Solar system dynamics over (too much) time

Some youtube or other flags this May study by Kaib and Raymond. This looks at the net dynamical effect of field stars on our planets' orbits. I think that this is the wrong study, but it may lead to the right study.

To start with the positive, dynamical studies be hard, yo. More math is better math.

"Net" means over the next five Gigayears; that's the classical life expectancy of our Sun. In particular is suspected a 0.25 mass star running within 55 AU, around 1.3 Gy from now. Sure, that would be Bad. But. Terrans should be looking only as far as ~250My from now, when our continents recombine under a more luminous (if less massive) sun. That is when we become an enormous desert, the Afar writ large. That is when (warmer!) Mars starts looking good. Especially when Jupiter vonZeipels it back to circular.

Which means: the study we need first isn't some somewhat-literally nebulous net effect of the stars we could run into. We need a study of the stars we probably will run into. We must start with K class Gliese 710 through 10kAU. The paper to its credit knows this, repeatedly citing Brown-Rein 2022 on Neptune.

Flybys tend to transfer orbital momentum off-system, pulling most planets away from our Sun. Of the planets, the Kaib-Raymond study rates Mercury's effect worst. (A higher Von Zeipel inclination-eccentricity may crash it into Venus, pushing superVenus into an Earth-annoying orbit.) If Mercury is, more-mercifully, yeeted away; the rest of us inyalowda might end up closer to our Sun; which none of us want, save Mars. Inner planets should fret further the movement of major asteroids into a Kirkwood Gap. Or the increased eccentricity of all these bodies... including Mars. THEIA II LET'S GOOO

If naught else we must ask what this flyby do to our Oort. In 2010 was found a 140 km monster, C/2014 UN271. This is now 16 AU. At 1/256 Earth irradiance it is expelling carbon-monoxide, an ice which (apparently) sublimes away at this temperature. It won't cross us. But what happens when hundreds of these things get dislodged?

Best case scenario, longer-term: the GJ 710 flyby raises Earth's semimajor to lower eccentricity. Earth gets colder, and still gets its supercontinent; but it emerges from the other end with the irradiance we get now.