Lowest altitude viable Mars orbit

(Explorer8939) writes:

Is it possible to be in Mars orbit and collide with Olympus Mons?

No. The summit of Olympus Mons is about 27 km above datum. The scale height
of the martian atmosphere is about 11.1 km, and the pressure at "datum" is
61 millibars, so the pressure at the summit is about 0.5 millibars, which
corresponds to the pressure (and density) at an altitude of only 55 km
on Earth --- barely out of the stratosphere, and well below the exosphere.
Hence, the atnospheric density at the top of Olympus mons is far too high
for a stable orbit.

For a second reality check, google on "mars atmospheric entry," and quickly
learn that peak heating for the Mars Pathfinder probe occurred at around
40 km above datum, and that the Mars Climate Orbiter burned up because
the english-versus-metric screwup meant that it had a closest approach
of about 57 km above datum instead of the planned 145 km above datum.


-- Gordon D. Pusch

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