Alpha Centauri is a triple star system that is one of the closest to our Solar System, only 4.3 light-years away.
In a paper accepted by the Planetary Science Journal, the possibility that material that has travelled to us from alpha Centauri by natural processes and could be currently within our Solar System is examined. An open-access version of the paper is available here at PSJ or here or Arxiv or here.
We show that, if the alpha Centauri system is ejecting material in a manner and at a rate similar to our own Solar System, there may be as many as 1 million asteroids from that system currently within the bounds of our Oort cloud, a distant boundary which represents the extreme outer limits of our planetary system. But most of these asteroids will be too far away to be seen telescopically, and there is only a very small (about 1 in a million) chance that one will venture close enough to the Sun to be picked up by our 'scopes. It is also possible that a few meteors from alpha Centauri appear in our own atmosphere every year, though they will be vastly outnumbered, by over a trillion to one, by meteors from our own Solar System, and will be difficult to pick out from that overwhelming background.
Video illustrations of our Sun and alpha Centauri within our Milky Way
If we could watch our Sun and alpha Centauri as they travelled along within our Galaxy for the last million years, what would their paths look like? These animations show us what we would see if we could watch them from a spaceship speeding along with them. Click on the illustration below to see an animation of the encounter circumstances on YouTube.
As part of this study, we have to assume that alpha Centauri is ejecting material out into the Galaxy. We have no way of measuring whether it is or not with current technology, but there are reasons to expect that it is. First and foremost, our own Solar System is ejecting material (mostly comets being gravitationally slingshotted out into the Galaxy by planets like Jupiter) and alpha Centauri is a mature system rather similar to our own in many respects.
This system is a good choice for this kind of case study for several reasons:
- It is the closest star to our Solar System, at 1.34 pc (about 4.3 light years, Akeson et al 2021). Its proximity increases the likelihood that material from this system can reach us.
- It is approaching our Solar System at 22 km/s (Evans 1967; Kervella et al. 2017; Wenger et al. 2000) and will pass within 200,000 astronomical units (about 1 parsec or 3.3 light years) of the Sun in 28,000 years. Thus we can expect that the amount of material delivered to us is increasing as the effective cross-section of the Solar System increases.
- This is a mature (5 billion years age (Akeson et al. 2021; Joyce & Chaboyer 2018; Thevenin et al. 2002)) triple star system that likely harbours planets. Though mature star systems likely eject less material than those in their planet-forming years, the presence of multiple stars and planets increases the likelihood of gravitational scattering of members from any remnant planetesimal reservoirs, much as asteroid or comets are currently being ejected from our Solar System.
- Two of the stars, alpha Cen A and B, are Sun-like stars. Their larger than typical stellar mass suggests that they likely formed from a more massive than typical protoplanetary disk, which might allow more mass to remain in unaccumulated form. In particular, the system might have developed an Oort cloud, which results from gravitational scattering of planetesimals from Neptune mass planets (Safronov 1972; Duncan et al. 1987; Tremaine 1993) which would provide a source of macroscopic bodies to eject via mechanisms much like those seen in our Solar System today.
If we see an asteroid or meteor, how can we tell if it is from alpha Centauri? In our study we showed that these objects would have particularly high speeds and only arrive from very specific directions, which should make identifying them much easier. Meteors from alpha Centauri would arrive primarily in the southern skies arriving from direction near or south of alpha Centauri's current position on the sky.
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Have a question or comment? Contact me (Paul Wiegert at pwiegert[the @ sign]uwo.ca)