A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Astronomy and Astrophysics » Astronomy Misc
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Searching for Theia, the mother of the Moon



 
 
Thread Tools Display Modes
  #31  
Old April 14th 09, 09:06 PM posted to sci.astro
dlzc
external usenet poster
 
Posts: 1,426
Default Searching for Theia, the mother of the Moon

Dear Yousuf Khan:

On Apr 14, 9:50*am, Yousuf Khan wrote:
Odysseus wrote:
In article , Yousuf Khan
wrote:


snip
But still wouldn't we see some sort of tail or other
formation on Earth at the point where the Moon
might have plopped off? I think we see a difference
in crustal thickness on the Moon between its
Earth-facing side and its space-facing side. But
we don't see a similar crustal difference on Earth.
Unless, we talk about the crustal diffences
between the oceanic plates and the continental
plates, but they're distributed all over the place. I
wonder if the formation of the Moon started this
entire continental plate business?


The Earth remains tectonically active; convective
and density-driven flows in the interior have had
plenty of time to smooth out irregularities or
asymmetries. As for the surface, the continents
must have been rearranged or recycled at least a
dozen times since the crust cooled -- so although
there might be some traces left, they'd be so well
buried or widely scattered as to be more or less
undetectable.


I'm thinking the existence of the continents
themselves are the smoking gun.


Pour water on the Moon, and you'll have "continents" too. They won't
follow tectonic plates around...

*Think about it this way, we know that there is an
imbalance in the crust of the Moon, but there
should be some sort of corresponding imbalance in
the crust of the Earth which we don't see.


The Earth kept the heavy materials, including fissible ones. The
Earth had an insulating atmosphere. The Earth has a larger volume-to-
surface-area ratio, so it will retain heat longer.

We *can't* still show the results of a "parting line"...

David A. Smith
  #32  
Old April 14th 09, 10:39 PM posted to sci.astro
Dr J R Stockton[_25_]
external usenet poster
 
Posts: 14
Default Searching for Theia, the mother of the Moon

In sci.astro message
ooglegroups.com, Tue, 14 Apr 2009 07:43:23, dlzc
posted:
On Apr 13, 8:03*am, Dr J R Stockton
wrote:


After your unsuccessful attempt to do that to me
in the matter of the gravity tractor, it seemed
appropriate to demonstrate to you how it should
be done. *One essential is to be factually correct.


I expressed concern over methods that a "gravity tractor" could push
away the object it is trying to "pull". You did nothing more in
addressing these concerns, than tell me I needed to do the math to
show it was a problem.



This sends the message that *you* had not done
the math, and simply don't "feel" it to be an issue.


If you received that message, your receiver is faulty. You asserted,
necessarily without proof, that the path of the asteroid might be
significantly affected, in comparison with the gravitational effect, by
heat from the tractor; it is for you to prove it. Manifestly you
cannot.

In any case, it does not matter; because Big G is in fact not at all
big, the intended propulsive force is small. Clearly the line of thrust
must average aft-wards, and the bulk of the thrust must miss the
asteroid. Therefore one could, if necessary, mount the engine on,
essentially, a long pole in the line of thrust so that the engine itself
was aft of the asteroid, and any repulsive force from it would be of
beneficial sign. Or one might interpose a thin shield.

Consider, in SI, an asteroid radius 50, density 2500, clearance between
exhaust and surface 5, tractor mass 5000, optimally orbiting. The
effective accelerating force is about 56 mN (gravity2.htm).

Postulate that the amount of the tractor's radiation impinging on and
absorbed by the asteroid could be equivalent to that from unit area at
temperature 1000. The Stefan-Boltzmann constant is 5.7e-8, so the power
is 5.7e4 (!!!); the force is that over c, or 0.19 mN. Less than 1 %; it
still needs to be resolved into the direction of motion; and in taking
the entire radiation from a square metre at a thousand K I've been very
generous indeed. We are of course not considering a typical chemical
rocket, which has a large hot engine; an electric engine will itself not
be hot; its exhaust may be, but it will also be narrow, optically thin,
or both.



