Super-Earth Plausibility

[WhiteWeasel]

I've already made thread about this, but it's really old. So I think it would be better to start anew.

Simply how big could a terrestrial or "rocky" planet get before becoming a gas giant? In my head I had an an idea for a short story (Which I probably won't write down, but still). With my serious ideas I like a mix of mostly softcore sci-fi with a few hardcore elements to make it feel believable, but not limit myself so much that my options can fit on a sticky note. And i've always want a giant life capable planet in one of my ideas.

As for the atmosphere would it be too much of a stretch to say when it was forming the area it was in was gas-poor so that's why the planet is huge, but didn't become a gas giant? Also could it be bigger in terms of radius or will it just compress down after a certain point?

I've experimented US, and earth 4 is probably going to be as big as it's going to get as believability will allow. But who knows?

[Diche Bach]

Is that a game interface you're showing us a picture of? What game?

I believe the prevailing theories about the formation of Earth and the solar system have been revised rather dramatically since my days in the geology class room, so I'm probably wise to just keep my mouth shut. Would be very interested to hear what anyone with some expertise has to say though!

Edited August 23, 2013 by Diche Bach

[Mr Shifty]

Is that a game interface you're showing us a picture of? What game?

That would be Universe Sandbox, which you can sometimes get for sale for $2 on Steam.

[NGTOne]

Well, as far I understand, it's more than just sheer mass - from what I understand, it's possible to have terrestrial planets way past the 10xEarth limit, and gas planets well below it.

For example, consider a gas planet in really low orbit over a star. Over time, its atmosphere is stripped away by hydrodynamic forces. The end result is that the planet's core is exposed, and it's superficially similar to a terrestrial planet. This is called a Cthonian planet.

This suggests something interesting - that a gas giant may have originated as a (large) terrestrial planet, and simply accreted enough gas that the terrestrial portion became a minority part of the overall planetary mass. Following under this hypothesis, the pressure and mass of the gas "squeezes" the terrestrial core into a more conventional planetary core (like the rock and magma of Earth do to its core). Any "rocky" mass the planet absorbed after this point (asteroids, wayward planets, what have you) would then tend to be assimilated into the core.

Following on this, I propose the following: that a solar system that has a large number of gas giants (like our own, which has 4, plus a number of smaller bodies, both planets and moons, with not-insignificant atmospheres) is also more likely to have terrestrial planets with atmospheres (be they Earth-like or not), because the materials required for atmosphere formation were present in sufficient abundance during its early formation.

As for the original question: yes, I think even Earth-10 would be possible; however, it would require far more stringent conditions to be met for it not to become a gas planet than for, say, Earth-1, or even Earth-4. Hypothetically, the more gas-poor a region of space is, the larger a terrestrial planet could become before the chances of becoming a gas giant became significant. Though, naturally, the more gas-poor your area is, the less likely your Earth-100 is to be habitable in the first place.

[magnemoe]

First, we have learned a lot after starting to discover planets outside our solar system. It looks pretty obvious to me that even current theories are rush jobs done by scientists who try hard to not look like idiots and keep their salaries, in short they are junk.

Why can not gas giants be created close to the star, you have double stars like Sirius with huge difference in size. Why not an larger difference?

One option who sounds plausible is that super earths is water planets. No not Laythe or Sparta but places where minimum ocean depth is hundreds of kilometers.

Main downside of super earths with rocky surface is that they would have to work hard to avoid picking up an Venus like atmosphere.

However they might have interesting moons.

[Diche Bach]

That would be Universe Sandbox, which you can sometimes get for sale for $2 on Steam.

Damn you Shifty! Another game that I must buy now . . .

First, we have learned a lot after starting to discover planets outside our solar system. It looks pretty obvious to me that even current theories are rush jobs done by scientists who try hard to not look like idiots and keep their salaries, in short they are junk.

Why can not gas giants be created close to the star, you have double stars like Sirius with huge difference in size. Why not an larger difference?

One option who sounds plausible is that super earths is water planets. No not Laythe or Sparta but places where minimum ocean depth is hundreds of kilometers.

Main downside of super earths with rocky surface is that they would have to work hard to avoid picking up an Venus like atmosphere.

However they might have interesting moons.

Well said Magnemoe! It is always difficult to generalize about a "population" (all the solar systems in the Milky Way for example) if you only have a sample size of one (Sol system).

