MarkE

Galactic distribution of heavy elements

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Do supernovae scatter their heavy elements (after iron-56) far away in space, which, as a result of this event, could be absorbed by exoplanets in another galaxy?

And why does Earth seem to have so many heavy elements? Shouldn't there be more heavy elements on Venus and Mercury instead?

Edited by MarkE

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The center of galaxies, and along the spiral arms, have more heavy elements than the outer and less dense regions because there are more giant stars packed closer together near the center of the galaxy that go supernova and scatter their heavy elements around.  Earth is in the galactic habitable zone because it is far enough away from the center of the galaxy with the deadly radiation but still close enough to populated regions to get enough heavy elements from supernovas.

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While a supernova would scatter elements into the galaxy, I doubt any of it would reach another galaxy.

As far as heavy elements in the inner planets go, Earth has a density of 5.52 g/cm3, Venus 5.24 g/cm3, and Mercury 5.43 g.cm3 .

Earth has the highest density, but is also the largest. This becomes a factor because as a  rocky planet gets larger, the pressure at its interior increases, which compresses the core and brings up the average density of the planet. 

Earth's radius is 5.4% greater than Venus' and its density is  5.3% greater.  Earth's Mass is 22.6% larger than Venus. We can assume that at least some of the average density difference is like due to the greater compression at the Earth's core due to its larger size. 

The Earth is only 1.7% denser than Mercury but its radius is 161.4% greater.   Mercury is smaller than Mars, and has a density 38.2% larger. From this we can conclude that Mercury has a higher percentage of heavier elements than the Earth does.    Exact values for the  total elemental make up for Venus or Mercury don't exist.  Only two landers have ever done a test of the crust of Venus, and this is not enough to tell us about the planet as a whole,  And the only mission to Mercury was a fly-by.  

 

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16 hours ago, Airbrush said:

Earth is in the galactic habitable zone because it is far enough away from the center of the galaxy with the deadly radiation but still close enough to populated regions to get enough heavy elements from supernovas.

Interesting! When/how did we get these heavy elements?

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@swansont The article states that the merger of two neutron stars could be an alternative source. A neutron star by itself is a potential result of a supernova, which makes it even more plausible that this is another source for the creation of heavy elements. I'm still interested when/how we, Earth, got them. 

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They were present in the cloud of gas and dust that the sun and solar system formed from. 

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On 12/12/2017 at 2:20 PM, Strange said:

They were present in the cloud of gas and dust that the sun and solar system formed from. 

As a result of a supernova in the neighbourhood a few million years before?

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1 hour ago, MarkE said:

As a result of a supernova in the neighbourhood a few million years before?

I guess it must have been a large number of supernovae in the billions of years previously. Just based on the amount of material - think how many stars and planets there are in our galaxy: as far as I know they all have roughly the same mix of elements and so there must have been vast numbers of supernovae to create all those heavy elements. (The first generation of stars were much bigger and shorter lived than current stars, because there weren't these heavier elements around.)

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7 hours ago, Strange said:

Just based on the amount of material - think how many stars and planets there are in our galaxy:

OK, I will think about it.

I have to admit I don't know much about them but here goes.

Almost all the mass of the solar system is the Sun, and it hasn't got much iron in it (0.003% by number of atoms I believe)

If I make the (dodgy) assumption that all the other stars and planets in the galaxy are similar then I conclude that the galaxy hasn't got much iron in it.

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On 12/11/2017 at 10:52 PM, MarkE said:

Do supernovae scatter their heavy elements (after iron-56) far away in space, which, as a result of this event, could be absorbed by exoplanets in another galaxy?

And why does Earth seem to have so many heavy elements? Shouldn't there be more heavy elements on Venus and Mercury instead?