I don't want you to supply the math. I am not interested in
"oneupmanship". I am not interested in being right. I am just
interested in someone providing answers to questions. I personally
thank you for being just like the pompous, cubicle-minded jerks that
sent me here nine years ago.


With enough effort, perhaps you can be speeded on your way. Usenet is
no place for those with an inferiority complex, however well-justified
it may be.

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity2.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
  #33  
Old April 14th 09, 11:44 PM posted to sci.astro
Yousuf Khan
external usenet poster
 
Posts: 594
Default Searching for Theia, the mother of the Moon

dlzc wrote:
Dear Yousuf Khan:

On Apr 12, 10:05 pm, Yousuf Khan wrote:
But still wouldn't we see some sort of tail or other
formation on Earth at the point where the Moon
might have plopped off?


No, it was essentially all liquified.


What if it was semi-liquified? Parts that are liquid, and parts that are
still solid. Read why I'm suggesting that below.

I think we see a difference in crustal thickness
on the Moon between its Earth-facing side and
its space-facing side.


The Earth provides a temperature above the CMBR, and some tidal
heating (before the Moon becomes tidally locked), so it would make
sense that the Earth-facing side had thinner crust.

But we don't see a similar crustal difference on
Earth.


Look where the tectonic plates are most finely broken.

Unless, we talk about the crustal diffences between
the oceanic plates and the continental plates, but
they're distributed all over the place. I wonder if the
formation of the Moon started this entire continental
plate business?


No, I'd put that squarely on structures internal to the Earth,
upwellings in the core flows and such.


I'm sure parts of the continents were produced by pure volcanic
activity, like you say. But I think the extreme level of
continentalization on Earth must've been started by the lopping off of
the Moon. You just have to look at the planet most nearest our size,
Venus, to see that it's got nothing near the continents we got. It's got
two major continents, Ishtar Terra & Aphrodite Terra. Ishtar is only
the size of the continental US, while Aphrodite is only half the size of
Africa. I think Venus' continents were probably produced through just
standard volcanic processes alone.

Venus Global Geography
http://www.windows.ucar.edu/tour/lin...ontinents.html

Venus - What the Earth would have been like
http://www.spacedaily.com/news/life-01x2.html

However, I think Earth's continents were started by the scar left over
from the Moon scission. Where the Moon plopped off the Earth, it left a
scar which became the basis of Earth's continents. The scar on Earth is
probably bigger than the area from which the Moon arose. And over the
years, the scars (the continents) redistributed themselves all over the
Earth through tectonics.

Our own Trojan asteroids.


Yes, an asteroid belt. But do we see anything like that for any
planet?


Jupiter?

Good question. I know Roche limit would apply had the Moon started
significantly closer...


If the Moon plopped off of a super-fast spinning Earth, the moment the
Moon left it might have reduced the Earth's spin substantially, and been
thrown a large enough distance away to avoid the Roche limit.

What would happen to Earth's (and the Moon's surface) if a "dust
cloud" at about 1000K blew by outside the heliosphere over a period of
a few centuries? This would allow the Sun to be an Easy Bake Oven
(R), and gloss over all sorts of formation details...



Sure, but why would you need a special dust cloud to blow by it? At that
time wouldn't there already be a lot of dust in the vicinity since the
Solar system was forming at the time?

Yousuf Khan
  #34  
Old April 14th 09, 11:53 PM posted to sci.astro
Yousuf Khan
external usenet poster
 
Posts: 594
Default Searching for Theia, the mother of the Moon

dlzc wrote:
Dear Yousuf Khan:

On Apr 14, 9:50 am, Yousuf Khan wrote:
I'm thinking the existence of the continents
themselves are the smoking gun.


Pour water on the Moon, and you'll have "continents" too. They won't
follow tectonic plates around...


They'll follow impact crater rims though.

