Roche's Limit

[frankglennjacobs@gmail.com]

Fair enough! You called my speculation a speculation and said to put it in with the other speculations.

 

Furthermore (also fair!) you said to re-write it as questions.

 

(Sort of annoyingly, you added, ". . . if you want to learn some science".)

 

 

Here goes BOTH:

 

In the dawn of time, the orbit of Jupiter (and maybe of some other gas giants) migrated.

 

Did they therefore likely come close to the Roche limit of other planets?

 

Would the tidal effect likely sweep up atmospheres and oceans?

 

Would the tidal effect of even closer encounters jerk big pieces of planetary crust away?

 

{I therefore verily speculate that such an encounter -- rather than the most-unlikely "double-bump" -- formed up the moon. Nyaah! So THERE!}

 

 

 

 

 

 

[Argent]

Here goes BOTH:

 

In the dawn of time, the orbit of Jupiter (and maybe of some other gas giants) migrated.

As a side note, today there are only two gas giants in the solar system, Jupiter and Saturn. Neptune and Uranus are more properly referred to as ice giants. All of these, and any others that may have been ejected from the system, or absorbed into the sun, did migrate.

 

 

Did they therefore likely come close to the Roche limit of other planets?

It is possible that some did. However, it is extremely unlikely that this did not occur en route to a collision. Not absolutely impossible, but highly improbable.

 

Since we have identified several rocky exoplanets, it seems unlikely they would have been formed by the same "odds against" process. For practical purposes the answer to the question is "no".

 

Would the tidal effect likely sweep up atmospheres and oceans?

 

It might, but since the planet is at that point on a collision course for the gas giant it is rather irrelevant. I suspect that the time required to "sweep up the fluids" would exceed the time available for it to occur, even if it was only the "glancing blow" encounter you envisage.

 

 

Would the tidal effect of even closer encounters jerk big pieces of planetary crust away?

 

No. The planet would begin to come apart.

 

 

I therefore verily speculate that such an encounter -- rather than the most-unlikely "double-bump" -- formed up the moon

 

 

Since your starting assumptions are flawed your speculation is without foundation and so it fails.

 

I don't understand your reference to a "double-bump" for lunar formation. The current hypothesis is a single bump of a protoplanet we have named Theia striking a proto-Earth. Where is the second bump?

 

Edited April 11, 2017 by Argent

[frankglennjacobs@gmail.com]

Very neat. "ice giants" v "gas giants". How about that?! And here I thought they were all alike as marbles in a bag!

 

The discovery of "Hot Jupiter" exoplanets has joggled my imagination into speculation and questions.

 

Did the rocky planets migrate as well?

 

Is the Solar System migration over now that most of the small stuff has been swept out of the solar main orbital plane?

 

Were the exo-hot-Jupiters fromed right down on the deck where we find them?

 

Were they formed several AU from their stars and migrated down to meet them?

 

Will they impact their stars?

 

Did previous such planets in our Solar System impact the Sun?

 

What effect would such a planet have in migrating its orbit past a rocky planet?

 

(I speculate what I speculated in my previous speculation, plus that out of a possible thousand rocky planets, only four partly survived the passing-migrating Jupiter treatment.)

P. S. Years back when I was excommunicated from Science Forum, the then-current thinking about the formation of the moon involved a very involved double bump. I am glad you have purged such heretical thinking from your catechism.

 

P.P.S. Encounters between planets involve anything from an orbital perturbation to a direct hit. There is a lot more space out there than rock. Not every Roche Limit encounter is the opening gun to a lithosphere-to-lithosphere collision, although I suppose most of them are. If Jupiter were to have passed Mars closely enough to take its atmosphere and ocean, how long would it be until they were far enough apart again so that the damage would stop continuing? An hour? Two?

[Argent]

Very neat. "ice giants" v "gas giants". How about that?! And here I thought they were all alike as marbles in a bag!

 

If you consider the basic information on mass, diameter, density and probable composition of the four giants in our system you will see that this division is both sensible and significant.

