Atmospheric Degeneration

HeloTeacher · 2002-01-27 11:59:53

I have a problem, I too am not a professional scientist, just an interested observer/would-be participant. I am trying to determine the rate at which atmoshpere escapes to space. Thius is often mentioned as "where the water went" or "where the original atmoshere went" but I'm not having a lot of luck figuring out how to determine the rate at which it goes. It would be rather ironic to flood the skies with air and then watch it all leak away.

Can anyone please tell me where to find this info (I am not currently living in a large enough center to have access to a university or equivalent library).

Thank you in advance.

Shaun Barrett · 2002-01-27 22:54:29

I can't direct you to a specific source of information, HeloTeacher, but from the old cerebral memory banks (such as they are!) I don't believe atmospheric leakage is a problem.
I've read heaps of stuff about Mars and terraforming over the years, and the general consensus of expert opinion is that it takes tens of thousands or hundreds of thousands of years to lose a significant amount of atmosphere from a place like Mars.
Certainly, your brand new atmosphere will immediately start to drift away into space, but it is so gradual (at least from a human perspective) that it will be no problem to keep up with it by importing gases from elsewhere. It's important to remember that humanity will be advancing as each century passes, so our technological ability will be increasing faster than the air is leaking!
It's difficult to imagine what technological marvels we will take for granted in a thousand years from now, so I think you can safely ignore this problem for the time being. Let's concentrate on MAKING the damned atmosphere first ..... we can worry about losing it later!!

Karl Evans · 2002-03-05 23:04:06

Hey, I had this idea while sitting in my Astro 1 class - since Venus has too much atmosphere (based on the surface pressure), and Mars has too little, couldn't we set up a space ferry that just looped ("cycled" seems to be the buzzword of the day) between the two planets (at whatever lazy interval and speed could be worked out to be economically attractive), scooping CO2 off the Venusian cloudtops and releasing it over Mars? We could even work out some clever thing like a big baggie to put it in and get it a lot closer to the surface before shooting it with a varmint gun; >pop< you've got a lot of CO2 that some hardy lichen or something could be converting into O2 for us mammals.
Sure, it'll take a long time, but I don't know where else we're going to get gases to terraform WITH. (Though my calc teacher likes to write "A MIRACLE OCCURS" when a student has forgotten something. I'm probably too new at this to get REALLY scathing with my sarcasm yet.)
BTW, Buzz Aldrin did some kind of publicity stunt-like thing acquiring the rights (or some such) to the Earth-Mars route... see http://sci.newsfactor.com/perl/story/16391.html for more info.
Well, here's hopin'...

Shaun Barrett · 2002-03-06 20:22:38

If you're going to all this trouble with cyclers transferring atmospheric gases from one planet to another, why drag CO2 to Mars when Mars already has plenty of it?
If you're trying to reduce Venus's atmospheric bulk, I think it's a forlorn hope. You could supply 90 planets with a thick CO2 atmosphere before you'd reduce Venus's air to a tolerable density!
We really only talk in terms of a 500 millibar CO2 atmosphere for Mars because there may be some chance of actually finding that much CO2 right there on Mars. It's a relatively simple thing (we like to imagine!) to use local resources. But, in fact, if we had the choice, we'd all rather add nitrogen to the Martian air; and lots of it, too.
Kim Stanley Robinson beat us all to it, I think, by suggesting cyclers between Titan and Mars; transferring almost pure (and much needed) nitrogen to Mars in bulk carriers which 'scooped' and 'cycled' in a ceaseless procession, like a celestial version of the broomstick in "The Sorcerer's Apprentice"!
No, I don't think CO2 is what we'll really need at Mars; too much like carrying coals to Newcastle! Give us nitrogen!!

Adrian · 2002-03-20 18:09:35

IANATS (I Am Not A Terraforming Scientist) but the idea of transporting mass quantities of *anything* from one planet to another fills me with horror; the sheer expense and inelegance of the system shocks me.

I would say that a successful terraforming process would involve transforming the planet with as little expense as possible and causing the minimal amount of damage to its surface; speed would be useful but not essential. I don't know the exact quantities of nitrogen on Mars, and in fact I doubt that anyone knows *for sure* - but if at all possible, I would think the best way to increase the N atmospheric levels would be to free it from compounds already on the planet.

And if that's not possible, we should just go and aerobrake a suitable asteroid in Mars' atmosphere.