I seem to recall that some of these exoplanet discoveries seemed to rather dramatically defy traditional wisdom about how solar systems tend to form. Specifically, I seem to recall that a few of those exoplanets are enormous gas giants that are rather close to their parent star, and revolving rather quickly.

I debated doing my major in geology instead of anthropology; I finally decided humans are more complicated so go with that (silly decision in retrospect). I envy the unborn who will one day get to do extrasolar geology, xenogeology or, astrogeology whatever the heck you want to call it.

Edited August 23, 2013 by Diche Bach

[NGTOne]

I debated doing my major in geology instead of anthropology; I finally decided humans are more complicated so go with that (silly decision in retrospect). I envy the unborn who will one day get to do extrasolar geology, xenogeology or, astrogeology whatever the heck you want to call it.

Well, we already have one xenogeologist - Harrison Schmitt was a civilian geologist who went up on Apollo 17.

Besides, look at me - I'm a computer science major. Doesn't mean I can't love physics and engineering and whatnot, am I right?

[Diche Bach]

Absolutely!

[WhiteWeasel]

Very fascinating information, I wonder what else is plausible? Could a moon support life as well if it was massive enough and had an atmosphere?

[NGTOne]

Very fascinating information, I wonder what else is plausible? Could a moon support life as well if it was massive enough and had an atmosphere?

Well, there is at least one moon in our own solar system with an atmosphere - Titan, a moon of Saturn. It's composed of various hydrocarbons and has a surface pressure approximately 150% that of Earth. It's believed that there are hydrocarbon "lakes" on the surface as well. The Huygens part of the NASA/ESA Cassini-Huygens probe landed on it a few years ago, and took some pictures, and the Cassini part has mapped large chunks of the surface using radar and other tools.

While it's not a perfect example, it's a perfect proof-of-concept - there is no reason a moon couldn't have an atmosphere, and retain it. From there, it's not far to life, even if it's not life as we know it.

[WhiteWeasel]

Curious, how extreme could a moon's inclination naturally get? 20, 30, 45 degrees, maybe more?

[NGTOne]

Curious, how extreme could a moon's inclination naturally get? 20, 30, 45 degrees, maybe more?

Depends on the origin of said moon. If it's a captured asteroid, its inclination could be anything.

As for moons that were formed by accretion, generally speaking they would tend to follow the plane of the solar system (as this is where the accretion disk that produces these moons tends to form). However, that being said, I suppose it isn't inconceivable that enough moons, acting in close proximity to each other over time, could succeed in altering each other's orbits to be more or less inclined. And, naturally, it should go without saying that a sufficiently large body (a rogue planet, for instance) might also disturb them into more-inclined orbits.

[Dockillar]

There is a technically no limit between a terrestrial planet's size, and the type of planet it is, a planet being big enough does not necessarily make it a gas giant, a gas giant will form in the outer, more hydrogen, helium, and methane rich areas, they grow large because they use gravitational force to pull these gases into gas planets, so in a sense, a gas giant literally, "eats" its area of gases up, which on a scale of a proto-planetary disc, is a HUGE area...

If a so-called "super earth" were to exist, it would literally have to take massive amounts of rocks, ice, or other solid materials into itself to form, and it is possible that other larger planets would be interfered by this huge body to collide and make it BIGGER!!!

The point is, planets grow big because of the area they form in, not because of their common large sizes, but their history and orbits around their star...

Its a cool idea though!

[Diche Bach]

There is a technically no limit between a terrestrial planet's size, and the type of planet it is, a planet being big enough does not necessarily make it a gas giant, a gas giant will form in the outer, more hydrogen, helium, and methane rich areas, they grow large because they use gravitational force to pull these gases into gas planets, so in a sense, a gas giant literally, "eats" its area of gases up, which on a scale of a proto-planetary disc, is a HUGE area...

If a so-called "super earth" were to exist, it would literally have to take massive amounts of rocks, ice, or other solid materials into itself to form, and it is possible that other larger planets would be interfered by this huge body to collide and make it BIGGER!!!

The point is, planets grow big because of the area they form in, not because of their common large sizes, but their history and orbits around their star...

Its a cool idea though!

This is largely what I had in mind in response to the OP too. I don't think there necessarily is an upper limit on how big a rocky planet can be and still evolve to have conditions that favor the evolution of life.

There may however be a lower size limit, because in the absence of plate tectonics, volcanism, or a magnetosphere it has been argued to be unlikely that a permanent atmosphere or surface water will form, both of which are regarded as essential to the development of life.

