Planet Design - moon(s)

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Planet Design - moon(s)

Postby Paladin » Thu Jun 25, 2009 1:48 pm

I was building a couple planets yesterday and got to thinking. Would a planet realistically be able to support human life without a moon? Without lunar tides, could life exist on the planet without technological interference (terrraforming, oxygen scrubbers/purifiers, etc)?
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Re: Planet Design - moon(s)

Postby rust » Thu Jun 25, 2009 1:56 pm

Paladin wrote:Would a planet realistically be able to support human life without a moon?
I would not see any major problem with this. Life on Earth has adapted
to the presence of the moon and its consequences, like the lunar tides,
but I see no reason why it should not have developed without a moon,
although this development would of course have been somewhat diffe-
rent.

Just imagine a planet like Mars, only somewhat bigger and closer to its
sun (to be able to hold more atmosphere and water and to have a war-
mer climate), but also without any moon worth mentioning. I see no rea-
son at all why life should not have developed quite well under such con-
ditions.
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Postby BP » Thu Jun 25, 2009 2:19 pm

Indubitably - probably 50% or more of Earth's oxygen comes from ocean life (phytoplankton mostly?). The regular tide's caused by the moon may contribute to evolutionary development of land creatures, but is not a requirement (waves caused by wind and tectonic activity could have substituted).

Additionally, habitable planets don't necessarily need to be able to evolve human type life - just support it.
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Postby Bygoneyrs » Thu Jun 25, 2009 2:30 pm

Ahh a moon is cool to have though, adds to the plot/sceen for roleplay and etc within the game.

You could have a moon that has H2O ice on it, with a slight atmorsphere, and have it circle a desert world with a lower Oxygen atmosphere. Thus colonists would need a breather to live there. Then make the would rich in minerials, but they mine their water from their own moon. Leaves plenty of room for all sorts of plots.

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Postby EDG » Thu Jun 25, 2009 3:27 pm

Would a planet realistically be able to support human life without a moon? Without lunar tides, could life exist on the planet without technological interference (terrraforming, oxygen scrubbers/purifiers, etc)?
Depends, but the answer is "quite possibly not". The tides aren't the issue, it's the fact that our moon was formed when something about the size of Mars slammed into Earth not long after it formed (giant impacts were not uncommon back then - the planets we see today are merely the survivors of that era, the ones in the most stable orbits and that didn't get hit by other worlds that were forming). When that impact happened, most of Earth's primordial atmosphere was also blasted into space and lost - so if we didn't have the moon, we'd have a much thicker primordial atmosphere, which means it'd take much longer for that to evolve into our secondary atmosphere and possibly the greenhouse effect from the thicker atmosphere would have roasted the planet by now.

Some scientists therefore think that a giant impact is required in order to have a habitable, earth-like surface environment.

You can also check this out:
http://www.astrosociety.org/education/p ... 33/33.html

The author (Neil F Comins) wrote a book called "What if... the moon didn't exist", which addressed this and a bunch of other "what if" questions. It's a really good resource for any worldbuilders out there.
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Postby kristof65 » Thu Jun 25, 2009 3:33 pm

In doing some research for designing my own aliens for a custom setting, it seemed to me that the current prevailing theories for evolution of sentient life was that our moon provides a stabilizing (yet cyclical) influence on Earth, thus contributing to the conditions needed for us to evolve to where we are today, and that it would be more likely for more complex forms of life to evolve on planets with moons providing similar stability.

There was no indication that a world would have to have a moon to be able to support life, only that moons that somehow stabilized the larger body's environment would more often tend to have complex life that evolved there. In the stuff I read, there were other examples of other ways that a planet could get the needed stabilization, it's just that moons were the easiest.

Finally, a disclaimer - this is a summary of my impressions of the material I read - basically it was a couple of world building books, and a couple specifically on aliens - all of them were aimed at helping science fiction writers make more believable worlds and aliens.
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Postby The Chef » Thu Jun 25, 2009 4:31 pm

also doesn't the moon serve as a barrier to lots of other deadly stuff that wants to kill us such as meteor strikes?

