Diameter of Solar System

[dougettinger]

Hello Ann,

I really like these sharp, precise replies. Thank you. I presume since Beta Pictoris is on the main sequence with no T-Tauri winds, that this dust disk will be naturally cleared away by the UV and lower solar winds of the star in about another 100 million years( ? ) So what is the modeled or estimated density of this disk. Perhaps there is an estimate of its mass compared with the star's mass (?)

I like your selected reason for the secondary scattered disk for Beta Pictoris since it has a definite plane. The scattered disks of our own star system are due to the random scattering of debris due to collisions and/or the sling shot ejections of the same by the planets. Are there any other reasons for our solar system's scattered disks ?

Non-believer of the Oort cloud,

[dougettinger]

I am not sure whether you are responding to my questioning the existence of the Oort cloud. I do notice that the disk fades away at about 200 AU radius and does not reveal a spherical component. These images do not corroborate the existence of an Oort cloud.

But they demonstrate that something like the scattered disc exists (which models show can produce an Oort cloud), and they also place constraints on the density of extrasolar dust and gas structures that we are capable of detecting.

Chris, thanks for you interest in trying to sway my belief (based on science, of course). So what is the estimated density of Beta Pictoris dust and gas structures ?

The difference between this Beta Pictoris disk structure and the Oort cloud is that the Oort cloud is suppose to have larger size objects such as medium size asteroids with volatiles that become comets when they are perturbed toward the inner solar system.
The Sun's own scattered disks range from 30 to 100 AU - not nearly enough to reach toward the far away Oort cloud. And there seems to be a sharp cut-off beyond 100 AU unless objects have yet to detected beyond these distances. Also, the SDO's are more planar than spherical in their range of orbits. I fail to see a connection between the this Beta Pictoris study and any Oort cloud.

Non-believer of the Oort cloud,

[Ann]

A rather old paper (from 1997) by Pawel Artymowicz, BETA PICTORIS: An Early
Solar System? describes and discusses the nature of the Beta Pictoris system.
See http://web.gps.caltech.edu/classes/ge13 ... c_araa.pdf

Pawel Artymowicz wrote:

A nebula with a particular surface density distribution decreasing
as 6.r/ r−3=2 with radius r , and just enough mass of refractory elements
to form (with 100% efficiency) all Solar System planets and comets, is called
the minimum solar nebula. Its mass is equal to 0.02 M (or only 0.013 M,
disregarding a massive Oort cloud of comets extending to approximately
10 to the power of 5 AU from the Sun). The actual mass of the primordial disk
in our system must have been several times the above minimum (Lissauer 1993);
most likely it was 0.05 to 0.1 M. A similar mass might have been present in the
pre-main sequence disk of β Pic, a star 1.7 times more massive than the Sun.
Observationally, disk masses range from 0.01 to 0.1 M, and their survival time
as massive optically thick structures around solar-type stars equals 3 to 10 Myr.

The quote above is not exact, since the Starship Asterisk page couldn't reproduce some signs or symbols used in the original text, and I made some explanations instead.

Please note that the text is old, and current ideas about the Beta Pictoris dusk disk may be different. But according to Pawel Artymowicz, the primordial disk of the solar system most likely contained a mass of 0.05 to 0.1 solar masses, and the Beta Pictoris disk may be similar.

Ann

[Chris Peterson]

I fail to see a connection between the this Beta Pictoris study and any Oort cloud.

The Oort cloud is generally presumed to have been populated out of the region of the scattered disc. It is easier to detect the scattered disc than the Oort cloud because of its greater density. When we observe a scattered disc about another star, it provides the first piece of evidence that we are looking at a "typical" stellar system structure (to the extent there is such a thing), and is an indicator that we might see an Oort cloud as well... once the instrumentation advances to the point that we might reasonably detect one.

[dougettinger]

So now I understand. The discovery of the scattered disk in Beta Pictoris is the first piece of evidence. But, I am not sure how a scattered disk leads to an Oort cloud. As I already mentioned there is a cut-off of 100 AUs beyond which not objects are found. If the Sun and outer planets were slinging objects outward there should be some distribution between 100 AU and 1 ly where the Oort cloud supposely resides. I also mentioned that the scattered disk is more planar than spherical; how does any modeler assume that the Oort cloud is spherical?

