Starship Asterisk*

dougettinger wrote:Now for my point - if the Sun's gravity field could hold these objects that were formed 1/1000th closer to the Sun and possessing varying trajectories, then why cannot this same gravity field capture similar sized objects with similarly varying trajectories from outside this sphere of influence when they are intersected by the Sun's path ?

Because the situations are completely different. All solar system bodies, including those in the Oort cloud, are gravitationally bound to the Sun because they all formed together in a nebula that collapsed due to self gravity. Any amount of material may have been ejected during the formation process; we have no way of knowing how much. But the stuff that remained did so precisely because it couldn't escape.

Due to the randomness of velocity vectors many of these objects should have nearly tangential vectors with the Oort cloud sphere and/or disk. The primary velocity vector, that of the Sun's direction, should be quite similar knowing how spiral galaxies work.

The Oort cloud is gravitationally insignificant. The Solar System has only five bodies to consider as far as gravitational influence: the Sun and the four gas giants. These all lie on about the same plane, but that plane is different from our orbital plane in the galaxy. So anything passing through the system as you describe is likely to do so at some significant angle off our planetary plane. That makes it nearly impossible to capture something, since such a capture requires at least two interactions (typically that would be with Jupiter and the Sun). Such a three-body interaction is unlikely even for something entering on the planetary plane; off this plane it's almost impossible.

Allow me to add another point of discussion - A question arises as to how these type of celestial bodies are formed between the stars where there is not sufficient heat from a forming protostar disk to create ice balls and/or molten cores. Scientists are now discovering very low mass brown dwarfs even with their own planets. So has anyone really established a lower boundary for what the smallest body can form in a GMC without having a typical size protostar disk ?

I think that the assumption is that all these bodies form in protostar systems, and are then ejected. Certainly there must be planet-sized bodies that are roaming interstellar space after being ejected from their parent star systems. But even if you assume that every star produced a few such rogues, the density remains extremely low and the likelihood of any encounter with another star is small (and the likelihood of a capture vastly smaller than that).

Chris Peterson wrote:The Oort cloud is gravitationally insignificant. The Solar System has only five bodies to consider as far as gravitational influence: the Sun and the four gas giants. These all lie on about the same plane, but that plane is different from our orbital plane in the galaxy. So anything passing through the system as you describe is likely to do so at some significant angle off our planetary plane. That makes it nearly impossible to capture something, since such a capture requires at least two interactions (typically that would be with Jupiter and the Sun). Such a three-body interaction is unlikely even for something entering on the planetary plane; off this plane it's almost impossible.

The Sun's gravity field is obviously significant to capture bodies for the Oort Cloud and continue to grasp them. The combination of this same gravity field and the perturbations of the Oort Cloud itself should be enough to capture the same size bodies as they intersect the Oort Cloud from outside. Then these captured bodies would eventually be perturbed inward in similar fashion as the original bodies that came from the inner solar system. I am assuming that various velocity vectors could be modeled for these captures.

Chris Peterson wrote:I think that the assumption is that all these bodies form in protostar systems, and are then ejected. Certainly there must be planet-sized bodies that are roaming interstellar space after being ejected from their parent star systems. But even if you assume that every star produced a few such rogues, the density remains extremely low and the likelihood of any encounter with another star is small (and the likelihood of a capture vastly smaller than that).

I believe you missed my point. I am not assuming that most bodies in interstellar space come from ejected denizens from forming star systems. Most interstellar orbs come from the same processes that stars and their planets come from, but the difference is that the forming condensation disks are miniature. This is similar to how scientists have been forced to scale down the size of protostar disks that formed recently discovered very small brown dwarfs and their planets.

The density of interstellar orbs and their sizes is much greater in my hypothesis than in current thinking. But, of course, their formation process must be justified. I value your comments.

Doug Ettinger
Pittsburgh, PA

dougettinger wrote:The Sun's gravity field is obviously significant to capture bodies for the Oort Cloud and continue to grasp them.

The Sun's gravity is not capturing bodies in the Oort cloud. These are simply bodies left from the formation of the Solar System that lacked the necessary velocity to escape. That is very different.

The combination of this same gravity field and the perturbations of the Oort Cloud itself should be enough to capture the same size bodies as they intersect the Oort Cloud from outside.

No. The solar escape velocity in the Oort cloud is on the order of a meter per second. Anything passing through the Oort cloud at greater than this will not be captured by the Sun. Anything passing through the region of the Oort cloud is extremely unlikely to be perturbed by the cloud itself, since it in only a few Earth masses distributed over something approaching a cubic light year. There is nothing there to capture anything.

