# What are the temperature and pressure inside the CO$_2$ deposit on Mars?

Within the CO$$_2$$ deposit near the south pole on Mars, according to this article 3 subunits have been found with one having a top CO$$_2$$ layer of about 300 meters thick covered by a water ice layer with a thickness of up to 20 meters (Figure 4).

Is it known what the temperature and pressure are within the subunits or could they be calculated or estimated ?

## 1 Answer

We can estimate the pressure pretty easily, since both water ice and $$CO_2$$ ice are flexible enough that the pressure and weight must be more or less in balance after a while. At the top of the $$CO_2$$ layer, we have a 20m column of ice above us, so the pressure is $$20 \rho g$$ where $$\rho$$ is the density of the ice ($$10^3 kg/m^3$$ near enough) and $$g$$ is local gravity ($$3.7 m/s$$ according to wikipedia).

So we get about $$75 kPa$$, roughly 0.75 Earth atmospheres. The density of dry ice depends on conditions, but is around $$1500 kg/m^3$$, so at depth $$d\, m$$ inside the dry ice layer we would find a pressure of $$75000 + 1500\times 3.7 \times d\,Pa$$ which is about $$75 + 5.6d\, kPa$$. So at the bottom of that dry ice layer we get about $$1.8 MPa$$ (18 Earth atmospheres).

I have no idea how to estimate the temperature.

• Thank you for the answer ! Better half an answer than nothing at all ! – Conelisinspace Sep 22 '18 at 16:22