Science Buddies: "Ask an Expert"

Hello,

I have a question that I can't really find a proper answer to with Google. I imagined a planet that is much like Earth in its proprieties, but the big difference is that its rotation period equals its orbit period - much like the Moon's. Only, it's a planet, as I said, so it orbits around a sun directly, unlike the Moon. My questions, basically, are two:

1) Is such a planet possible? I pretty much believe it is, but still want to make sure.
2) As there could be no "wall of night/day" where light would abruptly become absent, drowning the other half of the planet into immediate darkness, I assume there would be a zone, a sort of a line, something I came to call the "twilight zone". In the twilight zone, there would be a constant "not really a day, nor night, though" kind of state. So, what would be the temperature in this twilight zone? And what would the temperatures on the bright and dark side be, given that the planet's sun is much like ours and the planet is just as distant from it as the Earth is from our Sun?

I hope this isn't too much of a bother for you and also that you'll have fun thinking about it

Hi nagasadow,

That is a really interesting question, and it's great that you tried doing some of your own research before coming here for an answer. However, I do think there's some hope for finding more information on the internet - I tried googling "how hot would the earth be if one side always faced the sun" and a whole bunch of sites came up where people have asked the same question:

https://www.google.com/search?q=how+hot ... 8&oe=utf-8

It looked like the proper phrase for such a planet is "tidally locked" (e.g., the moon is tidally locked with the Earth, and in the situation you're describing, the Earth would be tidally locked with the sun). So, doing some more searching for "tidally locked planets" might help.

It looks like you should be able to get some estimates for what the "hot" and "cold" side temperatures of the Earth would be. The temperature in the "twilight zone" would be a little trickier. It's not like the Earth would be divided into three distinct zones with a dividing line in between them, and a constant temperature in each zone. The temperature would vary continuously, from the hottest part of the hot side to the coldest part of the cold side. It would probably experience the steepest drop in the "twilight zone" but that zone would not have a single constant temperature.

Hope that helps!

Ben

Adding a few thoughts to what bfinio wrote. Assuming a similar atmosphere as earth one thing you would get would be some serious winds. With the significant temperature difference between the 'hot' and 'cold' sides, anyone living in the 'twilight zone' had better batten down the hatches.

Calculating the temperature in the 'twilight zone' would not be trivial. Because of the atmospheric winds, like currents in the ocean, a good bit of the heat would eventually be transferred to the 'cold' side. I suspect that online the temperatures of Mercury's Sun side, dark side and its narrow but not nonexistent twilight zone are available. Of course the imagined 'Earth' would not be nearly as extreme, but it might give you some idea.