Thread: Rethinking planetary and Solar System creation models and theories

Since I was about the age of 10, I generally had a hard time with the "standard model" for solar system creation, or specifically the concept of core accretion. Now, with every new discovery of new solar systems, our long held concepts are sinking fast.

The long-held standard model theory goes like this:

Planets are formed from a protoplanetary disc of dust and gas that is orbiting a star. Gravity causes heavy elements such as metals and silica migrate towards the star due to their greater density, and lighter elements such as gasses to migrate towards the outer edges of the solar system.

Gravity then, over great periods of time, causes elements to condense into protoplanets, much like the dwarf planet Ceres and the asteroid Vesta, both of which are thought to possess a differential interior. As a result, rocky planets like Earth and Mars from closer to the star, gas planets like Jupiter and Saturn form farther from a star, and because all planets formed from the same disc, they all orbit their star in the same direction.

This theory perfect explains how a solar system like ours could potentially come into existence. The only problem cane in the early 1990’s when we discovered exosolar planets (planets outside of our solar system that orbit other stars), the vast majority of these solar systems contain planets as massive, (and even several times more massive), as Jupiter orbiting closer to their star than Mercury orbits to the sun. These types of planets are commonly referred to as “hot Jupiters” or “Super Jupiters.”

In addition, it also does not explain how the planet-sized terrestrial moons of the outer solar system could have formed so far away; specifically Jupiter’s Ganymede and Saturn’s Titan. Ganymede, with a diameter of 5,268 km (3270 miles), and Titan (1,575 kilometers [1,600 miles]) are both larger than the planet Mercury. Titan’s complex atmosphere and weather are also only rivaled by Earth and Venus, as far as rocky planets are concerned.

With new knowledge and understanding of moons in the outer solar system, and the discovery of dozens and dozens of exosolar planets, clearly the concept of core accretion and the standard model had to be rethought.
Then, a new explanation for all of the hot Jupiters came, but with a discouraging headline: Solar systems discovered with super Jupiters orbiting close to their star spells bad news for life as we know it.

The idea being that they these super-massive gas giants form far away from the star, as with the standard model, and then spiral inwards, ending up in tight, circular orbits extremely close to their parent star. The act of spiraling inwards is thought to pretty much destroy rocky Earth-like planets.
So, where could the theory have gone wrong?

Super Jupiters may not spell death for Earth-like planets; they could actually spell life.

Suppose that a planet ten times the mass of Jupiter orbits so close to its parent star that it does collide. Why wouldn't the explosion be great enough to hurl a large enough portion of that matter back into space to form planets made out of heavy elements? Perhaps it could.

Our Jupiter would have enough energy to cause about 100 billion tons of material to be released into space, but some of the largest exoplanets we've discovered could cause nearly one trillion tons of matter to be ejected into space.

The Earth is about 6,000 billion tons.

A few large impacts like that is enough to seed an already existing protoplanetary disc with heavier elements such as metals, primarily iron, and other silica that would allow what we refer to as terrestrial planets to be formed.

That does not take into account the amount of mass that would be shot back out into space due to the escape velocity caused by the explosion or the interactions of the star and a large magnetosphere of a gas giant.
Super-massive gas giant planets could actually accrete the metals and silica needed for an Earth-like terrestrial planet to form, bring that material close to a star, and release it in the best suited region of space for life to evolve on its own; the so-called “life zone.”

Would a Jupiter sized planet spiraling in towards a star really destroy all planets in its wake?

The answer is not necessarily.

Neither Jupiter nor Saturn destroys all of the objects in their path. Many of the objects get flung into different trajectories around the sun, and others are captured through a process known as aerocapture, and become natural satellites to the giant planets.

Along those lines, there have been Jupiter-esque planets found orbiting in "the life zone" of other stars, yet the discussion of Earth-like satellites orbiting these planets almost never comes to the surface. It is likely that life could evolve around a "blue moon" of a gas giant.

The Standard Model is not so “standard” anymore.

There is a distinct possibility that the first Earth-like planet found might not actually be a planet, but a moon orbiting a gas giant. The November 6th announcement of the discovery a fifth planet orbiting 55 Cancri that is Saturn-esque promps great excitement because this star has been watched for years, it has the most known planets outside of the sun, and the new planet is in the "life zone," thus it could have Earth-like moons surrounding it. (Universe Today has a nice write-up: Universe Today » Fifth Planet Found Orbiting 55 Cancri)

More pressingly, scientists need to work towards a new model for solar system creation, one that explains super Jupiters and distant rocky planets, and be open to the possibility that the Sol system (or solar system) once contained one or more hot Jupiters of its own.

