|
Size: 2398
Comment:
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Size: 3012
Comment:
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| Deletions are marked like this. | Additions are marked like this. |
| Line 29: | Line 29: |
| === Other stats === || || Ratio || Mars || Earth || || Radius km || 0.532 || 3390 || 6371 || || Gravity m/s^2 || 0.379 || 3.71 || 9.80 || weakened bones, muscles, cardiovascular and lymphatic system || || Escape Velocity km/s || 0.450 || 5.03 || 11.19 || || Escape Energy MJ/kg || 0.202 || 12.65 || 62.61 || light gases escape more quickly "" || Surface area Tm^2^ || 0.283 || 144 || 510 || || Insolation MW/km^2^ || 0.431 || 586 || 1361 || || Total Insolation PW || 0.122 || 21.2 || 173.5 || |
Mars
Water Vapor in the Martian Atmosphere
0.021% or 210 ppm, presumably by weight.
Atmosphere is 64 Pa. About 20 g/m³ (Earth is 1290 g/m³ at sea level. Equatorial wind speed up to 150 m/s, which produces a dynamic pressure equivalent to a 19 m/s (42 mph) wind on Earth. Scale height 11 km, Total mass 25e15 kg.
Air stripped away (about 200 g/s) by solar wind. Sun more energetic (with more UV) billions of years ago. At current loss rates, atmosphere would last 4 billion years.
Five million cubic kilometers of ice. At 1e12 kg/km³, that is 5e18 kg of frozen water. About 5e12 kg in the atmosphere, perhaps 0.01 Pa vapor pressure.
Mars global average temperature is -60C or 210 K (surface?) kT = 0.018 eV or 2.9e-21 J. 3.71 m/s² surface gravity, escape velocity 5.03 km/s.
Viking lander temperature (at 22°N) ranges from -89C to -31C, average -60C. Corresponding ice/water vapor pressures of 0.1 Pa, 34 Pa, and 1 Pa.
|
CO₂ |
H₂O |
CH₄ |
H₂ |
Molecular Weight, daltons |
44 |
18 |
16 |
2 |
Molecular Weight, kg |
7.3e-26 |
3.0e-26 |
2.7e-26 |
3.3e-27 |
Escape energy, joules |
9.2e-19 |
3.8e-19 |
3.3e-19 |
4.2e-20 |
Escape energy, eV |
5.74 |
2.3 |
2.1 |
0.26 |
So, the big question: if below-surface ice is -60K, and has a vapor pressure of 1.08 Pa, and the atmosphere above is 0.01 Pa, what keeps the ice from sublimating quickly, the vapor seeping to the surface, and raising the vapor pressure? There must be a cap layer of rock that is impermeable to water vapor, but how can that be, over an entire planet with significant surface topology?
The heat of fusion of ice is 330 J/g. Average Mars insolation is 605 W/m² (493 to 717), averaged over a day on the equator that is about 200 W/m². If 0.1% of that power made it down to the ice, it would evaporate at the rate of 1 meter per 1.7e9 seconds (54 years).
At higher latitudes, the average insolation is lower and temperatures are colder. Ice will be a lot more stable near the poles; perhaps the temperatures are low enough for the ice to condense from a 0.01 Pa concentration in the atmosphere.
Other stats
|
Ratio |
Mars |
Earth |
|
Radius km |
0.532 |
3390 |
6371 |
|
Gravity m/s^2 |
0.379 |
3.71 |
9.80 |
weakened bones, muscles, cardiovascular and lymphatic system |
Escape Velocity km/s |
0.450 |
5.03 |
11.19 |
|| Escape Energy MJ/kg || 0.202 || 12.65 || 62.61 || light gases escape more quickly "" || Surface area Tm2 || 0.283 || 144 || 510 ||
Insolation MW/km2 |
0.431 |
586 |
1361 |
|| Total Insolation PW || 0.122 || 21.2 || 173.5 ||
Rotational Stability
What (if anything) stabilizes the rotational axis of Mars? How fast do the poles shift?