Why is Earth so Dense ?

rod

Oct 22, 2019
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EL PIC, interesting question. The answer in astronomy today is the Minimum Mass Solar Nebula (MMSN) model used to explain spinning, protoplanetary disk around stars and the Sun. You must come up with the *right* mix of dust and gas, including CO gas and remember, there will be plenty of H, and He gas too to create via random, accretion the planets of the solar system. Today, we observe about 447 earth masses in the ecliptic from Mercury to Pluto. The MMSN starts out with many thousands of earth masses of dust and gas, some 4.5 billion years ago using the meteorite dating paradigm. Typically, the MMSN has about 1% dust and 99% gas content. From studies I have done, 1993 estimates ranged about 7,000 earth masses in the disk from the Sun out to 10 au or so. Other papers show at least 3330 earth masses in the early, spinning disk postulated, and still other reports indicate there could be more than 600,000 earth masses needed, see Preliminary Evidence That Protoplanetary Disks Eject More Mass Than They Retain,
All sources science Query accretion disks

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August 2021. Some reports attempted to simulate the origin of Mercury using a very small amount of disk mass, perhaps 2-5 earth masses for the inner solar system, protoplanetary disks - inner solar system planets,
All sources science Query accretion disks

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I keep a MS ACCESS DB updated on reports showing disk masses as I research this area. Once you can define the right disk mass size and dust to gas ratios, you must build the correct solid ratios that accrete into the known densities today. Showing how dust grains evolve into a full grown Earth is challenging :)
 
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rod

Oct 22, 2019
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In my opinion, the science of the MMSN and origin of the solar system evolving from the MMSN, looks like How Gas Clouds Evolve into People :)
 

EL PIC

Techno Cat
Dec 21, 2019
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Rod .. TY for answer.. but it’s going to take me some time to fully understand your first response.
The second response reminds me of Sagan’s Star Stuff which is probably better or more palatable than just saying we are the results of cosmic gas.
However it seems odd that the planet with the highest density is also the one with most water and organic life. Perhaps.. we are just a dense head species 🤣
 
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Jun 1, 2020
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Why is Earth so dense in our solar system ?
Logic would make Mercury most dense.
The hypothetical impact by Theia deposited extra iron and other heavy matter, whereby the lighter matter vaporized and escaped. Much of the lighter surface levels went into orbit forming one or two moons, though the two moon idea would soon combine into today’s Moon.

The result is how we now have greater density for Earth and the largest moon to planet mass ratio in the system.
 
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EL PIC

Techno Cat
Dec 21, 2019
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Hello ..
Somewhat Plausible Theory but hard to relate to the creation of many other moons around other planets in our solar system (over 200 and none for Mercury and Venus… the planets which are closest to Earth density).
 
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rod

Oct 22, 2019
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FYI. The postulated Theia giant impact model has Theia forming in different locations in the MMSN, some inside of where the proto-earth formed, others with Theia forming out near Mars location. What Helio suggest in post #5 concerning Theia depositing more iron inside the proto-earth after the giant impact could work with some models, others will have Theia with less iron too like Mars. An issue that I feel is missing in all such MMSN modeling for the planets Mars to Mercury, is the wide variety of exoplanets known today that orbit their parent stars closer than Mercury does to our Sun. Many have densities much lower than Earth and Mercury. This site shows 4575 exoplanets, NASA Exoplanet Archive (caltech.edu) , 4575 exoplanets. 1964 have orbits <= 0.388 au to their parent stars with average mass near 1.05 Jupiter, and average host star mass near 0.89 solar masses. Another site I use, The Extrasolar Planet Encyclopaedia — Catalog Listing (exoplanet.eu) , list 4874 exoplanets. 2242 orbit <=0.388 au from their parent stars, average exoplanet mass 2.42 Jupiter masses, average host star mass 0.905 solar masses.

What we observe in astronomy is many exoplanets that orbit very close to their parent stars with mean densities that are much lower than Mars, Earth, Venus, or Mercury (e.g. sub-Neptunes, sub-Saturns, hot jupiters, etc.). Do I hold that gas clouds evolve into people with heliocentric certainty? No I do not. The MMSN and protoplanetary, spinning disk model has much to offer but also many challenges in explaining, How Gas Clouds Evolve into People :)
 
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EL PIC

Techno Cat
Dec 21, 2019
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I was questioning why Earth is so dense and kinda see the formation of Moon and people to be a more off topic consideration.
But nice write up.
Satellite creation of Gas planets with Rocky Moons is interesting and I don’t believe in Theia Bakers Dozen
Not so sure on existence of Theia anyway.
 

Catastrophe

The devil is in the detail
Rod and Helio,

Would it be a fair summary to suggest that Earth has a higher density because it gained more metallic core from the Theia collision, whereas Mercury has a high density because its collision(s) caused loss of (silicate) mantle.
Earth gained core - Mercury lost mantle? Both increased in density differently?

Cat :)
 
Jun 1, 2020
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Would it be a fair summary to suggest that Earth has a higher density because it gained more metallic core from the Theia collision,...
Yes, this seems to be the mainstream view of how Earth had more iron core (by ratio) for its mass than any other planet. This theory also explains many of the unusual features found on the Moon, especially the Two-Moon hypothesis that resulted from the Theia impact but later formed into one moon.