Beyond that I think what matters most is: tidally locked orbits are unlikely to be conducive to life and the 'goldilocks' region around a star (not too hot, not too cold) is important. However, in some special instances, sufficient heat to maintain liquid water could come from other sources. For example, they hypothesize that Europa may have liquid oceans under its all ice surface as a result of tidal flexing by Jupiter's gravity.

The other thing obviously is that the planet absolutely must have a suitable mixture of the organic elements that are essential to carbon-based life (unless of course you want to consider the possibility of life based on other elements, which is pretty much pure science fiction I think).

[NGTOne]

The other thing obviously is that the planet absolutely must have a suitable mixture of the organic elements that are essential to carbon-based life (unless of course you want to consider the possibility of life based on other elements, which is pretty much pure science fiction I think).

Not necessarily - we live in an infinite (OK, near-infinite) universe. One of the best lines I ever read was, "If we've done it, nature has done it somewhere, but better" (I think it was Mr. Scotty of the Enterprise, though I may be paraphrasing a bit). If we can dream it, I'd bet that somewhere, somehow, nature has built it.

[Diche Bach]

Well, one thing I think we can be sure of: whatever elements might facilitate the molecules that are essential to life as we know it, meaning self-replicating (i.e., not crystals which do replicate but not through a self-driven process) 'vehicles' for packets of chemical information, they will have to exhibit similar capacity to form into complex reactive and catalytic biopolymers; in the case of Earth these being nucleic acids and proteins the basis for all life, including prions, which like viruses are not 'technically' alive.

My limited mastery of organic chemistry does not allow me to speculate what possible configurations of organic elements could suffice in place of good old carbon, nitrogen, oxygen, hydrogen, phosphorous, etc., as the building blocks of life. But I think the available options would be fairly limited simply from the standpoint of what would allow for the sort of chemical structures that could serve a similar role as do the nucleic acids and proteins. I think there has been speculation that, in some exotic context, "silicon-based" life could (maybe) evolve, but I have no idea if that is pure fantasy or not.

It seems unlikely that there is much in terms of unknown elements to be discovered out there in the cosmos, though I suppose if the unknown elements are organic and thus found only as traces in the large structures that can be spectroscopically examined, it is possible, though very unlikely.

So, I think it is reasonable to operate from the hypothesis that, life anywhere else in the cosmos is likely to be based on a very similar chemical basis as life on Earth.

[NGTOne]

So, I think it is reasonable to operate from the hypothesis that, life anywhere else in the cosmos is likely to be based on a very similar chemical basis as life on Earth.

Possibly - I'm still not going to discount life with alternative chemistries, but let's set that aside.

Now, here's the more interesting question: what form would this life take?

For instance, it was demonstrated in the '70s that, if you took the elements present in Jupiter's atmosphere and subjected them to electrical flashes (like, say, a lightning bolt), you would eventually end up with amino acids (the building blocks of life). Now, Jupiter isn't a particularly good example because the violent weather would drag any interesting molecules that formed down to the depths, where they would be reduced back down to their base elements by heat and pressure. But it raises some interesting questions - what kind of life might arise on a planet that isn't perfectly Earth-like (or even Earth-like at all), even if its biochemistry is like our own?

[lajoswinkler]

Biochemistry of the another planet would probably be rather similar to ours in its foundations. No doubt there'd be different pathways and some different chemicals.

That's because it can't be different. Element properties are universal, elements involved are abundant. You can bet it would be carbon based. Other elements don't offer enough possibilities or yield unstable compounds. Silicon lifeforms are probably a pipedream, and that's the best option after carbon.

The basics of morphology would be the same. Something similar to our bacteria. Multicelular organisms would have radial symmetry, and the more advanced ones, who acquired the ability to move through a dense fluid would be bilaterally symmetrical. That's to avoid drag and later, on dry land, tipping.

What we see on Earth is not, in its foundations, so special. It's like that because it's the most efficient option. You can expect interesting and wild morphological differentiation with highly evolved organisms that have a skeleton, but with those yucky, squishy dudes, there's no much option. I wouldn't be much surprised (although fascinated) if oceans of Europa contained things like tube worms and jellyfish, and lots of different bacteria-like species. In fact, I'd be surprised if those oceans were completely devoid of bacteria-like species.

[magnemoe]

Biochemistry of the another planet would probably be rather similar to ours in its foundations. No doubt there'd be different pathways and some different chemicals.

That's because it can't be different. Element properties are universal, elements involved are abundant. You can bet it would be carbon based. Other elements don't offer enough possibilities or yield unstable compounds. Silicon lifeforms are probably a pipedream, and that's the best option after carbon.

