Density and Viscosity for Solution: 80% Liquid Methane CH4 with Solution of 20% Gas Nitrogen N2 on Surface of Titan (the largest moon of Saturn)?

Question

Problem:

1. Need to estimate the density and dynamic viscosity of such a mixed fluid: 80% Liquid Methane CH4 with solution of 20% Nitrogen Gas N2 with temperature of 94K and pressure of 1,467 hPa (the surface environment on Titan, the largest moon of Saturn).
2. Will the effect of Nitrogen be ignorable to the composition's density and viscosity?
3. When the chemists say composition with 80% A + 20% B, do you mean percentage by volume or by mass? sometimes it seemed assumed as a common sense in the paper, but non-chemist people may find it obscure.

Research done:
Origin/Context: Table 1 of journal paper "Cassini radar observation of Punga Mare and environs: Bathymetry and composition". I tried wolframe alpha to give me an automatic answer, but its data base probably constrained to environment of earth. In situ data (to this date) does not exist for the liquid methane lake's fluid property on Titan, so we have to estimate it.

This might be too basic for any chemist, but I do find it quite difficult.

Appreciate any help!

Answer 1

Using NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP) – NIST Standard Reference Database 23, Version 9, I estimated the properties of a mixture of $80\ \%$ methane and $20\ \%$ nitrogen (by mass) at a temperature of $T=94\ \mathrm K$ and a pressure of $p=1.467\ \mathrm{bar}$.

At this temperature and pressure, the mixture is a liquid with a density of $\rho=486.24\ \mathrm{kg\ m^{-3}}$ and a viscosity of $\eta=161.13\ \mathrm{\mu Pa\ s}$.

By way of comparison, pure methane has a density of $\rho=447.14\ \mathrm{kg\ m^{-3}}$ and a viscosity of $\eta=176.28\ \mathrm{\mu Pa\ s}$.

You should check yourself if the difference is significant or if the contribution of nitrogen can be ignored.