Icy Super-Earths and their migration

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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 14th December 2009, 12:22 am

Okay. So... does a planet that's half rock, half ice, count as a terrestrial? Or a Neptune? D:

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Re: Icy Super-Earths and their migration

Post by TheoA on 14th December 2009, 2:27 am

50/50 Silicates to water would be a rocky planet for sure.

The Rocky core for Neptune is ~ to 15% of its mass.

It has long been a fear that the Earths atmosphere is anomalously thin as has been
postulated by others.

Our surface gravity, such as it is, is only exceeded by Jupiter and Neptune. (The term surface is used loosely here)

Ergo our Atmosphere should have been orders of magnitude thicker. Something in the Venus range of 100+ times our present
atmospheric thickness.

If so an Earth size planet might very likely be the wrong size to look for.

Something smaller, perhaps half our size is more likely to have a thinner atmosphere and easily detectable life.

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Re: Icy Super-Earths and their migration

Post by Stalker on 14th December 2009, 2:32 am

I think that the most important is its capacity to keep a dense and sprawling atmosphere. And I think especially as there is a continuum gaseous giant, the giants of ice and the terrestrial planets. And the ice is a rock as an other...
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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 14th December 2009, 4:04 am

TheoA wrote:Ergo our Atmosphere should have been orders of magnitude thicker. Something in the Venus range of 100+ times our present atmospheric thickness.

In the second page of this thread, the atmospheres of Venus and Earth are compared. In summary, the reason Earth's atmosphere is so thin is because a lot of the gases in the atmospehere were locked away in rocks and in the ocean.

http://solar-flux.forumandco.com/extrasolar-planetology-f5/sulfur-seas-lakes-or-rivers-in-venus-t412-15.htm

Sub-Earth-mass planets may not be the most friendly places for life, based on the difficulties in their achieving plate tectonics, sustained global magnetic fields, and such.

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Re: Icy Super-Earths and their migration

Post by TheoA on 14th December 2009, 2:24 pm

"In the second page of this thread, the atmospheres of Venus and Earth are compared. In summary, the reason Earth's atmosphere is so thin is because a lot of the gases in the atmospehere were locked away in rocks and in the ocean."

http://solar-flux.forumandco.com/extrasolar-planetology-f5/sulfur-seas-lakes-or-rivers-in-venus-t412-15.htm

thanx for the link. Very interesting discussion. I'm more concerned about the Hydrogen/Helium accumulation. Our rocky planets have very low levels of these gas which might be an anomaly.

It sure seems like these multi planet watery systems formed closed in. If so our low water, low H2/He rocky worlds might be very unusual.

Sub-Earth-mass planets may not be the most friendly places for life, based on the difficulties in their achieving plate tectonics, sustained global magnetic fields, and such.

True something mars sized, 1/4 of the Earth maybe too small. I'm thinking something 75%-60% Earth size.

Also WRT to tectonics. Venus is Earth size and never had any, even in early times. Too much silicates at our size, No.

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Re: Icy Super-Earths and their migration

Post by Lazarus on 14th December 2009, 4:05 pm

TheoA wrote:Very interesting discussion. I'm more concerned about the Hydrogen/Helium accumulation. Our rocky planets have very low levels of these gas which might be an anomaly.

It sure seems like these multi planet watery systems formed closed in. If so our low water, low H2/He rocky worlds might be very unusual.
The way I see it, it seems more likely the planets formed further out and migrated. Migration certainly seems to be a robust phenomenon, and the amounts of material likely to be found in the inner regions of planetary systems doesn't seem to be enough to form planets of the required masses. Plus much of the water would be located beyond the ice line anyway.
TheoA wrote:Also WRT to tectonics. Venus is Earth size and never had any, even in early times. Too much silicates at our size, No.
The case for early Venusian tectonics is certainly not closed. The present very dehydrated conditions on Venus do not make it a good comparison to Earth's tectonics: it is fairly well established that subduction zones on Earth are facilitated by the presence of water in the crust.

