Gravity + atmosphere of the Moon

[search]

Old but valuable<br />http://sirius.bu.edu/moontail/pressrel.txt <br /><br />Terraforming the moon harder than Mars:<br />http://www.geocities.com/marsterraforming/terraforming.html<br /><br />Question to NASA:<br />http://quest.arc.nasa.gov/mars/ask/new/Terraforming_our_moon.txt<br /><br />Better options:<br />http://en.wikipedia.org/wiki/Terraforming<br /><br />Elegant dreams:<br />http://www.orionsarm.com/tech/terraforming.html#intro

 

[mithridates]

That's not bad but either those links don't have exactly what I'm looking for or I've overlooked the part that contains the answer. What I'm most wondering about is the exact amount of atmosphere the Moon would need to start having wind, weather patterns, and a reduction in the difference in temperatures between light and shadow.<br /><br />Mars for example has an atmosphere with a total mass of 2.5 x 10^16 kg, and Earth has 5.1 x 10^18. As the moon has one quarter the surface area of Mars that would mean around 6 x 10^15 kg for the same pressure as Mars, but I assume it wouldn't need quite as much pressure as Mars does for weather patterns to form. What would be the minimum atmospheric pressure for that to happen? And would the benefits of 'climate' moderation, softening of lunar dust and possibly having the wind expose areas underneath the dust that otherwise would be missed be worth it? As long as the air used isn't poisonous to humans it wouldn't really matter as long as it were heavy and easy enough to create.<br /><br />I'm sure my numbers are off anyway. Please check them.<br /><br /> <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[ittiz]

I found a power point presentation which is on topic to this discussion by Nick Hoekzema (a NASA scientist): atmostalk.pdf<br /><br />Note to the anally inclined: The following paragraphs are <b style="font-size:18pt">speculation</b>.<br /><br />First off Hoekzema calculated that for most worlds thermal escape, which is what I assumed caused the greatest amount atmospheric loss, actually might not be that important. Hoekzema calculated that worlds with escape velocities as small as 0.8km/s could possibly hold a CO₂ atmosphere for billions of years if thermal escape were the only mechanism working.<br /><br />Using Hoekzema's equations I calculated that the Moon could possibly hold at atmosphere of <b>SF₆</b> for longer than the age of the solar system and also possibly SF₆/O₂ atmosphere for longer than the age of the solar system. Also apparently the weight and thickness of the SF₆ atmosphere would help defeat the two major causes of O₂ loss: Hydrodynamic outflow (simplistically an updraft), and sputtering (fast moving molecules hitting slower molecules causing a cascade of atoms leaving the planet/moon). Both effects rely on the average velocities of the molecules in a gas so the SF₆ "shields" the O₂ from the effects. To visualize what's occurring imagine a pool table with pool balls. Except some balls are light and small and some are big an heavy. Now if you shoot one of the small balls across a table with mostly large balls rather than light balls fewer balls will go in the sockets because when the small ball hits a large ball the small ball will slow down a lot and the large ball will barely speed up at all. This is the effect that reduces sputtering and hydrodynamic outflow. Although it's hard to doubt that some mechanism would still be required to hold the O₂ down, but it may not have to be

 

[vandivx]

"how much more mass would the Moon need to hold its own atmosphere, and would that be enough to cause any serious changes in tides over here?"<br /><br />did you notice that throughout this learned discussion apparently nobody noticed what the main original question was?<br /><br />I don't have enough knowledge to tell you how much mass you'd have to pile up on moon for it to hold onto some fricking exotic gas but I assume if you piled on enough mass to cause the gravitation of the Moon to increase to the point where it would kick off some heating up of the interrior due to gravitational pressure squeezing the Moon's interrior core which in turn would cause volcanic activity and heating up of various minerals and outgasing from the surface and development of the initial atmosphere that could further change later on, same as it did on Earth originally... so basically you'd need enough mass to start heating up the Moon's core, then things would take care of themselves IMO although there are many factors that must come together for a planet or a moon to hold onto its atmosphere, least of which is not its composition and how much heat from the sun is allowed to penetrate and heat up the surface of the planet or escape once it penetrates and many other such things...<br /><br />those propeler heads and worriers that worry about vacuum on Moon being spoiled by Apollo trips should have their heads checked - so what, should we commit suicide and be done with it to keep the cosmos clean and its vacuum unspoiled????<br /><br />vanDivX <div class="Discussion_UserSignature"> </div>

 

[search]

Hello mithridates<br />Interesting question<br /><br />"The effects of gravity and temperature work opposite to each other. A higher temperature tries to dissipate an atmosphere while higher gravity tries to retain an atmosphere. If the particle's average speed is close to the escape velocity, then those type of gas particles will not remain for billions of years. The general rule is: if the average gas molecule speed for a type of gas is less than than 0.2×(the escape velocity), then more than 1/2 of that type of gas will be left after one billion years. If the average speed is greater than that critical value, then more than 1/2 of that type of gas will be gone after one billion years."<br /><br />http://www.astronomynotes.com/solarsys/atmosesc.htm

 

[silylene old]

Interesting stuff! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[nexium]

I also noticed that the original question was left unanswered. If we double the mass of the moon, but only increase the radius by 3% ( heavy metals such as osmium, platimum and gold would do this, then the surface gravity would almost double from about 1/6 g to about 1/3 g = about the same as Mars.<br />If we imported enough nitrogen, oxygen and trace gasses and vapors to make one barr pressure at the medium elevation, this would decrease to 1/2 barr in a few million years, due to leakage into space. We could replace just the oxygen over the several million years resulting in a constant partial pressure of oxygen, which would be ok for humans, but perhaps not ok for organisms that fix atmospheric nitrogen. The day time high temperature would be perhaps 5 degrees c = 9 degrees f warmer than Earth, but a hard freeze would occur just before the dawn at the end of the 14 day long nights, even at the equator of the moon. A satisfactory water cycle would be difficult with seas, lakes and puddles covering perhaps 1% of the Moon's surface instead of the about 80% for Earth. Huge orbital mirrors would need to warm the polar regions of the Moon to prevent build up of huge ice caps at the North and South poles of the Moon.<br />Moving the moon 15 times closer to Earth would greatly reduce travel time to and from the moon, but would only reduce the fuel requirements by about 2% is my guess.<br />The doubling of the Moon's mass would increase the highes tides by about 60%<br />!5 times closer would produce huge tides, making most costal areas of Earth uninhabitable. Neil

 

[mithridates]

There was an article a few days ago about how impacts on the Moon seem to be about four times as frequent as we had expected. How much of an atmosphere would the Moon need to begin to protect itself from impacts of space debris? <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[mithridates]

Oh no, I have another question. How much of an atmosphere would be needed before it could transmit sound?<br /><br />I was thinking today about an ideal level for an atmosphere. Is there a perfect level that would allow sound to travel, vehicles to fly, protect settlements from bombardment by small pebbles and moderate the temperature somewhat yet still allow proposed mass drivers to work? The more I think about an atmosphere the less it would have anything to do with breathing and more to do with more practical matters. Apologies for all the questions but I have to idea where to find the answers on a matter such as this. <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[ittiz]

I think there will be sound as long as there is enough particles to create a cascade. How many per sq cm that is I don't know. Also the thinner the atmosphere is the quieter the sound is. If you have ever swam in a lake or the ocean and clacked two rocks together under water you'll noticed that the sound under water is extremely loud because of the dense medium the sound is traveling through.