Star Buzzed Our Solar System during Human Prehistory

If humans are still here when comets displaced by this get here, there are likely to be some people claiming they are a sign by God of his displeasure of their current society.

http://www.scientificamerican.com/article/star-buzzed-our-solar-system-during-human-prehistory/?WT.mc_id=SA_BS_20150227

February 21, 2015 |By Ron Cowen and Nature magazine

A recently discovered stellar neighbour of the Sun penetrated the extreme fringes of the Solar System—the closest encounter ever documented—at around the time that modern humans began spreading from Africa into Eurasia.

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The red dwarf star, which has a mass about 8% that of the Sun and is orbited by a 'brown dwarf' companion—a body with too little heft to sustain the thermonuclear reactions that enable stars to shine—was discovered in 2013 in images recorded by NASA’s Wide-field Infrared Survey Explorer (WISE) mission. It is relatively nearby, at about 6 parsecs (19.6 light years) away.

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Tracing the trajectory of the star and its brown dwarf companion back in time, Mamajek’s team found with 98% confidence that Scholz’s star passed within the Solar System's Oort cloud, a reservoir of comets, about 70,000 years ago.

The star sped through the outer Solar System at 83 kilometres per second, and came within 0.25 parsecs of the Sun (or 52,000 times the Earth–Sun distance), the team reports in the February 10 issue of Astrophysical Journal Letters. By comparison, the closest star to the Solar System known today, Proxima Centauri, lies 1.3 parsecs from the Sun. The encounter is the closest-known passage of a star that has a well-documented velocity and distance, the team says.

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Because Scholz’s star is puny and sped by quickly, it would have had a negligible impact on the Oort cloud, Mamajek notes. And any comets that the star might have sent hurtling towards the inner Solar System will not arrive for another few hundred thousand years, says Tremaine. However, more-massive stars penetrating the Oort cloud in the distant past might have triggered major comet showers that pummelled the planets and led to some of the mass extinction events on Earth, says Mamajek.