There is not enough CO2 or any other such gas on Mars to make an atmosphere better than 5% of Earth's, even if you razed the surface kilometers down and boiled

There is not enough CO2 or any other such gas on Mars to make an atmosphere better than 5% of Earth's, even if you razed the surface kilometers down and boiled the ice caps and installed an artificial magnetosphere. https://doi.org/10.1038/s41550-018-0529-6 https://doi.org/10.1038/s41550-018-0529-6 20 millibars is essentially the long-term limit without piping in gas from other planets or comets. There's plenty of science and exploration to be done on Mars, and efforts towards getting people there are admirable, but let's keep it red. Non-scientists (like Elon) should at least consider not ignoring the data we've spent billions of dollars collecting and confirming over the past 50 years.