<p>The basic condition is you'd need is a more massive, hotter star than our sun.  Not necessarily huge, but 1.5 - 2.5 times the mass of the sun should be enough because that corresponds to considerable extra luminosity and UV rays, so you could move the planet far enough away than Earth is from the sun and avoid any risk of tidal locking or slowing, so the planet could retain fast rotation period.</p>

<p>And you'd need a very thin atmosphere so the planet doesn't retain much heat under shadow.</p>

<p>If the star is bright enough in the sky that you'd get a burn in seconds under direct light, then shade probably wouldn't be cool unless it was permanent shade, as you noted, perhaps a cave. </p>

<p>If there's no atmosphere, you'd probably get colder temperatures than what you mention in shade, so some atmosphere, but a thin one.   Maybe somewhere between 1/10th of an ATM give or take and very low greenhouse gas, so basically very little water, CO2 or CH4.    1/10th of an ATM is just a very ballpark guess. </p>

<p>The only part I don't see happening is 3rd degree burns in seconds.   3rd degree burns by photon radiation from a star would probably require longer than that, unless the planet's surface was hot enough to melt rock.   Bad sunburn in minutes, sure.   3rd degree burns in seconds with your other criteria sounds unlikely to me.</p>

CC BY-SA 4.0
2019-01-16T13:42:18.607Z
2019-01-16T13:42:18.607Z
userLTK
<p>I want to know if there can be any planet that can fulfill the following conditions and if any planet has been observed with such characteristics:</p>

<ol>
<li>The planet must not be tidally locked.</li>
<li>The day-night cycle must be similar to our planet or smaller.</li>
<li>The planet must be so close to the star that the light emitted from the star 'burns' (can cause third degree burns to human skin within seconds after exposure).</li>
<li>Temperatures in the shadow cannot exceed 40-50°C (whether prolonged shadow during daytime or conditions during nighttime).</li>
<li>Atmosphere is not necessary.</li>
</ol>

CC BY-SA 4.0
2019-01-16T13:07:17.590Z
This sounds more like you're interested in world building. Note: You require the planet to be tidally locked. Then the planets day-night cycle is determined by this tidal lock, so it cannot be a free parameter. Other than that we know nothing about the spin-state of exoplanets. And especially not which temperatures are there in the "shadow".
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-01-16T20:05:54.737Z
I'm voting to close this question as off-topic because this belongs on world-building.SE
Carl Witthoft
<star><planet><orbit>
Possibility of certain conditions on a planet
Bogdan
# Possibility of certain conditions on a planet

(Asked by: username_0 on 2019-01-16)

I want to know if there can be any planet that can fulfill the following conditions and if any planet has been observed with such characteristics:

1. The planet must not be tidally locked.
2. The day-night cycle must be similar to our planet or smaller.
3. The planet must be so close to the star that the light emitted from the star 'burns' (can cause third degree burns to human skin within seconds after exposure).
4. Temperatures in the shadow cannot exceed 40-50°C (whether prolonged shadow during daytime or conditions during nighttime).
5. Atmosphere is not necessary.

**Tags:** star, planet, orbit

> **Comments:**
> **username_1**: This sounds more like you're interested in world building. Note: You require the planet to be tidally locked. Then the planets day-night cycle is determined by this tidal lock, so it cannot be a free parameter. Other than that we know nothing about the spin-state of exoplanets. And especially not which temperatures are there in the "shadow".  
> **username_2**: I'm voting to close this question as off-topic because this belongs on world-building.SE  

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## 1 answers

### Answer by username_3 on 2019-01-16. Score: 1 | Accepted answer

The basic condition is you'd need is a more massive, hotter star than our sun. Not necessarily huge, but 1.5 - 2.5 times the mass of the sun should be enough because that corresponds to considerable extra luminosity and UV rays, so you could move the planet far enough away than Earth is from the sun and avoid any risk of tidal locking or slowing, so the planet could retain fast rotation period.

And you'd need a very thin atmosphere so the planet doesn't retain much heat under shadow.

If the star is bright enough in the sky that you'd get a burn in seconds under direct light, then shade probably wouldn't be cool unless it was permanent shade, as you noted, perhaps a cave.

If there's no atmosphere, you'd probably get colder temperatures than what you mention in shade, so some atmosphere, but a thin one. Maybe somewhere between 1/10th of an ATM give or take and very low greenhouse gas, so basically very little water, CO2 or CH4. 1/10th of an ATM is just a very ballpark guess.

The only part I don't see happening is 3rd degree burns in seconds. 3rd degree burns by photon radiation from a star would probably require longer than that, unless the planet's surface was hot enough to melt rock. Bad sunburn in minutes, sure. 3rd degree burns in seconds with your other criteria sounds unlikely to me.


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