Truly from the non-believer of the Oort cloud,

[dougettinger]

A rather old paper (from 1997) by Pawel Artymowicz, BETA PICTORIS: An Early
Solar System? describes and discusses the nature of the Beta Pictoris system.
See http://web.gps.caltech.edu/classes/ge13 ... c_araa.pdf

Pawel Artymowicz wrote:

A nebula with a particular surface density distribution decreasing
as 6.r/ r−3=2 with radius r , and just enough mass of refractory elements
to form (with 100% efficiency) all Solar System planets and comets, is called
the minimum solar nebula. Its mass is equal to 0.02 M (or only 0.013 M,
disregarding a massive Oort cloud of comets extending to approximately
10 to the power of 5 AU from the Sun). The actual mass of the primordial disk
in our system must have been several times the above minimum (Lissauer 1993);
most likely it was 0.05 to 0.1 M. A similar mass might have been present in the
pre-main sequence disk of β Pic, a star 1.7 times more massive than the Sun.
Observationally, disk masses range from 0.01 to 0.1 M, and their survival time
as massive optically thick structures around solar-type stars equals 3 to 10 Myr.

The quote above is not exact, since the Starship Asterisk page couldn't reproduce some signs or symbols used in the original text, and I made some explanations instead.

Please note that the text is old, and current ideas about the Beta Pictoris dusk disk may be different. But according to Pawel Artymowicz, the primordial disk of the solar system most likely contained a mass of 0.05 to 0.1 solar masses, and the Beta Pictoris disk may be similar.

Ann

Ann, your reply is very interesting in regards to the size of primordial disks that includes Beta Pictoris. I remember reading the initial proto-star disk is hypothesized to be at least 3 times the mass of the star that it produces. When a young stellar object, YSO, is discovered its accretion disk is usually 10 to 20 % of the YSO's mass. When the star initially becomes a T-Tauri star, the accretion disk is now about 1 to 3 % of the stellar mass. As the T-Tauri star stage progresses, a so-called proto-planetary disk of 0.01 to 0.05 stellar mass remains to form the surrounding accreted planets. I am not sure from these numbers which ones are determined by observations and which ones are determined by postulated calculations and modeling (?) In fact I am not sure my total understanding of primordial disks is consistent and current (?) Perhaps you can help me become most current about understanding primordial disks. Thanks.

The pottery-making of the universe is spinning disks,

[neufer]

So now I understand. The discovery of the scattered disk in Beta Pictoris is the first piece of evidence. But, I am not sure how a scattered disk leads to an Oort cloud. As I already mentioned there is a cut-off of 100 AUs beyond which not objects are found. If the Sun and outer planets were slinging objects outward there should be some distribution between 100 AU and 1 ly where the Oort cloud supposely resides. I also mentioned that the scattered disk is more planar than spherical; how does any modeler assume that the Oort cloud is spherical?

The outer Oort cloud MUST be roughly spherical because:

• 1) The longest period comets enter the local solar system from all different directions.
  
  2) The dynamics of the outer Oort cloud has long been dominated by extra-solar system objects; e.g., passing stars.

<<Short-period comets are generally defined as having orbital periods of less than 200 years. They usually orbit more-or-less in the ecliptic plane in the same direction as the planets. The orbits of long-period comets take them far beyond the outer planets at aphelia, and the plane of their orbits need not lie near the ecliptic.

Based on their orbital characteristics, short-period comets are thought to originate from the centaurs and the Kuiper belt/scattered disc—a disk of objects in the trans-Neptunian region—whereas the source of long-period comets is thought to be the far more distant spherical Oort cloud.>>

<<The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane.

Astronomers believe that the matter composing the Oort cloud formed closer to the Sun and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System's evolution. However, citing the Southwest Research Institute, NASA published a 2010 article that includes the following quotation:

We know that stars form in clusters. The Sun was born within a huge community of other stars that formed in the same gas cloud. In that birth cluster, the stars were close enough together to pull comets away from each other via gravity.

It is therefore speculated that the Oort cloud is, at least partly, the product of an exchange of materials between the Sun and its sister stars as they formed and drifted apart.>>

[Chris Peterson]

So now I understand. The discovery of the scattered disk in Beta Pictoris is the first piece of evidence. But, I am not sure how a scattered disk leads to an Oort cloud. As I already mentioned there is a cut-off of 100 AUs beyond which not objects are found. If the Sun and outer planets were slinging objects outward there should be some distribution between 100 AU and 1 ly where the Oort cloud supposely resides. I also mentioned that the scattered disk is more planar than spherical; how does any modeler assume that the Oort cloud is spherical?