Of course all this is yet another reason why if you find a ~5 Earth mass planet orbiting a red dwarf you shouldn't claim it is habitable... or a 7-Earth mass one either...
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Re: Icy Super-Earths and their migration

Post by TheoA on 14th December 2009, 6:38 pm

The way I see it, it seems more likely the planets formed further out and migrated. Migration certainly seems to be a robust phenomenon, and the amounts of material likely to be found in the inner regions of planetary systems doesn't seem to be enough to form planets of the required masses. Plus much of the water would be located beyond the ice line anyway.

Which would be fine except for the parking mechanism involved. If the gas disappears beyond the snowline quickly does not the migration mechanism also disappear quickly. How do you migrate this far in past the snow line.

Also how do 3 or more such planets migrate in perfect lock step and all stop at the same time!!

Migration is also not so robust for smaller planet.

It is more plausible that these planets formed close to their present position.

Giant planet formation is thought be much more rapid than terrestrial types. So migrating Giant planets would likely have a lot more gas to work with.


Of course all this is yet another reason why if you find a ~5 Earth mass planet orbiting a red dwarf you shouldn't claim it is habitable... or a 7-Earth mass one either...

He! He! Got to agree with this. Hopefully certain teams take note.

The case for early Venusian tectonics is certainly not closed.
The present very dehydrated conditions on Venus do not make it a good
comparison to Earth's tectonics: it is fairly well established that
subduction zones on Earth are facilitated by the presence of water in
the crust.

Water facilitates but is not sufficient , no. Case in point Mars. Crust thickness/composition too matters.

That is an interesting detection, but still doesn't prove full blown plate tectonics. Mars to has tectonics. Some form of planet wide tectonics yes.

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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 14th December 2009, 10:41 pm

TheoA wrote:Which would be fine except for the parking mechanism involved. If the gas disappears beyond the snowline quickly does not the migration mechanism also disappear quickly. How do you migrate this far in past the snow line.
Type I migration. Planets produce spiral density waves in the surrounding disk matter. An imbalance occurs in the strength of the interaction between the inner waves and the outer waves. In most cases, the outer waves exert somewhat more torque on the planet than the interior wave, causing the planet to lose energy and migrate toward the star.

In general, because migration is caused by interaction between a planet and its protoplanetary disk, migration continues until either a planet merges with the star, or reaches the inner edge of its part of the disk. That's why hot Jupiters migrate inward and get piled up at periods of ~3 days, because that's about where such star's protoplanetary disks had their inner edge.

TheoA wrote:Also how do 3 or more such planets migrate in perfect lock step and all stop at the same time!!
If two or more planets are caught in resonance, then they will migrate together, keeping constant ratios of orbital periods.

Even for planets not in resonance, migration of one planet does not necessarily end the migration of other planets. Imagine a planetary system of multiple planets, all are migrating inward at their own independent rate, determined by the density of the protoplanetary disk that they are orbiting within (migration of planets doesn't have to be "in perfect lock step" if the planets are not in resonance).

One planet may migrate inward and stop at P = 5 days. Now that this is the planet's new home, it has some time to clear out the disk around this area, pushing the inner edge of the disk back. Second planet comes migrating in. It will either stop at the new inner edge, or if the migration is slow enough, settle into a 1:2 resonance with the first planet. The second planet, in whatever final position it settles in, works to clear out more disk matter, pushing the inner edge of the disk further back. Thus, we can have whole flocks of planets migrating inward without really making too much a mess of things.

TheoA wrote:Migration is also not so robust for smaller planet.
That's reasonable. For planets a few times the mass of Earth, it seems sufficient though.

TheoA wrote:It is more plausible that these planets formed close to their present position.
It is incredibly difficult for a multi-Earth-mass planet to form close to the star. There simply is not enough material due to the volume-limited space it has to work with.

TheoA wrote:Giant planet formation is thought be much more rapid than terrestrial types. So migrating Giant planets would likely have a lot more gas to work with.
Yes. As such, a giant planet migrating inward can scatter whatever else is in the way. Giant planets can migrate inward until they arrive at a gap in the disk.

TheoA wrote:Water facilitates but is not sufficient , no. Case in point Mars. Crust thickness/composition too matters.
The mass of a planet seems to be a major part of whether or not it can have plate tectonics. While the presence of water makes it easier, it doesn't guarantee the process can be done. For super-Earths, some may be massive enough to not need water to lubricate the process. The ability of a planet to have plate tectonics is related to how much interior heat it has, driving such mechanisms. The more massive a planet, the more interior heat it will have, the more the urge for the planet to undergo plate tectonics.

