Planetary formation

[Vkothii]

What we've been able to examine of the solar system so far, tells us that the planet we're on is unique.

It's unique in that it has essentially a liquid water "jacket', and it has continents.

The continental landmasses are the result of tectonic activity that water plays a key role in.
The granitic crust is poking up above the water because of ongoing distillation, or fractionation, of the lighter minerals.

The other (two) rocky planets that come anywhere close to Earth, don't have tectonics, or the same kind of granitic/basaltic separation of crustal features.

The Moon is a remnant of an early catastrophic collision of Earth with a Mars-sized planetary body, which added its granitic "load" to this planet, when it essentially melted it and the two planetary cores merged. The continental material then began distilling to the surface and this process continues today, billions of years after it started.

The appearance of continents on what, prior to the collision event, would have been a mostly watery planet, means the evolution of complex lifeforms like us, was possible.
Without a large moon to stabilise orbital precession which would see the Earth tipping periodically to much greater inclinations to the ecliptic, and much more severe climate, evolution might not have gone where it has.
Serendipitous, indeed.

[kaneda]

Are our tectonic plates due to the collision with another planetary body which cracked a previous solid crust?

I have read stories of beings who live on worlds with severe climates who live underground. Maybe that could have happened to us without a moon of the right kind.

[Vkothii]

The collision is the best explanation for the Moon's existence.
But we wouldn't have as much land I guess, if not for the extra helping of granitic minerals it added to the lithosphere.
There would have been a solid mineral crust like today, when the collision occured, but I don't know that anyone can really say much about what it looked like.

[Spud Emperor]

Vkothii, I've never taken life for granite!

Yes, serendipitous but not unique, you, of all people should appreciate this.

[blobrana]

"Australian National University (ANU) astronomers have found there is nothing special about the Sun after conducting the most comprehensive comparison of it with other stars – adding weight to the idea that life could be common in the universe.
Scientists have long argued about whether or not the Earth has some special characteristics that led to the evolution of life. "

Read more (http://info.anu.edu.au/ovc/Media/Media_Releases/_2008/_May/_20080521_sun.asp)

[Vkothii]

Life presumably has arisen anywhere conditions allow it to.
We only know about one place this has actually happened so far.

Without the Moon or large landmasses, there would probably still be Life on this planet, but it would be largely marine-based, perhaps, with little dry land to evolve on and the relative safety of being underwater, from the drastically different and more variable climate.

[draqon]

Vkothii...we only searched 100 years at most for life elsewere in the universe with methods that could not really detect the life as we know of it...wobbling of stars as a precursor of planets being there is most definitely not a precise method, so we got a long way to go until we can actually trace the elements in the exo-planets elsewere.

[orcot]

Current research shows that Venus started out the same like earth originally.
Mars confirms this by it's low atmosphere, it is yust small enough to prevent liquid water at the surface temprature (their will be a lot of exo terrestrial planets who have the exact same atmospheric density as mars has)
And titan proofs that it's far from unique to have a partial liquid and solid surface.

Their will be alot of partial liquid covered planets out there

[eburacum45]

"Australian National University (ANU) astronomers have found there is nothing special about the Sun after conducting the most comprehensive comparison of it with other stars – adding weight to the idea that life could be common in the universe.
Scientists have long argued about whether or not the Earth has some special characteristics that led to the evolution of life. "

Read more (http://info.anu.edu.au/ovc/Media/Media_Releases/_2008/_May/_20080521_sun.asp)

I am not quite sure what Robles and Lineweaver would consider to be an atypical star;
from their data
95% of stars are less massive than the Sun
81% of stars have a higher C/O ratio than the Sun
83% (or is it 92%) of nearby Sun-like stars rotate faster than the Sun (the different figures presumably depend on the definition of Sun-like)
93% of stars have larger galactic orbital eccentricities than the Sun
93% of stars have smaller velocity with respect to the Local Standard of Rest (that is, the Sun moves at a different speed to most of the nearby stars: in fact we move quite a bit more slowly)

Not entirely typical, after all.

I personally didn't think the Sun was particularly unusual until I read that paper; now my opinion has changed slightly- and in a different way to that suggested by the authors.

[orcot]

Our sun is a normal main sequence lonely star, that follows a typical orbit considering it's age

[Vkothii]

The Astrophysical Journal Letters, 673:L181–L184, 2008 February 1
© 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.

