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m1omg
2008-Oct-19, 08:48 AM
How would an Earth mass world look like in a Jupiter, Saturn, or Uranus equivalent orbit (or as an outer gas giant moon)?

PraedSt
2008-Oct-19, 09:02 AM
I think that if you took the Earth as it is now, and moved it:
In an outer orbit, probably a great big iceball.
As a moon, probably an iceball with cracks. Like Europa.
But I think that chemistry would come into play; atmospheric, carbon cycles, volcanoes, etc to influence the final outcome.

m1omg
2008-Oct-19, 09:39 AM
I think that if you took the Earth as it is now, and moved it:
In an outer orbit, probably a great big iceball.
As a moon, probably an iceball with cracks. Like Europa.
But I think that chemistry would come into play; atmospheric, carbon cycles, volcanoes, etc to influence the final outcome.

Thanks for answer, but you misunderstood my question.
I am talking about a naturally formed planet there, similiar to Earth only in mass, seas (but ethane or methane) and potential biosphere, not "moving Earth into the cold".
I think that such a planet should have great potential for advanced biosphere, I think it would be somewhat like Titan, but MUCH more active and with much more volatiles because of higher gravity, I think possibly with very dense atmosphere and completely submerged in methane or ethane or maybe ammonia seas, with active vulcanism, what can experts here like eburacum say about this?

PraedSt
2008-Oct-19, 09:45 AM
Thanks for answer, but you misunderstood my question

Oh yes, you're right. You said 'Earth mass'. Sorry! :doh:
But that would be planetary formation theories and stuff, which I don't know much about. So I'll go away and do some reading...

Romanus
2008-Oct-19, 01:57 PM
I dunno...I think being removed from the "warm" inner Solar System distances would make for a planet with a massive gaseous, hydrohelium atmosphere--probably not at massive as Uranus's or Neptune's, but probably too deep and dense to be biologically useful, IMO, especially at Saturnian distance and up.

I think the farthest you could put an interesting Earth-mass planet would be at say, Jupiter's distance; tectonically active, ice-covered oceans would make for an even more favorable Europa-like environment. The possibilities of volatile ammonia and CO2 chemistry at that distance would also be fascinating.

Just my two bits.

m1omg
2008-Oct-19, 04:16 PM
I dunno...I think being removed from the "warm" inner Solar System distances would make for a planet with a massive gaseous, hydrohelium atmosphere--probably not at massive as Uranus's or Neptune's, but probably too deep and dense to be biologically useful, IMO, especially at Saturnian distance and up.

I think the farthest you could put an interesting Earth-mass planet would be at say, Jupiter's distance; tectonically active, ice-covered oceans would make for an even more favorable Europa-like environment. The possibilities of volatile ammonia and CO2 chemistry at that distance would also be fascinating.

Just my two bits.

What about moons?

eburacum45
2008-Oct-19, 07:37 PM
I'm not an expert, m1omg; just an interested person like yourself...

Have you seen this article by Andrew LePage, about the possibilities of habitable moons?
http://www.skyandtelescope.com/resources/seti/3304591.html?page=1&c=y

As far as an Earth-mass moon orbiting a gas giant, that might occur sometimes. Moons of gas giants tend to have about 1/10,000 the mass of the primary;
http://space.newscientist.com/article/dn9336-upper-size-limit-for-moons-explained.html
If a gas giant has ten times as much mass as Jupiter, it will mass about 3000 times as much as the Earth, and its moons might be expected to have a third the mass of Earth in total. But that is only a rule of thumb, and I would expect Earth-mass moons to occur fairly frequently.

If a moon had a rocky and metallic core the same size as Earth's, it could have a considerable internal heat source and a magnetic field; but the surface would be colder, so it would have a thick layer of ice. This layer might be very thick indeed, thicker than the ocean layer of Earth, simply because there is much more water available out there, beyond the frost line, in the form of ice. You might get a water layer beneath the ice heated by volcanism, as well as by any tidal effects which might apply. A kind of super Europa.

Alternately your Earth-mass moon might be heated so much by tital effects that it resembles Io more; but with Earth-like gravity, it could hold on to a much thicker atmosphere than Io. Imagine an Earth covered in volcanoes, tidally locked (of course) and orbiting inside a thick torus of ionised gas stripped from its atmosphere by the gas giant.

m1omg
2008-Oct-19, 07:58 PM
I'm not an expert, m1omg; just an interested person like yourself...