Phobos · 2002-03-20 19:07:06

I tend to agree with Adrian. You'd need a pretty #### big scoop to terraform Mars by taking bites out of the atmosphere
of another planet. :0

gbbaker · 2002-03-23 06:10:57

From what I have read thus far (And I have examined it thoroughly and continue to reexamine it) on terraforming there are three things that I think could realistically be done to terraform mars. Actually 2 but one is a a temporary help or assist.

The first one is the widely accepted idea of mining and cooking up the regolith for the fluorine, sulfur and carbon gases and making SF6 and a couple of other PFC (perflurocarbons) gases that have a farely wide range of thermal absorbtion bands.
They cover a lot that CO2 and water vapor wouldn't and depending on which ones you use the greenhouse strengths of all of them are in the "thousands of times stronger than CO2 range" as a greenhouse gas and there lifetimes are thousands of years.
So that's a pretty well accepted method to terraform.
SF6 and pfc's.
It would have to have a mining machine and a cooker/combiner machine and I guess a waste handling machine. I don't really know all the mechanical details to it but I do know that that is the main answer to terraforming mars to get it to an earthlike average temperature of 288kelvin.
It puts a greehouse blanket of pfc's into the atmosphere with only something like ten or 12 parts per billion.
In process of doing this it releases the trapped CO2 in the poles (because of the temperature increase) and theoretically there is some loosely bound CO2 in the regolith outside of the equator.
So as the CO2 gets released it further increases the thermal range of the greenhouse blanket that is being created with the pfc's but the thing is ...is that most likely there is atleast 300 millibars of this CO2 (global total - poles and regolith) which in volume is orders of magnitude more than the pfc's that we created.
And as the CO2 starts subliming into the atmosphere it just keeps increasing as the hotter it gets the more CO2 gets released.
AND as this "runaway" (as it's called) is happening; the water is also evaporating which also has it's thermal range as a greenhouse gas and also adds to the atmosphere pressure.

Looking at it overall Fogg and McKay recently (in a new paper) did an evaluation of a wide variety of terraforming techniques and calculated it out based on predictions of 100 and 200 and 350 millibars of CO2 trapped globally. The whole purpose of the analysis was to look at effectiveness and the question of time scale was not really addressed seeing as there are still some open questions.
Plus I thought of a good technique that they didn't know about.
The whole paper basically states that pfc's will be the center role of any terraforming we do but we will have to employ more than one techinique.
However there are three major things (and one minor) that could reduce the effectiveness of using pfc's.

The first one is:
The surface temperature has to keep increasing faster than the atmosphere thickens with CO2 and water (there is a natural state of equilibrium that mars will try to get to)
so that the CO2 will continue to release.
At a certain pressure it won't release anymore in cold areas and so we are back to relying solely on the pfc's strength as it is being created and so the process slows down by magnitudes and completely stops in others.
But hold on...

The second one is:
The reflectivity of clouds.
As we release the greenhouse gases the clouds will form and reflect some of the sun away from the planet. It's not really figured in to the equations in Fogg and McKays paper but it is mentioned. It seems to me that it is a major factor though especially given all the water that we found with odyssey after this paper was written. After all with earth having an albedo of someething like .34 and mars at around .20 right now it seems to me like we should expect around a .05 increase so that would almost ruin everything since the whole effectiveness of using pfc's hinges on the surface temperature increasing faster than the atmosphere thickens.

The third one is:
The porousity of the regolith and how loosely the co2 is bound in it.
If the regolith has a good porousity (lots o holes) then as water trickles down the sun would defrost the CO2 and water out of the ground faster.

A minor one is:
Possibly CO2 clouds will serve to reflect some of the sun away as the project is ongoing.

Now that's as far as that paper is concerned.

The second method that I've heard of as a temporary measure to prop up and support the pfc/co2 process is using black lichen.
Black lichen seems to me like a good supporting mechanism to the pfc/co2 process so that we get an artificial albedo reduction while the process is occuring. Lichen could be engineered to be black and they do grow at very low temperatures but it would only be a surface coating and they have slow growth rates so we would have to alter them to grow faster along with possibly neccessitating bringing a large supply of them (tons!) to start the process.

The one I thought of was to use 4 very slow roving nuclear powered regolith heating machines with drills that drill down into the regoith about four or five feet and release a large batch of anaerobic iron eaters. The iron eaters will use the hydrogen in the water that is in the ground and ingest the rust and "reduce it". They turn it from (gee where are my notes?)......well anyways....
They turn the rust that's in the ground into magnetite. And magnetite is black (permanent albedo reduction). There is a great deal of rust on mars.