The basics of morphology would be the same. Something similar to our bacteria. Multicelular organisms would have radial symmetry, and the more advanced ones, who acquired the ability to move through a dense fluid would be bilaterally symmetrical. That's to avoid drag and later, on dry land, tipping.

What we see on Earth is not, in its foundations, so special. It's like that because it's the most efficient option. You can expect interesting and wild morphological differentiation with highly evolved organisms that have a skeleton, but with those yucky, squishy dudes, there's no much option. I wouldn't be much surprised (although fascinated) if oceans of Europa contained things like tube worms and jellyfish, and lots of different bacteria-like species. In fact, I'd be surprised if those oceans were completely devoid of bacteria-like species.

Agree with you here except its lots of strange small animals who is radically different think its more variations than within larger ones who tend to look much the same.

Probably as size put restrictions to design and you have far fewer species.

One interesting aspect with the gas giant ice moons is if bacteria frozen in ice could survive moving between them?

Getting thrown away from the moon after an impact should work however the impact on another might be harder to survive but perhaps an glancing hit would shatter the pieces and allow some part of it to come down without becoming hot gas.

[lajoswinkler]

Agree with you here except its lots of strange small animals who is radically different think its more variations than within larger ones who tend to look much the same.

Probably as size put restrictions to design and you have far fewer species.

One interesting aspect with the gas giant ice moons is if bacteria frozen in ice could survive moving between them?

Getting thrown away from the moon after an impact should work however the impact on another might be harder to survive but perhaps an glancing hit would shatter the pieces and allow some part of it to come down without becoming hot gas.

Evolution doesn't have a goal. It just is. There are small animals with weird configurations, but they're advanced versions we see today. Primitive animals we see in the fossils and the basis of morphology of simple avertebrates today, are very similar. It took a long, long time before multicellular life became rich in shapes.

There aren't many options. It boils down to what the animal does. If it's stationary, it can't go after the food, so it needs radial symmetry to increase its chances of catching a drifting piece. If it moves, it has a hydrodinamic shape, bilateral symmetry, sensors and mouth at the front, propellers and waste opening at the back.

Effect of the planet's size it's an interesting question. I'm not sure how it would affect animals floating in fluid, but high gravity would slow down the evolution of land animals. They couldn't grow large in size.

I think the size of fluid floating dudes is much more affected by the factors such as the position in the food chain and the abundance of food.

Panspermia between satellites without atmosphere has a lot greater chance of success. If something hits an Europa-like satellite, there'd be lots of material not affected by the heat thrown into escape orbit. If it lands on a similar satellite and somehow gets into the fluid environment that's not radically different, that's a start.

Atmospheres act as very efficient sterilizers, yes.

[magnemoe]

Evolution doesn't have a goal. It just is. There are small animals with weird configurations, but they're advanced versions we see today. Primitive animals we see in the fossils and the basis of morphology of simple avertebrates today, are very similar. It took a long, long time before multicellular life became rich in shapes.

There aren't many options. It boils down to what the animal does. If it's stationary, it can't go after the food, so it needs radial symmetry to increase its chances of catching a drifting piece. If it moves, it has a hydrodinamic shape, bilateral symmetry, sensors and mouth at the front, propellers and waste opening at the back.

Effect of the planet's size it's an interesting question. I'm not sure how it would affect animals floating in fluid, but high gravity would slow down the evolution of land animals. They couldn't grow large in size.

I think the size of fluid floating dudes is much more affected by the factors such as the position in the food chain and the abundance of food.

Panspermia between satellites without atmosphere has a lot greater chance of success. If something hits an Europa-like satellite, there'd be lots of material not affected by the heat thrown into escape orbit. If it lands on a similar satellite and somehow gets into the fluid environment that's not radically different, that's a start.

Atmospheres act as very efficient sterilizers, yes.

I know evolution don't have a goal, however I was also thinking of the cambrian explosion however that might be to advanced creatures for that you are talking about.

As for surviving asteroids, atmosphere brakes them, surprisingly the stuff who reach earth is often cold. probably because the outer part act as an heat shield who burns up and the time in atmosphere is to short to transfer heat into the body, while if you hit an moon at orbital speed I'm not sure how much would be left.

You need an large light gas gun and some ice cooled to -200 degree to test this.

Anyway an glancing blow should work and an impact will throw lots of stuff up.

Probably enough to throw stuff in system and perhaps interstellar distances.