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Aside from Terra, of course. I would say it's easily Mars. Though Mercury has both extreme heat and extreme cold, and I would imagine a narrow band of space where the temperature is moderate. Of course, it has no atmosphere.
Uranus is interesting with its extreme axial tilt. The Arctic and Antarctic cover almost the whole planet, excluding a narrow zone around the equator. Polar day and night last 42 years each. Living near the pole you would see 42 years of constant sunlight with highest sun altitudes reaching near the zenith followed by 42 years of pitch black darkness. Of course at that distance the sun is just another star in the sky, slightly brighter than others. If it ever gets terraformed it's definitely an interesting location to visit.
An exoplanet, I can't remember which one, is tidally locked to its star. The sun will forever remain in a single spot in the sky. Depending on location that can range from eternal zenith to twilight to darkness. The only possibly habitable locations would be near the twilight zone between the boiling sun facing side and the dark frozen outward side. The transition zone will probably constantly experience ultra violent storms due to huge temperature differences so it's no picnic. Another challenge for future terraformers.
Uranus is interesting with its extreme axial tilt. The Arctic and Antarctic cover almost the whole planet, excluding a narrow zone around the equator. Polar day and night last 42 years each. Living near the pole you would see 42 years of constant sunlight with highest sun altitudes reaching near the zenith followed by 42 years of pitch black darkness. Of course at that distance the sun is just another star in the sky, slightly brighter than others. If it ever gets terraformed it's definitely an interesting location to visit.
An exoplanet, I can't remember which one, is tidally locked to its star. The sun will forever remain in a single spot in the sky. Depending on location that can range from eternal zenith to twilight to darkness. The only possibly habitable locations would be near the twilight zone between the boiling sun facing side and the dark frozen outward side. The transition zone will probably constantly experience ultra violent storms due to huge temperature differences so it's no picnic. Another challenge for future terraformers.
That's probably the case for a planet like Gliese 581g, since it's tidally locked to tis star, assuming it exists and it's not a false positive. What I'd really love to see are potential climates o planets orbiting Alpha Centauri A or B. NASA has hardly looked over there yet, don't know why. But, I'm guessing they want to refine their planet hunting techniques before they look at our nearest neighbors.
Looking at the solar system, if Mars had a 99% thicker atmosphere, the temperatures would probably be pretty nice. Same goes for Venus for heat lovers if the atmosphere wasn't 90 times thicker than Earth's. The middle latitudes could have been subtropical in terms of temperature.
Inside the solar system, I'd say the surface of Mars is the best. It's really cold there which is a plus compared to some other planets (most of the time it's Antarctic-type cold, nothing that could freeze your skin off; the poisonous atmosphere is the main problem), and it has a landscape reminiscent of Earth's deserts. You also have the radiation coming in, but it isn't that bad. Mars also has the distinction of being the only planet in our system other than Earth where you can hear sounds with your own ears. Seriously, I read in Astronomy Magazine that an astronaut could close his eyes, hold his breath, open his visor, and listen to the sounds for as long as he could hold his breath. There is no other planet in our solar system besides Earth where you can do that and live to tell the tale. The closing eyes bit is due to the pressure differential.
The runner-up is high-altitude Venus. You can pretty much custom-tailor your climate, from perpetually warm to perpetually cool, depending on what altitude you select for your floating balloon colony. The atmosphere there has a lot of sulfuric acid in it, which means that more protection is needed for Venusian colonies and astronauts than Martian ones. Still, the conditions there are remarkably hospitable, especially compared to the surface, which is probably the most hostile place for humans in all of the inner solar system.
Outside of the solar system and in the known universe as a whole, I'd say Gliese 581 d is the most hospitable. If it has a lot of CO2 in the atmosphere, which isn't unlikely given its high mass, then it would be a habitable planet. Even better: the climate there would be on the cold side, which I'd really like. Not much else is known about the planet, though.
I doubt that even with Earth-like atmosphere and considerable amount of liquid water Mars will be habitable because its magnetic field is too weak to protect us from cosmic rays. Also, I'm not sure if Mars has strong enough gravity to keep atmosphere with high enough pressure for comfortable human living.
The equator of Mars may not be that bad. It does see temps over 20C in some instances.
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