Think about it this way, we know that there is an
imbalance in the crust of the Moon, but there
should be some sort of corresponding imbalance in
the crust of the Earth which we don't see.


The Earth kept the heavy materials, including fissible ones. The
Earth had an insulating atmosphere. The Earth has a larger volume-to-
surface-area ratio, so it will retain heat longer.

We *can't* still show the results of a "parting line"...



No, we can't show the original continent, no doubt, but I think the
existence of such large continents at all might be the clue that was
just lying there right under our noses, literally. Under our feet even.
Venus never grew continents quite as large as us.

Yousuf Khan
  #35  
Old April 15th 09, 12:56 AM posted to sci.astro
N:dlzc D:aol T:com \(dlzc\)[_440_]
external usenet poster
 
Posts: 1
Default Searching for Theia, the mother of the Moon

Dear Dr J R Stockton:

"Dr J R Stockton" wrote in message
nvalid...
....
With enough effort, perhaps you can be speeded
on your way. Usenet is no place for those with an
inferiority complex, however well-justified it may be.


Further insults, and continued pirating of an unrelated thread
noted.

David A. Smith


  #36  
Old April 15th 09, 01:13 AM posted to sci.astro
N:dlzc D:aol T:com \(dlzc\)[_441_]
external usenet poster
 
Posts: 1
Default Searching for Theia, the mother of the Moon

Dear Yousuf Khan:

"Yousuf Khan" wrote in message
...
dlzc wrote:
Dear Yousuf Khan:

On Apr 12, 10:05 pm, Yousuf Khan wrote:
But still wouldn't we see some sort of tail or other
formation on Earth at the point where the Moon
might have plopped off?


No, it was essentially all liquified.


What if it was semi-liquified? Parts that are liquid,
and parts that are still solid. Read why I'm
suggesting that below.

I think we see a difference in crustal thickness
on the Moon between its Earth-facing side and
its space-facing side.


The Earth provides a temperature above the
CMBR, and some tidal heating (before the Moon
becomes tidally locked), so it would make
sense that the Earth-facing side had thinner crust.

But we don't see a similar crustal difference on
Earth.


Look where the tectonic plates are most finely
broken.

Unless, we talk about the crustal diffences between
the oceanic plates and the continental plates, but
they're distributed all over the place. I wonder if the
formation of the Moon started this entire continental
plate business?


No, I'd put that squarely on structures internal to the
Earth, upwellings in the core flows and such.


I'm sure parts of the continents were produced by
pure volcanic activity, like you say.


I didn't say that, but those flows will have consumed the entire
crust of the planet over billions of years. If you want to look
for ther remains of "Mu", you'd need to look at subduction zones,
like north of New Zealand.

But I think the extreme level of continentalization on
Earth must've been started by the lopping off of the Moon.


Who says the opposite is not closer to the truth?

You just have to look at the planet most nearest
our size, Venus, to see that it's got nothing near
the continents we got. It's got two major
continents, Ishtar Terra & Aphrodite Terra. Ishtar
is only the size of the continental US, while
Aphrodite is only half the size of Africa. I think
Venus' continents were probably produced
through just standard volcanic processes alone.


Hard to see a strong parallel.

However, I think Earth's continents were started by
the scar left over from the Moon scission. Where
the Moon plopped off the Earth, it left a scar which
became the basis of Earth's continents.


.... or the floor of the Pacific ocean.

The scar on Earth is probably bigger than the area
from which the Moon arose. And over the years, the
scars (the continents) redistributed themselves all
over the Earth through tectonics.


You keep saying this, but there is no evidence of rock this old,
or concentrations of materials "idenitical" to that from which
the Moon is made.

Our own Trojan asteroids.


Yes, an asteroid belt. But do we see anything
like that for any planet?


Jupiter?


Jupiter is the major player, and I suspect assures that nothing
inside its orbit is stable long term. Maybe it could have forced
a slow migration of an Earth-trojan Theia into a collision...

Good question. I know Roche limit would apply
had the Moon started significantly closer...