Where bodies reside in a stellar system is determined by a combination of where they were formed, and where they subsequently move. Movements are the result of gravitational perturbation (which redistributes angular momentum between two or more bodies), and are subject to complex resonances created by the orbital positions of high mass bodies.

Most of the mass of a stellar system ends up substantially in one plane because of fluid dynamic processes early in the process. Once material is accreted into larger bodies and the system is cleared of most gas and dust, those processes go away. But perturbations will place bodies on random inclinations, so over time perturbed bodies accumulate in some sort of spherical shell or spherical cloud. That is one model of Oort cloud formation- bodies perturbed out of the scattered disc, and presumably structured into a quasi-spherical cloud shaped by resonances with the large planets. Numerical simulations demonstrate that this mechanism is physically possible, but don't offer much evidence one way or the other that it actually occurred in our own system, given all the unknowns about the early solar system environment.

[dougettinger]

Hello Neufer, thanks for stepping up to the plate. You beat me to the punch. I was just about to mention that the Sun's original cluster of stars should have played havoc with any forming Oort cloud at 1 ly away when some open star clusters are known to have stars that are only 1.5 lys apart. Your NASA quote is the first time that I have received any hint that there was a possible exchange of materials from two nearby birthed stars. So a close encounter of two young forming stars in the first billion years could have created the Late Heavy Bombardment (LHB). This idea is more appealing than the Nice theory for the cause of the LHB. Do you have any opinions on this matter?

Since comets are known to be more like asteroids than snowballs now, then long period comets from the Oort cloud with their high temperature-formed refractories had to originate from the inner solar system. Hence, the Oort cloud had to be created between the span of 200 to 400 thousand years for oligarchic accretion stage and 10 to 100 million years for the final merger stage of accretion of the inner solar system. In other words, any ejected body from the system is never totally ejected unless it is exchanged by a nearby sister star inside an open cluster before the stars diverge. Neufer, are you in fairly close agreement with this assessment?

Non-believer of the Oort cloud,

[neufer]

I was just about to mention that the Sun's original cluster of stars should have played havoc with any forming Oort cloud at 1 ly away when some open star clusters are known to have stars that are only 1.5 lys apart. Your NASA quote is the first time that I have received any hint that there was a possible exchange of materials from two nearby birthed stars. So a close encounter of two young forming stars in the first billion years could have created the Late Heavy Bombardment (LHB). This idea is more appealing than the Nice theory for the cause of the LHB. Do you have any opinions on this matter?

I'm sorta fond of Nice theories, myself.

Since comets are known to be more like asteroids than snowballs now, then long period comets from the Oort cloud with their high temperature-formed refractories had to originate from the inner solar system. Hence, the Oort cloud had to be created between the span of 200 to 400 thousand years for oligarchic accretion stage and 10 to 100 million years for the final merger stage of accretion of the inner solar system. In other words, any ejected body from the system is never totally ejected unless it is exchanged by a nearby sister star inside an open cluster before the stars diverge. Neufer, are you in fairly close agreement with this assessment?

I'm on a steep learning curve vis-a-vis the Oort cloud.

My agreement or disagreement is probably not worth a bucket of warm Spitzer.

[dougettinger]

The Nice theory is not so nice. Once a planet finds his or her orbit, then as the proto-star gains more mass the planet is allowed to gain some velocity. If the planet gains more mass, then it is allowed to slow down a little. Changing orbits more outwardly and/or crossing orbits is not so pretty. The theory is very lame.

Perhaps Chris' opinion about this little summary of Oort cloud origin may be worth a bucket of cold Spitzers.

Disliking the Nice theory,

[Chris Peterson]

The Nice theory is not so nice. Once a planet finds his or her orbit, then as the proto-star gains more mass the planet is allowed to gain some velocity. If the planet gains more mass, then it is allowed to slow down a little. Changing orbits more outwardly and/or crossing orbits is not so pretty. The theory is very lame.

You misunderstand the theory. All of the shifts in planetary position that occur in the Nice Model happen long after the protoplanetary gas disc has been consumed or dissipated. The Sun had already reached its present mass and was not changing... indeed, it was no longer a protostar at all.

The model does a very good job of explaining many of the features of the Solar System, and is therefore widely accepted by planetary scientists as a strong theory. To call it "lame" does not reflect well on your understanding. Even planetary scientists who prefer alternate explanations for the structure of the Solar System do not take that viewpoint.

[dougettinger]

The Nice theory is not so nice. Once a planet finds his or her orbit, then as the proto-star gains more mass the planet is allowed to gain some velocity. If the planet gains more mass, then it is allowed to slow down a little. Changing orbits more outwardly and/or crossing orbits is not so pretty. The theory is very lame.