...whereas Mercury has a high density because its collision(s) caused loss of (silicate) mantle.
Earth gained core - Mercury lost mantle? Both increased in density differently?
I don't know, or have forgoten, the Mercury explanation. It is logical, however, that protplanets during formation closer to the Sun would always consist of the heavier elements/molecules due to the Sun's radiation effects. Heavier molecules become more volitale with temperature, thus the lighter elements will escape from the disk region where a protoplanet like Mercury forms.

Also, the heavier elements/molecules, will be the first to migrate inward since solar radiation and wind will help suspend the lighter disk material. So I suspect the normal density for inner disk material, even if we could discount temperature circumstances, would favor the more dense disk materials. But that's just my opinion.
 
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Catastrophe

The devil is in the detail
Helio, I agree. I know Hot Jupiters must be formed further out, but:

" It is logical, however, that proto planets during formation closer to the Sun would always consist of the heavier elements/molecules due to the Sun's radiation effects. ". . . . . . . . .
But I do marvel at how they seem to hold onto so much H and He when really close to a star - comparatively within Mercury's orbit.

Cat :)
 

Catastrophe

The devil is in the detail
Mercury:

Scientists theorize that one such object slammed into young Earth to produce our planet's moon. "Collisions were frequent during the early stages of the solar system's formation," Chau said. ... This scenario more often formed a Mercury-like object in their simulations — as long as it didn't destroy the planet completely.23 Oct 2018
How Did an Oddball Planet Like Mercury Form? | Space

Planet Mercury a result of early hit-and-run collisions
https://www.sciencedaily.com › releases › 2014/07


8 Jul 2014 — According to a study published online in Nature Geoscience July 6, Mercury and other unusually metal-rich objects in the solar system may be ...


Planetary Smashup Left Mercury With a Massive, Metallic Heart
https://www.nationalgeographic.com › science › article


8 Jul 2014 — For about 100 million years, little Mercury grew up as rocky planets normally do. Dust swirling near the infant sun coalesced into clumps that ...


Mercury (planet) - Wikipedia
https://en.wikipedia.org › wiki › Mercury_(planet)


Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the ...


Cat :)
 
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Jun 1, 2020
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Helio, I agree. I know Hot Jupiters must be formed further out, but:

" It is logical, however, that proto planets during formation closer to the Sun would always consist of the heavier elements/molecules due to the Sun's radiation effects. ". . . . . . . . .
But I do marvel at how they seem to hold onto so much H and He when really close to a star - comparatively within Mercury's orbit.
Yes, I agree. Didn't we crunch some numbers not too long ago and discovered that they could hold their H & He elements in their atmospheres for a very long time, IIRC?

Of course, I think the mainstream view is that many, if not most, of these large exoplanets typically migrated inward, so their time very close to their star isn't that long-term.
 
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Jun 1, 2020
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Mercury:

Scientists theorize that one such object slammed into young Earth to produce our planet's moon. "Collisions were frequent during the early stages of the solar system's formation," Chau said. ... This scenario more often formed a Mercury-like object in their simulations — as long as it didn't destroy the planet completely.23 Oct 2018
How Did an Oddball Planet Like Mercury Form? | Space

Planet Mercury a result of early hit-and-run collisions
https://www.sciencedaily.com › releases › 2014/07


8 Jul 2014 — According to a study published online in Nature Geoscience July 6, Mercury and other unusually metal-rich objects in the solar system may be ...
That's a nice article. Perhaps the best description I've heard of the early planetary dynamics is that of a pinball machine. The best planetary formation model for the solar system seems to be the Nice model (a French town, I think) that has all kinds of wanderings and interactions with planets. But it's not a complete model since it can't seem to quite explain the orbits of the outer planets, or maybe it was only Pluto it had trouble with, not sure.
 
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rod

Oct 22, 2019
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For the all comments about pin ball and giant impacts, some known exoplanet systems do not fit this view. Those exoplanets have densities like Earth too.
 
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Catastrophe

The devil is in the detail
A little more reading so as not to fleece the peace getting grease from bees.

When was the nice model developed?

Around 2004 a team of scientists met in Nice, France and developed a new theory as to how the early solar system developed.30 Sept 2020

What Is the Nice Model, or How Did Our Solar System Form?
https://owlcation.com › stem › What-Is-The-Nice-Model


Search for: When was the nice model developed?

What does the grand tack theory attempt to explain?

Did Uranus and Neptune switch places?


Cat :)
 
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rod

Oct 22, 2019
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A little more reading so as not to fleece the peace getting grease from bees.

When was the nice model developed?

Around 2004 a team of scientists met in Nice, France and developed a new theory as to how the early solar system developed.30 Sept 2020
What Is the Nice Model, or How Did Our Solar System Form?
https://owlcation.com › stem › What-Is-The-Nice-Model


Search for: When was the nice model developed?

What does the grand tack theory attempt to explain?

Did Uranus and Neptune switch places?


Cat :)
Cat, do the Nice model or Grand Tack model, explain the origin of the planets Mercury to Mars from the tiny dust grains to full grown planets we see today?
 
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Catastrophe

The devil is in the detail
Not sure, Rod. With all the comings and goings, and hot jupiters with warm hearts basking in the Sun, "my '.ead urts" I don't know enough to give you an honest answer. I will put it on my "to do" list as it is obviously very important.

Cat :)
 
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