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.

Key takeaways

  • 70,000 years ago, Scholz’s star came within a light-year of the Sun, disrupting the outer solar system.
  • The star likely sent many comets and asteroids tumbling out of the Oort cloud.
  • Researchers found that over 10% of hyperbolic orbit objects came from the direction of the constellation Gemini, aligning with Scholz’s star’s path.
  • Eight objects, including ‘Oumuamua, have been identified as interstellar visitors, with some traveling at extraordinary speeds.
  • This study suggests we can predict and study interstellar objects by examining their origins and trajectories statistically.
Around 70,000 years ago, a supervolcano named Toba erupted, spewing over 670 cubic miles (2,800 cubic kilometers) of molten rock and debris into the atmosphere. This is supposed to have triggered a major struggle for mankind, eventually resulting in a population bottleneck that reduced our numbers to as low as 1,000 reproductive adults. According to a 2015 research, at this critical juncture in human history, a small reddish star was most likely passing within a light-year of the Sun, just skimming the outer border of the Oort cloud.
Previously, scientists assumed that this wandering star, known as Scholz’s star, moved pretty smoothly through the Oort cloud, affecting 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 in Monthly Notices of the Royal Astronomical Society: Letters, researchers examined the orbital history of 339 known small objects (such as asteroids and comets) with hyperbolic orbits that will eventually propel them out of the solar system. Running entire N-body simulations with these objects in reverse for 100,000 years allowed the scientists to properly identify the spot in the sky from which each body appeared to have originated.
Surprisingly, the scientists discovered that more than 10% of the objects (36) came from the direction of the constellation Gemini. This region in the sky is also exactly where astronomers would expect things to emerge from if they were nudged by Scholz’s star during its close pass 70,000 years ago.

“Using numerical simulations, we calculated the radiants, or positions in the sky, from which all these hyperbolic objects appear to come,” said lead author Carlos de la Fuente Marcos, an astronomer at the 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.”

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 discovering evidence that Scholz’s star had an old connection with the Oort cloud, the scientists discovered that eight of the objects they investigated (including  the recent interstellar visitor ‘Oumuamua) are moving so swiftly that they most likely originated beyond the solar system. Furthermore, these eight objects all have radiants that are pretty far separated from one another, implying that their orbital paths are distinct and uncorrelated. Two of these objects, C/2012 SI (ISON) and C/2008 J4 (McNaught), have extraordinary velocities of approximately 9,000 miles (14,500 kilometers) per hour, indicating that they are interstellar objects passing through our solar system.

Although further research is needed to corroborate the study’s conclusions, the results suggest that scientists may not need to wait for an interstellar object to slingshot around the Sun, as ‘Oumuamua did. Instead, statistical studies like this one could assist astronomers select the most likely extrasolar visitors for future research.

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