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If all other things were the same, how different would the earth be if it took 4 of our years (365*4 days) to travel around the sun?

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    $\begingroup$ This seems a little broad to me. Can you narrow it down to what exactly you are looking for? Societal impacts, military impacts, etc. $\endgroup$ – JDSweetBeat Apr 21 '15 at 14:33
  • $\begingroup$ It also occurs to me that the only difference would be when we celebrate New Years and how we measure the lifespan of people. Average lifespan would be 10-20 years in this scenario. A kid would be sexually mature in 2 1/2 years and other similar things. $\endgroup$ – JDSweetBeat Apr 21 '15 at 14:35
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    $\begingroup$ @DJMethaneMan There's considerably more to it than that. Orbital mechanics would require the Earth to be farther from the Sun to maintain the longer orbit. If the Earth slowed in its current orbit, it would decay into the Sun. Life may not ever exist on Earth as a result (either scenario). $\endgroup$ – Frostfyre Apr 21 '15 at 15:30
  • $\begingroup$ @Frostfyre I'm pretty sure the asker wants a planet with all the things adjusted too - so a brighter star to move the goldilock zone etc. $\endgroup$ – eimyr Apr 21 '15 at 15:46
  • $\begingroup$ @eimyr If the asker wants us to adjust not just the length of the sidereal year but also everything else to keep Earth's environment more or less unaffected except for the longer year and seasons, then that should be stated in the question. Since the question now has two answers based on Frostfyre's interpretation of it, such an edit would however now invalidate those answers, which is something we strive to avoid. $\endgroup$ – a CVn Apr 21 '15 at 16:37
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It's important to note that you can't just drop a planet in an orbit at an arbitrary distance from its sun, and expect things to just work. So, we will instead try to find the orbit that has an orbital period of four Earth years, and see what happens. If you don't care about the mathy and orbital-mechanicy stuff, then just scroll down for the TL;DR and answer.

Technically, you are looking to quadruple the sidereal orbital period of Earth, changing it from approximately 31,558,149 seconds to approximately 126,232,598 seconds (bear with me!), while leaving the masses of both the Sun and the Earth unchanged, and you are asking what effects such a change would have.

According to Kepler's Third Law, in the case of a small body orbiting a large central body (which is good enough for modelling the Earth in an orbit around the Sun), the orbital period can be calculated as $$ T = 2\pi{}\sqrt{\frac{a^3}{\mu{}}} $$ where $T$ is the orbital period in seconds (there we go), $a$ is the orbit's semi-major axis in km, and $\mu$ is the standard graviational parameter using the mass of the larger body which in our case works out to $1.32749351 \times 10^{11} \text{ km}^3 \text{ s}^{-2}$. Earth's orbit has a semi-major axis of 149,598,261 km (just about exactly 1 AU). In order to keep the calculations managable, I'm going to ignore the orbital eccentricity and just pretend that the Earth's orbit is perfectly circular; this simplification is unlikely to have any real effects on the outcome.

Plugging in the Earth's orbit around the Sun, we get $$ 31~558~149 = 2\pi{} \sqrt{\frac{149~598~261^3}{132~749~351~000}} = 2\pi{} \times 5~021~964 $$ which as we can see works out quite nicely (the error is less than 0.05%).

Now, we want to plug in the longer orbital period and solve for $a$, the semi-major axis of the orbit. In our case, the masses of both bodies remain the same so $\mu$ is unchanged. Hence, we know that $$ 126~232~598 = 2\pi{} \sqrt{\frac{a^3}{132~749~351~000}} $$

Solving for $a$:

$$ \begin{aligned} \frac{126~232~598}{2\pi} = 20~090~542 &= \sqrt{\frac{a^3}{132~749~351~000}} \\ 20~090~542^2 &= \left( \sqrt{\frac{a^3}{132~749~351~000}} \right)^2 \\ 4.036298779 \times 10^{14} &= \frac{a^3}{132~749~351~000} \\ 132~749~351~000 \times 4.036298779 \times 10^{14} &= a^3 \\ a = \sqrt[3]{a^3} &= \sqrt[3]{132~749~351~000 \times 4.036298779 \times 10^{14}} \\ a &\approx 376~997~587 \text{ km} \end{aligned} $$

Let's plug in this semi-major axis, and see what orbital period comes out.

$$ T = 2\pi \sqrt{\frac{376~997~587^3}{132~749~351~000}} \approx 126~232~596 $$

We wanted an orbital period of 126,232,598 seconds, and even with all this rounding everywhere, we got 126,232,596 seconds. I'd call that close enough.