The fact that the terrestrial planets are closer to the Sun then the gaseous and icy giants, actually support the accretion disk theory re planetary formation. And also in recent times, various stages of stellar system creation has been observed in distant systems.  The heavier elements are more inclined to fall towards the center, [to create the terrestrial planets] along with the fact that closer to the Sun, the lighter elements such as Hydrogen Methane etc were prevented fro condensing due to higher temperatures. These lighter elements went into  into creating the icy gaseous giants further out from the Sun, where temperatures  were more conducive.

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2 hours ago, John Cuthber said:

OK, I will think about it.

I have to admit I don't know much about them but here goes.

Almost all the mass of the solar system is the Sun, and it hasn't got much iron in it (0.003% by number of atoms I believe)

If I make the (dodgy) assumption that all the other stars and planets in the galaxy are similar then I conclude that the galaxy hasn't got much iron in it.

Nice. You made me think about it a bit more as I hurtle down the motorway. I did a quick search and found a paper that estimated the mass of iron around one supernova to be about half a solar mass - which sounds like a lot of iron. Not sure how typical it is though. 

That is about 150,000 earth masses. The earth is about 1/3 iron, so enough for 450,000 earths. 

There are about 100 billion planets in the galaxy so (if they were all earth-like) that would need more than 200,000 supernovae. 

Does that sound about right?

 

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On 14/12/2017 at 1:39 PM, Strange said:

Think how many stars and planets there are in our galaxy: as far as I know they all have roughly the same mix of elements.

Not exactly, our sun has an unusually high proportion of heavy elements. Even our solar system contains much more heavy elements than is typically the case. That's why it's interesting to me.

It's the unusualness that I'd like to examine, that's why I asked the question about the amount of heavy metals present on earth. If the accretion theory explains why Earth has this much heavy metals, why Venus has probably a little bit more of it, and Mercury even more (if I understand @beecee correctly) than there's no unusualness, and I withdraw my question.

But not all (heavy) elements and molecules on earth can be explained by accretion only, take for instance water. It's though that water has been delivered to Earth by meteorites.

Edited by MarkE

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1 hour ago, MarkE said:

Not exactly, our sun has an unusually high proportion of heavy elements. Even our solar system contains much more heavy elements than is typically the case.

I didn't know that. Do you have reference for the amounts (and possible explanations)?

1 hour ago, MarkE said:

But not all (heavy) elements and molecules on earth can be explained by accretion only, take for instance water. It's though that water has been delivered to Earth by meteorites.

I guess that is because water is not very heavy and also very volatile. So even if it had been present in the material making up the early earth, much of it would have evaporated again until things cooled down.

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@Strange I recently heard this from Alex Filippenko, but unfortunately he didn't say anything about the amounts.

Our sun is quite unique for multiple reasons: there are only 5% Sun-like stars in the Milky Way (30% of which have Earth-mass planets in the habitable zone) and less than 3% are orbited by hot Jupiter-like planets. Only 1% of these run in a circular orbit (which is necessary for terrestrial planets to orbit). 

This is why I'm interested in how our Sun differs from other stars. For instance: do other stars also change their magnetic orientation every once in a while? (Our Sun changes its magnetic orientation every 11 year).

Edited by MarkE

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2 hours ago, MarkE said:

@Strange I recently heard this from Alex Filippenko, but unfortunately he didn't say anything about the amounts.

Interesting. I will see if I can find out more...

There is a forum called CosmoQuest (naff name) where there are a lot of people interested in astronomy and related subjects (including some professional astronomers). You could try asking there; you'll might get more knowledgable answers. 

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4 hours ago, MarkE said:

Our sun is quite unique for multiple reasons: there are only 5% Sun-like stars in the Milky Way (30% of which have Earth-mass planets in the habitable zone) and less than 3% are orbited by hot Jupiter-like planets. Only 1% of these run in a circular orbit (which is necessary for terrestrial planets to orbit). 