The idea is that only one injection is needed since the organisms will travel with the heat source. The machines are simple and could be doubled up with other weather instruments. They simple touch down, inject their loads, drill in and heat up until approximately 50% of the mass underneath them is converted and then they just move over slightly and drill back in and heat up again. In a pac man like fashion they can be remote controlled easily. It's a uphill battle but for the purposes of albedo reduction in the long term it's permanent and as it plugs along the environment (for them) gets warmer and warmer. Even without the use of pfc's it can be started at the equator since there is sufficient water there in most places for the purposes of a project like this.
Also; in contrast to the way "pfc's/co2 release" act in such a way as to have a decreased effect as time goes on this method I propose increases it's temperature effect on the environment as time goes on with it's main product being an increased surface temperature.
The limiting factor is that as far as I know "anaerobic iron eaters" are mesophilic (living between 25 and 40 celsius) as far as I know so they will rely on the machines greatly and of course the details will have to be all worked out and simulations done so that it is determined that the organisms will indeed travel and propagate with the heat source through the underground martian regolith.
However there are a lot of "BIG PLUSES" to using this method as an assist to pfc's. You can read all about them and debates I've had in the "red views" thread here or over on the space.com message boards on any of the terraforming mars or related threads.

Michael Bloxham · 2002-04-02 19:10:15

Just thought I might add my own two cents in here.
Recent evidence suggest that mars did indeed contain a once thick atmosphere. This once thick atmosphere was probably stripped away when it repeatable passed by earth 3 millenia ago. Interestingly enough, the gravitational effects of one of these pass-bys probably caused the Great Flood of genesis. Which in turn stripped off half of our own atmosphere. Which also continues into another theory. And that is that our atmosphere was once twice as thick as it is today. Just look at the bones of a pteradactyl. The wings of the pteradactyl were far too stubby for effecient flight in todays atmosphere. In an atmosphere twice as thick, however, flight would have been quite comfortable. I beleive this theory answers another question; How did the dinosaurs find enough food to keep themselves alive? Scientists have beem baffled by this mystery for years. But if the atmosphere was thicker at the time of the dinosaurs, they would have received a much higher amount of oxygen; Allowing them to metabolise food much more effeciently. After the atmosphere was stripped, the dinosaurs began metabolising at a much slower rate. And in the end, the dinosaurs simply starved to death. All just theory ofcourse, but a very interesting theory. As it solves a few ancient problems like, Why did the ancient civilizations fear mars so much? The answer, ofcourse, is the dire gavitational affects it had on earth. It would have caused massive earthquakes and floods. And the fact that it appeared in the sky 50 times the size of the moon. No wonder they feared mars! Ancient transcripts suggest mars would swing close to earth every 104 years. How it got into its present day orbit, I'm not sure. But it seems likely that both Mars and Earth had a much thicker atmosphere in the past.

Shaun Barrett · 2002-04-03 07:43:23

Brace yourself, Michael. I suspect most of the Mars Society members are going to have trouble with most of the stuff you have just mentioned.
Just to get a handle on where you're coming from here, may I ask you how old you personally believe Earth is?
:0

Michael Bloxham · 2002-04-03 13:29:18

Its also interesting to note that the earths magnetic poles changed numerous times before 1000bc. Why they have stopped changing, no one knows. But for me its obvious. As for the age of the earth, well thats sort of hard to tell. If we were to discard carbon dating, then the only way to tell how old the earth was is by looking at the sedimentary layers. Ofcourse these layers grow extremely slowly, so the earth has to be really really old, right? Yes... But if we considered the great flood, which probably rose above sea level by atleast 15000ft... Now most of us know that when you add different types of soils in a water-filled cup, shake it around, and leave it to settle, the end result is sedimentary layers. I know this is just conjecture, but it all fits together so well! So, how old is the earth? It might just be a lot younger than we think.