 

Did the rocky planets migrate as well?

 

 

Almost certainly, but not to the same extent as the giants. Migration was promoted by gravitational interaction with the giants and drag effects with the protoplanetary disc.

 

Is the Solar System migration over now that most of the small stuff has been swept out of the solar main orbital plane?

 

 

The migration has been over for close to 4.5 billion years. Stability came quickly on astronomical and geological time scales. Even although the Late Heavy Bombardment was still ongoing 3.8 billion years ago this was not associated with any significant migration.

 

Were the exo-hot-Jupiters fromed right down on the deck where we find them?

 

Almost certainly not. The temperatures close to the protostars would have been to high for the accumulation of ices and gases.

 

Were they formed several AU from their stars and migrated down to meet them?

Will they impact their stars?

 

Yes.

Some will some won't. (I suspect the majority will not.)

What effect would such a planet have in migrating its orbit past a rocky planet?

 

The orbit of the rocky planet would be changed, probably substantially.

 

I speculate what I speculated in my previous speculation, plus that out of a possible thousand rocky planets, only four partly survived the passing-migrating Jupiter treatment

 

While the four solar system giants were doing a lot of moving around and this movement, especially that of Jupiter, influenced what was happening in the inner solar system, I am not aware of any strong suggestion that any giants moved through the system en route to absorption by the sun.

 

Years back when I was excommunicated from Science Forum, the then-current thinking about the formation of the moon involved a very involved double bump. I am glad you have purged such heretical thinking from your catechism.

 

 

I don't know what may have been said back then, but I am not familiar with any reference to a double bump. If anyone can contribute on this I would appreciate it.

 

If Jupiter were to have passed Mars closely enough to take its atmosphere and ocean, how long would it be until they were far enough apart again so that the damage would stop continuing? An hour? Two?

I find this question similar to asking "If alien bio-robots had been injected into the Earth's biosphere by different alien entities at different points since the late Proterozoic, could this account for the appearance of the major phyla?" That is, your question is grounded in so many assumptions and possibly misunderstandings that it is not practical to answer it. So here is the impractical answer - several hours, but not days.

 

Warning: I am a complete amateur in these matters. Though I have read quite widely on the subject I have no professional qualifications related to astronomy at all. I have tried to convey that lack of formally acquired knowledge by phrases such as "I think that", or "I understand that". If you, or anyone, has data that conflicts with anything I have said please post it.

Edited April 12, 2017 by Argent

[frankglennjacobs@gmail.com]

Thank you, um 'Argent'.

 

I do appreciate the straight answers.

 

Years back -- as it were, in a former lifetime -- the Science Forum honchos would give me answers something like "What drivel!" and "You know absolutely nothing, because you can't do the math."

 

This is a most refreshing change.

 

In my first speculation in this century (which I mistakenly put into a now-locked new thread) I speculated that this new knowledge about migrating planetary orbits removed the temptation to blame all the astro-physical damage on the probably-mythical Niburu.

 

Seeing that Jupiter (or some other planet) had probably migrated thru the Solar System, that would account for everything from perturbed orbits to altogether missing planets.

 

Technical question: By "drag" do you mean the accumulated force on a planet caused by all those little space thingies banging into it as it goes along?

 

Thank you again.

[frankglennjacobs@gmail.com]

Straight technical question: Is the "drag" that causes migrations the gravitational interaction with other planets, meteoroids, dust and gas still in orbit at that time around a star?

 

Speculative question: Were there likely more planets before the migration? That is, did any get destroyed in collisions?

 

Straight speculation: Migrating planets, great and small, influenced one another with everything from orbital perturbations to head-on lithosphere-to-lithosphere collisions -- and every sort of inconvenience in between.

 

Be so kind as to answer. Thank you.

[Argent]

It is primarily drag with dust and gas. There are two types of migration.

 

Type 1 Migration - the planet is insufficiently massive to clear a gap in the disc and so it is driven inward by a density wake in the disc. This also reduces orbital eccentricity.

