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I've been toying with an idea for ages that I think could be pretty fun but I want to make sure it's not wildly unrealistic before going too far with it.

The idea is that the Equator is fiercely hot, no human can pass over it unaided and the poles are temperate, habitable etc. This is possible (I hope!) because I have an Earth which is slightly closer to the Sun (smaller orbital radius) and has 0 (or close to it) axial tilt.

The closer distance to the Sun combined with the lack of tilt could cause the Equator to become much, much warmer than it is now and have the poles at a more reasonable temperature.

One thing that comes to mind is that there will be periods of vast daylight and vast night time as there is now in Northern Scandinavia/America due to the glancing angle of the Sun in the higher latitudes, but are there any geographical/physics reasons why this won't work (various amounts of fudging and hand waving permitted.)

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  • $\begingroup$ Is there actually a question here ? Equator would be hotter but not impossible to cross. Probably. It would be very humid but the heavy cloud cover would limit the increase of temperature. $\endgroup$ – Vincent Apr 22 '15 at 23:54
  • $\begingroup$ I'm just wondering if it makes sense in concept. For example maybe the temperature required to make the equator too hot to walk over means the poles will be too hot (or still too cold) based on albedo, surface area, solar activity etc. Not my areas of expertise. $\endgroup$ – RichK Apr 23 '15 at 0:30
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    $\begingroup$ I'm confused about the last paragraph. If there's no axial tilt, there will be no seasons, and everywhere will have twelve hours of daylights every day. $\endgroup$ – abcde Apr 23 '15 at 3:37
  • $\begingroup$ As abcde says, no tilt means change in daylight exposure. You get half the day exactly, regardless of how close to the poles you are (though the precise amount of time might not be 12 hours: that of course depends on the rotation speed of the planet). One other thing: if you're closer to the sun then your year is shorter. Going closer in on the goldilocks zone means your year shortens to probably around 310 days or so. $\endgroup$ – eharper256 Apr 23 '15 at 19:11
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If you want an impossible-to-cross equator, the first thing you need to do is get rid of the oceans.

A region too hot for unassisted humans is actually quite simple: you simply need the heat index to be consistently above 54 C during the heat of the day. If the region is more than a night's travel across (about 30km or so), a human won't be able to cross it without dying of heatstroke.

The problem with creating an impassible equator here on Earth is the oceans, and to a lesser extent, rivers: even a low-tech traveler can submerge themselves during the day to keep cool. You'll need a continuous band of land circling the equator to prevent this. As a benefit, if this band is broad enough, the natural atmospheric circulation (moisture generally moves from east or west, not north or south) will keep it dry, preventing equator-crossing rivers.

You may not need to do anything about the axial tilt: the equator doesn't have much seasonal variation in temperature.

Temperate poles is actually the harder part of what you want: without an equatorial ocean, you don't have the heat-moving currents that make places like Scotland and Norway habitable. You'll need to make up for this by moving the planet closer to its sun, and I don't know if you can get it close enough without making the entire planet uninhabitably hot.

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  • $\begingroup$ Thanks for answer - I hadn't considered the oceans, bit silly considering how big they are :-/ $\endgroup$ – RichK Apr 23 '15 at 22:47
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As a supplement to Mark's answer:

One of the hottest place on Earth is Dallol Ethiopia. The hottest north has an average temperature of 38,6 C with daytime temperature often above 50 but nights are colder.

What you want is a large landmass with no ocean close because it could bring precipitation inland. As I mentioned earlier, you don't want a cloud cover because it tarps humidity and prevent the energy of the sun to reach the ground. Having no season reduce the temperature swings but people could still survive during nighttime and go into hiding during the day. To be sure that they will be cooked like roasted chickens, you also need to have a nighttime temperature over 54 or pretty high.

if the trip is taking several days, the actual region of Ethiopia is not deadly but it's a very difficult trip. Increasing temperatures a little and making the area larger would probably be enough to make travelers can't survive for long. Without precipitations, rivers (if any) would be dried out before reaching the hottest point in the desert. It would be possible to bring water but the quantity would be too large. A normal adult need at least 3 to 4 l of water per day in a temperate climate. This number would surely rise in a very hot climate. 1 l of water is 1 kilogram, so this will get very heavy.

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