From the perspective of an outside body, the Solar System is essentially the Sun and Jupiter, with a tiny influence from the remaining three gas giants. That's it. To be captured into a solar orbit, or into an orbit around a planet, that body will need to pass very close to an existing planet (or the Sun), and be diverted from there around another. This just isn't a likely scenario, and can't really happen for any object entering from off the plane of the system.

I believe you missed my point. I am not assuming that most bodies in interstellar space come from ejected denizens from forming star systems.

No, I didn't miss your point. I just disagree with your assumption that small bodies are formed in dust clouds. I don't think there is any evidence supporting that. I think that whatever small bodies exist in interstellar space originated in protostar systems. The gas density isn't high enough in molecular clouds to allow Pluto-sized bodies to form before stars form.

I was thinking about this. If a planet has rings, like saturn and capture theory applies whereby a meteorite or comet gets caught in orbit... is there a possibility that the object would get broken up in a sandpaper like effect by the other smaller rocks. i.e. eroded away?

Paul

Chris Peterson wrote: No, I didn't miss your point. I just disagree with your assumption that small bodies are formed in dust clouds. I don't think there is any evidence supporting that. I think that whatever small bodies exist in interstellar space originated in protostar systems. The gas density isn't high enough in molecular clouds to allow Pluto-sized bodies to form before stars form.

I am trying to priortize your objections to the solar system or any other star system capturing interstellar objects. I believe I am hearing the strongest objection is due to the actual existence of larger objects in interstellar space. If these objects existed in the required amount of density then it is probable that they could be captured. Is my thinking correct on these matters ?

Whatever triggers a protostar or protoplanet to form is not well understood. Protostar disks are typically about 3 times the mass of the star forming inside the disk from observed data. For the newly discovered brown dwarfs with their own planets, their protostar disk need only be about 3 times the range of masses for brown dwarfs which is 13 to 80 Jupiter masses. This is indeed a surprisingly, fairly small protostar disk. In fact, since astrophysicists don't understand the trigger for forming disks inside GMC's, there is no reason for having a firm grasp on what the lower limit of a forming proto-body disk is.

However, the newest theorized lower limit protostar disk may be publicized. Do you know of any ?

Doug Ettinger
Pittsburgh, PA

dougettinger wrote:I am trying to priortize your objections to the solar system or any other star system capturing interstellar objects. I believe I am hearing the strongest objection is due to the actual existence of larger objects in interstellar space. If these objects existed in the required amount of density then it is probable that they could be captured. Is my thinking correct on these matters ?

No. My objection is that capturing bodies that are not already gravitationally bound to the Sun is almost impossible. It requires an interaction with two massive bodies (probably Jupiter and the Sun, but any of the gas giants could be involved). The only way this can realistically happen is if the captured body enters on the plane of the Solar System. So even if interstellar space were full of debris and rogue planets, I still wouldn't expect any captures.

Whatever triggers a protostar or protoplanet to form is not well understood. Protostar disks are typically about 3 times the mass of the star forming inside the disk from observed data. For the newly discovered brown dwarfs with their own planets, their protostar disk need only be about 3 times the range of masses for brown dwarfs which is 13 to 80 Jupiter masses. This is indeed a surprisingly, fairly small protostar disk. In fact, since astrophysicists don't understand the trigger for forming disks inside GMC's, there is no reason for having a firm grasp on what the lower limit of a forming proto-body disk is.

Nevertheless, there are reasonably well understood mechanisms that terminate the collapse- hydrogen fusion in the case of stars, and electron degeneracy pressure in the case of brown dwarfs. I think that any molecular cloud with a high enough surface density to support gravitational collapse will produce one of these. I know of no mechanism that would both allow gravitational collapse, and stop the process with a planet sized terrestrial or icy body.

Chris Peterson wrote: I think that any molecular cloud with a high enough surface density to support gravitational collapse will produce one of these. I know of no mechanism that would both allow gravitational collapse, and stop the process with a planet sized terrestrial or icy body.

I am not sure what is meant by the term "surface density". I believe it is merely the density of particles divided by the surface of the volume that contains the particles. Is this correct ?

After gravitational collapse is triggered at a certain point, the surrounding clump of materials requiring this surface density may only have enough material to generate a small body and not enough material to start electron degeneracy to make even a brown dwarf. Running out of material in a certain cloud clump can be the reason for stopping the process. Yet enough heat could be generated through gravitational collapse to condense atoms and molecules to form ices and even molten materials. What is wrong with this thinking ?

Doug Ettinger
Pittsburgh, PA

dougettinger wrote:I am not sure what is meant by the term "surface density". I believe it is merely the density of particles divided by the surface of the volume that contains the particles. Is this correct ?

I would assume surface density means density at the surface. Density would increase towards the center, much as the density of water in our oceans increases the deeper you get.

OK. Now I understand.

DBE