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I'm creating a mars re-entry simulation and i need a model for density variation w.r.t. altitude on mars. I know that earth can often be modeled using an exponential density model with a "sea level" reference density and a scaling height $h0$. Can mars be modeled similarly? If so, what would the reference density and scale height be for mars? If not, what model is typically used for martian atmospheric density variations with altitude?

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According to NASA's fact sheet, scale height is 11.1km, surface density 0.020 kg/m3.

Here's some additional information if you want to incorporate a more detailed model than the simple exponential.

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    $\begingroup$ For more on Mars' "sea level", see this great answer. $\endgroup$ – uhoh Sep 18 '17 at 2:01
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What you're looking for is called MarsGRAM. You can request it there. It is quite sophisticated and is based on a large amount of data and global atmosphere modeling. MarsGRAM will generate Mars atmosphere profiles for a given time of the Martian year, location, and atmospheric dust loading, and will also generate randomly varied atmospheres given the relevant uncertainties, for use in Monte Carlo simulations.

If you want to do something simpler, you would at a minimum have to account for the seasonal variation in the total mass of the Martian atmosphere. It is quite significant. Also the dust loading can significantly change the distribution of density with altitude, annoyingly making the atmosphere more dense higher up where you don't care, and less dense nearer to the surface where you do care.

If you want to land something on Mars that costs millions or billions of dollars, you should not use MarsGRAM either. You should consult with Mars atmosphere experts to construct an atmosphere model for your case.

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