You misunderstand the theory. All of the shifts in planetary position that occur in the Nice Model happen long after the protoplanetary gas disc has been consumed or dissipated. The Sun had already reached its present mass and was not changing... indeed, it was no longer a protostar at all.

The model does a very good job of explaining many of the features of the Solar System, and is therefore widely accepted by planetary scientists as a strong theory. To call it "lame" does not reflect well on your understanding. Even planetary scientists who prefer alternate explanations for the structure of the Solar System do not take that viewpoint.

I fully realize the Nice theory is trying to address the Late Heavy Bombardment (LHB) period that occurred about 600 hundred million years after the birth of the solar system. By this time the Sun was on the main sequence and the planets had mostly settled into stable orbits. Resonance between the outer planets caused the some of these planets to be perturbed into orbits of larger diameter thereby disturbing the KBO's. I was merely hinting orbital characteristics should generally only be affected largely by changes in the mass inside the planet's orbit or perhaps by its own mass changing.

I am very sorry if I hurt someone's feelings by using the word, "lame". All logical theories deserve careful consideration. Let's move on to a related topic that I posted and was never addressed.

"Ann, your reply is very interesting in regards to the size of primordial disks that includes Beta Pictoris. I remember reading the initial proto-star disk is hypothesized to be at least 3 times the mass of the star that it produces. When a young stellar object, YSO, is discovered its accretion disk is usually 10 to 20 % of the YSO's mass. When the star initially becomes a T-Tauri star, the accretion disk is now about 1 to 3 % of the stellar mass. As the T-Tauri star stage progresses, a so-called proto-planetary disk of 0.01 to 0.05 stellar mass remains to form the surrounding accreted planets. I am not sure from these numbers which ones are determined by observations and which ones are determined by postulated calculations and modeling (?) In fact I am not sure my total understanding of primordial disks is consistent and current (?) Perhaps you can help me become most current about understanding primordial disks. Thanks."

I am not only asking Ann, but also anybody in the forum as to whether I have an adequate understanding of accretion and proto-planetary disks. Thank you for providing any clarifications or confirmations.

[Chris Peterson]

I fully realize the Nice theory is trying to address the Late Heavy Bombardment (LHB) period that occurred about 600 hundred million years after the birth of the solar system.

This is not what the Nice model is trying to address. The model deals with the position of bodies in the Solar System. The LHB is a consequence of the model, not the purpose of the model.

I was merely hinting orbital characteristics should generally only be affected largely by changes in the mass inside the planet's orbit or perhaps by its own mass changing.

This is not the case. There are no mass changes at all included in the Nice model (or other dynamical models of planetary position). All orbital shifts are explained by gravitational perturbations, primarily resonant ones.

[neufer]

[b][color=#0000FF]Number of particles from the Sun hitting Voyager 1. Credit: NASA[/color][/b]

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Voyager 1 May Have Left the Solar System
by Nancy Atkinson, Universe Today, October 8, 2012

<<While there’s no official word from NASA on this, the buzz around the blogosphere is that Voyager 1 has left the Solar System. The evidence comes from this graph, above, which shows the number of particles, mainly protons, from the Sun hitting Voyager 1 across time. A huge drop at the end of August hints that Voyager 1 may now be in interstellar space. The last we heard from the Voyager team was early August, and they indicated that on July 28, the level of lower-energy particles originating from inside our Solar System dropped by half. However, in three days, the levels had recovered to near their previous levels. But then the bottom dropped out at the end of August.

The Voyager team has said they have been seeing two of three key signs of changes expected to occur at the boundary of interstellar space. In addition to the drop in particles from the Sun, they’ve also seen a jump in the level of high-energy cosmic rays originating from outside our Solar System.

The third key sign would be the direction of the magnetic field. No word on that yet, but scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space.

“These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space,” said Edward Stone, the Voyager project scientist for the entire mission, who was quoted in early August. “We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space.” Stone added that the data are changing in ways that the team didn’t expect, “but Voyager has always surprised us with new discoveries.”

Voyager 1 launched on Sept. 5, 1977, is approximately 18 billion kilometers (11 billion miles) from the Sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 15 billion km (9.3 billion miles) from the Sun.>>

[dougettinger]

I fully realize the Nice theory is trying to address the Late Heavy Bombardment (LHB) period that occurred about 600 hundred million years after the birth of the solar system.

