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For this question lets take a trip to Slyo Dacas:

enter image description here

Slyo Dacas (sil-yo-dak-iss) is a world roughly the same size of Earth with a decent magnetic field and no moons.

The world is a bit drier than earth, its seas are shallower and smaller and its land more bit more arid on average.

The planet has plate tectonics, a day of 24 hours, and a year of 365 days.

The main difference though is its orbit: highly eccentric.

There are no seasons due to almost no axial tilt. However, since the orbit changes the climate so drastically for simplicity sake I will say it has seasons. Summer with the planet's orbit at closest approach to its star, and winter at it farthest reach.

Winter features the coolest temperatures where the poles are below freezing and the seas are at their greatest size and coolest temperatures. The planet looks a lot like the above picture.

Summer temperatures rise drastically. Most of the water evaporates into the atmosphere and massive cyclones rage across the planet drenching everything in hot rain.

enter image description here

A lot like this.

Now we know that erosive agents here on Earth help shape just about everything from mountains, coastlines, rivers, even individual rocks.

This planet has most of those processes as well, but in a more advanced pace and on a yearly schedule. The planet is also a bit drier. So taking these details into account my question is:

What can we expect from this terrain acted upon by rapid changes in climate?

Example: Would there be more sandy deserts, smoother canyons? No ocean cliffs? Please provide explanations.

Bonus questions:

How could plant and animal life adapt to survive the changes during the year?

Where would be the most likely/unlikely places to find that life?

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    $\begingroup$ I fear any celestial body that has a magnetic field so dense I can touch it. $\endgroup$ – Frostfyre Aug 24 '15 at 20:17
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    $\begingroup$ I love to see these questions. Something worries me though. When you say "highly eccentric" I think an eccentricity of e=0.5 or something outrageous like that but the planet you've described isn't anywhere near that eccentric. Can you clarify? $\endgroup$ – Green Aug 24 '15 at 22:28
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    $\begingroup$ Beautiful pictures, how do you draw them? $\endgroup$ – 2012rcampion Aug 24 '15 at 23:16
  • $\begingroup$ @Green: When I say highly eccentric I was referring mostly in comparison to most planets. In reality I have no idea what the eccentricity for this world should be for the effects listed above. I just know that most planets have orbits more circular than this one. $\endgroup$ – Josh Belmont Aug 25 '15 at 5:11
  • $\begingroup$ @2012rcampion: I create them in Photoshop. All of these are either already in the feature movie I'm writing, or could possibly make an appearance in following movies. Actually these are the most basic of the planetary drawings I do, most are featured in detailed "space scenes" along with an extended planet biography. $\endgroup$ – Josh Belmont Aug 25 '15 at 5:14
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The greatest change would be a much higher preponderance of "chaotic terrain" caused by flash floods.

Consider that the bulk of the planetary water will start forming snow as the orbit moves away from the sun, and by the time it reaches the farthest part of the orbit, there will be a deep, dense snowpack which has been frozen very hard due to the extreme cold.

As the planet approaches the sun in the "spring" part of the orbit, the deep, cold snowpacks will begin to thaw, but this won't be a gradual process; the deep cold of winter will make it take longer to thaw, while each day the insolation will become much greater as the planet approaches the Sun. The snowpacks will melt suddenly and catastrophically, releasing flash floods which will rapidly make their way to the lowest elevations (most of the water will rush into the low oceanic basins.

Huge wadi's, deep canyons and even "chaotic terrain" caused by major water features overflowing and breaching their barriers will be common. There will be huge accumulations of silt in the oceans and large deltas will be found at the ends of rivers. Geologists will delight in the amount of sedimentary rock, and over millions of years, we should expect to find large areas of sedimentary rocks like shale and sandstone being quite common.

The life on this planet will need to adapt to the hydrological cycle as well as the wildly fluctuating insolation, and we should see lots of interesting adaptations, ranging from deep roots to massive migrations, or even life cycles designed to take advantage of this (for example, a creature which might use migratory sea birds to take its eggs or spores inland for hatching and development, then riding to sea with the "spring" floods for the remainder of the life cycle).

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I'd say you'd have at least a couple things:

  1. Cracks - There would be a lot of cracks in this planet caused by a lot of freeze/thaw cycles. During the fall, there would be a lot of rain. The rain would fill up small cracks in rock/ground/anything. During the winter, the water would freeze and expand, enlarging cracks and generally breaking stuff up.
  2. Lots of Sand - When the rocks cracked, they would leave sand behind. During windstorms, this sand would be blown about sand-blasting everything, and making everything smoother. Think smoothed out rocks, plants, etc.
  3. Deep Canyons - There would be huge rainstorms and snowfalls on this planet. During the Summer, a lot of the water would evaporate into the air. When the air cools during Fall and Winter, the water will come out of the air in the form of precipitation. During the rain and when the snow melts, erosion would be cutting deeper and deeper canyons into the planet. These would be deeper than Earth's (assuming they're the same age) because rainfall and thawing would involve a lot more water (even though there's less of it than Earth).
  4. Short, Low, Well-built vegetation (I'm assuming you want vegetation) - As you said, the drastic differences between Winter and Summer would cause cyclones and windstorms around the planet. Any tall plants would have more surface exposed to the wind, which would probably uproot or otherwise destroy them.
  5. Animals would either hibernate, or live underground - Any animals outside during Fall or Spring would probably not survive the giant storms on this planet. Animals living underground would be able to eat the roots of plants and other animals living underground. Other animals would find a safe place to hibernate during dangerous transition periods.

Some other things to think about: The oceans would probably settle without the moon constantly mixing them. (see Tidal Forces)

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What can we expect from this terrain acted upon by rapid changes in climate?

I suspect that the terrain won't be much different from Earth, other than because of no moon to help keep the mantel and crust a little more active, mountains will likely be lower, balanced by a bit less water and no moon for less erosion leaving things surprisingly similar to earth features. Smaller and fewer lakes rivers and oceans etc.

How could plant and animal life adapt to survive the changes during the year?

Plants handle winter pretty easily now, many plants also go dormant in desert climes until the rains come then burst into life. Many will also live in what lakes and oceans exist while they exist. Some plants change quickly between a wet and dry environment, and these would be even better adapted to such, likely absorbing large amounts of water like cactus's. Now if the clouds actually obscure the sunlight during the summers, it will help keep the worst of the scorching away, but it will make it harder for photosynthesis. So plants will have to store food during the 'spring', to help survive the 'summer' and produce 'fruit' in the 'fall' before 'winter' comes back.

Where would be the most likely/unlikely places to find that life?

Anyplace that water will puddle as rivers lakes and oceans. Likely will stay much closer to the equator since that will have the longest 'unfrozen' seasons, since the poles are going to warm up the slowest because of the angle of the sunlight hitting it. A couple years of the poles not thawing out could quickly lead to a lot more of the available water being trapped in polar ice.

Land animals would likely be in foot hill type areas, near places that lakes will fill up but with enough upland to stay 'dry'.

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