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Postby Rikki Tikki Traveller » Thu Jun 25, 2009 4:49 pm

The moon helps stablize the Earth's spin as well. Our axis is tilted at 23degrees and has been for a long time. Mars on the other hand has evidence of once having had a much larger and a much smaller axial tilt. This of a spinning top. The direction of the rotation axis precesses a lot as it rotates, but if you watch closely, you will also see that it changes it's angle quite a bit too. The moon helps limit that for the Earth, so our climate is more stable due to the moon. That may or may not help the development of life and intelligence.
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Postby daryen » Thu Jun 25, 2009 5:39 pm

EDG wrote:Depends, but the answer is "quite possibly not". The tides aren't the issue, it's the fact that our moon was formed when something about the size of Mars slammed into Earth not long after it formed (giant impacts were not uncommon back then - the planets we see today are merely the survivors of that era, the ones in the most stable orbits and that didn't get hit by other worlds that were forming). When that impact happened, most of Earth's primordial atmosphere was also blasted into space and lost - so if we didn't have the moon, we'd have a much thicker primordial atmosphere, which means it'd take much longer for that to evolve into our secondary atmosphere and possibly the greenhouse effect from the thicker atmosphere would have roasted the planet by now.
So, to put it in much simpler terms, if the Earth had not had the impact that formed the moon, it would have had too thick of an atmosphere and effectively become another Venus?
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Postby BP » Thu Jun 25, 2009 6:31 pm

FYI: A week ago today The Lunar Reconnaissance Orbiter launched - the first NASA lunar launch in 10 years IIRC.

My dad was heavily involved in the LAMP instrument - which will map the entire surface including the dark side in the far UV. One of its goals is to look for ice and frost specially at the poles. (P.S. the full abbreviation of part of the instrument packages is LAVA LAMP :roll: )

(I'm looking forward to some cool maps next year when the scans are all done :D ).
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Postby AndrewW » Thu Jun 25, 2009 6:43 pm

BP wrote:FYI: A week ago today The Lunar Reconnaissance Orbiter launched - the first NASA lunar launch in 10 years IIRC.
Don't forget it wasn't the only one launched. The Lunar Crater Observation and Sensing Satellite was launched on the same rocket.
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Postby BP » Thu Jun 25, 2009 7:06 pm

AndrewW wrote:Don't forget it wasn't the only one launched. The Lunar Crater Observation and Sensing Satellite was launched on the same rocket.
Yep -part of the same launch - NASA figured out a double duty with the extra lift capability. The impactor part should expell a 6 mile plume visible from earth based telescopes sometime in Oct. IIRC.

While LAMP looks for surface water-ice/frost - LCO looks for sub-surface ice in permanent shadow inside a crater!
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Postby EDG » Thu Jun 25, 2009 7:27 pm

BP wrote:(P.S. the full abbreviation of part of the instrument packages is LAVA LAMP :roll: )
The guys that think up the NASA acronyms are awesome. MESSENGER is my favourite (very appropriate given that's the name of the Mercury orbiter) :)
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Postby Rikki Tikki Traveller » Thu Jun 25, 2009 8:42 pm

BP wrote:
AndrewW wrote:Don't forget it wasn't the only one launched. The Lunar Crater Observation and Sensing Satellite was launched on the same rocket.
Yep -part of the same launch - NASA figured out a double duty with the extra lift capability. The impactor part should expell a 6 mile plume visible from earth based telescopes sometime in Oct. IIRC.

While LAMP looks for surface water-ice/frost - LCO looks for sub-surface ice in permanent shadow inside a crater!
Lunar Crater Observation and Sensing Satellite...

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Postby BP » Fri Jun 26, 2009 12:54 am

EDG wrote:...The guys that think up the NASA acronyms are awesome. ...
LAMP evolved from ALICE which went aboard ROSETTA - the ESA comet chaser...

But my personal favorite is still DEEP IMPACT.


Back on topic - '...impact happened, most of Earth's primordial atmosphere was also blasted into space and lost - so if we didn't have the moon, we'd have a much thicker primordial atmosphere...' - a different mass/velocity impact could have resulted in no moon, but the loss of the atmo... so a 'moon' may not be a requirement but an impact or cataclysm might.

As for its effect on the Earth's species - I seem to recall that the moon is moving away from the earth and should escape orbit entirely (in a long while) - and that working backwards the models predicted the Moon was in a very close orbit (billions of years ago) and at a much different inclination. I wonder how much greater/different its impact on early evolution (if any)?

