by Nitpicker » Tue Oct 07, 2014 1:23 am
Chris Peterson wrote:
Nevertheless, the observation about the martian atmosphere is correct. The scale height of the atmosphere on Mars is 30% greater than that of Earth's... which is why meteor and meteorite production is similar on the two planets, and why aerobraking maneuvers work as they do.
(It sometimes makes sense to compare Olympus Mons and Everest, but other than representing their respective planet's highest points, they have little in common. Olympus Mons is three times higher, with its peak in an entirely different atmospheric regime than the top of Everest. If you were at that peak, you wouldn't even know you were on a mountain based on visual clues, just on a big plain with exceptionally thin air.)
I confess I had never heard of the term "scale height" as it pertains to atmospheric pressure, until I read that Wikipedia article on the Atmosphere of Mars. Having now read a bit further, I find it curious that scale height is considered a convenient measurement, given that it is only constant for a constant temperature, and the temperature of the atmosphere varies considerably and non-linearly with altitude, on both Earth and Mars.
Atmospheric Temperature Profile of Earth shown here:
http://en.wikipedia.org/wiki/Atmospheric_temperature
Atmospheric Temperature Profile of Mars shown here:
http://www.windows2universe.org/mars/ex ... ofile.html
By my calculations:
1) the scale height of Earth's atmosphere varies from about 5.6 to 8.6 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 65 km, T ~ 240 K).
2) the scale height of Mars's atmosphere varies from about 4.6 to 10.7 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 120 km, T ~ 130 K).
(Some of my numbers might be a bit off here, they are just quick calculations.)
...
Not related to scale height, but I really like the comparison diagrams showing Olympus Mons against France, Mount Everest and Mauna Kea, here:
http://en.wikipedia.org/wiki/Olympus_Mons
[quote="Chris Peterson"]
Nevertheless, the observation about the martian atmosphere is correct. The scale height of the atmosphere on Mars is 30% greater than that of Earth's... which is why meteor and meteorite production is similar on the two planets, and why aerobraking maneuvers work as they do.
(It sometimes makes sense to compare Olympus Mons and Everest, but other than representing their respective planet's highest points, they have little in common. Olympus Mons is three times higher, with its peak in an entirely different atmospheric regime than the top of Everest. If you were at that peak, you wouldn't even know you were on a mountain based on visual clues, just on a big plain with exceptionally thin air.)[/quote]
I confess I had never heard of the term "scale height" as it pertains to atmospheric pressure, until I read that Wikipedia article on the Atmosphere of Mars. Having now read a bit further, I find it curious that scale height is considered a convenient measurement, given that it is only constant for a constant temperature, and the temperature of the atmosphere varies considerably and non-linearly with altitude, on both Earth and Mars.
Atmospheric Temperature Profile of Earth shown here:
[url]http://en.wikipedia.org/wiki/Atmospheric_temperature[/url]
Atmospheric Temperature Profile of Mars shown here:
[url]http://www.windows2universe.org/mars/exploring/MPF_temp_profile.html[/url]
By my calculations:
1) the scale height of Earth's atmosphere varies from about 5.6 to 8.6 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 65 km, T ~ 240 K).
2) the scale height of Mars's atmosphere varies from about 4.6 to 10.7 km and is roughly 7 km where meteors tend to begin to ablate (z ~ 120 km, T ~ 130 K).
(Some of my numbers might be a bit off here, they are just quick calculations.)
...
Not related to scale height, but I really like the comparison diagrams showing Olympus Mons against France, Mount Everest and Mauna Kea, here:
[url]http://en.wikipedia.org/wiki/Olympus_Mons[/url]