If the Moon plopped off of a super-fast spinning Earth,
the moment the Moon left it might have reduced the
Earth's spin substantially, and been thrown a large
enough distance away to avoid the Roche limit.


Roche applies to gravitationally bound objects. An object that
is entirely liquid could get some additional "attraction" from
self-affinity...

What would happen to Earth's (and the Moon's
surface) if a "dust cloud" at about 1000K blew by
outside the heliosphere over a period of a few
centuries? This would allow the Sun to be an Easy
Bake Oven (R), and gloss over all sorts of formation
details...


Sure, but why would you need a special dust cloud
to blow by it?


Insulation between the Earth and the Sun lowers our temperature.
And there was a post recently that the Earth is passing through
such a dust cloud, if not as thick as it would need to be.

At that time wouldn't there already be a lot of dust
in the vicinity since the Solar system was forming
at the time?


Only dust outside our orbit places us "in the oven".

David A. Smith


  #37  
Old April 15th 09, 01:20 AM posted to sci.astro
N:dlzc D:aol T:com \(dlzc\)[_442_]
external usenet poster
 
Posts: 1
Default Searching for Theia, the mother of the Moon


"Yousuf Khan" wrote in message
...
dlzc wrote:
Dear Yousuf Khan:

On Apr 14, 9:50 am, Yousuf Khan wrote:
I'm thinking the existence of the continents
themselves are the smoking gun.


Pour water on the Moon, and you'll have "continents" too.
They won't
follow tectonic plates around...


They'll follow impact crater rims though.


Only in "local detail". The gross structure is different:
http://rst.gsfc.nasa.gov/Sect19/Sect19_3.html

Think about it this way, we know that there is an
imbalance in the crust of the Moon, but there
should be some sort of corresponding imbalance in
the crust of the Earth which we don't see.


The Earth kept the heavy materials, including fissible
ones. The Earth had an insulating atmosphere. The
Earth has a larger volume-to-surface-area ratio, so it
will retain heat longer.

We *can't* still show the results of a "parting line"...



No, we can't show the original continent, no doubt,
but I think the existence of such large continents at
all might be the clue that was just lying there right
under our noses, literally. Under our feet even. Venus never
grew continents quite as large as us.


If the Earth+Moon mass lobed, not single but double, then the
supercontinent that spawned all of ours today was likely
*opposite* where the Moon departed.

David A. Smith


  #38  
Old April 15th 09, 02:08 PM posted to sci.astro
Dr J R Stockton[_25_]
external usenet poster
 
Posts: 14
Default Searching for Theia, the mother of the Moon

In sci.astro message , Tue, 14 Apr 2009
17:30:10, John Park posted:
Dr J R Stockton ) writes:
In sci.astro message , Sun, 12 Apr 2009
16:52:19, Yousuf Khan posted:
Dr J R Stockton wrote:
Any gravitationally-bound two-body system has five Lagrange points; if
the mass ratio is less than about 25:1, or if there are other
sufficiently massive bodies near by, no points are dynamically stable,
except in special cases - in which case they would not be the points for
which Lagrange is known.


What's special with the 25:1 mass ratio?


The arithmetic is non-trivial. The actual figure is from
27(m1m2 + m2m3 + m3m1) = (m1 + m2 + m3)^2
as m3 - 0
m1^2 - 25 m1m2 + m2^2 = 0
so
m1/m2 = 25 ± Root ((625-4) / 2) = 24.9599 .

^^^^^^^^^^^^^^^^^^^^^^^^

( 25 ± Root (625-4) ) / 2, I think.


Agreed : transcription error.



What's special about this limit, m3 -- 0, that makes it the case
universally referred to? Any reason m2 = m3 shouldn't occur, for instance?


One only gets a two-body system when one of m1, m2, m3 is negligible.
And that is the practical case.

ISTM that Lagrange would surely have given some consideration to the
more general case - and probably gave up on it quite rapidly; or else
almost no-one could understand him on it.

