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Drakheim
2004-Mar-10, 07:43 PM
This is a generalized analogy at best just so youíre forewarned.

Not including the sun and not including Jupiter.

Take all the planets, all the moons, all the asteroids, comets and all the rest of the debris that donít fit into any of the above categories.

Combine all that stuff into one lump o matter. Then double what you have collected.

Am I right in assuming that ALL of that would have less mass than the planet Jupiter?

And if so, Jupiter has to be 80 (??) times more massive to become a brown dwarf?

Manchurian Taikonaut
2004-Mar-10, 07:51 PM
including kupier belt, Oort cloud, and Trojans or defenders of Troy, and space dust?

Drakheim
2004-Mar-10, 07:58 PM
including kupier belt, Oort cloud, and Trojans or defenders of Troy, and space dust?

Err.. I guess so. :-s

Manchurian Taikonaut
2004-Mar-10, 08:08 PM
I don't know if the Oort cloud should be included? Some people sat the Oort cloud is 190,000 AU away others say its 80,000AU the total mass of comets in the Oort cloud is said to be 140 times that of Earth, but others say its much smaller. If you are going to include the Oort cloud and other space debris, dusts and rock, I'd think Jupiter might be just slightly smaller in mass ( Jupiter is said to be 317 earths mass).

Kaptain K
2004-Mar-10, 08:10 PM
Basically correct, although I think the lower limit for brown dwarfs is 13 MJ. I think the 80 MJ limit is for red dwarfs. I could be mistaken on this, so somebody correct me if I am.

Spaceman Spiff
2004-Mar-10, 08:37 PM
Basically correct, although I think the lower limit for brown dwarfs is 13 MJ. I think the 80 MJ limit is for red dwarfs. I could be mistaken on this, so somebody correct me if I am.

Yep, that's right. You'd get a fraction more than Saturn's mass. The Sun contains 99.85% of all matter in the solar system, and Jupiter contains 2/3 of the rest in round numbers. The asteroid belt contains less than a Moon's worth of material, if I recall correctly. The Kuiper belt contains less than an Earth's worth. The only contributor of any uncertainty is the Oort cloud, now thought to contain just several Earth's worth of material.

While the designations are a bit fuzzy near the boundaries, the minimum mass for a bonafied star, i.e., an object that can stably sustain hydrogen fusion of sufficient energy rate to offset that lost at the surface as photons, is about 0.08 Msun or about 80 Mjupiter. The mininum mass for a brown dwarf has been designated as a massive object that can generate significant energy from the fusion of deuterium in its central regions (via the second step of the p-p chain). This is supposed to happen for masses above approximately 13 Mjupiter. Note that this doesn't last long because deuterium (heavy hydrogen) is rare in the universe (about 3 parts in 1 million) compared to regular hydrogen. Objects more massive than about 60 Mjupiter will fuse Lithium in to Helium for brief durations -- but Lithium is even more rare.

But the jovian/brown dwarf boundary is obscured in our undertanding due to issues related to their formation (isolated gravitational collapse vs. gravitational collapse in a dusty gas disk vs. condensation in dusty gas disk). Are they really a continuum of objects, or are they parallel objects?

Drakheim
2004-Mar-10, 08:40 PM
But the jovian/brown dwarf boundary is obscured in our undertanding due to issues related to their formation (isolated gravitational collapse vs. gravitational collapse in a dusty gas disk vs. condensation in dusty gas disk). Are they really a continuum of objects, or are they parallel objects?

:-s :-s :-s :-s

Fire bad... tree pretty.
:lol:

Spaceman Spiff
2004-Mar-10, 08:50 PM
But the jovian/brown dwarf boundary is obscured in our undertanding due to issues related to their formation (isolated gravitational collapse vs. gravitational collapse in a dusty gas disk vs. condensation in dusty gas disk). Are they really a continuum of objects, or are they parallel objects?

What I mean is do Jovians form in early solar system disks via condensation and/or local gravitational instabilities and have a range of masses which overlap the lower end of the brown dwarfs which form via isolated gravitational collapse (i.e. not within an accretion disk surrounding the formative star)? Or do jovians and brown dwarfs form one big happy family of objects, that form via gravitational collapse along a continuum in mass, regardless of their origins in a disk or not?

Celestial Mechanic
2004-Mar-10, 08:57 PM
Think of the mass hierarchy this way:

The Sun is 99.85% of the mass of the Solar System.

About 2/3 of the residue is Jupiter (and its satellites, I'll leave this as understood in the future).