Have you seen this article by Andrew LePage, about the possibilities of habitable moons?
http://www.skyandtelescope.com/resources/seti/3304591.html?page=1&c=y

As far as an Earth-mass moon orbiting a gas giant, that might occur sometimes. Moons of gas giants tend to have about 1/10,000 the mass of the primary;
http://space.newscientist.com/article/dn9336-upper-size-limit-for-moons-explained.html
If a gas giant has ten times as much mass as Jupiter, it will mass about 3000 times as much as the Earth, and its moons might be expected to have a third the mass of Earth in total. But that is only a rule of thumb, and I would expect Earth-mass moons to occur fairly frequently.

If a moon had a rocky and metallic core the same size as Earth's, it could have a considerable internal heat source and a magnetic field; but the surface would be colder, so it would have a thick layer of ice. This layer might be very thick indeed, thicker than the ocean layer of Earth, simply because there is much more water available out there, beyond the frost line, in the form of ice. You might get a water layer beneath the ice heated by volcanism, as well as by any tidal effects which might apply. A kind of super Europa.

Alternately your Earth-mass moon might be heated so much by tital effects that it resembles Io more; but with Earth-like gravity, it could hold on to a much thicker atmosphere than Io. Imagine an Earth covered in volcanoes, tidally locked (of course) and orbiting inside a thick torus of ionised gas stripped from its atmosphere by the gas giant.

I assume you are talking about moon around a Jupiter-like gas giant, because wouldn't it be covered by hydrocarbons in Saturn distance?Something like super-Titan?

Btw I am curious how such an super Europa would appear with it's thick atmosphere, volcanism and ionised torus, and would it be possible that so much volcanism would cause all the ice to melt, even on the surrface, by either greenhouse warming or direct heating from the volcanic activity?

Delvo
2008-Oct-19, 10:48 PM
Are you telling me that the gas giants are NOT already just rocky planets with really really thick atmospheres?

Invader Xan
2008-Oct-20, 12:38 AM
There are some theories suggesting that if Titan had formed closer to the Sun, it might've ended up a lot like Earth. It's possible then, that an Earth-like planet further out would be a lot like Titan.

All the components are there... Nitrogen, water, hydrocarbons... Titan's only difference is its size. Normally such a small planet would've had its atmosphere stripped away by the solar wind -- but Titan has the protection of Saturn's magnetic field. :)

eburacum45
2008-Oct-20, 01:14 AM
Sure; We could call such planets SuperTitans. Of course simply adding the prefix 'super-' to a world will get annoying if you do it too much; but planetologists (or whatever they like to call themselves) already talk about 'superterrestrials' and 'superMercurys'.
Supertitans will gradually shade into small gas giants with increasing mass.
The exact appearance of these outer system worlds will also be affected by their temperature and rotation rate.

Moons of Jupiter have fewer volatiles the closer they orbit to that planet; so it seems likely that large cold moons elsewhere will also be less gaseous. Titan is colder, and a long way from Saturn, itself a quieter and smaller planet than Jupiter.

Titan more closely resembles what I would expect a smaller icy planet, orbiting by itself, to look like.

Romanus
2008-Oct-20, 10:27 PM
I didn't include moons because of two possible fudge factors: radiation belts, which if strong would erode even a dense atmosphere, and a possible relation between planetary mass and satellite mass (recently published, though the link eludes me ATM) that may make Earth-mass moons less common than previously thought.

timb
2008-Oct-20, 11:33 PM
Sure; We could call such planets SuperTitans. Of course simply adding the prefix 'super-' to a world will get annoying if you do it too much; but planetologists (or whatever they like to call themselves) already talk about 'superterrestrials' and 'superMercurys'.
Supertitans will gradually shade into small gas giants with increasing mass.

Surely they will resemble ice giants such as Neptune before they resemble gas giants such as Saturn. The composition of Titan is much closer to that of an ice giant than it is to that of Saturn or Jupiter. Gas giants are overwhelmingly H/He, whereas ice giants are only about 15% H/He. What is the difference between the proposed classification super-Titan and an ice giant anyway?