 

Type 2 Migration - the planet clears a gap in the disc, but is still tied to the disc's viscous evolution. Some researchers see this as more an exchange of angular momentum between disc and planet.

 

This is, from my perspective at least, a complex subject and difficult to simplify. Please ask more questions as it will help me sort out my understanding, such as it is.

 

We know, that many planets were destroyed in collisions. That is how the final planets were formed, by the collision and agglomeration of many protoplanets. The only way in which there could be no collisions is if we have the nature of planetary formation entirely wrong.

 

In terms of late stage collisions we have lots of evidence:

- The "missing mantle" on Mercury, which is explicable by a large glancing blow.

- The retrograde revolution of Venus

- The crustal dichotomy on Mars

- The peculiar orientation of Uranus's spin axis

 

Yes, there were all kinds of collisions, but the odds on the kind you seem hell bent on proposing are seriously stacked against. If you wish to argue the case you need to gather supporting evidence, or develop a well reasoned argument. So far you have neither.

[frankglennjacobs@gmail.com]

Thank you again, Argent.

 

Again, I have no theory. I wouldn't know what to DO with a theory -- or even a hypothesis -- since I have no idea about the math.

 

This is, again, a SWEG -- a mere speculation. It doesn't even rise to the level of a proposal.

 

And, to show you where I'm coming from, I think maybe I was thrown out of Science Forum for speculating that Niburu had done all that planetary damage. The stuff about a Flat Earth was only jokingly sarcastically thrown in with the material on the aether.

 

The new idea (well, new to me!) that planetary orbits migrate relieves Niburu of all the blame. Not to even be considered any more!

 

"Hell-bent" is way overstating my zeal. I never even bothered to find out what kind of math is involved in understanding the issue.

 

It would appear to me that of the proto-planets disrupted by the gravity of some migrating planet, only three partly survive: Earth, Mars and the un-named planet formerly between Mars and Jupiter. (You have added Mercury, with a "missing mantle" and Venus with the strange rotation.)

 

Since you have taught me that planets migrated down toward the sun, moved on by the drag of the protoplanetary disk -- and most probably were either destroyed on the way or absorbed into the sun -- that's a lot of collisions. Way more than I ever imagined. Surprise! Surprise!

 

With that sort of set-up, it is surprising that ANY planets remain in the inner Solar System.

 

How did Venus keep its vast atmosphere? What sort of encounter could cause it's strange rotation? Or is Venus a sort of Junior Jupiter stranded in place on its way? Or is it still headed down toward the sun?

 

How'd Jupiter stop where it is? Same way? Run out of dust? Or is it still migrating?

 

I am trying to understand the "wake" of which you spoke: The tremendous tonnage of stuff surrounding a planet is almost all moving in approximately the same orbit with it. However a passing giant pulls all sorts of gas and dust along behind it -- and in from all sides. This adds up to, perhaps, the mass of a small planet, centered behind. This is continually pulling the giant back and slowing up its progress-in-orbit. Further, the giant's gravity pulls gas and dust to itself as infall. That which hits it anywhere at all (except in back) adds to the mass of the giant, but not to its energy. This is a new idea to me and I am only guessing. Let me guess some more here: Every gravitation pull on anything transfers energy somewhere. This will either go to entropy, heat or movement.

 

As to results of near collisions, it has been pointed out that I am relying on very rare "just right" Roche-Limit encounters.

But many things in the Universe came about by "just right" encounters. However the moon got there is because something went "just right". I propose that astrophysicists contemplate whether it was as a "just-right" Roche-Limit partial-disruption of Proto-Earth.

[Argent]

OK. I have done a piss poor job of explaining things, since your last post is filled with misunderstandings. When I am actually awake I shall respond with an attempt to correct those misunderstandings.

[frankglennjacobs@gmail.com]

I am not the judge of your explanations.

 

I appreciate the effort you have made in explaning.

 

I went and read some about ice giants and gas giants. Yes, they are quite different.

