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Cuneiformist
The Imperfectionist
USA
4955 Posts |
 Posted - 01/14/2008 : 15:29:11
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The MESSENGER trip to Mercury is getting a lot of news today. It is apparently going to study a number of anomalies in Mercury that we haven't yet been able to understand.
One of the most interesting is Mercury's iron core:Mercury is extraordinarily dense, leading researchers to estimate that its iron-rich core potentially makes up about two-thirds of the planet's mass, a startling figure double that of Earth, Venus or Mars. In other words, Mercury's core might take up roughly three-quarters of the world's diameter.
One theory explaining this bizarre density is that huge impacts billions of years ago might have stripped Mercury of its original surface, Vilas explained, collisions that also shifted the planet toward the sun to its current location. Another theory suggests Mercury simply formed where it now lies.
To see which theory concerning Mercury's origins might be right, MESSENGER's battery of miniaturized scientific instruments will scope out the planet's geology. Understanding how Mercury formed will shed light on how all the planets evolved, Solomon said. |
I was curious about this since the iron core of other solar bodies has been a topic discussed here at some length. And for a moment, I thought this might add fuel to the fire. But then it struck me that Mercury's iron core is directly associated with its density. That is, its iron core makes it dense. And they didn't even factor in the Z-axis.
So I guess it's back to the drawing board for some people.
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Dave W.
Info Junkie
USA
26022 Posts |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/15/2008 : 11:03:03 [Permalink]
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| I didn't know this was considered such a big anamoly. In general isn't greater density / heavier elements expected in celestial bodies the closer to the sun you get? |
-Chaloobi
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/15/2008 : 11:26:26 [Permalink]
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I find it hard to believe that Mercury didnt form where it is, the only one Im unsure of is pluto.
| In general isn't greater density / heavier elements expected in celestial bodies the closer to the sun you get? |
Thats the way I understand it. Though our data from extrasolar planets may suggest otherwise. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 01/15/2008 : 11:38:32 [Permalink]
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Originally posted by chaloobi
I didn't know this was considered such a big anamoly. In general isn't greater density / heavier elements expected in celestial bodies the closer to the sun you get? |
Perhaps, but clearly something is wrong. In an article entitled "A vaporization model for iron/silicate fractionation in the Mercury protoplanet" by Fegly and Cameron (Earth and Planetary Science Letters, 82 [1987] 207-222), they write that:| Urey [1,2] first noted that the anomalously high density of the planet Mercury impies an iron to silicate ratio larger than that for any other terrestrial planet. In fact the mean density of 5.44 g/cm3 (uncompressed ~5.3 g/cm3) implies an iron to silicate mass ratio of about 66:34 to 70:30, which is about twice as large as that of any of the other terrestrial planets, the Moon, and the Eucrite Parent Body [3]. By comparison, the mean density of the Earth is 5.52 g/cm3, corresponding to an uncompressed density of ~4.45 g/cm3 [4]. |
So it looks like the iron-richness skips over Venus (since the Big Two are Earth and Mercury) and so there is something anomalous. |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/15/2008 : 11:40:46 [Permalink]
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| How exactly do we get data on Venus's composition, considering the impenitrable atmosphere? Is it purely a mass thing? |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Dave W.
Info Junkie
USA
26022 Posts |
Posted - 01/15/2008 : 20:25:41 [Permalink]
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It's a mass and volume (density) thing, coupled with the idea that because the planets all coalesced out of the same proto-planetary disk, their composition should be roughly similar.
Venus and Earth have the same uncompressed density, so it's reasonable to conclude that it's made of more-or-less the same ratio of stuff.
Plus, people have landed vehicles on Venus. They just don't last long.
There's a great story about a Venus lander that was being built in the U.S. On the probe was a window, and this window needed to be made of diamond. Two diamond windows (the size of a dime) were ordered, from France. One was to go into the ship, the other was a spare. A rather large import duty was placed on these by the government, due to their high price. Once the probe was launched, the company that made the probe applied to get the import duty on one of the windows refunded, since it had been exported again. And the government refunded the money, agreeing that Venus was not a part of U.S. territory.
I wish I knew more details. May look for them tomorrow. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
Visit Dave's Psoriasis Info, too. |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/16/2008 : 06:27:00 [Permalink]
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| The Soviet landers Venera 9 and 10 took the first pictures of Venus' surface. Venera 14 and 15 took the first color photos of the surface. The Soviets sent a lot of probes to Venus for some reason. Back in '89 Magellan from the US created fairly high resolution radar maps of Venus' surface and found via the sparsity of craters and the uniform crater density that the entire surface of the planet was effectively remade about 200 million years ago. I found that tidbit particularly interesting when it was announced. |
-Chaloobi
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/16/2008 : 06:34:37 [Permalink]
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Well at least God is staying busy, he gets cranky unless he gets to resurface a planet every once in awhile.
