An astronomer has predicted that our Sun may have many more close encounters with other stars than we thought, which may have major implications for life on Earth.
Coryn Bailer-Jones from the Max Planck Institute for Astronomy in Germany used data from ESA’s Gaia satellite to monitor the motion of more than 300,000 stars. From this, he then modelled how a total number of 1 billion stars in our galaxy might move over time. The findings are published in the journal Astronomy and Astrophysics.
He found that our Sun experiences “close” encounters with between 490 and 600 stars every million years. Close here is defined as 16.3 light-years (5 parsecs). For much closer and potentially damaging encounters, 6.5 light-years (2 parsecs), he predicts about 87 every million years, almost double previous estimates.
(While other stars like Proxima Centauri are within this range, it should be noted they are considerably lower in mass than other stars predicted to encounter our Sun.)
The danger is that a passing star could perturb the Oort cloud, a region of comets thought to extend up to a light-year from our Sun. If the star is massive enough, or comes close enough, it could send comets our way, potentially causing extinction-level events.
“What’s interesting is that because the rate of encounters is quite high, there’s probably a lot of comets being thrown into the Solar System all the time,” Bailer-Jones told IFLScience.
“Away from the Oort Cloud, what if some massive star near the end of its life came nearby and went supernova? That could have happened in the past, we have evidence for close supernovas leaving deposits on Earth.”
Don’t be too alarmed just yet, though, because there isn’t any evidence for impending encounters that might end life on Earth. Indeed, Bailer-Jones says that the risk of impacts from near-Earth objects (NEOs) like asteroids remains much higher.
But in about 1.3 million years, a dwarf star called Gliese 710 is expected to come quite close to Earth. Previous estimates suggest it will pass only about 1 light-year away. Gaia data, however, suggests this will be much closer, perhaps only about a quarter of a light-year away, or 16,000 times the Earth-Sun distance. This is well within the predicted region of the Oort cloud.
(Bailer-Jones notes this updated figure was first spotted in the Gaia data by a group of Polish astronomers last year. His study confirms the finding.)
Whether close encounters with other stars actually has an effect on our Solar System isn’t clear. Some theories suggest that passing stars could have been responsible for extinction events on Earth, such as comet impacts or supernovas. We don’t have any direct evidence for this yet.
It’s interesting to note, though, that the estimate of about 87 close encounters every million years stretches into the past, as well as the future. It’s probable, therefore, that we’ve had plenty of ancient visitors.