Very interesting.  Where do you get this info?  Does it tell you what percentage of ALL stars in the Milky Way have Earth-mass planets in the habitable zone?  What I really want to know is what percentage of stars have habitable-mass planets (Earth-mass or half-Earth-sized or superearths) with circular orbits.  That would allow complex life to evolve.

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@Airbrush  I've learned this a while ago from professor Laird Close. I don't know with certainty whether this percentage accounts for ALL stars in the Milky Way, because that would imply that all 100 billion stars, all of them, have already been studied, which seems rather unlikely to me. Moreover, the search for exoplanets would be over, which leads me to answer your last question about what percentage of stars have a habitable-mass planet: these small planets are very hard to detect, they're never detected directly but indirectly, because the slight wobble of a star indicates indirectly a massive Jupiter-like planet orbiting it, but an Earth-like planet doesn't effect its star that much. Maybe in the future we're able to use a different technique to detect Earth-like planets with Earth-like masses. 

@Strange I've followed your recommendation to visit the Cosmoquest forum. My question however somehow didn’t get through :o. I have no idea why, but I decided to move to another astronomy forum with the same question. There I've received a lot of response.

First off, I have to admit that I was wrong! Well, I blindly quoted a professor who turned out to be wrong. The lecture I referred to was released in 2006. Dr. Filippenko was probably relying on old data that does not reflect the current best values. The metallicity of the Sun and population I stars has been revised downward in the past 10 years, and it could be that the mix of values was not properly vetted.

About the changing of Sun’s magnetic orientation: it is expected that all stars do this. It's just hard to observe, but there is no proof whatsoever that our Sun is unique in this behaviour.

About helioseismology, our sun that occilates every so much minutes: this also appears to be universal, that’s why it’s called ‘asteroseismology’. Unfortunately, I didn’t receive any examples of other stars who show this type of behaviour, but a little bit of research revealed Solar-like occillators, Cepheid variables, RR Lyrae variables and so on, all types of star occilation.

About the unusualness of the heavy elements in our Sun and in the Solar System in general: our Sun does not have an unusually high abundance of heavy elements. It has an average composition for Population I stars. Older stars formed long before the Sun have fewer heavy metals, and stars younger than the Sun have more heavy metals than the Sun. The metallicity of the Sun has decreased over the last few decades, but our Sun has an average composition of heavy metals for stars that were formed near the same time. 

So, thanks for your comments, it lead me to find out more about the true nature of our universe!

Edited by MarkE

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45 minutes ago, MarkE said:

I've followed your recommendation to visit the Cosmoquest forum. My question however somehow didn’t get through :o. I have no idea why, but I decided to move to another astronomy forum with the same question. There I've received a lot of response.

CQ has some quite strict anti-spam measures - that might be the reason. Anyway, glad you found some good answers. And thanks for updating us!

BTW:you might be interested in the article I linked in this thread: 

 

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Posted (edited)

Hello everyone, was interesting to read your site

Edited by mongol

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Earth has plate tectonics which brings heavy elements to the surface.  Mercury and Mars don't have any of that, and I think Venus has very little surface recycling.  For a planet to be habitable may require plate tectonics to bring the heavy elements necessary for life to the surface, if I remember correctly.

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On 12/11/2017 at 8:33 AM, Janus said:

And the only mission to Mercury was a fly-by. 

There were actually two missions to Mercury.  The 1973 launch of Mariner 10 made its closest approach to Mercury in 1975 as it flew by.  Then there was the MESSENGER (MErcury Space, Surface ENvironment, GEochemistry, and Ranging) probe, launched in August 2004 and made its first flyby of Mercury in 2008.  The MESSENGER probe made a total of three flybys of Mercury, two flybys of Venus, and a flyby of Earth between 2008 and 2011 before settling into orbit around Mercury.  The spacecraft remained in orbit around Mercury between 2011 and 2015, before it ran out of fuel and crashed into Mercury in 2015.

See also Mercury's Secrets Revealed by Soon-to-Crash Spacecraft

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