Evolution of Mid-Infrared Excess around Sun-like Stars: Constraints on Models of Terrestrial Planet Formation

M. R. Meyer,1 J. M. Carpenter,2 E. E. Mamajek,3 L. A. Hillenbrand,2 D. Hollenbach,4 A. Moro-Martin,5 J. S. Kim,1 M. D. Silverstone,1 J. Najita,6 D. C. Hines,7 I. Pascucci,1 J. R. Stauffer,8 J. Bouwman,9 and D. E. Backma10

ABSTRACT

We report observations from the Spitzer Space Telescope regarding the frequency of 24 μm excess emission toward Sun-like stars.
Our unbiased sample is composed of 309 stars with masses 0.7-2.2 M and ages from <3 Myr to >3 Gyr that lack excess emission at wavelengths ≤8 μm.
We identify 30 stars that exhibit clear evidence of excess emission from the observed 24 μm/8 μm flux ratio. The implied 24 μm excesses of these candidate debris disk systems range from 13% (the minimum detectable) to more than 100% compared to the expected photospheric emission.
The frequency of systems with evidence for dust debris emitting at 24 μm ranges from 8.5%-19% at ages <300 Myr to <4% for older stars.
The results suggest that many, perhaps most, Sun-like stars might form terrestrial planets.

Received 2007 June 28; accepted 2007 December 5; published 2008 January 9

Are "Sun-like" stars chemically and spectrally similar and of a similar vintage, or also in similar galactic orbits (i.e. not asymmetrical), or what?

[kaneda]

Many stars come in twos and threes.

We have discovered tholins, complex amino acids and such in space. we also know there is water outside the solar system. Certainly the ingredients for life and almost certainly enough planets, no matter how small the chance.

[Vkothii]

Sure, there are organic molecules in space. Carbon being what it is, it readily forms complex structures.

We know there are plenty of other stars like our one, but just how unusual is the local set of circumstances, in terms of a stable environment that's also conducive to the evolution of carbon-based chemistry?

Any time the planet has gone through stages that haven't been conducive to that evolution, the result hasn't been "good" - mass extinctions are found throughout the fossil record.
It seems the ongoing evolution of complex carbon-based life requires a quite narrow window of opportunity, which this solar system has managed to provide for the most part on this planet.

I suppose there must be planets with a similar history and stable environment somewhere, but with large landmasses and a large moon to keep them from tipping over, because they had a fortuitous collision with another planet?

We might well discover signs of life on Mars, it isn't all that far from a planet teeming with it, but given the lack of opportunity for complex evolution, it might not look very exciting.

[Ophiolite]

I don't agree with your conclusion, Vkothii, that the protoplanet collision that produced the moon was responsible for providing the Earth with granitic landmasses. I suggest that collision reduced the amount of grantic material available by removing the light ends of basaltic fractionation. Evidence for this lies in the lunar composition.

It may be that thi reduction in granitic material prohibited the formation of a planet wide granitic crust that would have seen the nascent plates lock in place at an early date.

[Vkothii]

I suggest that collision reduced the amount of grantic material available by removing the light ends of basaltic fractionation.The Earth already had a mixture of granitic and basaltic minerals, presumably all of the rocky planetoids and those that became planets had much the same ratio of lighter to heavier minerals.

The big difference with the rocky planet we're on, is the obvious tectonic activity, not found on any similar type of body (so far).
That's what is unique - the tectonics and how liquid water drives the process, to a large extent.

The collision presumably means the Earth has absorbed some of the material from the colliding body, apart from the dense Ni-Fe core.
What evidence do you suggest supports your idea that the lighter fractions were removed - didn't the collision essentially expel some of the Earth's outer layers into space? Why would minerals - even melted ones, diffuse into space subsequently? Or what process would have expelled lighter minerals from the surface, selectively?

[Ophiolite]

What evidence do you suggest supports your idea that the lighter fractions were removed - didn't the collision essentially expel some of the Earth's outer layers into space? Why would minerals - even melted ones, diffuse into space subsequently? Or what process would have expelled lighter minerals from the surface, selectively?
1. The moon is composed of lighter fractions. While the surface preponderances of anorthosite is partially a reflection of fractional crystallisation and segragation by flotation of feldspars, the overall bulk composition of the moon is - I believe - at the lighter end compared with terrestrial composition. (If I am mistaken in this my hypothesis is falsified.)
2. The moon formed from about 10% of the matter ejected by the proto-planet collision. It seems reasonable, as a starting point, to assume that the composition of the material that formed the moon was the same as the 90% that was lost to space.
3. The loss of this lighter fraction would have depleted crust and upper mantle of granitic material and inhibited the formation of a planet wide sialic crust.

