Space and Physics
PUBLISHED
The closest star to the Sun is Proxima Centauri, about 4.2 light-years away. This has not always been the case, as all stars in the galaxies move about. Observations suggest that just 2.5 million years ago, there was a star that passed very close to the Solar System, and this passage might still have consequences we can see today.
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Data from the ESA Gaia observatory, which produced the most accurate map of the Milky Way, indicates the close passage of the star in question, HD 7977, at around 4,000-25,000 astronomical units (1 AU is the Earth-Sun distance) from the Sun. Now, a team proposes that by studying the orbits of new comets, HD 7977 passed by at 6,000-10,000 AU. That’s just 35 to 58 light-days away, which is very close in cosmic terms. It may have set off a new comet shower.
Long-period comets are those with orbits that stretch for millions of years, usually pristine and coming from somewhere in the Oort cloud. They are influenced by the Milky Way’s disk as a whole, but can get nudged into the inner Solar System by something passing by so close that its gravity alters their trajectory. These comets are known as new comets because they are entering the Solar System for the first time. Comets that have gone through the inner Solar System have shorter periods due to the interactions with the planets.
“The distribution of comet orbits suggests we are living through an unusual time where HD 7977 has dominated the generation of new comets and not the larger gravitational field of the Milky Way, as it usually would," Planetary Science Institute senior scientist Nathan Kaib said in a statement.
"This would also mean we’re living through the late stages of a pretty rare and powerful comet shower.”
There is a twist, though. The Kaib and collaborator Sean Raymond from the Université de Bordeaux decided to run simulations to see how the passage of this star would affect the comet population and what kind of distribution we should be seeing. While the observations match the idea of a stellar disturbance, the simulated comet orbits do not really look like the observed ones.
“Like many other works that simulate long-period comet production, we find that our comets’ orbit sizes aren’t a great match to the observed distribution. It’s possible we’re missing some important physics from our simulations, and it’s conceivable that this has caused us to misinterpret comet orbit data,” added Raymond.
The Solar System might be more complex than thought; the effect of comet jets could also play a more prominent role, accounting for the discrepancy here. Maybe it's multiple factors. While the puzzle remains to be solved, researchers know it will only take a little patience to get to an answer.
“The nice thing about our prediction is that it will be testable pretty soon," said Kaib.
"Gaia is still publishing new data on the motions of stars, and in 6-12 months, it should be able to improve our understanding of HD 7977’s motion and tell us if we are right or wrong."
The work was presented at the American Astronomical Society Division on Dynamical Astronomy.
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