TheoA wrote:That is an interesting detection, but still doesn't prove full blown plate tectonics. Mars to has tectonics. Some form of planet wide tectonics yes.
Somehow I don't figure that the detection of MEarth-1 b was aimed at proving plate tectonics. If Mars had such plate tectonics in the past, it certainly doesn't now. The planet is geologically rather dead inside. Only thing now days that seems to have any is Earth, which is the most massive terrestrial body in the solar system, and has water oceans to lubricate the process.

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Re: Icy Super-Earths and their migration

Post by TheoA on 15th December 2009, 5:19 pm

I'd love to continue this discussion esp. with the new planetary announcements, but this maybe the wrong place.

Wonder if some of these notes could be moved to a new thread in planetology.

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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 15th December 2009, 6:20 pm

TheoA wrote:I'd love to continue this discussion esp. with the new planetary announcements, but this maybe the wrong place.
Wonder if some of these notes could be moved to a new thread in planetology.
Moved to mechanics, as the discussion is more about planets in general.

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Re: Icy Super-Earths and their migration

Post by TheoA on 15th December 2009, 7:30 pm

Thanx for the move Sirius

Type I migration. Planets produce spiral density waves in the surrounding disk matter. An imbalance occurs in the strength of the interaction between the inner waves and the outer waves. In most cases, the outer waves exert somewhat more torque on the planet than the interior wave, causing the planet to lose energy and migrate toward the star.

Isn't type 1 dominant under certain calmer disk conditions, irrespective of size. They are also thought to be incredibly fast from 1 AU in. The first planet might benefit but not the later ones.

That's why hot Jupiter's migrate inward and get piled up at periods of ~3 days, because that's about where such star's protoplanetary disks had their inner edge.

Wouldn't Star/Planet tidal forces be a much more effective 3 day period breaking mechanism.

Also the low material density past the snowline might slow the Giant planet migration much earlier, at the 3 AU distance or more while the Giants appear to get a hundred time closer in.

There has to be considerable material in the inner region to keep inward migration going.

One planet may migrate inward and stop at P = 5 days. Now that this is the planet's new home, it has some time to clear out the disk around this area, pushing the inner edge of the disk back. Second planet comes migrating in. It will either stop at the new inner edge, or if the migration is slow enough, settle into a 1:2 resonance with the first planet. The second planet, in whatever final position it settles in, works to clear out more disk matter, pushing the inner edge of the disk further back. Thus, we can have whole flocks of planets migrating inward without really making too much a mess of things.

That is a pretty good explanation.What does make me nervous is that this pumping action can be both inward and outward for smaller planets.It just seems too strange to imagine all the planets only moving inwards, in a clockwork manner. Very odd if you ask me, but perfectly plausible.

Also gap clearing requires mass~30e, at which point type 2 would immediately kick in.

Any smaller Type 1 has few parking mechanism options.

It is incredibly difficult for a multi-Earth-mass planet to form close to the star. There simply is not enough material due to the volume-limited space it has to work with.

True, but this would be the only major complication to deal with compared to the multiple leaps of logic required with the migration mechanism at smaller sizes. i.e. the disk conditions have to be just so, the first planet has to stop just so, the disk has to communicate to the next planet just so, The gas has to be gone but there should be just enough other material, etc.

According to this paper, http://arxiv.org/abs/0908.1380

if a planet forms or get close to the X-point it should accumulate enough material in situ to form larger planets.Admittedly this is for migration.

So the material can be there if a mechanism can be found to transfer it early on.

The more massive a planet, the more interior heat it will have, the more the urge for the planet to undergo plate tectonics.

Plate tectonics as I understand it involves the continual recycling of the crust, with both subduction and crustal spreading also involving some other faulting. This is distinct from mere tectonics, which Io for instance has in abundance.Mars too has some tectonics as many of its volcanoes for instance continue to remain active.

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Re: Icy Super-Earths and their migration

Post by TheoA on 16th December 2009, 3:09 pm

Apologies if this has been posted earlier.

Terrestrial Planet Formation in Extra-Solar Planetary Systems

Fig. 4 is very interesting.

It shows models of inner planet formation after a giant planet has migrated thru.