[Vkothii]

OK, here we go

1. The Moon is believed to be composed of mostly mantle material from the larger of the two colliding bodies, ejected by the collision.

2. The Moon is the aggregate of the ejected material - presumably most of what ended up in orbit formed the Moon, not 10% - what happened to the rest? - which means, where is it?

3. There isn't any evidence (I'm not aware of any) that the collision caused a preferential loss of lighter (i.e. granitic) minerals, instead there was a loss of mantle material, a gain of dense (presumably mostly Ni-Fe) material that sank into the core, and a bit of added lighter stuff, too. The resulting planet (Earth) would then be somewhat bigger, but would have lost a Moon-sized amount of mantle. There's the question of the extent and separation of the impactor. And how or if that's related to an early large continental mass.

Then the stratification processes would have had more energy for the diffusion of lighter material to the surface, but not I think, out into orbit. The water jacket would have been mostly vapour at this point, and there wouldn't have been oceans again until it cooled down a bit. Some of this water is now part of the lunar stratification.

Our system is essentially a failed binary star system. Binaries are quite common in main-sequence solar-mass types.
Jupiter nearly got to be just a bit bigger than a big gas giant, and might have been the other star in a binary system, so not too pleasant for rock #3.

[Ophiolite]

1. The Moon is believed to be composed of mostly mantle material from the larger of the two colliding bodies, ejected by the collision. While this is the most popular of the current views on the subject it is by no means beyond the point of questioning. For example, in an intersting review (Bowen Lecture: The origin of the Moon and the early history of the Earth revisited) H.S.O'Neill makes this observation: "The Earth and Moon share the same depletions of the slightly volatile elements Li and Mn, which depletions are considerably larger than in any other solar system planetary body. Unless such similarities are dismissed as a collection of unexplained coincidences, then the Moon and the Earth derive from a similar but not identical mixture of proto-Earth and impactor; the different proportions being reflected by their different FeO contents."
2. The Moon is the aggregate of the ejected material - presumably most of what ended up in orbit formed the Moon, not 10% - what happened to the rest? - which means, where is it?Rather unlikely. Kokubo, E., J. Makino, and S. Ida 2000.
Evolution of a circumterrestrial disk and formation of a single moon. Icarus 148 , 419-436.
The efficiency of incorporation of disk material into a moon is 10--55%,.
This is by far the highest figure (55%) I have ever seen. Other simulations generally report 10%, or at most 20% of debris being incorporated in the moon.

The resulting planet (Earth) would then be somewhat bigger, but would have lost a Moon-sized amount of mantle. And you don't feel it might have lost some of the crust in the process? And that crust, even at that stage in proto-Earth evolution would not, you seem to feel, be extensively granitic in composition? And so the Earth would not have suffered a relative loss of granitic material, you would argue?

[Vkothii]

The picture I have is of an impactor about 1/3 the size of pre-impact Earth, and a largely inelastic collision - in which a significant amount of the momentum of both is converted into heat energy. The impact ejected mantle (and some crustal) material into orbit.
The impactor would not have lost much of its crustal layer into space, so the new planet got an extra helping of magma (containing a melt of lighter minerals) and dense core material.
The central dense core of the impactor sank into the dense core at the centre of the larger planetoid.

So after the core of the impactor has been assimilated, what about the remaining mass of the impactor, by now presumably mostly absorbed, or just a vague bump on the surface? The proximal half and the core are now melted into the newly-formed planet; the distal half is "squished" over the impact area - say an area thats 30-40% of the new, roughly spherical object. Because it's now a liquid "blob", it settles into an oblate spheroid.
How well has the distal part of the impactor been "assimilated", or mixed into the magmatic stratification by now, after a single impact event? One thing there's only an estimate of is the kinetic energies of either body at the time.
Another is the amount of angular momentum either body had, whether there was an initial grazing-type collision that slowed the rotation of the pre-impact Earth, and if there was then a second collision, or we can only guess the dynamics of the actual event: the only clues left are the Moon + Earth system, and maybe a few meteorites somewhere "out there".

