Puzzle of Moon's Origin

[bison]

The giant impact hypothesis, in which an impactor about the size of Mars, called Theia, struck Earth and formed the Moon, has been strengthened by recent scientific work. The new analysis addresses the problem of how the Moon and Earth could be so similar in composition, if, as believed, the former is made up mostly of material from the impactor.

It now appears that Earth and Theia were 'sister' planets, formed at about the same time and place in our solar system. This makes their like composition more understandable.

Link to Nature article, below:

http://www.nature.co...solved-1.17279

Edited April 9, 2015 by bison

[keithisco]

Something that has been tugging at my few remaining neurons for a while, is that Mars appears to have lost most of its atmosphere at more or less the same time as Theia impacted the Earth leading to the creation of the Moon.COULD it be that Theia, on an elliptical orbit actually grazed the Martian atmosphere and caused the major loss of it's atmosphere?

I don't know, but it is an interesting hypothesis

[Taun]

Something that has been tugging at my few remaining neurons for a while, is that Mars appears to have lost most of its atmosphere at more or less the same time as Theia impacted the Earth leading to the creation of the Moon.COULD it be that Theia, on an elliptical orbit actually grazed the Martian atmosphere and caused the major loss of it's atmosphere?

I don't know, but it is an interesting hypothesis

That is an interesting thought, but I would think that if another planetary body drifted close enough to Mars to siphon off it's atmosphere, it would have been close enough to have collided with Mars ...

[Mr.United_Nations]

Would that also explain Mar's two moons?

[bison]

It's common to state that Deimos and Phobos are captured asteroids, yet their nearly circular, low inclination orbits argue against this, as do some other considerations. It's theorized that they could be remnants of a large collision event, somewhat like the one supposed to have created Earth's Moon. Such an event might have been a factor in the loss of Mars' atmosphere, if large enough.

[keithisco]

That is an interesting thought, but I would think that if another planetary body drifted close enough to Mars to siphon off it's atmosphere, it would have been close enough to have collided with Mars ...

I think that would depend on the angular momentum and velocity of the supposed "grazing" body. I have not done any calculations to support this, it is just an idea at the moment.

[Ashyne]

The moon is an artificial satellite. Within it is a massive alien ship with the moon's crust as a disguise for its true form. What this alien ship does is to project a "smokescreen" effect on our planet as it orbits around the Earth, distorting what we see to hide the existence of alien life outside this solar system. The alien ship transmits false data back to us, relays to our telescopes and observatories what it wants us to see. Our probes that go far into the solar system send data back that is grabbed by the alien ship, distorted and then relayed to us. The truth is that until we go on manned missions past the Moon's orbit, we will always be living under a veil of lies.

[RedSquirrel]

The moon is an artificial satellite. Within it is a massive alien ship with the moon's crust as a disguise for its true form. What this alien ship does is to project a "smokescreen" effect on our planet as it orbits around the Earth, distorting what we see to hide the existence of alien life outside this solar system. The alien ship transmits false data back to us, relays to our telescopes and observatories what it wants us to see. Our probes that go far into the solar system send data back that is grabbed by the alien ship, distorted and then relayed to us. The truth is that until we go on manned missions past the Moon's orbit, we will always be living under a veil of lies.

Any evidence that would convince your average layperson?

[KevinP]

There's been a couple rather viable theories put out over the years. I'm starting to see some good validity in the possibility of an impact rather than a large object the size of the moon to get snagged by Earth's gravity. That'd be one heck of a catcher's mitt.

[bison]

The article from the BBC, linked below, also mentions a couple of other recent studies. These discuss newly found differences in the composition of the Earth and Moon. These apparently had their origin in meteoric debris that fell mostly on Earth, but also somewhat on the Moon, early in the solar system's history, but not so early as the date given for the giant impact.

http://www.bbc.com/n...onment-32219494

Edited April 9, 2015 by bison

[Herr Falukorv]

The moon is an artificial satellite. Within it is a massive alien ship with the moon's crust as a disguise for its true form. What this alien ship does is to project a "smokescreen" effect on our planet as it orbits around the Earth, distorting what we see to hide the existence of alien life outside this solar system. The alien ship transmits false data back to us, relays to our telescopes and observatories what it wants us to see. Our probes that go far into the solar system send data back that is grabbed by the alien ship, distorted and then relayed to us. The truth is that until we go on manned missions past the Moon's orbit, we will always be living under a veil of lies.

Oh I didn't know that! I have always thought the moon was made of cheese. I guess it really doesn't matter now does it because both ideas are equally plausible.

[aquatus1]

The moon is an artificial satellite. Within it is a massive alien ship with the moon's crust as a disguise for its true form. What this alien ship does is to project a "smokescreen" effect on our planet as it orbits around the Earth, distorting what we see to hide the existence of alien life outside this solar system. The alien ship transmits false data back to us, relays to our telescopes and observatories what it wants us to see. Our probes that go far into the solar system send data back that is grabbed by the alien ship, distorted and then relayed to us. The truth is that until we go on manned missions past the Moon's orbit, we will always be living under a veil of lies.

Wow...

How does it replicate the gravity of an object the size of the moon?

[Waspie_Dwarf]

Any evidence that would convince your average layperson?

Forget the average layperson, any evidence at all would be a start.

[David-C]

I'm sure this is a stupid question but if something the size of Mars hit the Earth and out popped the Moon, shoudn't there be a Moon sized hole somewhere on the Earth?

