New Research Sheds Light on Risks of Interstellar Objects Hitting Earth

Three interstellar objects (ISOs) have been identified as having visited our inner solar system, with the most recent being the comet 3I/ATLAS. Following its predecessors, Oumuamua in 2017 and 2I/Borisov in 2019, 3I/ATLAS is currently making its closest approach to the Sun. Research has begun to explore the potential risks these objects pose to Earth, particularly the impact threat from ISOs.

The solar system, which has existed for approximately 4.6 billion years, has experienced numerous ISO encounters throughout its history. While many may have collided with Earth in the past, it remains unclear how many ISOs are currently on a collision course with our planet. Recent studies suggest that ISOs could still pose a significant impact risk today.

In a paper titled “The Distribution of Earth-Impacting Interstellar Objects,” lead author Darryl Seligman, an assistant professor in the Physics and Astronomy Department at Michigan State University, and his colleagues aim to understand the potential impact risks posed by ISOs. Their findings are available on arxiv.org. The research focuses on the expected orbital elements, radiants, and velocities of ISOs that could impact Earth.

While the study does not provide a definitive number of ISOs, it examines their expected distribution based on simulations. The authors primarily focus on ISOs ejected from M-stars, also known as red dwarfs, which are the most prevalent star type in the Milky Way. The researchers acknowledge that their choice of focusing on M-star kinematics is somewhat arbitrary due to the uncertainty surrounding the motion of ISOs.

Through their simulations, the research team generated a synthetic population of approximately 10 billion ISOs to estimate around 10,000 potential Earth-impacting objects. The results indicate that ISOs are twice as likely to approach from two specific directions: the solar apex and the galactic plane.

The solar apex refers to the direction in which the Sun is moving relative to other stars, while the galactic plane is the flat region of the Milky Way that contains most stars. ISOs are more likely to be drawn from these areas, as the solar system’s motion increases the likelihood of encounters, much like driving through rain while moving forward.

The study reveals that ISOs originating from both the solar apex and the galactic plane tend to impact Earth at higher velocities. Interestingly, the subset of ISOs that could actually collide with Earth tends to have lower velocities. This is attributed to these ISOs being low-eccentricity hyperbolic bodies. The Sun’s gravitational influence can capture these slower-moving objects, potentially directing them into Earth-crossing paths.

Seasons also play a role in the impact risk, as higher-velocity ISOs are more likely to arrive in spring when Earth is moving toward the solar apex. Conversely, winter months present a higher frequency of potential impactors due to Earth’s orientation towards the solar antapex.

Geographically, low latitudes near the equator face the greatest risk of ISO impacts, with a slightly elevated risk observed in the northern hemisphere, home to nearly 90% of the global population.

While the research focuses specifically on ISOs ejected from M-dwarf systems, the authors believe that their findings could extend to other kinematic distributions. They emphasize that their study does not predict the number of ISOs in the solar system due to the lack of available data.

The implications of this research are significant for future observations. The findings will inform astronomers at the Vera Rubin Observatory and its Legacy Survey of Space and Time as they work to better understand the distribution and potential risks of ISOs. As the scientific community continues to explore these celestial objects, this research provides a foundation for identifying potential impact events and enhancing our understanding of the risks posed by interstellar visitors.

With the arrival of new observational capabilities, astronomers are poised to gather data that could either validate or challenge these initial findings. As our awareness of ISOs grows, understanding their trajectories and impact probabilities becomes paramount for planetary safety.