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Searching for Theia, the mother of the Moon



 
 
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  #21  
Old April 13th 09, 03:48 PM posted to sci.astro
dlzc
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Default Searching for Theia, the mother of the Moon

Dear Yousuf Khan:

On Apr 12, 10:05*pm, Yousuf Khan wrote:
N:dlzcD:aol T:com (dlzc) wrote:
Also if a Mars-sized object hit Earth, wouldn't we
see a somewhat lopsided Earth? They say that
most of Theia sunk to the core of Earth, but that
would require displacement of everything that was
already at the core of the Earth. It would require
the Earth to have blown up and come back
together for such perfectly round mixing of the
combined bodies to happen again. And the Earth
would look a bit younger than the other planets in
the Solar System, because it would look like it
formed later.


There is no need for Earth+Theia to do more than
melt. *There was plenty of extra energy to permit
that. *Then the products spin, with a very oblate
shape, a lobe starts to form as the system is
unstable, the lighter materials get pulled up into
the lobe, and the lobe parts. *See it in lava lamps
sometimes.


The Earth-Moon Lava Lamp Theory. I think this was
actually the popular theory about the Moon's
formation back in the 60's, wasn't it? They were
very familiar with lava lamps back then. :-)


Yes....

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.

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.

Now if Theia was actually a Mars-sized black
hole instead, then it could easily make its way
to centre of the Earth and provide power source for
the magnetic field that Earth has.


Mars *massed* black hole, you mean. *No the
structure of the Earth is not solid enough to
permit that... we'd flow in.


Then I wonder if we'd flow in and become part of a
black hole,


Yes, no choice.

or would the mass of the Earth, being greater than
the black hole, turn the black hole into a neutron
star (neutron planet, maybe)?


Mass uniformly distributed outside has zero net pull on the interior.
And again, the entire planet would end up as a neutron star, no
choice... given a neutron star core. The Earth would be about 3"
diameter or 6" diameter either way.

I mean a merger of two solid planets can't be
nearly as simple as say the merger of galaxies,
which have large gaps in between.


Agreed. *I would expect quite a bit of debris.
*Locally, the Moon would sweep that. *But in our
solar L4 and L5...


Our own Trojan asteroids.


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

Besides the collision theory, and the capture theory,
why can't the Moon have simply formed where it is
now? That would seem to be the simplest answer.


We have records that date back to 2.2 Gy ago that
says the Moon was much closer.


I don't mean really in the exact orbital position it is in
right now. I meant that it formed naturally somewhere
in orbit around the Earth.

There's a lot of rules about how large a satellite can
get given the main planet's mass. Apparently the
Moon is too large to fit those models. But why?


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

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...

David A. Smith
  #22  
Old April 13th 09, 04:03 PM posted to sci.astro
Dr J R Stockton[_25_]
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Posts: 14
Default Searching for Theia, the mother of the Moon

In sci.astro message , Sun, 12 Apr
2009 10:24:59, "N:dlzc D:aol T:com (dlzc)" posted:

Your sagacity is imperceptible.


He corrected my misunderstanding on the next post. Thanks for
taking this opportunity to **** on me. I hope I have saved a
baby cat from being kicked somewhere near you.


You should be aware that Usenet is not an instantaneous medium
throughout : this site transfers News twice a day.

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.

--
(c) John Stockton, nr London UK. Turnpike v6.05 MIME.
Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links.
Check boilerplate spelling -- error is a public sign of incompetence.
Never fully trust an article from a poster who gives no full real name.
  #23  
Old April 13th 09, 04:16 PM posted to sci.astro
BradGuth
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Posts: 21,544
Default Searching for Theia, the mother of the Moon

On Apr 12, 10:10*pm, Yousuf Khan wrote:
wrote:
Discovery of water in Moon's ancient rocks challenges collision
theory.
http://news.bbc.co.uk/2/hi/science/nature/7497715.stm
A global ocean, such as exists on Europa, Titan or Earth, *can
explain
the topography and composition of lunar surface. Especially the
separation of highlands anorthosite from mare basalt. *John Curtis


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?

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?

* * * * Yousuf Khan


Vacuum and water simply do not mix, especially if there's and IR~UV
energy to deal with. However, at first whatever sufficiently thick
ice and vacuum get along rather nicely if there's a sufficient rocky
core of 7.35e22 kg to work with.