Shaun Barrett · 2002-04-04 01:22:37

As close as you can tell from what you believe to be the facts, Michael, would you say Earth's age is:-

(a) Less than ~6000 years.
(b) From ~6000 to ~10,000 years.
? From ~10,000 to ~100 million years.
(d) From ~100 million to ~4 billion years.
(e) ~4.6 billion years.
:0

AndyM · 2002-04-04 03:33:56

Micheal, I've read several of your posts and I have a couple of points which I'd like to make in the same reply even if they pertain to different topics.

a) The magnetic poles are still changing position today. The magnetic declination is the angle between the geographic north pole and the magnetic north pole and this angle changes every year. You'll find the value on all good maps. The time it takes for the magnetic poles to reverse is on the oder of tens of tousands of years and not hundreds of years. This is directly supported by geological evidence: molten lava from the ocean ridges contain ferro-magnetic compounds that align with the magnetic field and as the lava reaches the ocean floor it solidifies. Thus the compounds show how the magnetic field has changed in the past. It also shows that the earth is much older than a few thousand years since we can observe the rate at which the the ocean plates move apart and hence the rate at which the lava is deposited.

b) There is other evidence besides carbon dating that shows that the earth is much older that a few thousand years. For example, the moon's orbital period around the earth (~29 days) exactly matches its rotation about its own axis. (This is why we see the same face of the moon all the time.) This would be a pretty strange coincidence. The reason is that the interaction of the tidal forces between the earth and the moon has slowed down the rotation of the moon just as they are slowing down the rotation of the earth. We can measure this decrease in angular velocity and in many thousands of years, the earth's rotation will equal the orbit period of the moon, i.e. an earth day will equal a month. (For a full explanation see "Bad Astronomy" by Plait.) This effect takes millions of years to happen and hence the earth and moon can not be a few thousand years old. There are many other examples like this that show the earth to be much older than the Bible suggests.

c) You refer to the "ancients" several times when talking about mars. How old are these ancients? Greek astronomers in bc made tables of the motion of heavenly bodies yet they seem unaware of the regular 104 year mars passage that you mention. Likewise Arabic astronomers. Then in the 16 century Kepler was able to deduce laws of planetary motion from the observed motions of the planets. This means that his data was very accurate. Why is something this spectacular not written about explicitly but only through vague references?

d) Jet streams are horizontal winds, not vertical winds. They are high-altitude, high-speed winds that usually separate the colder winds from the warmer winds. Balloonists use jet streams to travel around the world.

I will be interested in hearing your views and ideas as long as they can be backed up by evidence. If your views require the doctrine of "created antiquity", i.e. that the earth was created to look as if it was billions of years old, or similar ideas then it is impossible to refute any claim that you make and hence, we can not have a scientific discussion.

Michael Bloxham · 2002-04-04 13:48:06

Sorry. I didn't mean to bring up an argument. I just get so excited... Anyway, this whole Mars theory of mine is just conjecture. Im not a geologist nor do I have the time for research to back my theory. The information I gathered was from what I have kept in the back of my head for years. When I added it all together, It just fitted so well. I must have got a bit too carried away. But it is still interesting to think of how mars might have affected earth in the past. As for the Jet Streams, maybe I have the wrong word. From memory they were vertical winds, but maybe they were horizontal ones after all. I will try to find the article. But in any case, vertical or horizontal, the question still holds. Does mars have Jet Streams?

Disland · 2002-06-08 10:17:12

Ok this is a real long shot and does not follow on from this topic very well, but check out

New scientist wind power rain maker news
I'm not sure how exactly this technology could be used on Mars but I have a feeling that pumping water droplets into the atmoshere may help induce a climatalogical cycle or at least provide rain water for crops using free wind energy. With all the water ice supposedly under the surface on Mars it may be possible to heat the drill part of the turbine to melt the ice and then draw it up into the atmosphere.

Anyway, not sure whether this is totally useless idea but the article is an interesting read for those interested in Earth's problems too. I would like to here any comments or ideas on this matter.

cheers
Disland

Earthman · 2003-12-21 21:04:51

I have read theorys on differing amounts of H2o & Co2 existing in different parts of our orbits at different times in history. We do gather water from space. Sometimes in "biblical" amounts, IE: the Noarian flood.

~Eternal~ · 2003-12-22 10:54:30

Erm how exactly could the great flood devour half the atmosphere?
I mean at 2 bars Noahs head would have exploded no?
And doens't water only devour CO2 and similar carbon based gases?

JoeDaWolf · 2004-01-14 18:22:13

I saw a program on Nova a little while back (I think it was Nova.) It was exploring the decreasing magnetic field strength of earth, and the program showed how researchers came to the conclusion that we are overdue for a switching of polarity within the magnetic fields.