The models show the formation of 3-10 Me planets, particularly water enriched.

Hints at these planets we now are finding?

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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 18th December 2009, 3:35 am

TheoA wrote:They are also thought to be incredibly fast from 1 AU in. The first planet might benefit but not the later ones.
As I understand it, as the planet migrates inward, it doesn't necessarily deplete the disk too severely, but rather, displace matter from one side of its orbit to the other side of its orbit. As it does this, it loses orbital energy. There'll be enough matter in the disk for further migration of other planets. Also, if a giant outer planet migrates inward and catches the inner planet in resonance, the inward migration of the outer planet can push the inner planet's orbit further in.

TheoA wrote:Wouldn't Star/Planet tidal forces be a much more effective 3 day period breaking mechanism.
If the planet is tidally locked to the star (with a circular orbit), than there will be minimal tidal lowering of the orbit. The presence of multi-Gyr-old hot Jupiters is suggestive enough of this. However the population of stars with hot Jupiters is somewhat younger than those stars without, suggesting that for at least some systems, stars can absorb their hot Jupiters within the stellar lifetime.

TheoA wrote:It just seems too strange to imagine all the planets only moving inwards, in a clockwork manner. Very odd if you ask me, but perfectly plausible.
Assuming a uniform disk density around the planet's orbit, there will be more disk matter exterior to the orbit than interior, because there is simply more volume of material exterior to that orbit. This means that, again assuming everything is nice and uniform, a planet will migrate inward. Of course in reality, it's not always so nice and uniform.

There are mechanisms through which planets can migrate outward. http://arxiv.org/abs/0910.1004v1

TheoA wrote:if a planet forms or get close to the X-point it should accumulate enough material in situ to form larger planets.Admittedly this is for migration. So the material can be there if a mechanism can be found to transfer it early on.
I read something on the Oklo blog about the possibility that Gliese 876 c was able to funnel enough material from outside its orbit toward the star, allowing for the in situ formation of d. I don't suppose we'll know how well that hypothesis holds up until we make some direct observations of d though.

TheoA wrote:Plate tectonics as I understand it involves the continual recycling of the crust, with both subduction and crustal spreading also involving some other faulting. This is distinct from mere tectonics, which Io for instance has in abundance.
Io has a source of energy due to tidal interacton with the rest of the Jovian system. This provides the heat source that the moon cannot produce through gravitational compression (due to its low mass).

TheoA wrote:Mars too has some tectonics as many of its volcanoes for instance continue to remain active.
I haven't heard this, do you have a reference?

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Re: Icy Super-Earths and their migration

Post by Lazarus on 18th December 2009, 3:11 pm

TheoA wrote:Apologies if this has been posted earlier.

Terrestrial Planet Formation in Extra-Solar Planetary Systems

Fig. 4 is very interesting.

It shows models of inner planet formation after a giant planet has migrated thru.

The models show the formation of 3-10 Me planets, particularly water enriched.

Hints at these planets we now are finding?
If this were the mechanism for forming water-rich super-Earths close to the stars, you'd expect the frequency of super-Earths to trace the frequency of hot Jupiters, this does not appear to be the case.

With regard to multi-planet systems, they don't seem to suffer from the 3-day pileup as much as the apparently single planet population. I've seen a few simulated models of planet formation + migration which result in populations of objects in the inner system after the gas disperses. And sure turbulence reduces the efficiency, but one of the problems is that non-turbulent type I migration dumps planets into the star far too quickly.
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Re: Icy Super-Earths and their migration

Post by TheoA on 21st December 2009, 12:40 pm

The Hot Jupiter most likely spirals into the star on Type 1 migration leaving the water enriched planets behind.

Wonder if that would leave any sort of signature.

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Re: Icy Super-Earths and their migration

Post by Lazarus on 21st December 2009, 7:54 pm

For a start Jupiter-mass planets open a gap in the disc which means they undergo type II migration not type I.

This idea still doesn't explain the occurrence of super-Earths in systems that appear to be inefficient in producing gas giants, such as M dwarfs and low-metallicity systems.