As another aside - I recall a moon orbiting an asteroid was found some time back and Pluto has several moons 'now' - are there any cases of moons having moons in our solar system - and how possible/probable is that in terms of stability or uniqueness of masses. (The same for rings?)
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Postby EDG » Fri Jun 26, 2009 1:40 am

BP wrote:As for its effect on the Earth's species - I seem to recall that the moon is moving away from the earth and should escape orbit entirely (in a long while) - and that working backwards the models predicted the Moon was in a very close orbit (billions of years ago) and at a much different inclination. I wonder how much greater/different its impact on early evolution (if any)?
IIRC it won't escape orbit within the lifetime of the solar system, it'll take a long time for it to get to that stage (by which point the Earth may well be gobbled up by the sun, if its orbit doesn't expand first)

As another aside - I recall a moon orbiting an asteroid was found some time back and Pluto has several moons 'now' - are there any cases of moons having moons in our solar system - and how possible/probable is that in terms of stability or uniqueness of masses. (The same for rings?)
Moons can have satellites, but very briefly - the orbits are all unstable (largely because of the primary body) and they all collapse onto the satellite surface in a geological blink of an eye.
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Postby BP » Fri Jun 26, 2009 2:32 am

EDG wrote:...IIRC it won't escape orbit within the lifetime of the solar system, it'll take a long time for it to get to that stage (by which point the Earth may well be gobbled up by the sun, if its orbit doesn't expand first)
Thought it was somewhere on the order of 1/2 billion years - a ways before the boiling Earth period - but I'd go with your IIRC more than my own :wink:

EDG wrote:...Moons can have satellites, but very briefly - the orbits are all unstable (largely because of the primary body) and they all collapse onto the satellite surface in a geological blink of an eye.
I take that as a no to any such discoveries in our solar system. Any opinion on that 'geological blink' with regards to modeling Traveller systems - and under what unique conditions it would exist long enough to provide a reasonable Traveller setting (thousands of years would allow ample time)...

I would think a binary moon system might have a little better chance at stability - but be even a greater rarity. Though Charon and Pluto have a barycentric orbit if I recall and Pluto is smaller than the moon - having them orbit a planet stably would probably require extremes of distance/low mass of star and distance from planet...
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Postby EDG » Fri Jun 26, 2009 2:42 am

BP wrote:Thought it was somewhere on the order of 1/2 billion years - a ways before the boiling Earth period - but I'd go with your IIRC more than my own :wink:
The numbers I've heard are more like 8-10 billion years hence. The Sun's got about another 5 billion left on the clock.

I take that as a no to any such discoveries in our solar system. Any opinion on that 'geological blink' with regards to modeling Traveller systems - and under what unique conditions it would exist long enough to provide a reasonable Traveller setting (thousands of years would allow ample time)...
Well you'd be talking about a cataclysmic event of somesort to make the moon's satellite in the first place (like a big impact), which could itself probably affect the primary as well as the moon. Thousands of years would probably be at the long end, given that the satellite would have a short orbital period around the moon.

I would think a binary moon system might have a little better chance at stability - but be even a greater rarity.
I think actually that's even less stable.
Though Charon and Pluto have a barycentric orbit if I recall and Pluto is smaller than the moon - having them orbit a planet stably would probably require extremes of distance/low mass of star and distance from planet...
They're only a double planet *now* because they're so far from the sun. If they were at earth's distance I think solar tides would screw up the "binary-ness" pretty quickly.
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Postby Rikki Tikki Traveller » Fri Jun 26, 2009 1:28 pm

Actually, it may not escape.

There is currently a tranfer of rotational energy from the Earth to the Moon. Therefore, the moon is moving slowly away from the Earth and the Earth's rotation is slowing down.

Eventually, the Earth will become Tidally locked to the Moon, like the moon is now. At that point, the moon will no longer be moving away from the Earth. Then, due to friction, the two will slowly begin to move towards each other, eventually crashing together, they will still be tidally locked the entire time.

The question becomes, will the solar gravitic effects be strong enough to pull the moon away at that point of greatest distance, or can the Earth hang on to the Moon?
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Postby Dave Chase » Fri Jun 26, 2009 7:00 pm

Rikki Tikki Traveller wrote:Actually, it may not escape.

... Therefore, the moon is moving slowly away from the Earth and the Earth's rotation is slowing down.

Eventually, the Earth will become Tidally locked to the Moon, like the moon is now. At that point, the moon will no longer be moving away from the Earth. Then, due to friction, the two will slowly begin to move towards each other, eventually crashing together, they will still be tidally locked the entire time.
Sounds like you work for the United States Enviormental Proctection Agency.
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The question becomes, will the solar gravitic effects be strong enough to pull the moon away at that point of greatest distance, or can the Earth hang on to the Moon?
And so we (U.S.A.) need to tax not only the U.S. but the entire world to the tune of $17,000,000,000,000,000,000,000.00 to be spent over the next 20 years to stop this great castrophic diasester from taking place.

NOTE: the amount listed is counting the rate of inflation versus the loss of the U.S. Dollar against forgein markets. If done in current terms it would only have 12 zeros to the left of the decimal. :)

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