While going into the possible reasons for the decrease in strength, they mentioned how Mars has almost no magnetic field left (I found a site which supports this: [http://www-ssc.igpp.ucla.edu/personnel/ … mars_mag/)]http://www-ssc.igpp.ucla.edu/personnel/ … mars_mag/)

Now the reason why this is important is because the program mentioned the effects that the changing magnetic field will do to Earth: At some moment in time we will have no magnetic field, and for a period ranging from a few hundred to a few thousand years, we will have a very weak magnetic field. The result of this is that, yes the atmosphere will bleed into space, but as somebody mentioned earlier, (and as was mentioned on the show) this won't have much effect (it would take a much longer period to lose a considerable portion of the atmosphere.)

The other main result would be the increased rates of cancer. We are constantly bombarded with charged particles from the sun- solar wind as it is commonly called- and our magnetic field deflects much of these away from the earth and our atmosphere. What does this mean for future plans to send humans to Mars since Mars has almost no magnetic field strength (less than 10^-4 in magnitude in comparison to earth's)?

~Wolf

P.S. Not to mention the muscle and bone atrophy that will be experienced both during the long trip there, and the small gravity on Mars (unless I?m mistaken and Mars? gravity is comparable to Earth?s- I?m not sure of this fact.)

JoeDaWolf · 2004-01-14 19:13:33

I made a mistake in my math- The numbers on the site compare Mars' magnetic field strength of 180 million years ago with the present day Earth's; the site says Earth is 30 times stronger today than Mars was in the past, which means that Mars? is even less today. Despite the numbers, 1/30 is still too little to support unprotected life.

Also, earlier on the page, it mentions that because of the low gravity on Mars, a lot of the lighter gases escaped from Mars' atmosphere in the distant past- wouldn't it cost a lot/ take up a lot of resources to continually replenish this loss of gases? Is it even feasible to keep an atmosphere with the low surface gravity?

~Wolf

Icom_Fan · 2004-01-15 04:24:45

If you want Mars to retain an atmosphere, all that you need to do is increase the mass of Mars. Luckily there is a handy source of raw materials next door in the form of the Asteroid Belts. Also, if you feel the need for more water and organics, you could use cometary cores from the outer solar system. The side benefit is that you reduce the a number of objects that could attain an Earth-crossing orbit.

JoeDaWolf · 2004-01-15 17:05:24

Earth is appx 9.3 times as massive as Mars (5.9742 ? 10^24 kg / 6.4191 ? 10^23 kg), and its radius is about 0.53 times as small (3395 km / 6371 km).

If you do the math, Mars has appx .38 the surface gravity of Earth, which means you would need to add 1.63 times the mass of Mars (1.46 x 10^24 kg) to simulate the gravity of Earth, and it would need to be appx evenly distributed...

Shaun Barrett · 2004-01-16 19:16:52

Hi Joe!
I believe there's a fundamental error in your calculations regarding a 'bulked-up' Mars.

You specify adding an extra 1.63 times the present Martian mass, bringing it up to 2.63 times its present figure.
Mars is currently 0.107 times Earth's mass.
Your new Mars would therefore be 2.63 times 0.107, or approximately 0.28 times Earth's mass.

With a present radius of 0.53 times Earth's radius, Mars' volume as a ratio of Earth's is 0.53 cubed. In other words, Mars' volume is 0.1489 times Earth's.

For the sake of simplicity, let's assume all the extra mass you've added is the same density as the present average martian density. Thus, adding 1.63 times the present martian mass will produce a body 2.63 times the present volume.
The NewMars/Earth Volume Ratio will now be
2.63 times 0.1489, which equals 0.39

The radius of your NewMars, will therefore be the-cube-root-of-0.39 times Earth's radius, or 0.73 of an Earth radius.

Your NewMars will have a radius 0.73 times, and a mass 0.28 times, that of Earth.
Therefore, its surface gravity, allowing for the inverse square law of distance, will be
0.28g/(0.73 times 0.73)
= 0.525g

The NewMars you specify wouldn't simulate the gravity of Earth but it would produce just over half of Earth's surface gravity. I've often considered a scenario whereby proto-Mars gathered more mass during its formation, 4.5 billion years ago, and wondered what effect it might have had on the evolution of the martian environment.
I wonder whether a Mars with a 0.5g surface gravity would look any different compared to the one we see today? Would it have held on to a denser atmosphere and remained more clement, or would we need still more gravity to make any appreciable difference?
???