Amusingly enough, one of the potential signatures of a star which has "eaten" a gas giant is enhanced lithium abundance.
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Re: Icy Super-Earths and their migration

Post by TheoA on 22nd December 2009, 4:42 pm

Sirius_Alpha wrote: Also, if a giant outer planet migrates inward and catches the inner planet in resonance, the inward migration of the outer planet can push the inner planet's orbit further in.

Interesting. I would assume that this would involve the exchange of some angular momentum causing the outer planet to slow down.

Sirius_Alpha wrote:However the population of stars with hot Jupiter's is somewhat younger than those stars without, suggesting that for at least some systems, stars can absorb their hot Jupiter's within the stellar lifetime.

Good to know. I thought there was some suggestion that at least some Hot junipers were bloated enough to essentially evaporate in under a stella lifetime as well.

Sirius_Alpha wrote:there will be more disk matter exterior to the orbit than interior, because there is simply more volume of material exterior to that orbit. This means that, again assuming everything is nice and uniform, a planet will migrate inward.

Disk thickness might have something to say about this. Esp. for smaller planets. As the planet moves in the Hill radius prevents a gap from forming, preventing type 2 migration.

Type 1 is more unpredictable and can move the planet outwards as well.


Sirius_Alpha wrote:There are mechanisms through which planets can migrate outward. http://arxiv.org/abs/0910.1004v1

That would explain so much about Neptune and Uranus in our own system would it not. Though these two are not thought to be in resonance right now, they are oh so close to a 1:2 resonance.

Sirius_Alpha wrote:I read something on the Oklo blog about the possibility that Gliese 876 c was able to funnel enough material from outside its orbit toward the star, allowing for the in situ formation of d. I don't suppose we'll know how well that hypothesis holds up until we make some direct observations of d though.

A quick search came up with this very informative post.

http://oklo.org/2007/07/10/gj-876-d/

I had completely forgotten about this post. Even though this particular mechanism would mean a volatiles starved planet.

Looks like it is possible that both migration and in situ formation can be active in the same system, which would explain some of the variety we are seeing.

Sirius_Alpha wrote:I haven't heard this, do you have a reference?

See the Mars/Methane story recently that almost immediately degenerated into a is there/isn't there life battle.

I thought, the mostly likely reason, that it came from volcano's, was just as interesting.

Sirius_Alpha wrote:This idea still doesn't explain the occurrence of super-Earths in
systems that appear to be inefficient in producing gas giants, such as
M dwarfs and low-metallicity systems.

I wouldn't even call it an idea.

Just a discussion on how Icy Super terrestrial planets form.

It's just migration is so much less effective and orderly in smaller planets, that its odd to find these orderly systems.

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Re: Icy Super-Earths and their migration

Post by Sirius_Alpha on 23rd December 2009, 11:24 pm

While the methane production related to volcanism hasn't been ruled out, it does not seem that your claim of "Many of its volcanoes continue to remain active" is well supported. Do we both agree on the definition of volcano as a magma-producing mountain?

The production of methane, if related to volcanic activity, is likely the simple mixing of water and magma. Not necessarily active volcanoes.

Judging by the issued image, the methane sources seem to not be correlated too well with the volcanoes.


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Re: Icy Super-Earths and their migration

Post by Diakonov on 24th December 2009, 8:44 am

Maybe methane is produced not by volcanism, but by geisers. In Mars HIRISE there may have some images that look like geisers being active. To me that's the explanation of methane. Or maybe even by microbes near such geisers that would be a source of nutrients.

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Re: Icy Super-Earths and their migration

Post by TheoA on 26th December 2009, 8:45 pm

You are right Sirius.

They are only thought to have some activity still.

Some lava flows have been dated to 2 million years or so through crater counting.

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Re: Icy Super-Earths and their migration

Post by TheoA on 1st January 2010, 1:38 pm

PLANET FORMATION AROUND STARS OF VARIOUS MASSES: HOT SUPER-EARTHS

Apologies if this has been posted before.

Nice little round up of recent papers on this subject.

Lots of little nuggets of info.

- Beyond Snow line migration is still best candidate.
- Super Critical Steam type planets possible.
- Dry super earths likely caused by collisions with rocky planetesimals that drives off the volatiles. (Did not know that!)
- Gravitational scattering not a good candidate.
- Hydrogen accumulation possible but counteracted with evaporation.
- Disappointingly close in super earth formation is unlikely. But they don't really explain why.

-

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