Origin of the Moon

[halcyondays]

I know there has been a lot of new discussion in recent years about the origin of the Moon. I refer to the theory that the Earth was hit by a Mars-sized body, producing debris which coalesced into what became the Moon. So far, so good. However, what is the actual evidence which has led to this theory becoming fairly widely accepted ? Thanks.

 

[MeteorWayne]

Briefly, it is cofirmed by the mineralogical makeup of the earth and moon, and the angular momentum of the earth-moon system. <br /><br />I'll grab some more details. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[halcyondays]

Thank you, gentlemen. If I could push this on a bit further : if it is the case that Moon material today is similar to Earth material, what happened to the 'Mars sized body' material after the collision ? Or do we assume that that was also similar to the Earth and the Moon ? How much of the 'Mars-sized body' material remained on Earth and what proportion of the Moon today is from Earth and from the other body ? For that matter, how much of the other body's material remains on Earth, and could it even be detected at this distance ? Or was the collision a glancing one, which left the other body, or most of it, careening off into another orbit ? And, if so, where is it now ? Too many questions, I know - but thanks to those who respond. <br /><br />MW - look forward......

 

[MeteorWayne]

To summarize the the best of my ability the answers to your questions...<br /><br />Both the earth and the moon are a combination of the original earth and the impactor. Basically, the impact melted both the earth and the other body, so both are a mix. A large amount of material was ejected into what became a ring around the earth (how spectacular that would have looked!), some of which returned to the earth from it's gravity, some of which was ejected into the solar system, and some of which coalesced into the moon.<br />As far as the proportions, I would say it's too hard to say, though to a certain extent it's irrelevant, since both were bodies created in this same region of the solar system, the composition was likely pretty similar.<br /><br />One effect was that much of the heavier elements (Iron, Nickel, etc) appear to have remained with the earth, so we have more of such material and the moon has less, composed more of mantle type material. In any case, defining precise percentages requires knowing in detail such things as the exact mass of the impactor, the angle and velocity of the impact, etc. Since we don't know for sure, we juat can't be precise. <br />However, the calculations are pretty robust as far as the end result (As I recall); the earth mostly absorbing the bulk of the other object, and the ring formation. In other words, even for a reasonable range of size and impact scenarios, the end result is the same, only the proportions differ.<br /><br />Per the latest simulations, (I'ts been a while since I read it) most of the other object remained in the earth-moon system, again, exactly how much depends on the impact circumstances.<br /><br />I haven't had time yet to go through my Science and Nature collection yet to find the latest simulations, hopefully I can give you more detail then.<br /><br />It's not too many questions ! <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[eagledare]

HalcyonDays I have a theory that seems far fetched but here it is anyway.<br /><br />Very many millions of years ago Earth was like Venus. No moon and no life. All activity settled down as the earth cooled and water began to appear and then life sarted. It biult up to the time of the Dinosaurs and water was plentyfull. Some natural event that we don't know about yet happened and our Moon was born from earth and the water dissapeared. All life ended and earth was like Mars at the moment. No apparent water and no magnetic fields.Many millions of years pased again and water started to apear again and with it the life cycle started. <br />At the moment water is in abundance again and we are at the point of the 2nd moon being born.<br />The same process happened on all the planets. Have a look at the other thread " Origins of the moons"<br />

 

[3488]

It is worth remembering that if the moon did form from a gigantic impact (a big if mind you), the Earth was barely 60 million years old at the time. The Earth's crust was weak & thin, & may not even had fully formed, the Earth almost certainly still had oceans of liquid rock.<br /><br />However the Earth HAD differentiated into the planet we recognise today, a double layered core, mantle & at least a partial crust.<br /><br />The impact would not have stopped the Earth's internal dynamo.<br /><br />AFAIK, the Earth's internal dynamo has never stopped, although the magnetic field has collapsed & reappeared in the opposite polarity many times.<br /><br />Another point about the formation of the moon. True the compostion of the lunar rocks match those of the Earth's mantle very well, but it is still too early IMO to say that this is proof of the formation of the moon being from a gigantic impact. <br /><br />At present, we do not have rock samples from Mercury & Venus & then see how similar & / or different they are to the Earth's mantle rocks (we may have Mercury & Venus meteorites, but they remain unidentified at present).<br /><br />We will know more when the MESSENGER spacecraft makes the first Mercury encounter & then does a full mutispectral scan & particularly when MESSENGER arrives in Mercury orbit & scans the Caloris Basin, which may have exposed rocks from Mercury's mantle. This data will be compared to lunar samples & the Earth's own mantle rocks.<br /><br />Concerning the extinction of the dinosaurs. True they did not die out overnight, but they still died out over a very short geological time period.<br /><br />Almost certainly this was two fold.<br /><br />Firstly towards the end of the Cretacious period, the Earth was undergoing vastly increased volcanic activity, poisoning much of the lower troposphere. Then the Deccan lava traps erupted in what is now modern day India. This was nothing less than disastrous. Huge quantities <div class="Discussion_UserSignature"> <p><font color="#000080">"I suddenly noticed an anomaly to the left of Io, just off the rim of that world. It was extremely large with respect to the overall size of Io and crescent shaped. It seemed unbelievable that something that big had not been visible before".</font> <em><strong><font color="#000000">Linda Morabito </font></strong><font color="#800000">on discovering that the Jupiter moon Io was volcanically active. Friday 9th March 1979.</font></em></p><p><font size="1" color="#000080">http://www.launchphotography.com/</font><br /><br /><font size="1" color="#000080">http://anthmartian.googlepages.com/thisislandearth</font></p><p><font size="1" color="#000080">http://web.me.com/meridianijournal</font></p> </div>