 

I believe I understand your commentary on collisions.

 

Almost every single case of Roche Limit disruption leads within hours to a head-on lithosphere-to-lithosphere collision. About a generation ago, we got to WATCH just such a collision between a comet and Jupiter.

 

Without doing the math, it seems to me that all the planets, planetoids and planetesimals in the inner Solar System were destroyed in just such train-wrecks, with the manifest exceptions of Earth and Mars. (And if the Asteroids were ever part of a planet, about 99% of that one fell into Jupiter, too.) You have added Venus and Mercury to that list -- perturbed but not destroyed.

 

Technical question: Is the current thinking that the giant planets migrate down toward the sun as long as there is enough trash in the orbital plane to slow them down?

 

Technical question: Are the remaining giant planets still up there because their predecessors cleared the orbital space?

 

Technical question: Do the Exo Hot Jupiters migrate right on down into their stars?

 

Technical question: Do those stars keep on bringing forth new giants?

 

Technical question: Do stars keep on bringing forth new rocky planets?

 

Technical question: Is Sedna sort of a junior icy planet?

 

Technical question: Can an asteroid be captured without (1) bringing along a twin to be ejected from the system? -- (2) providing its own sacrificial twin by breaking up on approach?-- or (3) losing lots of energy in the atmosphere. (Each case is, of course, one of those "just-right" circumstances.)

[Argent]

Technical question: Is the current thinking that the giant planets migrate down toward the sun as long as there is enough trash in the orbital plane to slow them down?

No. While migration is caused by interaction with the gas and dust in the protoplanetary disc, it is halted by two things:

1. The dissipation of the disc.
2. Orbital resonances between giant planets.

Technical question: Are the remaining giant planets still up there because their predecessors cleared the orbital space?

No. They are still there because of orbital resonances.

 

Technical question: Do the Exo Hot Jupiters migrate right on down into their stars?

I've answered this before. Some do, some don't.

 

Technical question: Do those stars keep on bringing forth new giants?

Absolutely not. Stars never bring forth giant planers, regular planets or dwarf planets. All planets arise from a protoplanetary disc.

 

Technical question: Is Sedna sort of a junior icy planet?

Probably not. The ice planets form around a rocky core that then acts as a powerful attractor for ices and gases. Sedna likely formed by heterogenous accretion in the manner of the terrestrial planets. That said, I've not read anything specifically on Sedna's formation.

 

Technical question: Can an asteroid be captured without (1) bringing along a twin to be ejected from the system? -- (2) providing its own sacrificial twin by breaking up on approach?-- or (3) losing lots of energy in the atmosphere. (Each case is, of course, one of those "just-right" circumstances.)

Not easily, but it is not impossible.

 

Without doing the math, it seems to me that all the planets, planetoids and planetesimals in the inner Solar System were destroyed in just such train-wrecks, with the manifest exceptions of Earth and Mars. (And if the Asteroids were ever part of a planet, about 99% of that one fell into Jupiter, too.) You have added Venus and Mercury to that list -- perturbed but not destroyed.

 

This suggests you are still not getting it. Forget the giant planets. They didn't forage into the terrestrial zone. Yes, they influenced the orbits through gravitational interaction, but some of the inner protoplanets were not occasionally plunging into Jupiter.

 

The asteroids were never part of a planet. Jupiter's gravitational influence saw to that.

 

Imagine fifty or so Mar's sized worlds forming sunwards of Jupiter. Now imagine them colliding with each other until we are left with the four terrestrial planets and very minor debris. Now you are closer to the truth.

[frankglennjacobs@gmail.com]

Thank you.

 

What got me off on this speculation was the news that any number (dozens? hundreds?) of "Hot Jupiters" had been found. (I suppose the really short-orbit giant planets have the easiest signtures to read.)

 

That is why I asked if those planets had been formed close to their stars, where we find them now -- or formed way up and migrated down.

 

That leads us to our own Solar System, with no "Hot Jupiter". No indication that Jupiter ever traveled thru the inner Solar System.