This is not what the Nice model is trying to address. The model deals with the position of bodies in the Solar System. The LHB is a consequence of the model, not the purpose of the model.

I was merely hinting orbital characteristics should generally only be affected largely by changes in the mass inside the planet's orbit or perhaps by its own mass changing.

This is not the case. There are no mass changes at all included in the Nice model (or other dynamical models of planetary position). All orbital shifts are explained by gravitational perturbations, primarily resonant ones.

Hello Chris,

I fully realize that no mass changes are taking place 600 million years after the birth of the Sun and its planetary systems, but I still have a difficult time understanding how resonances change orbits dramatically. I do understand a little about resonances causing the alignment of the orbital periods of the Jovian moons and causing the gaps in the asteroid belt.

So I have a couple of questions about resonances of the outer planets. Why did it take 600 million or perhaps 700 million years for these resonances to perturb Neptune and Uranus? Certainly, these planets have come into conjunction with Jupiter and Saturn thousands of times over this time period (especially for closer orbits) to begin resonating and perturbing each other much sooner. Also, how is angular momentum conserved by the ice planets moving outward? And, if the planets were much closer together in the beginning how did the neccessary concentrated accretion occur in a narrower belt of the disk. Finally, how did Neptune achieve almost a perfect circular orbit? What possible perturbations in the outer perimeter could have rounded Neptune's original elliptical orbit?

Yes, I do have a little prejudice about the the Nice theory and wrongly accuse them of devising a storyline to explain the LHB period. The main problem for the Nebular Hypothesis and its attending accretion theories is how the ice planet embryos can be created in the diminishing density of the outer proto-planetary disk. I reckon their modeling of resonance for perturbations hit right on the money at 600 million years (?)

Still disliking the Nice theories,

[dougettinger]

[b][color=#0000FF]Number of particles from the Sun hitting Voyager 1. Credit: NASA[/color][/b]

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---

Voyager 1 May Have Left the Solar System
by Nancy Atkinson, Universe Today, October 8, 2012

<<While there’s no official word from NASA on this, the buzz around the blogosphere is that Voyager 1 has left the Solar System. The evidence comes from this graph, above, which shows the number of particles, mainly protons, from the Sun hitting Voyager 1 across time. A huge drop at the end of August hints that Voyager 1 may now be in interstellar space. The last we heard from the Voyager team was early August, and they indicated that on July 28, the level of lower-energy particles originating from inside our Solar System dropped by half. However, in three days, the levels had recovered to near their previous levels. But then the bottom dropped out at the end of August.

The Voyager team has said they have been seeing two of three key signs of changes expected to occur at the boundary of interstellar space. In addition to the drop in particles from the Sun, they’ve also seen a jump in the level of high-energy cosmic rays originating from outside our Solar System.

The third key sign would be the direction of the magnetic field. No word on that yet, but scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space.

“These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space,” said Edward Stone, the Voyager project scientist for the entire mission, who was quoted in early August. “We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space.” Stone added that the data are changing in ways that the team didn’t expect, “but Voyager has always surprised us with new discoveries.”

Voyager 1 launched on Sept. 5, 1977, is approximately 18 billion kilometers (11 billion miles) from the Sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 15 billion km (9.3 billion miles) from the Sun.>>

Hello Neufer,

Thank you very much for this Voyager 1 update. The data is highly tantalizing. Voyager 1 is about 120 AU's from the Sun which is beyond the SDO's and KBO's. NASA may have truly found the edge of the universe. The verdict is still out for the Oort cloud. Could you tell me in which direction Voyager 1 went with respect to the Sun's velocity vector ( ? ) More data on the magnetic field or the gravity field would be super.

Gratefully yours,

[saturno2]

To purpose of diameters
I think it is better handle diameter to indicate the size
of an astronomical object.
Use radius and diameter simultaneously can cause confusion

[dougettinger]

Conversion from radius to diameter is a factor of two if the object is roughly round or spherical.

Conversion of times can really be confusing. Is the time expressed measured from the Big Bang or from the present.

Doug

[Chris Peterson]

Conversion of times can really be confusing. Is the time expressed measured from the Big Bang or from the present.

It's only confusing if the person stating the time doesn't also state the conditions. But that true for nearly all units, isn't it?

[dougettinger]

Sometimes the author neglects to state the conditions or I may neglect the conditions that are stated far away in another paragraph.

Always working hard to be less confused,
Doug

[saturno2]

Indeed. The explanations about the Kuiper Belt, Scattered Disk, and
the Oort Cloud, are a little confusing, not didactic. ( In Internet )