# Can a planet with 2/3 Orbital eccentricity sustain life?

On a planet where it is Earth-like, the orbit around the sun is a bit longer than 1 Earth year, and the orbit is on 2/3 eccentricity, but where only the "2" part is inside the Goldilocks zone.

In winter everything freezes over, at about -200ºC surface temperature.

Could animal and plant life sustain this period by implementing something similar to existing hibernation/dormancy?

Could humans survive in the environment given stasis chambers?

This question is inspired by the first short story in The Eisenhorn Trilogy, I will look up the name later.

• In an eccentric orbit, a proportionally longer time is spent in the part farther from the sun. I'm not sure that your parameters fit actual orbital mechanics well. – Oldcat Feb 17 '15 at 17:24
• The problem with phrasing questions using 'could it' is that the term can mean a wide range of things. Do you mean 'could it' as in 'is it likely?' or 'is it at all theoretically possible given technology from 1000 years from now?'. – GrandmasterB Feb 17 '15 at 19:30

The eccentricity of an orbit is defined as $$e=\frac{r_a-r_p}{r_a+r_p}$$ where $$r_a$$ and $$r_p$$ are the distances to the farthest and closest points of the planet's orbit from the star. If $$e=2/3$$, then $$r_a=5r_p$$, which is quite significant. It seems that the planet will not remain in the habitable zone for its entire orbit.

However, it turns out that it doesn't have to. The flux on a planet's surface scales like $$F\propto a^{-2}(1-e^2)^{-1/2}$$ where $$a$$ is the semi-major axis, with $$a=(r_a+r_p)/2=3r_p$$. Given that $$e=2/3$$, the eccentricity factor is only $$(1-(2/3)^2)^{-1/2}=(5/9)^{-1/2}\approx1.34$$ which actually isn't that much. In other words, the mean flux is not substantially different from the flux incident on a planet orbiting at $$3r_p$$ with $$e=0$$.

In winter everything freezes over, at about -200ºC surface temperature.

The effective temperature at a distance $$r$$ from the star is proportional to $$r^{-1/2}$$. Therefore, at $$r=r_a=5r_p$$, $$T(r_a)\approx0.45T(r_p)$$. At $$r=a=3r_p$$, $$T(a)\approx0.58T(r_p)$$. In other words, ignoring things like thermal inertia and atmospheric currents, the temperature at aphelion should not be substantially different from the temperature of the planet in the habitable zone. So even if we ignore thermal inertia, such dramatic temperature swings seem a little unlikely.

Could animal and plan life sustain this period by implementing something similar to existing hibernation/dormancy?

We did see that at the closest approach, temperatures will be significantly higher than at the habitable zone, and as planets move quicker when they're closer to the star, it seems likely that there will indeed be hibernation of some sort - just when it's hot. They'll need to either hibernate for much of a year or else just adapt to the conditions. But the environment there is pretty hostile to life. For the other half of the orbit, though, things seem more conducive to life.

if during that 1/3 of the year it is freezing and the whole planet gets down to -200C then there isn't enough time to warm it up well. Though I suspect that the whole planet wouldn't be able to plunge to those temperatures in the allotted time either.

Bacteria and many plants could easily handle something like that, but the life forms would take a much longer time to evolve, since 1/3 of the time they are basically in stasis, the whole planet, not just part of one hemisphere.

If humans have the tech to have stasis chambers they would likely have the tech needed to survive straight through the 'winter'. Scientists on Antarctica winter over down there and they frequently get temps below -100F before you count the windchill. It would be a strange planet with most animal life living in the deep oceans and lakes where they generally won't freeze out. Maybe smaller animals could make deeper underground burrows to hibernate in, with larges numbers to keep the temperature warm enough not to kill.

Humans can survive deep underground where is bit warmer, but they will need to have a way to get energy. Lots of solar/wind/nuclear to power underground aquaculture to produce all food.

Any materials will be hard to manufacture for such extreme conditions.

It still would be easier than in space/asteroids (you can dig for more material resources) but not by much. Better move along to find a star system with more habitable planets.

Unlikely any native life can develop in such extreme conditions. So any life would be transplanted from outside.

I got through an awful long calculation here to demonstrate how an eccentric orbit would change the temperature on an planet. The result was basically, that it would only affect the surface and a few meters down into the earth. That means, that any animal could simply dig itself down to a warm spot and thereby survive the winter. Plants could all die at fall and regrow from the seed in spring. I think, it would be surprisingly easy to survive this. However, there are two conditions:

1. The summers must be hot enough.

2. The planet must get enough heat, that it can stay warm below the surface.

I don't think there's much question that life of some sort could thrive under those conditions. Looking at our own peaceful planet, for example, I don't think the chemosynthetic organisms around deep-sea vents would even NOTICE if the upper ocean periodically froze down to a kilometer or two. (Indeed, the Snowball Earth Hypothesis supposes that the entire planet glaciated without killing off existing unicellular life, although that's a different matter from having life evolve in a climate with deep cycles.)

Humans? Well, if they managed an interstellar trip through the vacuum of deep space, I'm thinking a long, cold winter would pose a fairly minor technological challenge.