[aquatus1]

Nah, after a collision of that scale, there's no more Earth, Moon, or Theia, just a liquid mass of molten rock congealing into two orbiting bodies.

[Waspie_Dwarf]

I think that would depend on the angular momentum and velocity of the supposed "grazing" body. I have not done any calculations to support this, it is just an idea at the moment.

How could Theia survive the initial impact with the Earth? This is an impact that supposedly involved so much energy that, as aquatus says, it melted the entire planet. It seems highly unlikely that the smaller body could survive.

Indeed the giant impact hypothesis explains the Earth's relatively large iron core and the moon's relatively small core by assuming that Theia was largely absorbed by the Earth, with it's core material sinking to to join that of Earth. It also explains the fact that lunar rock samples are similar to those of the Earth but show subtle differences by assuming that the mantle material of Theia became part of the moon.

This leaves a poblem for your hypothesis; if the giant impact hypothesis is correct then Theia did not survive and could not be responsible for the loss of the Martian atmosphere. If the giant impact hypothesis is wrong then there was no Theia anyway.

The other, obvious, question is, if Theia did survive the impact with the Earth and then had a close encounter with Mars, where is it now? The impact that created the moon was believed to have occurred 4.5 billion years ago. Mars was known to have had a dense atmosphere until at least 3.8 billion years ago. To do what you suggest Theia would have had to have survived within the inner solar system for 700 million years before disappearing without a trace.

Even if your calculations suggest that Theia could have removed the Martian atmosphere you are going to need to do an awful lot of explaining to suggest how it got there in the first place.

Edited April 10, 2015 by Waspie_Dwarf
many MANY typos due to sticking keys on my keyboard.

[Lilly]

...The other, obvious, question is, if Theia did survive the impact with the Earth and then had a close encounter with Mars, where is it now? The impact that created the moon was believed to have occurred 4.5 billion years ago. Mars was known to have had a dense atmosphere until at least 3.8 billion years ago. To do what you suggest Theia would have had to have survived within the inner solar system for 700 million years before disappearing without a trace.

This pretty much puts the final nail in the coffin of that idea.

[paperdyer]

Any evidence that would convince your average layperson?

Nah - Doctor Who explained the Moon as a huge Space Dragon egg.

[paperdyer]

Nah, after a collision of that scale, there's no more Earth, Moon, or Theia, just a liquid mass of molten rock congealing into two orbiting bodies.

This would have to be the case or the Earth and the Moon wouldn't be a round as they are. Maybe the Earth's current size is the result of twosmaller bodies colliding with the current Earth forming and the Moon being sent off.. We'll never really know, but discussing theories can be fun.

[paperdyer]

This pretty much puts the final nail in the coffin of that idea.

Yes, but the key word is "believed". Scientists have been known to re-evaluate timelines as new data is presented and discovered. Again, we'll probably never know.

[Waspie_Dwarf]

Yes, but the key word is "believed". Scientists have been known to re-evaluate timelines as new data is presented and discovered. Again, we'll probably never know.

It is possible to set a latest possible date for the formation of the moon, since we have samples of the moon and these can be dated. We also have a fairly good idea of the age of the solar system. This means that we can be fairly sure of the time frame that the hypothetical great impact occurred, since it must have occurred since it must have happened after the planets were formed but before the earliest rocks on both the Earth and the moon were formed. whilst it may be possible to narrow don the time frame of the impact there is no option to drastically change it.

With Mars we do not yet have any samples on Earth s the surface features can not be precisely measured, however the early history of the solar system is reasonably well understood, especially relating to the frequency and size of impact craters. It is, therefore, possible to make a reasonable estimation of the age of particular regions on Mars. By knowing which regions of Mars show evidence of water an estimate of when the conditions were suitable for liquid water can be made. Since liquid water on the surface of Mars requires a thicker atmosphere then an estimation of when that existed can be made. This estimation gives the LATEST date at which these conditions could have existed, any major revisions (and we are beginning to see them happen) will push this date to more recent times.

The 700 million years I have quoted is the best case scenario for keithisco's idea.

Even if it wasn't the best case scenario my point still stands. His idea requires a planet to have survived a major impact which melted the proto-Earth, then to have survived in an elliptical orbit between the Earth and Mars for several hundred million years. In that time it managed to avoid impacting either the Earth, moon or Mars, it also failed to disrupt the orbits of these bodies. Then at some stage it made a close enough pass to Mars that it ripped away the Martian atmosphere, but did not impact Mars, or significant alter the Martian terrain. Then having done all this it just vanished.

Do you really think there is ANY time frame that makes these series of events likely?

Edited April 10, 2015 by Waspie_Dwarf

[Waspie_Dwarf]

This would have to be the case or the Earth and the Moon wouldn't be a round as they are.

Not true.

Any body over a certain size achieves what is know as hydrostatic equilibrium. The force of gravity forces them into a near spherical shape. You simply can not have an object the size of the Earth (or the moon for that matter) that is irregular in shape.

Edited April 10, 2015 by Waspie_Dwarf

[TripGun]

The perfect roundness of the moon throws me off this theory.

[clare256]

Velikovsky was right! It was Venus!!

(please note: sarcasm)

[Waspie_Dwarf]

The perfect roundness of the moon throws me off this theory.

The moon isn't "perfectly" round, no known astronomical body is.

Secondly gravity would force the moon into it's spherical shape HOWEVER it was formed.