Elliptical orbits

[Red Giant]

For a sci-fi story I'm working on I have life on a planet in a highly elliptical orbit. How would life have developed on such a planet.

[Siguy]

Useful diagram:

We start with Winter. At its furthest from the star (lets say for example - further than Mars is to the Sun) the moon is plunged into freezing temperatures. The oceans world wide freeze over and the moon becomes one big snowball. However just a few meters below the ice the ocean is still in a warm liquid state. The atmosphere thins as more and more moisture is frozen into the icy crust. If the moon was to endure these freezing temperatures for long then the ice would slowly thicken until almost all the ocean was frozen, but the moon is not to experience this cold for long as it swings back towards the sun and begins to warm up.

With Spring the temperature has begun to rise rapidly. The ice that once covered the moon is now just a collection of icebergs. Soon even these will be gone as the temperature continues to rise. Although its position is relative to Earth and the Sun at this moment, it is still moving closer to the parent star. The first substantial clouds and a rising humidity trap further heat in the moon’s atmosphere.

Summer arrives as the Planet and its moons reach their closest position to the star (let’s say closer than Venus is to the Sun). the temperature now is blisteringly hot. The ocean’s surface is evaporating at a rapid rate and with huge storms whipping up the seas, the definition between ocean and atmosphere becomes almost a blur. the height of Summer is short lived though as the planet slingshots round the star and heads back out into space.

Finally the temperatures begin to subside as Autumn sets in. All the water vapour boiled off the ocean’s surface cools down into immense clouds and a global rainy season showers the moon. Soon the rains will cease and poles begin to freeze. Then the advance of the ice progresses as the moon heads out further into the cold of space.

http://www.christianthrower.com/?p=15

[Red Giant]

This is really useful. Thank you for the image and the link.

[eburacum45]

One thing to note is that the maximum temperature will occur somewhere slightly after periastron. The planet will heat up as it approaches the closest point to the star, but will remain hot and continue to heat up, somewhat more slowly, as long as the planet is near the star. It will only reach its coolest point some time after apastron, as it will continue to cool down during the long, cold section of its orbit.

This effect is sometimes called thermal inertia, although I seem to recall that meteorologists don't like the term.

[tony873004]

The planet's speed is not constant. It will linger at apastron, and rush through periastron. If one hemisphere is experiencing winter during periastron, it will be more mild than the other hemisphere. The low sun angle will help take the edge off the close distance, and at apastron, the high sun angle will take some of the edge off the far distance.

[RalofTyr]

Winters should be the longs followed by shorter springs/fall and a real short summer.

[Red Giant]

Ok. I will keep that in mind.

[RalofTyr]

There's one problem with 16 Cygni B.

Given this article,

http://www.newscientist.com/article/dn9336

The size limit for a moon orbiting that world would be about 2/3rds the size of Mars. Now, like Europa, the moon can have water on it, however, given it's age, as stated here,

http://www.solstation.com/stars2/16cygni2.htm

of 9.5 billion years, any moon with water on it would have a large amount of their water evaporate over the eons.

Any moons orbiting that world would probably look like Mars, with little to no water.

Now, if the moon had an orbit in which tidal stress afflicts it, like Io, then the a moon might have a thicker atmosphere, as outgassed gasses.

The atmosphere might get really thick during summer time and thin out during winter, as the carbon dioxide turns into snow*.

It would get cold enough on that moon for CO2 to freeze right? (I don't really know)