The discovery of the Interstellar Objects (ISOs) known as Oumuamua in 2017 and Comet Borisov in 2019 sparked widespread curiosity among scientists and the public alike. These enigmatic visitors left many questions in their wake: What are their origins? Where did they come from? Despite their fleeting presence and our limited ability to study them closely, they revealed an intriguing fact: objects from the Milky Way are traversing our galaxy.

While the specific origins of these ISOs remain unclear, it stands to reason that there are countless others out there. How many more extraterrestrial entities from neighboring star systems might be making a visit to our Solar System?

The Alpha Centauri star system, our closest stellar neighbor, comprises three stars: Alpha Centauri A, Alpha Centauri B—two stars in a binary orbit—and Proxima Centauri, a faint red dwarf. This entire system is on a trajectory toward us, presenting a prime opportunity to investigate how material transfers between star systems occurs.

Recently, a study set to appear in the Planetary Science Journal delves into the potential material transfer from Alpha Centauri to our Solar System, investigating how much of it could have already arrived. Titled “A Case Study of Interstellar Material Delivery: Alpha Centauri,” this research is conducted by Cole Greg and Paul Wiegert from the Department of Physics and Astronomy and the Institute for Earth and Space Exploration at the University of Western Ontario in Canada.

The authors assert, “Interstellar material has been detected in our Solar System, yet we lack details regarding its origins and methods of transportation. Here, we showcase Alpha Centauri as a case study for the delivery of interstellar material to our Solar System.” Alpha Centauri is believed to host planets and is hurtling towards us at a speed of 22 km/s, equating to approximately 79,000 km per hour. In roughly 28,000 years, it will achieve its closest proximity, coming within about 200,000 astronomical units (AU) from the Sun. Greg and Wiegert contend that ejected material from Alpha Centauri can indeed reach us, with some already in our vicinity.

As a mature star system estimated to be around five billion years old, Alpha Centauri likely has planets but is expected to expel less material compared to younger systems. Nevertheless, the presence of multiple stars and planets suggests a significant potential for material ejection. “While mature star systems tend to expel less material than their younger, planet-forming counterparts, the gravitational interactions involving multiple stars and planets raise the likelihood of scattering fragments from any residual planetesimal reservoirs—similar to what we see as asteroids or comets being ejected from our own Solar System,” the researchers noted.

We clearly understand that significant objects like Borisov and Oumuamua can reach our Solar System, and interstellar dust is also capable of traversing this vast distance. The Cassini probe identified some of this dust, as research from 2003 highlights. Existing ejection models for star systems largely stem from observations of how our own Solar System ejects material; Greg and Wiegert built upon these models in their recent study.

The findings indicate a significant potential for material from Alpha Centauri to exist within our Solar System. The researchers estimate “the number of Alpha Centauri particles larger than 100 m in diameter residing within our Oort Cloud is around 1 million.” However, locating these particles is a challenge, as most likely dwell in the distant reaches of the Oort Cloud. The duo emphasized that “the observable fraction of such objects remains limited,” with a mere one-in-a-million chance of one being found within 10 AU of the Sun.

The researchers employed simulations to estimate the volume of material that could arrive from Alpha Centauri. Their model spanned an impressive 110 million years, from t = -100 million years to t = +10 million years. Throughout this period, Alpha Centauri expelled approximately 1,090,000 particles. These particles were released in various directions and velocities, and only a small fraction came close to the Sun. “Only a minuscule percentage of the AC ejecta approached the close approach (CA) distance to the Sun. Specifically, 350 particles had a CA with the Solar System, representing about 0.03% of the total ejected,” they stated.

The results point to actionable pathways through which particles from Alpha Centauri could encroach upon our Solar System. How large can these particles grow?

The researchers indicate that smaller particles, which would manifest as meteors upon entering Earth’s atmosphere, face considerable challenges en route. They confront numerous forces, including magnetic fields, resistance from the interstellar medium, and potential destruction via collisions or sputtering. “Small particles navigating the interstellar medium (ISM) encounter effects not accounted for here,” they acknowledge.

Through their analysis, they calculated the minimum size required for a particle to endure the journey. “We assessed the key parameters for each of the 350 close approaches, determining the minimum size necessary for a grain traversing that trajectory to withstand all three detrimental forces,” the authors wrote. They concluded that a grain measuring a median of 3.30 micrometers could survive the journey.