Closer Look at the Triggers of Cosmic Disaster
Max Planck Institute for Astronomy | 2017 Aug 31
[img3="Image of the Comet C/2012 S1 (ISON), taken with the TRAPPIST–South national telescope at ESO's La Silla Observatory on the morning of Friday 15 November 2013, whose likely origin is the Oort cloud. This comet is definitely not colliding with Earth, but it shows the typical appearance of comets entering the inner solar system, including the typical tail made of gas and dust. Credit: TRAPPIST/E. Jehin/ESO"]http://www.mpia.de/4370061/zoom-1503582804.jpg[/img3][hr][/hr]As stars pass close by our solar system, they can nudge comets from the distant Oort cloud into the inner regions around the Sun. Thus, stellar encounters are an important factor in determining the risk of large cosmic impacts on Earth. Now, Coryn Bailer-Jones from the Max Planck Institute for Astronomy has used data from the ESA satellite Gaia to give the first systematic estimate of the rate of such close stellar encounters. Every million years, up to two dozen stars pass within a few light-years of the Sun, making for a near-constant state of perturbation.
Comets colliding with Earth are among the more violent and extensive cosmic catastrophes that can befall our home planet. The best known such impact is the one which, 66 million years ago, caused or at least hastened the demise of the dinosaurs (although it is not known whether the blame in this case falls on a comet or an asteroid).
It must be said that, to the best of current knowledge, impacts with regional or even global consequences are exceedingly rare, and occur at a rate of no more than one per million years. Also, monitoring systems give us a fairly complete inventory of larger asteroids and comets, none of which is currently on a collision course with Earth.
Still, the consequences are serious enough that studies of the causes of comet impacts are not purely academic. The prime culprits are stellar encounters: stars passing through our Sun's cosmic neighborhood. The outskirts of our solar system are believed to host a reservoir of cold and icy objects – potential comets – known as the Oort cloud. The gravitational influence of passing stars can nudge these comets inwards, and some will begin a journey all the way to the inner solar system, possibly on a collision course with Earth. That is why knowledge of these stellar encounters and their properties has a direct impact on risk assessment for comet impacts. ...
Close Encounters of the Stellar Kind
ESA | Science & Technology | Gaia | 2017 Aug 31
The movements of more than 300 000 stars surveyed by ESA's Gaia satellite reveal that rare close encounters with our Sun might disturb the cloud of comets at the far reaches of our Solar System, sending some towards Earth in the distant future.
As the Solar System moves through the Galaxy, and as other stars move on their own paths, close encounters are inevitable – though 'close' still means many trillions of kilometres.
A star, depending on its mass and speed, would need to get within about 60 trillion kilometres before it starts to have an effect on the Solar System's distant reservoir of comets, the Oort Cloud, which is thought to extend out to 15 trillion kilometres from the Sun, 100 000 times the Sun–Earth distance.
For comparison, the outermost planet Neptune orbits at an average distance of about 4.5 billion kilometres, or 30 Sun–Earth distances.
The gravitational influence of stars that pass near the Oort Cloud could perturb the paths of comets residing there, jolting them onto orbits that bring them in to the inner Solar System.
While this is thought to be responsible for some of the comets that appear in our skies every hundred to thousand years, it also has the potential to put comets on a collision course with Earth or other planets. ...
The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release - C.A.L. Bailer-Jones
- arXiv.org > astro-ph > arXiv:1708.08595 > 29 Aug 2017