The meaning of "super-X" is extremely vague and often (especially in the expression "super-Earth") seems merely to mean that the body in question is more massive (but not too much more massive) than "X", not that it bears any structural similarity. I think this is bad and misleading usage but it it obviously makes more attractive copy to describe an exoplanet as a "super-Earth" (wow! it must be just like Earth only better!) rather than "a planet of completely unknown composition at least five times the mass of Earth", so it will be with us forever.



There are some theories suggesting that if Titan had formed closer to the Sun, it might've ended up a lot like Earth.

That's like saying if my mother had been a mare I would have ended up a lot more like Mr. Ed.


As far as an Earth-mass moon orbiting a gas giant, that might occur sometimes. Moons of gas giants tend to have about 1/10,000 the mass of the primary;

A migrating gas giant might conceivably capture the embryos of terrestrial planets, resulting in larger rocky satellites than that rule of thumb predicts. But then our hypothetical "planet" wouldn't be "out there".

Ivan Viehoff
2008-Oct-21, 11:05 AM
How would an Earth mass world look like in a Jupiter, Saturn, or Uranus equivalent orbit (or as an outer gas giant moon)?
My guess is that there is quite a large number of possibilities, most of them rather surprising. Look how diverse the moons of the gas giants are, and how surprised we were when we found them. One could hypothesize that our particular solar system does not represent a very large cross-section of the possibilities, since it is the result of its own particular environment and history. But since we can't even say very much about Pluto without sending a probe, I don't expect we are going to get very much detailed information about smaller extra-solar planets and their moons any time soon. So who can say, in reality?

ASEI
2008-Oct-21, 11:18 AM
My understanding is that the frost line is also roughly the "hydrogen retention line". If you're working out how a planet will evolve in a solar system, and you want something other than a gas giant, the escape velocity from your seed mass has to be less than (or in the neighborhood of) the average gas velocity of the hydrogen within the planet's atmosphere at a certain distance from the sun.

Otherwise, hydrogen piles on and you get a gas giant or an iceball.

If the thermal velocity is too great compared to escape speed., all the hydrogen containing compounds bake out and you get a bare rock-ball.

m1omg
2008-Oct-21, 12:07 PM
My understanding is that the frost line is also roughly the "hydrogen retention line". If you're working out how a planet will evolve in a solar system, and you want something other than a gas giant, the escape velocity from your seed mass has to be less than (or in the neighborhood of) the average gas velocity of the hydrogen within the planet's atmosphere at a certain distance from the sun.

Otherwise, hydrogen piles on and you get a gas giant or an iceball.

If the thermal velocity is too great compared to escape speed., all the hydrogen containing compounds bake out and you get a bare rock-ball.

Incorrect.Ask Titan.

timb
2008-Oct-21, 12:12 PM
My understanding is that the frost line is also roughly the "hydrogen retention line". If you're working out how a planet will evolve in a solar system, and you want something other than a gas giant, the escape velocity from your seed mass has to be less than (or in the neighborhood of) the average gas velocity of the hydrogen within the planet's atmosphere at a certain distance from the sun.

Otherwise, hydrogen piles on and you get a gas giant or an iceball.

If the thermal velocity is too great compared to escape speed., all the hydrogen containing compounds bake out and you get a bare rock-ball.

Bodies greater than about 10 ME accrete gas quickly from the protoplanetary disk. Smaller ones don't.

m1omg
2008-Oct-21, 01:34 PM
Bodies greater than about 10 ME accrete gas quickly from the protoplanetary disk. Smaller ones don't.

So my 1 ME terrestrial planet is going to stay safe.

Btw my avatar is an image of such a hypothetical Super-Titan planet posted on Shatters.net (Celestia) forums that inspired me to create this discussion :)
Here's the link to a bigger version; http://www.shatters.net/forum/download/file.php?id=67&mode=view
The link to the whole thread http://www.shatters.net/forum/viewtopic.php?f=2&t=9581&st=0&sk=t&sd=a&hilit=images&start=210

cjameshuff
2008-Oct-21, 02:08 PM
Incorrect.Ask Titan.

