A recently launched European Space Agency satellite, Gaia, is expected to reveal which other stars may have had close encounters with us in the past or could in the future.
The star was named after astronomer Ralf-Dieter Scholz, from the Leibniz Institute for Astrophysics in Potsdam, Germany, who discovered it in 2013.