APOD: Evolution of the Moon (2012 Mar 20)

[fafers]

My question, up for anyone who wants it: many planets have moons... and, while I'm not well-read on the subject, my impression has been that this theory (huge planet-sized impact ejecting and fragmenting off material to form the moon) has only been advocated for earth's moon. Do we have a reason to think that we have a "special case" scenario here? Or is this thought to be a general process for most moons?

I'm not sure if it's thought to be general for most moons, but it is definitely thought to be one of the processes for their formation. In the Solar System, this process has been advocated for Charon, too.

[Tszabeau]

Ever try to teach evolution to a person who has a preconceived incorrect notion of what it is? This flippant use of the word "evolution" contaminates my students' brains, as well as the national discussion of science in general. I stand by my comment.

Treating the word 'evolution' as if it is a religiously sacred concept, that applies ONLY to Darwinism, is what's confusing you and your students. On the contrary, it's a common everyday kind of concept.

[Anthony Barreiro]

What a lovely video. I'm going to share it with friends who love looking at the Moon. And the other LRO tour of the Moon video is pretty cool, too.

I enjoyed the music and the sound effects, but I don't have any cats here at work.

In the Random House Dictionary, the first definition of "evolution" is "any process of change or growth; development." Darwinian evolution is the third definition. If I were teaching Darwin's theory of evolution, I would probably start by discussing the general use of the term and clarifying its special meaning in biology. Students learn more when you relate something new to something they already know.

For what it's worth, Mercury, Mars, and Saturn are all retrograde currently, and Venus is approaching retrograde. Given the level of vitriol on Starship Asterisk currently, I'm looking forward to reading some fulminating screeds about astrology! (Is there an emoticon for <poking with a sharp stick>? Tee hee.)

[BMAONE23]

Rocky planets with moons
Earth - Luna
Believed to have been reformed after a catastrophic impact
Mars - Phobos
------- Deimos
Both are likely captured asteroids
Pluto - Charon (could be similar to Luna)
-------- Nix (unknown)
-------- Hydra (unknown)
-------- P4 (unknown)
Nix, Hydra, & newly discovered P4 could be remnants of a possible impact that created Charon
New Horizons might answer some or none of these questions

The remaining bulk of large Moons orbit Gas Giants or Ice Giants. It is unlikely that an impact of a gas giant would produce a viable stable rocky moon so they might have formed along side their planetary hosts during the accretion process

[Mooner]

Interesting vid, but I have two very basic questions I feel embarrassed to ask.

My first question is; would material 'expelled' from early-history Earth automatically be pulled back into an Earth orbit at a certain distance from the Earth proportionate to it's mass?

And a second question; from where exactly on Earth was this massive chunk of Earth expelled?

Thanks in advance.

[petsie]

is there another place than youtube to view the link behind the words "impacted the earth"? Youtube will not show that in germany due to ownership issues regarding the music
Thanks in advance,
Peter

[Chris Peterson]

My first question is; would material 'expelled' from early-history Earth automatically be pulled back into an Earth orbit at a certain distance from the Earth proportionate to it's mass?

Nearly all of the ejected material either fell back to the Earth or collapsed into the Moon. Very little achieved escape velocity from the Earth-Moon system.

And a second question; from where exactly on Earth was this massive chunk of Earth expelled?

No way of knowing, and since the collision pretty much melted the entire surface, after which the Earth kind of reformed, the question itself may not mean much.

[bystander]

is there another place than youtube to view the link behind the words "impacted the earth"? Youtube will not show that in germany due to ownership issues regarding the music
Thanks in advance,
Peter

Same video, different music: http://www.youtube.com/watch?v=T6CMvSKsHBo

The sequence was lifted from a Discovery Channel special, but I've been unable to find the episode.

[Mooner]

Thanks Chris for the rational explanation.

One follow-up question, would such a massive ejection of Earth material send one super-chunk-sized Moon material into an Earth-Moon gravitational system in relatively quick fashion (with minor fragments ultimately falling back to Earth), or would there more likely have been multiple larger chunks of material ejected from Earth in addition to many more smaller chunks expelled, which gradually over many years would have formed at various distances from the Earth - themselves eventually lumping together to form a single big moon? I'm just trying to wrap my head around the likely physics behind the actual process, as the video starts from an already-formed starting point. Thanks for any reply.

[SJoe]

I wouldn't say a "chunk" was knocked out exactly.

I don't kow how factual the video is, but it shows an decent illustration of how the formation works. I think.

http://www.youtube.com/watch?v=2sr-MriOCzw

I suggest turning the volume down too.

[petsie]

Same video, different music: http://www.youtube.com/watch?v=T6CMvSKsHBo

I found this with Pink Floyd's "The Great Gig In The Sky" at 5min.com but thought I found the wrong one. This can't have too much to do with the formation of the moon (blue planet with oceans, cooled continents, even cities more than 4 gigayears ago )

Thank you very much!