Titan's an iceball. Io would be a better attempt at a counterexample...but gas giant moons are in a similar situation, in that direct heat from the forming gas giant and continuing tidal heating can drive off volatiles if they form close enough to the planet. Even then...Io's the only gas giant moon in the solar system that's not at least half water ice.

m1omg
2008-Oct-21, 02:14 PM
Titan's an iceball. Io would be a better attempt at a counterexample...but gas giant moons are in a similar situation, in that direct heat from the forming gas giant and continuing tidal heating can drive off volatiles if they form close enough to the planet. Even then...Io's the only gas giant moon in the solar system that's not at least half water ice.

Who said anything about composition?If ice is the material of choice of nature to build terrestrials in the cold ares, then my planet would be made of ice instead of a silicate rock.Anyways, water ice IS A ROCK in these cold areas.A rock harder than granite.

And it was already said that things smaller than 10 Earth masses WILL NOT start to accrete hydrogen.

m1omg
2008-Oct-21, 02:19 PM
My guess is that there is quite a large number of possibilities, most of them rather surprising. Look how diverse the moons of the gas giants are, and how surprised we were when we found them. One could hypothesize that our particular solar system does not represent a very large cross-section of the possibilities, since it is the result of its own particular environment and history. But since we can't even say very much about Pluto without sending a probe, I don't expect we are going to get very much detailed information about smaller extra-solar planets and their moons any time soon. So who can say, in reality?

I agree,But, for the sake of discussion, let's speculate...when we will discover some such planets we can compare...

cjameshuff
2008-Oct-21, 02:29 PM
Who said anything about composition?

ASEI did, in the text you quoted and said was incorrect, giving Titan as a counterexample: "Otherwise, hydrogen piles on and you get a gas giant or an iceball."



And it was already said that things smaller than 10 Earth masses WILL NOT start to accrete hydrogen.

Not large amounts of elemental hydrogen, but hydrogen-rich low-density volatiles like water, ammonia, and light hydrocarbons like methane and ethane.

m1omg
2008-Oct-21, 02:37 PM
ASEI did, in the text you quoted and said was incorrect, giving Titan as a counterexample: "Otherwise, hydrogen piles on and you get a gas giant or an iceball."




Not large amounts of elemental hydrogen, but hydrogen-rich low-density volatiles like water, ammonia, and light hydrocarbons like methane and ethane.

Lol, are you totally missing the point of this thread?
I said I am talking about a cold Earth analogue, with a lot of liquid volatiles on the surface, even completely DRENCHED in liquids and complex chemistry, and volcanic activity, not a dry rockball.

Ok sorry I overlooked the iceball part, I just say that it definitely wouldn't runway accumulate hydrogen, helium and other light gases and create an ice or gas giant.

chornedsnorkack
2009-Feb-16, 07:16 PM
Uranus and Neptune are much denser than Saturn. Therefore they must have a larger proportion of substances denser than hydrogen and helium, whether ice, rock or iron.

But Uranus and Neptune also are far less dense than Titan or Triton. It follows that they cannot consist of ice with only a thin atmosphere, because if they were, they should be compressed by gravity to far larger densities.

Titan and Triton have nitrogen and methane atmospheres, but little free hydrogen or helium.

Roughly how big and how massive would an icy body have to be in order to retain hydrogen and helium as appreciable components of atmosphere, but not a thick layer (that is, somewhere between 0,01 atm and 100 atm)?

dodecahedron
2009-Feb-16, 07:26 PM
Sure; We could call such planets SuperTitans. Of course simply adding the prefix 'super-' to a world will get annoying if you do it too much; but planetologists (or whatever they like to call themselves) already talk about 'superterrestrials' and 'superMercurys'.

Are they adversely affected by kryptonite?

RalofTyr
2009-Feb-16, 09:07 PM
1. An Earth like world, a terrestrial world that formed in the inner parts of the solar system then migrated outwards, would be frozen, with a thin atmosphere of trace amounts of exotic gases, well, exotic as found on Earth.

2. A world with the same mass as Earth, but formed in the outer parts of the solar system, would be rather large, less dense and probably having a thick atmosphere of hydrogen and other gases that were out in the solar system during the formation time.

Both types would be volcanic, the first one much more so than the second type.

Say, doesn't Neptune have the same mass or gravity as Earth?

dodecahedron
2009-Feb-16, 09:40 PM
Say, doesn't Neptune have the same mass or gravity as Earth?

Neptune's mass is 17x Earth. Gravity is a hair more than Earth normal.