 

That's why I asked if some previous giant planet had ever migrated thru down here, wrecked whatever existed at the time, and then been absorbed by the sun. (And became "The Late Great Hot Jupiter"?)

 

Some of the asteroids are shaped like potatoes. At least one of them appears to be solid metal. That indicated to my unscientific mind that they were poured out hot and rotating, and not formed by little "asteritos" banging into each other..

 

Jupiter migrated. So it was not always where it is now. Speculate unto your self that a planet was once where the Asteroid Belt is, and, when Jupiter migrated to its present station, that planet (and maybe several others?) was disrupted. Speculate that 98% of the blobs fell into Jupiter, some were entirely ejected from the Solar System and some remained in that approximate orbit, rotating into potato shaped asteroids as they cooled.

 

Again, this is not a theory. It is not a hypotheses. It is not a position nor a proposal. It is only a notion, a SWEG, reinforced in my dark, unscientific mind by the neat photographs of some of the potato-shaped asteroids.

 

- - - - - -

 

It was the fairly recent collision of a comet with Jupiter that got me going on the "captured asteroid" idea. But there was never a chance of it being captured. It broke up when it got to it's own Roche Limit, did one most-eccentric orbit and impacted plop plop plop plop.

 

Every close encounter of two bodies has five possibilities.

 

PLAN A: Straight-on impact.

 

PLAN B: A clean miss with a resultant perturbed orbit.

 

PLAN C: Great loss of energy in atmospheric friction could result in an orbit of sorts. However, at the end of the first orbit is impact. Plop!

 

PLAN D: When one body breaks up and everything is "just right" and part of one body is ejected in one of those famous "just right" space-shuttle slingshot maneuvers, and the energy gained by the ejected part is lost by another part and just happens to be "just right", part goes into orbit and stays there.

 

PLAN E: The approaching body is drawn into the atmosphere of the other, and just happens to lose "just right" amount of energy to go into orbit.

 

I don't know of any other hypothetical case in which a solid body can be "captured". As you said, very difficult and improbable.

 

I imagine, therefore, that successful captures tend to be very messy, with fractal physics making lots and lots of little pieces for each big piece.

Edited April 16, 2017 by frankglennjacobs@gmail.com

[Argent]

Some of the asteroids are shaped like potatoes. At least one of them appears to be solid metal. That indicated to my unscientific mind that they were poured out hot and rotating, and not formed by little "asteritos" banging into each other..

You are correct. That is wholly unscientific. Rather than speculating wildly why not read a book or two on the subject, or dip into some research papers?

 

As the protoplanetary disc cools, minerals condense out of it. The character of the minerals depends upon the temperature and the composition of the disc at that point. For the generalities we are dealing with here, we can assume the disc to be well mixed and thus of uniform composition. The microscopic mineral grains combine into dust particles, then larger groupings, boulder sized and larger, then planetesimals, up to a few kilometres across, then protoplanets.

 

The larger planetesimals and protoplanets heat up, through the process of accretion and the abundance of short-lived radioactive elements. This leads to segregation into iron rich cores and silicate rich mantles. Subsequent disruption by collision with similar bodies my produce an asteroid that is primarily silicate, or iron.

 

Jupiter migrated. So it was not always where it is now. Speculate unto your self that a planet was once where the Asteroid Belt is, and, when Jupiter migrated to its present station, that planet (and maybe several others?) was disrupted. Speculate that 98% of the blobs fell into Jupiter, some were entirely ejected from the Solar System and some remained in that approximate orbit, rotating into potato shaped asteroids as they cooled.

Why would I make such a speculation when the weight of evidence is against it and a perfectly satisfactory explanation, that fits the facts and the simulations, is available. No planet formed in the asteroid belt because Jupiter's gravitational influence disrupted the formation of any such body.

 

I recommend using your energy and imagination to study some facts. This will avoid the waste of coming up with speculations that do not fit the available facts.