The Venus lander had time to take a picture or two before being crushed, what a waste of rubles. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/16/2008 : 08:23:55 [Permalink]
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Originally posted by BigPapaSmurf
Well at least God is staying busy, he gets cranky unless he gets to resurface a planet every once in awhile.
The Venus lander had time to take a picture or two before being crushed, what a waste of rubles.
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It probably overheated. The article I read said that the landers were cooled down before they entered Venus' atmosphere. Not sure how that was done but it seems countering Venus' heat is a bigger engineering problem than countering the pressure. Besides, if the probe couldn't handle the pressure, it would probably fail right away, not crush a little at a time. So in that case there would be no pictures. |
-Chaloobi
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 01/16/2008 : 08:49:09 [Permalink]
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BTW, this is the official site for the mission. We've got the first look at the planet's previously unseen side:
And more on the core question (pun intended):| There are three major theories to explain why Mercury is so much denser and more metal-rich than Earth, Venus, and Mars. Each theory predicts a different composition for the rocks on Mercury's surface. According to one idea, before Mercury formed, drag by solar nebular gas near the Sun mechanically sorted silicate and metal grains, with the lighter silicate particles preferentially slowed and lost to the Sun; Mercury later formed from material in this region and is consequently enriched in metal. This process doesn't predict any change in the composition of the silicate minerals making up the rocky portion of the planet, just the relative amounts of metal and rock. In another theory, tremendous heat in the early nebula vaporized part of the outer rock layer of proto-Mercury and left the planet strongly depleted in volatile elements. This idea predicts a rock composition poor in easily evaporated elements like sodium and potassium. The third idea is that a giant impact, after proto-Mercury had formed and differentiated, stripped off the primordial crust and upper mantle. This idea predicts that the present-day surface is made of rocks highly depleted in those elements that would have been concentrated in the crust, such as aluminum and calcium. |
Still nothing about the Z-axis. |
| Edited by - Cuneiformist on 01/16/2008 08:52:16 |
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/17/2008 : 11:40:30 [Permalink]
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| Actually the mass is from the internal mini-neutron star dynamo, there is only a small thin iron shell.[/mozina] |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 01/17/2008 : 11:43:40 [Permalink]
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Originally posted by BigPapaSmurf
Actually the mass is from the internal mini-neutron star dynamo, there is only a small thin iron shell.[/mozina]
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Oops-- you are actually correct. I've completely mangled Mozina's argument. The sun has an iron surface, but a neutron star core.
Still, a point left unanswered is how he can posit a radical model for the sun that includes a significant percentage of heavy elements and yet have its density be the same as for models where the sun is almost entirely H and He! I mean, they didn't seem to get it wrong with Mercury's composition and density... |
| Edited by - Cuneiformist on 01/17/2008 11:44:25 |
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chaloobi
SFN Regular
1620 Posts |
Posted - 01/17/2008 : 11:43:54 [Permalink]
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Originally posted by BigPapaSmurf
Actually the mass is from the internal mini-neutron star dynamo, there is only a small thin iron shell.[/mozina]
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Then the next big question is what is keeping that shell from collapsing? |
-Chaloobi
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BigPapaSmurf
SFN Die Hard
3192 Posts |
Posted - 01/17/2008 : 12:07:09 [Permalink]
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| Internal pressure, solves that. What Im still wiating for is where the iron came from in the first generation of stars. |
"...things I have neither seen nor experienced nor heard tell of from anybody else; things, what is more, that do not in fact exist and could not ever exist at all. So my readers must not believe a word I say." -Lucian on his book True History
"...They accept such things on faith alone, without any evidence. So if a fraudulent and cunning person who knows how to take advantage of a situation comes among them, he can make himself rich in a short time." -Lucian critical of early Christians c.166 AD From his book, De Morte Peregrini |
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Cuneiformist
The Imperfectionist
USA
4955 Posts |
Posted - 01/17/2008 : 12:20:50 [Permalink]
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Originally posted by BigPapaSmurf
Internal pressure, solves that. What Im still wiating for is where the iron came from in the first generation of stars.
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No, I think Dave did the math, and the internal pressure would have to be at something like a million degrees, at which point iron isn't very solid.
And YOUR question is answered by the fact that, according to Mozina, the Big Bang is a sham and he favors a steady-state sort of model. His model has all sorts of problems, but still. He has actually thought about the iron question in that respect.
If you look at his site/blog, he is always happy to cite some press release nothing that iron is present in some far-away star, the implication being that the Big Bang model is all wrong. |
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Iron Core: Mercury