[Vkothii]

If the material that got ejected by the collision only aggregated back together by 55% at most, where is the rest of it? Did it get pushed out of orbit or something?

[EndLightEnd]

Indeed it is strange for a satellite.

Still pissed we havent been back in 30 years.

[orcot]

I wonder if mars had a similar fate considering it's southern hemisphere is so much higher then it's northern hemisphere, where the ejected material falled back in a selective band around a planet.

If this happens often then their must be lot's of moons yust like our own in the universe, however it would also have it's advantages if the material felled back onto a narrow band near a planets equator. It would nearly sepperate the 2 hemispheres by a km high mountain range that would by it's high altitude form a polar circle around it's equator, reflecting much of the stars light by witch it can support live much nearer to it's sun. It would make a interesting decor for a scifi book if anything interesting would happen there

[Vkothii]

A significant amount of the ejecta would have re-impacted with the planet, as well. I'm fairly sure the latest theory is that most of the mantle material in orbit ended up as the Moon, although it is believed to have a small remnant iron-rich core.

Mars lost its atmosphere because it didn't get big enough to hold on to it. Venus lost its oceans because it got too hot, or couldn't recycle carbon from the atmosphere, like the Earth does.

[Ophiolite]

Vkothii, not ignoring your responses. Too much work. Will reply next week.

[blobrana]

"Higher than expected levels of sodium found in a 4.6 billion-year-old meteorite (Semarkona meteorite (http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=7252256)) suggest that the dust clouds from which the building blocks of the Earth and neighbouring planets formed were much denser than previously supposed."

Read more (http://news.webindia123.com/news/articles/India/20080620/979160.html)

See also
http://www.astronomy.com/asy/default.aspx?c=a&id=4862

[Vkothii]

Without the Moon or large landmasses, there would probably still be Life on this planet, but it would be largely marine-based, perhaps, with little dry land to evolve on and the relative safety of being underwater, from the drastically different and more variable climate.Except that: "without the moon" means what: "without any collision"?
Would the tectonic processing, and the subduction which depends on liquid water, have started up without the collision...?

The assumption, is that the early pre-collision planetary body had oceans, and probably island chains, but so did Mars and Venus.
They both ended up as fizzers, where Evolution of anything resembling complex organic life, didn't get any get-go.

[orcot]

Except that: "without the moon" means what: "without any collision"?
Also what without the added 9% mass.

[Vkothii]

Eh?

[orcot]

Eh?
A mars sized chunck of rock hit the earth, witch basivly means that a rougly 10% earth mass colided with a 91% earth mass object to form the earth100% and the moon1%.

Without it there would only be around 95% gravity for certain and other planet rotated once every 8h in the beginning offcourse the moon impact might have had something to do with that it's also uncertain wether or not we would still have had a magnetic field.

I do wonder what would have happened if that large protoplanet got in orbit wihout hitting the proto earth. We would have ended up with a Mars sized moon

[jsispat]

Current research shows that Venus started out the same like earth originally.
Mars confirms this by it's low atmosphere, it is yust small enough to prevent liquid water at the surface temprature (their will be a lot of exo terrestrial planets who have the exact same atmospheric density as mars has)
And titan proofs that it's far from unique to have a partial liquid and solid surface.

Their will be alot of partial liquid covered planets out there
all planets have same material because all planets are living thing like tree and procedure of there birth is also same. just like all tree in same forest has same material mostly but few tree infected only

[Enmos]

all planets have same material because all planets are living thing like tree and procedure of there birth is also same. just like all tree in same forest has same material mostly but few tree infected only

With what ?

[EndLightEnd]

Neptune has retrograde rotation. Scientists still trying to figure that one out.

[orcot]

Neptune has retrograde rotation. Scientists still trying to figure that one out.
Captured plutoid with a twist

[Yorda]

why not just stick with the 5000 year old empedocles' theory of planetary formation, which says that planets form from the ether? why invent this weird theories about things colliding and forming the moon? earth is moonchild, moon is not the child of earth

[Vkothii]

Yes, we should return to the tried and trustworthy Ptolemaic world map too, I think.

[orcot]

... actually when the first astronauts went into space. This is what they saw
http://z.about.com/d/scifi/1/0/H/5/-/-/HOGF_discworld_500x280.jpg
it turns out the universe is rather silly but please keep it a secret