About 3/4 of the residue after removing Jupiter is Saturn.

Uranus and Neptune roughly split the residue after removing Saturn, with about 1/15 of the residue being left as the terrestrial planets, asteroid and Edgeworth-Kuiper belts.

Earth and Venus roughly split this residue, with about 1/10 left over.

Mars is a little less than 2/3 of this residue, Mercury a little less than 1/3, maybe 3 to 5 percent being the remainder.

Pluto+Charon is maybe 1/5 to 1/2 of the remainder. Ceres, the largest of the main-belt asteroids has a mass less than 1/7 that of Pluto, Quoaor has even less.

The last item is a bit uncertain.

Drakheim
2004-Mar-10, 09:17 PM
But the jovian/brown dwarf boundary is obscured in our undertanding due to issues related to their formation (isolated gravitational collapse vs. gravitational collapse in a dusty gas disk vs. condensation in dusty gas disk). Are they really a continuum of objects, or are they parallel objects?

What I mean is do Jovians form in early solar system disks via condensation and/or local gravitational instabilities and have a range of masses which overlap the lower end of the brown dwarfs which form via isolated gravitational collapse (i.e. not within an accretion disk surrounding the formative star)? Or do jovians and brown dwarfs form one big happy family of objects, that form via gravitational collapse along a continuum in mass, regardless of their origins in a disk or not?

Ahh.. I get what your saying now.

JohnOwens
2004-Mar-10, 09:23 PM
...Objects more massive than about 60 Mjupiter will fuse Lithium in to Helium for brief durations -- but Lithium is even more rare.

I think you've gotten something a little bit backwards here. :-?

Spaceman Spiff
2004-Mar-10, 10:51 PM
...Objects more massive than about 60 Mjupiter will fuse Lithium in to Helium for brief durations -- but Lithium is even more rare.

I think you've gotten something a little bit backwards here. :-?

I know what you are thinking, but in this case it's not at all backwards. The reaction is:

p + 7Li --> 4He + 4He
p + 6Li --> 4He + 3He

where p is a proton, and the number out in front of the element is the sum of the number of protons, neutrons. Lithium is a weird nucleus, which probably accounts for its rarity.

JohnOwens
2004-Mar-10, 11:24 PM
...Objects more massive than about 60 Mjupiter will fuse Lithium in to Helium for brief durations -- but Lithium is even more rare.

I think you've gotten something a little bit backwards here. :-?

I know what you are thinking, but in this case it's not at all backwards. The reaction is:

p + 7Li --> 4He + 4He
p + 6Li --> 4He + 3He

where p is a proton, and the number out in front of the element is the sum of the number of protons, neutrons. Lithium is a weird nucleus, which probably accounts for its rarity.

Dang, I was even thinking of qualifying that by saying "I won't say it doesn't happen, but it's not fusion if it does." #-o It's still half-fusion, half-fission in a way, though. I assume it does have a net effect of converting binding energy mass into another form of energy, rather than absorbing it? (Is exothermic rather than endothermic, you know what I mean.)

Spaceman Spiff
2004-Mar-10, 11:37 PM
...Objects more massive than about 60 Mjupiter will fuse Lithium in to Helium for brief durations -- but Lithium is even more rare.

I think you've gotten something a little bit backwards here. :-?

I know what you are thinking, but in this case it's not at all backwards. The reaction is:

p + 7Li --> 4He + 4He
p + 6Li --> 4He + 3He

where p is a proton, and the number out in front of the element is the sum of the number of protons, neutrons. Lithium is a weird nucleus, which probably accounts for its rarity.

Dang, I was even thinking of qualifying that by saying "I won't say it doesn't happen, but it's not fusion if it does." #-o It's still half-fusion, half-fission in a way, though. I assume it does have a net effect of converting binding energy mass into another form of energy, rather than absorbing it? (Is exothermic rather than endothermic, you know what I mean.)

I would guess both reactions are exothermic (or they sure wouldn't help at all to offset the energy lost at the surface of the brown dwarf), but I'd have to double check. The binding energy/nucleon of 6Li, for example, is less than that of 4He. Li is just weird.

But, yes, the term "fusion" here is a bit ambiguous.

JohnOwens
2004-Mar-11, 12:11 AM
I know what you are thinking, but in this case it's not at all backwards. The reaction is:

p + 7Li --> 4He + 4He
p + 6Li --> 4He + 3He

where p is a proton, and the number out in front of the element is the sum of the number of protons, neutrons. Lithium is a weird nucleus, which probably accounts for its rarity.

