<p>You're asking if the temperature of the side facing the star will increase without bound. Almost anytime you're talking about a real, physical system, "without bound" just doesn't happen. Think about it - if the temperature was always increasing, eventually the planet will be hotter than the star its orbiting. At that point, why would it continue to get hotter? At some point, the system will settle into an equilibrium where the incoming radiation is balanced by the rate of cooling, at which point the planet won't get any hotter.</p>

CC BY-SA 3.0
2018-03-28T20:03:55.067Z
2018-03-28T20:03:55.067Z
Nuclear Hoagie
<p>Hot objects radiate heat. The hotter something is, the faster it radiates heat.</p>

<p>The side of the planet that faces the sun would heat up until the rate at which it is absorbing heat from the star is equal to the rate at which it is radiating heat. Once it reaches this point it will be stable, and neither heat up more or cool down.</p>

<p>As a simple analogy, consider standing next to a heater or a fire. You will heat up, but you won't heat up forever. You will reach thermal equilibrium.</p>

CC BY-SA 3.0
2018-03-28T20:04:44.517Z
2018-03-28T20:04:44.517Z
James K
<p>Okay, say we have a tidally locked planet that has one side facing its star. On the side that always faces the star, my question is will that side facing the star always be increasing in temperature? If the side is always facing the star, it doesn't have time to cool. </p>

CC BY-SA 3.0
2018-03-28T21:48:31.320Z
An example of a known tidally locked exoplanet is [Kepler 10b](https://en.wikipedia.org/wiki/Kepler-10b).  The dayside temperature is 1833 K and the night side temperature is just 50 K.    On the dayside peak temp is high enough to melt most common metals.  On the nightside both Nitrogen and Oxygen will become a liquid.
StephenG - Help Ukraine
CC BY-SA 3.0
2018-03-29T17:30:21.413Z
@StephenG Why go that far?  :-) .  For all practical thermodynamics purposes, Hg is tidally locked
Carl Witthoft
CC BY-SA 3.0
2018-03-29T19:46:04.720Z
@carlwitthoft There are of course plenty of solar system examples, and more info is [here](https://en.wikipedia.org/wiki/Tidal_locking#List_of_known_tidally_locked_bodies) including the theory.
StephenG - Help Ukraine
<tidal-locking>
Would a tidally locked planet be always increasing in temperature?
StellarExile
# Would a tidally locked planet be always increasing in temperature?

(Asked by: username_0 on 2018-03-28)

Okay, say we have a tidally locked planet that has one side facing its star. On the side that always faces the star, my question is will that side facing the star always be increasing in temperature? If the side is always facing the star, it doesn't have time to cool.

**Tags:** tidal-locking
> **Comments:**
> **username_1**: An example of a known tidally locked exoplanet is [Kepler 10b](https://en.wikipedia.org/wiki/Kepler-10b).  The dayside temperature is 1833 K and the night side temperature is just 50 K.    On the dayside peak temp is high enough to melt most common metals.  On the nightside both Nitrogen and Oxygen will become a liquid.  
> **username_2**: @StephenG Why go that far?  :-) .  For all practical thermodynamics purposes, Hg is tidally locked  
> **username_1**: @carlwitthoft There are of course plenty of solar system examples, and more info is [here](https://en.wikipedia.org/wiki/Tidal_locking#List_of_known_tidally_locked_bodies) including the theory.  

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## 2 answers

### Answer by username_4 on 2018-03-28. Score: 8 | Accepted answer

Hot objects radiate heat. The hotter something is, the faster it radiates heat.

The side of the planet that faces the sun would heat up until the rate at which it is absorbing heat from the star is equal to the rate at which it is radiating heat. Once it reaches this point it will be stable, and neither heat up more or cool down.

As a simple analogy, consider standing next to a heater or a fire. You will heat up, but you won't heat up forever. You will reach thermal equilibrium.


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### Answer by username_3 on 2018-03-28. Score: 5

You're asking if the temperature of the side facing the star will increase without bound. Almost anytime you're talking about a real, physical system, "without bound" just doesn't happen. Think about it - if the temperature was always increasing, eventually the planet will be hotter than the star its orbiting. At that point, why would it continue to get hotter? At some point, the system will settle into an equilibrium where the incoming radiation is balanced by the rate of cooling, at which point the planet won't get any hotter.


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