Originally Posted by Rev. Rob

Planets are formed from a protoplanetary disc of dust and gas that is orbiting a star. Gravity causes heavy elements such as metals and silica migrate towards the star due to their greater density, and lighter elements such as gasses to migrate towards the outer edges of the solar system.

Nope. Rocky planets form closer to the star because it's too warm for the lighter elements to condense there. It's not a gravitational "migration" of heavier elements. It's thermal effect, and eventually the star's T-Tauri phase blows the gas and dust out of the new solar system. Planet formation is now thought to occur in less than ten million years from the ignition of hydrogen fusion in the star.

Originally Posted by Rev. Rob

This theory perfect explains how a solar system like ours could potentially come into existence. The only problem cane in the early 1990’s when we discovered exosolar planets (planets outside of our solar system that orbit other stars), the vast majority of these solar systems contain planets as massive, (and even several times more massive), as Jupiter orbiting closer to their star than Mercury orbits to the sun. These types of planets are commonly referred to as “hot Jupiters” or “Super Jupiters.”

The "hot jupiters" are large gas giant planets orbiting very close to their primary.

"Super jupiters" are planets with significantly greater mass than Jupiter.

The two terms are not exclusive.

There's a selection effect in the search process. Bigger planets and planets closer to their primary make the star wobble more, hence they're easier to find than smaller or more distant planets.

Originally Posted by Rev. Rob

In addition, it also does not explain how the planet-sized terrestrial moons of the outer solar system could have formed so far away;

Sure it does. The larger lumps in the proto-solar disk created swirls and eddies of their own. Since Jupiter and the rest of the giant planets are out in the ice zone, their moons have a larger proportion of lighter elements in their composition as compared to the terrestrial planets closer to the sun.

Earth's moon, of course is a seperate case.

Originally Posted by Rev. Rob

Suppose that a planet ten times the mass of Jupiter orbits so close to its parent star that it does collide. Why wouldn't the explosion be great enough to hurl a large enough portion of that matter back into space to form planets made out of heavy elements? Perhaps it could.

Because the star is mainly hydrogen and helium, and it's not going to selectively eject a higher percentage of heavier elements.

Remember that part about gravitational differentiation I "wronged" you on above? That's because a protosolar disc doesn't provide resistance to gravity, it looks a lot like Saturn's rings. But once a body condenses and has enough mass to self-differentiate, then yes, the heavier elements will sink to the core. This includes the central star.

An impacting planet isn't going to delve into the deep layers where the heavier elements are. Remember, it's travelling nearly tangentially to the star's surface when it impacts.

And...all the problems you listed about coalesence in the first place, the ones you didn't have wrong? They crop up again.

Originally Posted by Rev. Rob

Our Jupiter would have enough energy to cause about 100 billion tons of material to be released into space, but some of the largest exoplanets we've discovered could cause nearly one trillion tons of matter to be ejected into space.

The Earth is about 6,000 billion tons.

That means it would take six (6) of those super jupiters to impact one star nearly simultaneously and then have all the matter conserved to coalesce into one earth.

Get the picture?

Originally Posted by Rev. Rob

A few large impacts like that is enough to seed an already existing protoplanetary disc with heavier elements such as metals,

Nope. Can't do it. The accreted superplanet has to spiral into the star from a place in the middle regions of the disc, and as it spirals inwards it sweeps up all the loose matter in it's path, effectively clearly large swaths of proto-disc that thus no longer exist to be seeded.

Originally Posted by Rev. Rob

Would a Jupiter sized planet spiraling in towards a star really destroy all planets in its wake?

Most likely. It's crossing orbits and travelling slower than the objects in the circular orbits it crosses, and it's not like it's making a single pass in a hyperbolic dive, no. It's slowly winding inwards, and practically every object inside it's orbit has an opportunity to interact with the intruder, and get creamed or ejected.

Originally Posted by Rev. Rob

The answer is not necessarily.

Neither Jupiter nor Saturn destroys all of the objects in their path.