[frankglennjacobs@gmail.com]

Ah! Such zeal! Commendable. Thank you for continuing to answer me and educate me. As I said, "Ah ahm an 'ard case!"

 

As I understand the Scientific Process, it goes something like this:

 

1. Observe something.

 

2. Scratch your head, wondering, "Now WHY would it DO a thing like that?"

 

3. Speculate how it could happen..

 

4. Devise an experiment to de-bunk the speculation.

 

5. Speculate another way around the mulberry bush.

 

6. Repeat steps 2 thru 4 as necessary.

 

Well, I'm stuck on step 3, because I have not devised an experiment to do step 4.

 

So I just ask you, because you know a lot of things I don't know.

 

Speculation A: Them there asteroids just always was there and that's all there is TO it.

 

Speculation B: The asteroids came from collisions between any number of protoplanets billions of years ago. The pieces went all directions and at al velocities. Those that were going faster went farther and the giant planets got most of them Those that were slower stayed within the inner Solar System and the rocky planets got most of them.

 

Speculation C: God put them there to sort out the Vile Heretics from the True Believers.

 

Speculation D: Jupiter or some previous occupant chewed up a lot of planetesimals over time, but didn't spit out very much.

 

Speculation E: They might have made a planet in time, but Jupiter's tremendous gravity kept them from accreting -- and most of them fell into Jupiter over the millions of years anyway.

 

Speculation F: Some of them made up little bitty planetoids, heated up enough to melt themselves, then were disrupted when they smacked into each other or made really close misses.

 

Speculation G: The devil made 'em do it.

 

Speculation H: The asteroids were part of a planet or planets that got disrupted and scattered by unknown forces. This pitiful remnant is all that is it (them?) in the general area of its (their?) ancient orbit(s).

 

Since I cannot do an experiment on the asteroids, I can only let them do such experiments as they do by themselves -- and watch the results.

 

Experiment: See if they look like potatoes -- as tho they had been poured out molten and rotating -- and cooled and hardened accordingly. Hmmmmmm. I see. Some of them do. Inconclusive. Experiment fails for lack of a control group.

[frankglennjacobs@gmail.com]

I looked up six articles (suitable for children) about the origin of asteroids.

 

Not one said a single word about their shapes -- although any number of actual photos show many of them, um, ah, THAT shape.

[Argent]

Frank, your description of the scientific method has omitted a very important step. That is understandable, since it is implicit, though not explicit, in most descriptions of the scientific method. Before you start speculating it is wise to know what the current thinking is about a subject. An in depth understanding of the data, the hypotheses and the theories is required before embarking on improvements.

 

This is one of the great strengths of science. Newton referred to is as "standing on the shoulders of giants". You don't have to explore every possibility, every potential answer. You see what others have concluded and why they have concluded it. Where necessary you rerun their experiments to confirm their findings, or modify them slightly to strengthen or undermine their conclusions.

 

You have chosen to do one thing. Contemplate the shape of asteroids. From this contemplation you have made a provisional conclusion as to how they may have formed. You have done this purely because you think their shape "looks like" they have been "poured out molten". That is not a scientific approach. For one thing you have failed to consider any of the following:

 

The elemental composition of the asteroids.

The mineral composition of the asteroids.

The density of the asteroids.

The internal structure of the asteroids.

The age of the asteroids and the dates of significant events in their history.

The orbital characteristics of the asteroids.

The variation of the first three variables in relation to the last.

 

Not to mention the many details of planetary formation as currently understood.

 

Given the immense amount of data you have chosen to ignore I can see no reason whatsoever to give your speculation any further attention. I recommend, again, that you do some proper study on the subject, then you will be less likely to propose flawed ideas. I am happy to continue to answer all sensible questions you may have, but I am unlikely to indulge any of your obsessions that are based on "well it looks to me as if".

[frankglennjacobs@gmail.com]

Then we part. If not friends, somewhat better acquainted.

 

You have been very helpful to me -- even kind.

 

You have shown me somewhat of the current thinking on collisions, captures and asteroids.

 

Thank you.