A world in perpetual twilight?

May 23, 2011 10:20 AM

If an exoplanet had a light side and a dark side (like Earth's moon, slowly spinning in orbit to keep one face towards earth), might life evolve around the penumbra?

Assume it's too hot on the sun-facing side to support life and too cold on the permanent-night side. Can MeFi's planetary scientists suggest ways in which liquid water and life might evolve in the longitudinal band of twilight that crosses the equator and both poles?

Acknowledgments to the best answers in my as-yet-unwritten scifi novel :)

posted by rdc to Science & Nature (14 answers total)

The phrase you are looking for is "tidally locked" and I think I saw an episode of Nova or maybe The Universe (on the History Channel) that was about hypothetical life on other planets that had a segment about life in the twilight area of such a planet...I look around to see if it's online.
posted by Green Eyed Monster at 10:28 AM on May 23, 2011

Best answer: Related previously
You might want to include 'Tidally Locked' in your search terms.
posted by vacapinta at 10:29 AM on May 23, 2011

Best answer: It was National Geographic.
posted by Green Eyed Monster at 10:30 AM on May 23, 2011

Best answer: The idea has been considered before, it's not entirely far fetched.

Here is a short blog post about a scientific poster on the subject.

I've always wondered how windy it would be...
posted by rocketpup at 10:30 AM on May 23, 2011

Response by poster: Not even ten minutes. I am in awe, Mefolks.
posted by rdc at 10:37 AM on May 23, 2011

I saw a thing on discovery channel or natgeo if the earth stopped spinning. I would think life could arise in this area since this special stated it would be the best area for life to head to if this happened.

It wil lall depend on if there was land there though .
posted by majortom1981 at 10:51 AM on May 23, 2011

A lot of it depends on how cold the dark side ends up being. If it's cold enough, eventually the whole atmosphere precipitates out there as ice, and then any life that may have existed will die.
posted by Chocolate Pickle at 11:11 AM on May 23, 2011

There would be some monster wind storms and not the kind that you would want to be above ground to experience.
posted by JJ86 at 12:49 PM on May 23, 2011

Just to note, the moon doesn't have a permanently dark (or light) side. It has one side pretty much permanently pointed at the earth. All parts of it get sunlight.
posted by iotic at 1:42 PM on May 23, 2011 [3 favorites]

It might be possible for life to evolve specifically for that biome, but it wouldn't be like what we are familiar with. Earth is a global system, and the atmosphere, water cycle, magnetic field and a hundred other things would change everywhere- the small band of twilight would be as drastically altered as the rest of the planet.

Our oxygen-nitrogen atmosphere and the carbon dioxide one that it replaced were both based on global processes. Similar complex systems probably won't appear in such a radically different scenario.

It's more likely that life fairly unfamiliar to us- hardier to radiation, incredibly tolerant to massive changes in heat, pressure, chemical composition of surrounding gasses- would evolve to eke out a living.
posted by spaltavian at 3:59 PM on May 23, 2011

I came here to say the same thing that iotic said. The moon does not actually have a light and dark side; it has a near side and a far side. When the moon is full, the near side is facing the sun. When the moon is new, the far side is facing the sun. I know that doesn't directly answer your question but, just, you know, for future reference.
posted by Lobster Garden at 4:35 PM on May 23, 2011

The line is called the "terminator." I swear I've read speculative short stories about life evolving on the terminator but I can't find anything now. Unfortunately "terminator" is a completely ungoogleable word, so it probably doesn't help you that much.
posted by miyabo at 6:47 PM on May 23, 2011

Another point to consider with tidally locked planets is that if they have a a highly elliptical orbit the planet's rotation is such that if the orbit were a perfect circle with a radius of the orbit's perihelion. In practice, this means that the day/night terminator varies slightly throughout the orbit. An example of this is Mercury.
posted by veedubya at 6:01 AM on May 24, 2011

Ach! Messed that up! I meant that the planet's rotation would be as if the orbit were a perfect circle with a radius of the orbit's perihelion.
posted by veedubya at 6:04 AM on May 24, 2011