Thermal Inertia

https://nathaniel.putzig.com/research/ti_primer.html

(paragraph separation is mine)

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"As the name implies, thermal inertia represents the ability of a material to conduct and store heat, and in the context of planetary science, it is a measure of the subsurface's ability to store heat during the day and reradiate it during the night.

 

While compositional differences (ie, mineralogy) will have some effect, for a terrestrial planetary surface such as that of Mars, 'I' will depend predominantly on the physical properties of the near surface materials such as particle size, degree of induration (ie, cementation of grains), rock abundance, and exposure of bedrock (rocks will have a much higher thermal inertia than sand or dust - that is, it takes longer to heat rocks up during the day and to cool them off at night.

 

For example, on a visit to the desert you may notice that sandy areas are much hotter at midday than adjacent rocks, and the sand cools off quickly after sunset whereas the rocks remain warm well into the evening)."

 

 

 

Thermal inertia is defined as [units in square brackets]:

I = (kρc)½ [tiu = J m-2 K-1 s-½]

where:

k = thermal conductivity [W m-1 K-1]
ρ = density [kg m-3]
c = heat capacity [J kg-1 K-1]