Recent research has highlighted a growing understanding of the risk posed by interstellar objects (ISOs) impacting Earth. Three known ISOs have traversed our inner Solar System: Oumuamua, which appeared in 2017; 2I/Borisov, an interstellar comet that visited in 2019; and currently, 3I/Atlas, another comet making its way through the Sun-warmed region. These findings raise important questions about the potential impact history of Earth and the ongoing risk from similar objects.
The study titled “The Distribution of Earth-Impacting Interstellar Objects,” led by Darryl Seligman, an assistant professor in the Physics and Astronomy Department at Michigan State University, aims to quantify this risk. The research, available on arXiv, investigates expected orbital elements and velocities of ISOs that could potentially impact our planet.
Despite the absence of precise data on the number of ISOs, the authors focus on their expected distribution and the influence of M-star kinematics. M-stars, or red dwarfs, are the most abundant type of star in the Milky Way, suggesting that a majority of ISOs are likely ejected from such systems. While the choice of M-star kinematics is somewhat arbitrary, it serves as a useful model for understanding ISO behavior.
Through simulations, researchers generated a synthetic population of approximately 10 billion ISOs, ultimately identifying around 10,000 that could impact Earth. The simulations reveal that ISOs are predominantly likely to approach from the solar apex and the galactic plane, the latter being the region where most stars, including our own, are situated.
The solar apex is the direction the Sun moves through the Milky Way, akin to a car driving through rain and encountering more drops head-on. Conversely, ISOs coming from the galactic plane have a higher chance of collision due to the density of objects in that area. Interestingly, while ISOs from these regions possess higher velocities, those that could impact Earth tend to be slower-moving. This occurs because the gravitational influence of the Sun preferentially captures low-eccentricity hyperbolic bodies, shifting them into potential Earth-crossing trajectories.
Seasonal variations also affect the likelihood of ISOs reaching Earth. The highest impact velocities are expected in spring, when the planet moves toward the solar apex. In contrast, winter presents more frequent potential impactors, as Earth is positioned toward the solar antapex, the area from which the Sun is moving away.
Geographically, areas near the equator face the most significant risk from potential ISO impacts. The northern hemisphere, which houses nearly 90 percent of the global population, also experiences a heightened risk. Importantly, the researchers note that their findings are specifically applicable to ISOs ejected from M-dwarf systems, and different assumed kinematics could yield varied results.
The study does not predict the number of ISOs that may threaten Earth, as quantifying that figure is currently impossible. Seligman and his team deliberately refrained from making definitive predictions about impact rates, stating, “In this paper we intentionally do not make any definitive predictions about the rates of interstellar impactors.”
Nonetheless, these insights lay groundwork for future observational efforts, particularly with the Vera Rubin Observatory and its Legacy Survey of Space and Time. This initiative will enable astronomers to gather data on ISOs and assess the validity of the research findings. As scientists continue to explore the potential for interstellar objects to impact Earth, this study provides a foundational understanding of where and when these encounters are most likely to occur.
