BBC News - Earth may once have had two moons

BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929

On 8/3/11 7:27 PM, Yousuf Khan wrote:
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


Pretty hard to prove that the Earth didn't have tens
of thousands of moons... 4, 3, 2, and finally one, given
the current theory of the formation of the moon from an
impact!

On 03/08/2011 8:45 PM, Sam Wormley wrote:
On 8/3/11 7:27 PM, Yousuf Khan wrote:
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


Pretty hard to prove that the Earth didn't have tens
of thousands of moons... 4, 3, 2, and finally one, given
the current theory of the formation of the moon from an
impact!

I was thinking the same, but I wonder if the smaller moon would've still
been bigger than Pluto?

Yousuf Khan

"Yousuf Khan" wrote in message
...
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


"For decades, scientists have been trying to understand why the near side of
the Moon - the one visible from Earth - is flat and cratered while the
rarely-seen far side is heavily cratered and has mountain ranges higher than
3,000m"

Really? The fact that one side of the moon is partially shadowed from
asteroid impacts by earth wouldn't have anything to do with it?

On 03/08/2011 9:17 PM, Vince Morgan wrote:
"Yousuf wrote in message
...
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


"For decades, scientists have been trying to understand why the near side of
the Moon - the one visible from Earth - is flat and cratered while the
rarely-seen far side is heavily cratered and has mountain ranges higher than
3,000m"

Really? The fact that one side of the moon is partially shadowed from
asteroid impacts by earth wouldn't have anything to do with it?

How do you figure the Earth shadows the Moon from impacts? Asteroids can
whiz in between the Earth and Moon quite regularly. If it comes in
closer to the Moon, then it may likely hit the Moon.

Also the Moon's didn't always rotate in sync with its Earth orbit. That
tidal locking occurred only after several billion years. Certainly at
around the time that the craters were forming on the Moon, during the
Late Heavy Bombardment, the Earth and Moon were only 100 million years
old, and the Moon hadn't yet tidally locked at that point.

Yousuf Khan

On 8/3/11 9:07 PM, Yousuf Khan wrote:

Also the Moon's didn't always rotate in sync with its Earth orbit. That
tidal locking occurred only after several billion years. Certainly at
around the time that the craters were forming on the Moon, during the
Late Heavy Bombardment, the Earth and Moon were only 100 million years
old, and the Moon hadn't yet tidally locked at that point.

Yousuf Khan

Do you know when the moon did become tidally locked? If so When?
If not, why couldn't it have become tidally locked right away? What's
your evidence?

Yousuf Khan wrote:
On 03/08/2011 9:17 PM, Vince Morgan wrote:
"Yousuf wrote in message
...
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


"For decades, scientists have been trying to understand why the near
side of the Moon - the one visible from Earth - is flat and cratered
while the rarely-seen far side is heavily cratered and has mountain
ranges higher than 3,000m"

Really? The fact that one side of the moon is partially shadowed
from asteroid impacts by earth wouldn't have anything to do with it?

How do you figure the Earth shadows the Moon from impacts? Asteroids
can whiz in between the Earth and Moon quite regularly. If it comes in
closer to the Moon, then it may likely hit the Moon.

Also the Moon's didn't always rotate in sync with its Earth orbit.
That tidal locking occurred only after several billion years.
Certainly at around the time that the craters were forming on the
Moon, during the Late Heavy Bombardment, the Earth and Moon were only
100 million years old, and the Moon hadn't yet tidally locked at that
point.
Yousuf Khan

Given the much greater strength of tidal forces when the Moon was closer to
Earth after its formation, I would have expected synchronism to have taken
place pretty quickly. Though it is true that large impacts on the Moon
might be able to break the synch, it would be re-established after a few
million years.

I thought the difference between the two hemispheres was attributed mainly
to the relative thickness of the crust. On the near side, the thinner crust
meant that magma could flow to the surface without too much difficulty, but
on the farside with its thicker crust, this would not happen easily, hence
the absence of maria.

--
Mike Dworetsky

(Remove pants sp*mbl*ck to reply)

Dear Yousuf Khan:

"Yousuf Khan" wrote in message
...

On 03/08/2011 9:17 PM, Vince Morgan wrote:
"Yousuf wrote in message
...
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929


"For decades, scientists have been trying to understand why
the near side of the Moon - the one visible from Earth - is flat
and cratered while the rarely-seen far side is heavily cratered
and has mountain ranges higher than 3,000m"

Really? The fact that one side of the moon is partially
shadowed from asteroid impacts by earth wouldn't have
anything to do with it?

How do you figure the Earth shadows the Moon from impacts?
Asteroids can whiz in between the Earth and Moon quite
regularly. If it comes in closer to the Moon, then it may likely
hit the Moon.

True. The Earth shadows some "normal" impacts (path includes Earth at some
point), but otherwise will have little effect.

Also the Moon's didn't always rotate in sync with its Earth
orbit. That tidal locking occurred only after several billion
years.

If it lobed off the Earth, it may have been nearly locked, day one.

Certainly at around the time that the craters were forming
on the Moon, during the Late Heavy Bombardment, the Earth
and Moon were only 100 million years old, and the Moon
hadn't yet tidally locked at that point.

Maybe, not "certainly".

Do note however that the lunar crust is "much" thinner on the side facing
Earth, so it would not have supported much in the way of mountains during
the Late Heavy Bombardment, whereas the far side (with its lack of radiative
heat sink at ~293K) could have gotten much stiffer, sooner.

David A. Smith

"Yousuf Khan" wrote in message
...
BBC News - Earth may once have had two moons
http://www.bbc.co.uk/news/science-environment-14391929

A better news reference is
http://www.nature.com/news/2011/1108....2011.456.html

The actual paper is at
http://www.nature.com/nature/journal...ture10289.html

As is Nature's style, its first paragraph acts as an abstract and
contains the key results, but you will need a subscription or payment
to view more than this.

In article ,
"Vince Morgan" writes:
The fact that one side of the moon is partially shadowed from
asteroid impacts by earth wouldn't have anything to do with it?

Probably not. The Earth subtends very little solid angle in the
Moon's sky. Also, you have to explain not only the surface terrain
differences but also differences in (at least) crust thickness and
chemical composition.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

On 04/08/2011 2:34 AM, Mike Dworetsky wrote:
Given the much greater strength of tidal forces when the Moon was closer
to Earth after its formation, I would have expected synchronism to have
taken place pretty quickly. Though it is true that large impacts on the
Moon might be able to break the synch, it would be re-established after
a few million years.

I thought the difference between the two hemispheres was attributed
mainly to the relative thickness of the crust. On the near side, the
thinner crust meant that magma could flow to the surface without too
much difficulty, but on the farside with its thicker crust, this would
not happen easily, hence the absence of maria.

Well, I found the following site which estimates that it took around 7
million years for the Moon to lock on Earth.

shatters.net • View topic - Moon Systems, Tidal Locking and Age
http://www.shatters.net/forum/viewtopic.php?f=7&t=13956

Which is remarkably quick in my mind, I had thought it would take
several hundred million years at the quickest.

Yousuf Khan