Your planet's orbit has a semi-major axis of a shade under 377 million km, or 2.52 AU. For comparison, Mars has a semi-major axis of 1.524 AU, and most of the asteroid belt is concentrated around a distance of 2.2 to 3.2 AU from the sun.

In effect, you'd be placing Earth in the middle of the asteroid belt.

That's hardly "leaving all other things the same" and just giving the orbit a gentle nudge.

Since sunlight intensity obeys the inverse-square law and consequently drops with the square of the distance, you're looking at $\frac{1}{2.52^2}$ or less than 1/6 the amount of sunlight compared to Earth's current orbit.

Even if we handwave away the asteroid belt itself, it seems safe to say that life on Earth would not take kindly to such a scenario, and it's probably a safe bet that Earth would quickly freeze over from the much lower solar input received.

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For our sun, as stated previously, it wouldn't be an Earth-like planet. But I presume, you want an Earth-like planet, so let's give you a new sun that works. Note: this is obviously speculative, and I'm also going to hand-wave that we've got Earth-like systems and life.

TL;DR

You have a very tumultuous and changing (exciting) 'Earth' around another star, in both climate, weather, plant, and animal activity.

Climate

Temperatures - Seasons are now four times as long, so your temperatures will be more extreme. Very cold winters, and very hot summers. Long transitions between them.

Sea Level / Coasts - Your poles melt and freeze; If one of your poles accumulates significantly more ice, then that pole's summer, the sea level will rise significantly. The Antarctic has a lot more ice than the Arctic, so the southern summer will see sea level rises.

EDIT Rivers - Oh yeah, your rivers will likely freeze/go dry each year depending on size and location.

Oceans - You would have very dramatic global streams as very warm, shallow water surges towards the poles and cold, dense, deep waters return. This would make early seafaring much faster, but:

Storms - With incredible warming along the equator for half the year (each hemisphere's summer), bringing tremendous hurricanes. Also, in the extreme summers, very high equatorial pressure will push warm moist air into the low pressure zones in the north bringing more tumultuous weather.

Flora & Fauna

Assuming 'Earth-like'

Plants - Obviously adaptability to extreme temperatures will be stronger than what we see on our Earth; hardier trees and plants, longer germinating season for seeds. Your plants may evolve to have two types of growing seasons: a type of surface feature during the winters, and another during the summers - or maybe even four.

Animals - Most likely, this is highly nomadic for air, sea, and land dwellers (where possible), due to the extreme weather and lack of plants during the winter / abundance of plants during the certain seasons. Your lake & river dwellers will have to be ready for very hot or very cold (or both) temperatures. Because of extreme temperatures, your greatest variety of life will be those isolated (on islands or in lakes/rivers), where they have much different plants and climates.

There is a lot of activity going on here at Earthv2!

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Well since the orbital period is dependent on the distance from the sun, we would be orbiting outside of Mars (1.9 years) though a bit closer than Jupiter (11.9 years), I'll leave someone else to do the math for the exact distance.

but looking at this

enter image description here

the planet would be outside of our sun's goldilock's zone. So in our solar system it would likely be a frozen ball. So we would need a larger/hotter sun to push the zone out farther or we would be dealing with a completely different type of life.

Whether that is all underwater which could be the case of Europa, a body that heats the water under the ice crust to keep it liquid, or a completely different type of chemistry that doesn't need liquid water.

I would also expect that should the sun provide a similar living conditions to earth, with similar declination of the poles, that the poles would have much more severe extremes, with a lot more migration of animals into and out of the regions for the seasons. I would also expect a much larger number of animals to be hibernators of some kind, to at least sleep through the worst few months of the long winter.

the farther north or south you go I would expect more grassland/tundra since it would be harder for perennial plants to survive the long harsh winters.

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  • $\begingroup$ I did the math... you end up in the middle of the asteroid belt, which sounds plausible to me. It's cold out there, though. :-) $\endgroup$ – a CVn Apr 21 '15 at 16:16

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