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View Full Version : A Question Of Increased Earth Insolation.



BigDon
2018-May-18, 07:22 PM
Talking with acquaintances at the local brew house and was surprised to find out just how many nominally well educated people have no clue as to the lunar day and night cycle. Most thinking it was similar to Earth's, instead of two weeks on, two weeks off.

Then one of them supposed out loud about how weird would it be for us to have the same day/night cycle as the Moon. Well, if it was just a light issue, most plants would adapt well. Paleontologists studying the extreme southern environment during the Cretaceous replicated the year around light conditions in a blacked out greenhouse and almost all conifers and the southern hemisphere analogs to conifers all adapted immediately, as long as you started with a light cycle. Seems their food storage capacity is much more robust than suspected. They even went as far as making an artificial cycle and found out four months of continuous light to mature trees would offset eight months of continuous darkness.

But sunlight does more than feed trees, doesn't it? In response to us adopting a lunar day/night cycle I did my best Forrest Gump reply. "And that's a bad thang..." (Spoken slower and more drawn out than a Mr. Macay's "That's bad, m'kay?")

One, what do the sims usually say happens when you lengthen the day so radically? I'm only guessing, but my guess says "worst case scenario" And real soon too.

Two, roughly about how many years until you achieve a 95% total bio extinction rate? I'm sure those pesky deep sea, deep seabed bacteria could linger for decades, if not centuries, before they're baked into a ceramic glaze.

eburacum45
2018-May-20, 03:00 PM
The conditions in the Arctic/Antarctic Cretaceous are not really analogous to the conditions on an Earth with a very long day-night cycle. For a start the Sun is at a very low angle at the poles, even when it is above the horizon for weeks on end; on an Earth with a Lunar day-length, the Sun would be directly above the ground for hundreds of hours on end, and the ground could be baked dry. Similarly the night would get very cold. Bodies of water distributed evenly around the planet could regulate the diurnal temperature range significantly, but there would be a layer of ice on the top of lakes and seas that would need to melt every morning.

I suspect that life could adapt to this, and possibly even thrive- but it would be nothing like Earth life.

Ken G
2018-May-22, 03:37 PM
That raises an interesting question-- if the Earth were tidally locked to the Sun, so always was in day or night depending on where you were, what would be the temperature variation? It would be far less than on the Moon because the Earth's atmosphere would help a lot to share the heat. In fact you can get some clue to the importance of global heat sharing by looking at overnight temperature curves, which show a significant tendency to saturate even over just 8 or 10 hours. Extrapolating the saturation trend, it looks like the asymptotic drop might be something like 30 degrees Fahrenheit at most. So my initial guess would be that the day/night variation wouldn't be much more than that, and the noon/midnight variation might be 50 degrees F or some such thing. That would likely freeze water on the dark side, but my guess is that life would go on without too much extinction in the regions near the terminator.

StupendousMan
2018-May-22, 09:37 PM
I have a strong feeling that if the Earth were to be tidally locked to the Sun, the atmosphere would not rotate (much) west-to-east as it does now, and so its ability to transfer heat would be very much smaller. Koll and Abbot (2016)

http://adsabs.harvard.edu/abs/2016ApJ...825...99K

seem to provide some evidence in this direction.

Ken G
2018-May-22, 11:01 PM
That's a good point, the coriolis force is quite helpful in stirring the heat exchange, and that would be almost completely lacking. So there would probably only be a narrow region right around the terminator where the temperatures were livable, and it might be very difficult to keep that region from losing its water. Fodder for science fiction, no doubt.

eburacum45
2018-May-23, 09:30 PM
As I've mentioned before on this forum, a tidally-locked planet does rotate - once a year. And in a red dwarf system the years can be very short in the 'habitable' zone- a few Earth days, or even less. So west-east rotation would still occur, and smear heat around the planet.

Ken G
2018-May-24, 10:33 AM
As I've mentioned before on this forum, a tidally-locked planet does rotate - once a year. And in a red dwarf system the years can be very short in the 'habitable' zone- a few Earth days, or even less. So west-east rotation would still occur, and smear heat around the planet.

Of course it rotates once a year, since we're talking about the Earth, but once a year wouldn't be enough to do much. It would be 1/365 the coriolis effect we have now, I doubt that could be very effective at setting up jet streams and so forth. But yes, for habitability of very different planets than Earth, it's important to bear in mind.