Notice how among many odd things there's still no objective science as
to ice coexisting in 1 AU space.

~ BG
  #24  
Old April 13th 09, 04:25 PM posted to sci.astro
Dr J R Stockton[_25_]
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Posts: 14
Default Searching for Theia, the mother of the Moon

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 .

The reference that I had in mind for that is apparently dead. The page
has quietly moved to http://wmap.gsfc.nasa.gov/media/ContentMedia/lagra
nge.pdf, and gives a different form.

Isn't the Sun-Jupiter mass ratio over 1000:1?


Yes. Re-read what you quoted.

--
(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.
  #25  
Old April 13th 09, 08:26 PM posted to sci.astro
[email protected]
external usenet poster
 
Posts: 5
Default Searching for Theia, the mother of the Moon

On Apr 12, 10:10*pm, Yousuf Khan wrote:
wrote:
Discovery of water in Moon's ancient rocks challenges collision
theory.
http://news.bbc.co.uk/2/hi/science/nature/7497715.stm
A global ocean, such as exists on Europa, Titan or Earth, *can
explain
the topography and composition of lunar surface. Especially the
separation of highlands anorthosite from mare basalt. *John Curtis


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.

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


  #26  
Old April 13th 09, 10:51 PM posted to sci.astro
BradGuth
external usenet poster
 
Posts: 21,544
Default Searching for Theia, the mother of the Moon

On Apr 13, 12:26*pm, wrote:
On Apr 12, 10:10*pm, Yousuf Khan wrote: wrote:
Discovery of water in Moon's ancient rocks challenges collision
theory.
http://news.bbc.co.uk/2/hi/science/nature/7497715.stm
A global ocean, such as exists on Europa, Titan or Earth, *can
explain
the topography and composition of lunar surface. Especially the
separation of highlands anorthosite from mare basalt. *John Curtis


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.

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 otherwise not capable of excluding a lithobraking encounter with
an icy Selene, and subsequent capture process that would have taken
hundreds of years after Selene encountered Earth, before the
terrestrial skies would have cleared enough to even notice that we'd
obtained a moon.

~ BG
  #27  
Old April 14th 09, 02:35 AM posted to sci.astro
Odysseus[_1_]
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Posts: 534
Default Searching for Theia, the mother of the Moon

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.

--
Odysseus
  #28  
Old April 14th 09, 03:43 PM posted to sci.astro
dlzc
external usenet poster
 
Posts: 1,426
Default Searching for Theia, the mother of the Moon

On Apr 13, 8:03*am, Dr J R Stockton
wrote:
In sci.astro message , Sun, 12 Apr
2009 10:24:59, "N:dlzcD:aol T:com (dlzc)" posted:

Your sagacity is imperceptible.


He corrected my misunderstanding on the next post.
Thanks for taking this opportunity to **** on me. *I
hope I have saved a baby cat from being kicked
somewhere near you.


You should be aware that Usenet is not an
instantaneous medium throughout : this site transfers
News twice a day.

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.

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.

As long as this "place" exists, it is a permanent record of behavior,
a resource for research, and the only news magazine I get. The ads
suck...

David A. Smith
  #29  
Old April 14th 09, 05:50 PM posted to sci.astro
Yousuf Khan
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Posts: 594
Default Searching for Theia, the mother of the Moon

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. 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 crustal
imbalances should correspond to where the Earth and Moon separated from
each other. Now, the Moon has no major tectonic activity (apart from
some early vulcanism), so the crustal imbalance on the Moon stays
basically where it was originally. The Earth has all kinds of tectonic
activity and over the course of billions of years those continents ...
er, imbalances in the crust ... break up and drift all over the place,
redistributing themselves over the Earth in several places.

I'm not saying that all of the continents arose as a result of the break
out of the Moon, but I'm sure the initial continents must have started
that way. The remaining mass of continents may have formed as a result
of vulcanism, and some flexure in the crust as the Earth readjusted
itself to a round shape.

Yousuf Khan
  #30  
Old April 14th 09, 06:30 PM posted to sci.astro
John Park
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Posts: 155
Default Searching for Theia, the mother of the Moon

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.

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?

--John Park




 




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