JoeDaWolf · 2004-01-16 19:59:13

g = GM/r^2.... If the Mars radius is 0.53 times as small, then dividing by that squared will appx = 4 (1/ (1/2)^2) = 4)

Since the small size of the radius helps make up for the small mass in making 'g' bigger, you only need to 2.63 times the mass of Mars to simulate Earth's gravity, hence you add 1.63 times the mass of Mars.

The only thing I didn't consider was the new radius if u added a lot of mass- I assume it won't be too influential in the new calculation of gravity... (The whole idea is not conceivable, so let's not even argue it- but I see the reason for your concern)

And yes, a Mars with a higher g would have more of an atmosphere. Also, you need a high mass to keep the dynamo in the core hot so it can keep turning to create a magnetic field.

Meanwhile, no one has answered the more serious question about the magnetic field...

~Wolf

Shaun Barrett · 2004-01-25 07:40:12

Hi again, Joe!
Sorry I haven't come back to you in a while but there's been a lot of good stuff going on at Mars just lately!

It's surprising how much effect the inverse square law actually has on surface gravitational acceleration. By mass alone, you'd expect Mars to have less than 11% of Earth's gravity at the surface, but the fact that Mars' surface is nearly twice as close to its centre of gravity as Earth's surface is, you get nearly 4 times the effective gravity. In this case 0.38g.

But getting back to the magnetic field problem, Earth has had countless magnetic pole reversals over the eons but there's no evidence of any damage to species alive here at the time of these reversals.
This is because the magnetic field isn't that important when it comes to protection from the charged particles of the solar wind and, more importantly the very energetic solar flares which occur periodically. Our atmosphere is our protection.
If the magnetic field were all that stood between us and the solar wind, polar explorers would be irradiated with fast-moving particles directed to the poles by the field and would die a horrible death. This doesn't happen because the atmosphere is just as thick and protective at the poles, of course, as it is at the equator. In fact, Earth's magnetic field greatly concentrates the solar wind at the poles, producing the Aurora Borealis and Aurora Australis as charged particles slam into the atmosphere at high speed, and yet it still poses no threat to a human standing at either the north or south pole.

But the magnetic field does protect our atmosphere from the worst effects of something called 'sputtering' by the solar wind, whereby the upper atmosphere would be eroded by the incessant high speed wind of particles streaming by. This is a process which it's believed may have played a major role in stripping away the martian atmosphere over geological time, since Mars is thought to have lost its magnetic field early in its history.

While any atmosphere we 'build' around Mars will immediately start to leak away due to Mars' lesser gravitational grip on the molecules and because of solar wind sputtering (no global field), it will take anything up to 10 million years to lose most of our new air.
During this time, a human standing unprotected on the surface will be as safe from radiation as anyone standing here on Earth (depending to some extent on the density of that air, of course).

I don't think atmospheric degeneration is going to be anything we'll need to worry about; we'll have millions of years to do something about it.
I'm more concerned about creating the atmosphere in the first place!

JoeDaWolf · 2004-01-25 10:38:30

Why do you say it would take 10 million years? If there's not enough gravity, then the gases that are too light just need to transverse from the surface to outer space.

Going back to what you said about protection at the North and South Pole: Aren't "inhabitants" of these regions only there for, usually, at most, a year. And aren't there only, at most, just a thousand or so scientists? The effects of charged particles could require years to decades of exposure for there to be a significant increase in health problems, and to be able to see these results you might need a population size more varied and bigger than a mere few thousand people.

Additional note: If solar wind isn?t such a main problem, then why is it such a concern to NASA? They give astronauts protection for trips that only last days to weeks.

The program I saw on Nova also showed some serious concern, especially if the field strength was weak for only a few hundred years (and they even talked about the possibility that it would be weak for a few thousand years) during the pole reversal.

~Wolf

DonPanic · 2004-02-13 16:24:48

LO

the moon's orbital period around the earth (~29 days) exactly matches its rotation around its own axis. (This is why we see the same face of the Moon all the time.) This would be a pretty strange coincidence.

That's all but a coincidence, what's said is a tautology.
If you always see the same face of the Moon,
then the Moon's orbital period around the Earth (~29 days)
exactly matches its rotation around its own axis, and reciprocally.
The reason why we see the same face of the Moon,
taking Earth as reference of the Earth-Moon system,
Moon stopped to rotate, is that Moon isn't a sphere,
it's like if its rotation axis didn't match with its gravity center.
This introduced as a crank effect that did slow down its rotation period
till it matched exactly a synchrone rotation period.
The same phenomenon happened with many of jovian and saturnian satellites.

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