The further the mass of m3 gets from zero towards the masses of m1
and/or m2, the less "Lagrange" the points become; AFAIK, they may merge,
fizzle out, or wander off to infinity.

Read http://groups.google.com/group/rec.a...earch?group=re
c.arts.sf.science&q=In+order+to+be+stable%2C+the+m asses+of+the+three+bod
ies+must+obey+the+formula&qt_g=Search+this+group !

--
(c) John Stockton, nr London, UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
  #39  
Old April 15th 09, 03:07 PM posted to sci.astro
Dr J R Stockton[_25_]
external usenet poster
 
Posts: 14
Default Searching for Theia, the mother of the Moon

In sci.astro message , Tue, 14 Apr 2009
18:44:01, Yousuf Khan posted:

However, I think Earth's continents were started by the scar left over
from the Moon scission. Where the Moon plopped off the Earth, it left a
scar which became the basis of Earth's continents. The scar on Earth is
probably bigger than the area from which the Moon arose. And over the
years, the scars (the continents) redistributed themselves all over the
Earth through tectonics.


An impactor of the postulated speed size, and angle would have left the
Earth's crust and much of the mantle, at least, substantially molten for
many millennia, AIUI : and the Moon was not "excavated" as a lump, but
accumulated from material splashed into orbit.

Remember, any body which falls from infinity and is not slowed
significantly by the atmosphere will hit the Earth's surface at 40,000
kph or more, substantially greater than the speed of sound in a solid.
The impact is by no means as gentle as is flying a supersonic plane into
a substantial cumulo-granite formation.



If the Moon plopped off of a super-fast spinning Earth, the moment the
Moon left it might have reduced the Earth's spin substantially, and
been thrown a large enough distance away to avoid the Roche limit.



A super-spinning Earth could not have accreted; an impact large enough
to speed it up that much would spatter it.

Spinning-up a gravitationally-bound ball would cause material in a
multitude of relatively small pieces to pour up off the Equator; only a
ball bound by uneven solid strength could come apart in lumps.

--
(c) John Stockton, near London.
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
Correct = 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with "" or " " (SoRFC1036)
  #40  
Old April 15th 09, 11:42 PM posted to sci.astro
Yousuf Khan
external usenet poster
 
Posts: 594
Default Searching for Theia, the mother of the Moon

wrote:
On Apr 12, 10:10 pm, Yousuf Khan wrote:
The scientists in the article you quoted were trying to fit it around
the collision hypothesis. They were speculating that the water came up
to the Moon during the collision event. Why do you think that's not
plausible?

Colision temperature ~7000 K (if memory serves) would split
water into oxygen and hydrogen, the latter escaping into space.
Absence of water from the Moon is a tenet (perhaps even the
lynchpin) of the collision theory.


So you're saying that these guys are trying to keep a theory alive that
has wide support and appeal, even though their observations may have
just killed it?

Also which model do you think is more likely for the Moon, if not the
collision model? The capture model, or the Earth-Moon co-formation model?

The evidence for global ocean confirms the commonality
of planetary origins. Capture or co-formation are less
incompatible with a global ocean on the Moon. John Curtis


But capture would indicate slightly different origins. Same solar
system, different sub-locations. There might be enough commonality in
the same solar system, but maybe there are some localized conditions
that aren't the same? If the Moon were captured vs. co-formed, then
would be different ingredients, like water?

Yousuf Khan
 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ESA watched full Moon withering behind Mother Earths shadow (Forwarded) Andrew Yee[_1_] News 0 March 7th 07 10:21 PM
Theia (Proto-Luna) was probably a gas planet Andrew Nowicki Space Science Misc 0 September 21st 06 11:58 PM
How long do we keep searching for ETs? Rakesh Sharma SETI 8 September 18th 04 06:40 AM
Searching for a lost URL Andy Dix UK Astronomy 2 April 1st 04 05:45 PM
Searching 6960 manastro Amateur Astronomy 0 February 29th 04 11:04 AM


All times are GMT +1. The time now is 02:59 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.