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Wandering star shook up the prehistoric solar system

70,000 years ago, a nomadic star came within a light-year of the Sun, likely sending dozens of comets and asteroids tumbling out of the solar system.
ancientstar
A wandering star passed within one light-year of the Sun roughly 70,000 years ago. At the time, modern humans were just beginning to migrate out of Africa, and Neanderthals were still sharing the planet with us.
José A. Peñas/SINC
Around 70,000 years ago, a supervolcano named Toba erupted, blowing roughly 670 cubic miles (2,800 cubic kilometers) of vaporized rock and debris into the air. This is thought to have caused a massive struggle for humanity, ultimately leading to a population bottleneck that whittled down our numbers to as few as 1,000 reproductive adults. According to a 2015 study, during this pivotal point in human history, a small reddish star also was likely passing within a light-year of the Sun, just skimming the outer rim of the Oort cloud (the extended shell of over a trillion icy objects that is thought to cocoon the outer solar system).

Previously, astronomers believed that this wandering star — dubbed Scholz’s star — passed relatively peacefully by the Oort cloud, influencing very few (if any) outer solar system objects. But, according to a new study, researchers now think that Scholz’s star may have caused more of a ruckus than we initially gave it credit for.

In the study, published February 6 in Monthly Notices of the Royal Astronomical Society: Letters, researchers analyzed the orbital evolution of 339 known minor objects (like asteroids and comets) with hyperbolic orbits that will eventually usher them out of the solar system. By running full N-body simulations with these objects in reverse for 100,000 years, the team was able to accurately estimate the point in the sky where each body appears to have come from.

Surprisingly, the team found that over 10 percent of the objects (36) originated from the direction of the constellation Gemini. This spot in the sky also happens to be exactly where astronomers would expect objects to come from if they were nudged by Scholz’s star during its close pass 70,000 years ago.

“Using numerical simulations, we have calculated the radiants, or positions in the sky, from which all these hyperbolic objects seem to come,” said lead author Carlos de la Fuente Marcos, an astronomer at the Complutense University of Madrid, in a statement.

“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 said. “The pronounced over-density appears projected in the direction of the constellation of Gemini, which fits the close encounter with Scholz’s star.”
statsignificance
This graphic from the study shows the distribution and statistical significance of the radiants (points of origin in the sky) for all objects analyzed. The dark blue spot of high statistical significance toward the right shows that many more objects come from this area of the sky than would be expected by chance. This location is also where objects ejected by Scholz’s star would appear to originate.
Carlos de la Fuente Marcos, et al.
In addition to finding evidence that Scholz’s star had an ancient interaction with the Oort cloud, the team also determined that eight of the objects they studied (including the recent interstellar visitor ‘Oumuamua) are traveling so quickly that they likely originated from outside the solar system. Furthermore, these eight objects all have radiants that are relatively well separated from the others, which suggests their orbital paths are unique and uncorrelated. Two of these objects, C/2012 SI (ISON) and C/2008 J4 (McNaught), have extreme velocities of around 9,000 miles (14,500 km) per hour, which strongly indicates they are interstellar objects zipping through our solar system.

Although more research is needed to confirm the study’s findings, the results show that astronomers may not need to wait to study an interstellar object until it serendipitously slingshots around the Sun like ‘Oumuamua did. Instead, statistical studies like this could be used to help astronomers proactively identify the most likely extrasolar visitors for future analysis.

A free pre-print version of the study is available online at arXiv.org.
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