They're not spiralling inwards crossing circular orbits, either.

Originally Posted by Rev. Rob

Along those lines, there have been Jupiter-esque planets found orbiting in "the life zone" of other stars, yet the discussion of Earth-like satellites orbiting these planets almost never comes to the surface. It is likely that life could evolve around a "blue moon" of a gas giant.

Yep. It's not discussed much in scientific circles because it's impossible to know if those planets have satellites or not. That's the realm of science fiction.

Originally Posted by Freedom for All

Nope. Rocky planets form closer to the star because it's too warm for the lighter elements to condense there. It's not a gravitational "migration" of heavier elements. It's thermal effect, and eventually the star's T-Tauri phase blows the gas and dust out of the new solar system. Planet formation is now thought to occur in less than ten million years from the ignition of hydrogen fusion in the star.

Thanks for adding the part of what I was missing in regards to the thermal effect. I am not familiar with this process. I am not saying that you're wrong, but can you shed some light on it?

Here is my understanding of the standard model (borrowed from the University of Washington):

In the standard model of the formation of the solar system, we begin with an enormous cloud of gas and dust, which is slowly rotating counterclockwise. Because there is mass in this cloud, it begins to collapse under gravity. This spinning cloud has angular momentum (like and ice skater), and so as it collapses, it must spin more rapidly.


During this time, the particles can slip past each other easily, since the cloud is not very dense. The heavier particles, like iron and uranium, are more strongly attracted towards the center, and so the fraction of heavy atoms becomes higher near the center of the cloud.


As the cloud collapses, it becomes denser. Eventually, it becomes dense enough for particles to begin to collide, and sometimes stick together, forming larger particles. This is called condensation. These larger particles are orbiting the center of the cloud counterclockwise, because the smaller particles were traveling in that direction. As these larger particles begin to collide with other particles of the same size, they 'regularize' the orbits. That is, the collisions with particles moving slightly outward in their orbits are as common as collisions with particles moving slightly inward in their orbits, causing the orbit of the growing body to become more and more circular, and less elliptical.


Similarly, particles which are travelling north are as common as those going south. As these particles collide, their velocities average out, causing the cloud to flatten into a disk.


The cloud continues to collapse because of gravity, and to spin faster because of the conservation of angular momentum. Larger and larger particles form, which are rotating and orbiting counterclockwise, just like the original cloud. Eventually, most of the large particles have been gathered up into a few large bodies, and continue adding mass by running into lots of smaller particles. This is called accretion.

Back to the topic...

The "hot jupiters" are large gas giant planets orbiting very close to their primary.

"Super jupiters" are planets with significantly greater mass than Jupiter.

The two terms are not exclusive.

Oh, I wasn't using them to be interchangable. I was talking specifically about planets that are both "Super Jupiters" and "Hot Jupiters" at the same time. That is to say, planets that are several size the mass of Jupiter that are in closer-than-Mercury orbits around their stars.

There's a selection effect in the search process. Bigger planets and planets closer to their primary make the star wobble more, hence they're easier to find than smaller or more distant planets.

No doubt.

Sure it does. The larger lumps in the proto-solar disk created swirls and eddies of their own. Since Jupiter and the rest of the giant planets are out in the ice zone, their moons have a larger proportion of lighter elements in their composition as compared to the terrestrial planets closer to the sun.

So, what you're saying is that bodies such as Titan and Callisto, and Ganymede were really formed in the orbits of Saturn and Jupiter, respectively?

I strongly doubt this theory, which is more of a fringe theory (IMO) and is not widely accepted. It is far more likely that the aforementioned planet-sized objects formed in solar orbit and were later captured by their respective planets.

Because the star is mainly hydrogen and helium, and it's not going to selectively eject a higher percentage of heavier elements.

An impacting planet isn't going to delve into the deep layers where the heavier elements are. Remember, it's travelling nearly tangentially to the star's surface when it impacts.

That's a good point, but it doesn't have to. The large planet is not likely to completely crash into the star. It will be torn apart and X% of it will be flung out into the system. Then, of the parts that do impact the star, Y% will be original planetary material.

Yep. It's not discussed much in scientific circles because it's impossible to know if those planets have satellites or not. That's the realm of science fiction.

No, it just takes a discovery like the most recent on at 55 Cancri to get the conversation going. By your take, all of astrobiology is "science fiction."