I've actually read, that the upper part of the atmosphere, where a returning Falcon 9 booster does retro burns to slow down, is similar to Mars (in terms of pressure I guess).

edit: found a paper on the topic https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201700...

also: https://arstechnica.com/science/2016/04/spacex-has-already-d...