The scenario described is almost certainly the end of human civilization and the majority of life on earth. Assuming I’ve done the math right, an aphelion of ~5

The scenario described is almost certainly the end of human civilization and the majority of life on earth. Assuming I’ve done the math right, an aphelion of ~5 AU and perihelion of ~0.9 AU gives a highly eccentric (e = 0.69) orbit taking 5 years. I’m just guessing here, but I imagine each orbit would start with 6-8 months of relatively normal temperatures as we made or closest pass by the sun, a year or so worth of dropping temperatures, 2.5 years of deep, deep freeze, and a year of slow warming as we approach the sun again. Each orbit is probably going is probably going to see the planet spending at least 3 years competely outside the habitable zone. I’d expect virtually all life as we know it on the surface to die in the first orbit. With enough warning we might be able to dig some deep facilities that could harness geothermal energy to generate power and avoid freezing. They might be able to use hydroponics or something to sustain themselves for a long time, but to what end?