by Ann » Fri Nov 10, 2023 5:06 am
johnnydeep wrote: βThu Nov 09, 2023 7:11 pm
Chris Peterson wrote: βThu Nov 09, 2023 5:33 pm
johnnydeep wrote: βThu Nov 09, 2023 4:25 pm
Ok, thanks for weighing in. I knew you would.
![:) :ssmile:](./images/smilies/smile.gif)
And I stand corrected. But is there really enough of a gravitational effect from a star passing within 1 ly of the Sun to be able to - however minutely - perturb its planets' orbits? Let's see now: if the force of the Sun's gravity on Saturn is F at Saturn's distance of 10 AU, and a Sun-like star approaches within 1 ly (63000 AU), that would be 6300 times as far, and so its gravitational force would be 6300*6300 less. That's 40 million times smaller! But I guess even that tiny amount could perturb things significantly over a hundred million years?
The time scale is likely only a few thousand years for a passing star. But the issue isn't simple gravitational force, it's tidal forces. Differentials. You pull on Jupiter just a little differently than you pull on Saturn, you make tiny changes to the semimajor axes or eccentricities of each, and over millions of years those two tweak each other a little differently, with changes that cascade through the whole planetary system.
Ah. Yet, the planets of our Solar System have been stable enough over a few billion years to still allow life to arise and flourish on Earth, though the hapless dinosaurs might feel a bit differently.
But will we be significantly less likely to survive during a merger with Andromeda than without? Apparently, Gleise 710 has a 95% chance of approaching within 17000 AU of the Sun in 15 My. Thanks to Mischa Schirmer above for the link to the Wikipedia article about planetary system
instability, and which referenced this study:
https://arxiv.org/abs/1805.07581 wrote:New stellar encounters discovered in the second Gaia data release
C.A.L. Bailer-Jones, J. Rybizki, R. Andrae, M. Fouesneau (Max Planck Institute for Astronomy, Heidelberg)
Passing stars may play an important role in the evolution of our solar system. We search for close stellar encounters to the Sun among all 7.2 million stars in Gaia-DR2 that have six-dimensional phase space data. We characterize encounters by integrating their orbits through a Galactic potential and propagating the correlated uncertainties via a Monte Carlo resampling.
After filtering to remove spurious data, we find 694 stars that have median (over uncertainties) closest encounter distances within 5 pc, all occurring within 15 Myr from now. 26 of these have at least a 50% chance of coming closer than 1 pc (and 7 within 0.5 pc), all but one of which are newly discovered here. We further confirm some and refute several other previously-identified encounters, confirming suspicions about their data. The closest encounter in the sample is Gl 710, which has a 95% probability of coming closer than 0.08 pc (17 000 AU). Taking mass estimates from Gaia astrometry and multiband photometry for essentially all encounters, we find that Gl 710 also has the largest impulse on the Oort cloud.
Stars passing close to us are worrying, there's no question about that.
But what happens during a galactic collision? When two massive galaxies collide? The galaxies, particularly the least massive one, are torn apart and ripped open because of the
terrible tidal forces ripping through the entire galaxies. No part of any of the galaxies, particularly the least massive ones, are spared.
Take a look at the simulation in the video below. It's a simulation of what will happen when the Milky Way and Andromeda collide and merge. Do you really think that
any solar system in the Milky Way will be spared and stay undisturbed and orderly during such a collision?
Click to play embedded YouTube video.
Bear in mind that the Milky Way is believed to collide with the Large Magellanic Cloud before we ram Andromeda, and the Magellanic train wreck is going to be very significant, too. Can we really be sure that the the Earth's orbit around the Sun is going to stay unaffected when the LMC crashes into us?
Ann
[quote=johnnydeep post_id=334967 time=1699557066 user_id=132061]
[quote="Chris Peterson" post_id=334963 time=1699551217 user_id=117706]
[quote=johnnydeep post_id=334961 time=1699547157 user_id=132061]
Ok, thanks for weighing in. I knew you would. :ssmile: And I stand corrected. But is there really enough of a gravitational effect from a star passing within 1 ly of the Sun to be able to - however minutely - perturb its planets' orbits? Let's see now: if the force of the Sun's gravity on Saturn is F at Saturn's distance of 10 AU, and a Sun-like star approaches within 1 ly (63000 AU), that would be 6300 times as far, and so its gravitational force would be 6300*6300 less. That's 40 million times smaller! But I guess even that tiny amount could perturb things significantly over a hundred million years?
[/quote]
The time scale is likely only a few thousand years for a passing star. But the issue isn't simple gravitational force, it's tidal forces. Differentials. You pull on Jupiter just a little differently than you pull on Saturn, you make tiny changes to the semimajor axes or eccentricities of each, and over millions of years those two tweak each other a little differently, with changes that cascade through the whole planetary system.
[/quote]
Ah. Yet, the planets of our Solar System have been stable enough over a few billion years to still allow life to arise and flourish on Earth, though the hapless dinosaurs might feel a bit differently. :ssmile:
But will we be significantly less likely to survive during a merger with Andromeda than without? Apparently, Gleise 710 has a 95% chance of approaching within 17000 AU of the Sun in 15 My. Thanks to Mischa Schirmer above for the link to the Wikipedia article about planetary system [url=https://en.wikipedia.org/wiki/Stability_of_the_Solar_System]instability[/url], and which referenced this study:
[quote=https://arxiv.org/abs/1805.07581]New stellar encounters discovered in the second Gaia data release
[size=150]C.A.L. Bailer-Jones, J. Rybizki, R. Andrae, M. Fouesneau (Max Planck Institute for Astronomy, Heidelberg)[/size]
Passing stars may play an important role in the evolution of our solar system. We search for close stellar encounters to the Sun among all 7.2 million stars in Gaia-DR2 that have six-dimensional phase space data. We characterize encounters by integrating their orbits through a Galactic potential and propagating the correlated uncertainties via a Monte Carlo resampling. [color=#0040FF]After filtering to remove spurious data, we find 694 stars that have median (over uncertainties) closest encounter distances within 5 pc, all occurring within 15 Myr from now. 26 of these have at least a 50% chance of coming closer than 1 pc (and 7 within 0.5 pc), all but one of which are newly discovered here. We further confirm some and refute several other previously-identified encounters, confirming suspicions about their data. [i][b]The closest encounter in the sample is Gl 710, which has a 95% probability of coming closer than 0.08 pc (17 000 AU)[/b][/i].[/color] Taking mass estimates from Gaia astrometry and multiband photometry for essentially all encounters, we find that Gl 710 also has the largest impulse on the Oort cloud. [/quote]
[/quote]
Stars passing close to us are worrying, there's no question about that.
But what happens during a galactic collision? When two massive galaxies collide? The galaxies, particularly the least massive one, are torn apart and ripped open because of the [i][b]terrible[/b][/i] tidal forces ripping through the entire galaxies. No part of any of the galaxies, particularly the least massive ones, are spared.
Take a look at the simulation in the video below. It's a simulation of what will happen when the Milky Way and Andromeda collide and merge. Do you really think that [b][i]any[/i][/b] solar system in the Milky Way will be spared and stay undisturbed and orderly during such a collision?
[youtube]https://www.youtube.com/watch?v=4disyKG7XtU[/youtube]
Bear in mind that the Milky Way is believed to collide with the Large Magellanic Cloud before we ram Andromeda, and the Magellanic train wreck is going to be very significant, too. Can we really be sure that the the Earth's orbit around the Sun is going to stay unaffected when the LMC crashes into us?
Ann