Yes, correct this versions atmosphere is much thinner than the original for some reason, fortunately it can easily be fixed by going into the planetgenerationdefinition.sbc and editing this:

<Atmosphere>
<Breathable>true</Breathable>
<OxygenDensity>0.09</OxygenDensity>
<Density>0.12</Density>
<LimitAltitude>1.0</LimitAltitude>
<MaxWindSpeed>80</MaxWindSpeed>
</Atmosphere>

The original Penumbra atmosphere looks like this:

<Atmosphere>
<Breathable>true</Breathable>
<OxygenDensity>0.8</OxygenDensity>
<Density>1</Density>
<LimitAltitude>1.0</LimitAltitude>
<MaxWindSpeed>80</MaxWindSpeed>
</Atmosphere>

If it's convenient I can edit this version but I see you have already uploaded an edit.

Air is not .8, it seems to be .02. Atmo thrusters are usless. Good news is that the planet is mostly Ice.