Dang, I was even thinking of qualifying that by saying "I won't say it doesn't happen, but it's not fusion if it does." #-o It's still half-fusion, half-fission in a way, though. I assume it does have a net effect of converting binding energy mass into another form of energy, rather than absorbing it? (Is exothermic rather than endothermic, you know what I mean.)

I would guess both reactions are exothermic (or they sure wouldn't help at all to offset the energy lost at the surface of the brown dwarf), but I'd have to double check. The binding energy/nucleon of 6Li, for example, is less than that of 4He. Li is just weird.

But, yes, the term "fusion" here is a bit ambiguous.

Sorry, I guess I should have been more specific. I was using a mental picture ("model" might imply a bit more thorough thinking than actually went into it) of the proton and Li fusing for a split second into a 8Be or 7Be, then immediately fissioning into the two He. (momentary pause while I fetch my trusty CRC Handbook of Chemistry and Physics....)
OK, half-life of 8Be is listed as 0.067 fs, so that would be pretty nearly instantaneous. 7Be's is 53.29 days, though. Now looking at decay mode... 8Be says 2 alpha, which is just like what you've got above. For 7Be, it says it does an orbital electron emission, which I don't know about specifically (it's abbreviated 'EC', which always led me to assume it was 'electron capture', rather the opposite), but I would guess from the name that it would have to produce a 7B, but that's such an odd duck it isn't even listed here.

Anyway, though, looking at the net reaction masses... p + 7Li - 2 * 4He (grr, I want subscripts & superscripts! Mass belongs after the symbol) = 0.01863 amu, or 0.232% of original mass converted into energy. p+6Li - 3He - 4He = 0.00446 amu, or 0.0635% of original mass.
So the net reaction is certainly exothermic, though not as much as some of the others.

None of which, of course, really helps clear up whether it's a fusion followed by a fission, or one big transmogrification all at once. :-?

Brady Yoon
2004-Mar-11, 12:50 AM
I don't know if this calculation is correct, but if there are 1 trillion comets in the Oort Cloud and the average diameter of each is 10 km, and since Jupiter is 140,000 km wide, Jupiter is 14,000 times wider, it has 1.24(10)^13 the volume (more than 10 trillion times 8-[ ). If we assume Jupiter and the comets have close to the same density, and there are 1 trillion comets, Jupiter is still 10 times the mass of the entire Oort Cloud. If we include the asteroid belt, which is only 1/10 the mass of the moon, and all the other planets, which are only about 1/3 the mass of Jupiter, and the Kuiper Belt, while quite massive, is still probably around only the mass of Mercury or Mars, then that doesn't amount to much. However, if we are severely underestimating the number of comets in the Oort Cloud, my calculation would be way off. #-o And then the sun is 1,000 times more massive than Jupiter. I think the solar system is made of four main categories-
1. The Sun, which completely dominates the solar system, with 99.8 % or so of its mass.
2. Jupiter and the gas giants, which form the remainder of the mass,
3. The comets, which include the monster size KBO's and the trillion comets out there,
4. The smallest group, which includes everything else, with most of the mass in terrestrial planets and Pluto and satellites and moons. The rest, which is a tiny fraction, makes up the asteroid belt and interplanetary dust.
This could be totally wrong though. #-o

Brady Yoon

Spaceman Spiff
2004-Mar-11, 03:21 AM
Sorry, I guess I should have been more specific. I was using a mental picture ("model" might imply a bit more thorough thinking than actually went into it) of the proton and Li fusing for a split second into a 8Be or 7Be, then immediately fissioning into the two He. (momentary pause while I fetch my trusty CRC Handbook of Chemistry and Physics....)
OK, half-life of 8Be is listed as 0.067 fs, so that would be pretty nearly instantaneous. 7Be's is 53.29 days, though. Now looking at decay mode... 8Be says 2 alpha, which is just like what you've got above. For 7Be, it says it does an orbital electron emission, which I don't know about specifically (it's abbreviated 'EC', which always led me to assume it was 'electron capture', rather the opposite), but I would guess from the name that it would have to produce a 7B, but that's such an odd duck it isn't even listed here.

Anyway, though, looking at the net reaction masses... p + 7Li - 2 * 4He (grr, I want subscripts & superscripts! Mass belongs after the symbol) = 0.01863 amu, or 0.232% of original mass converted into energy. p+6Li - 3He - 4He = 0.00446 amu, or 0.0635% of original mass.
So the net reaction is certainly exothermic, though not as much as some of the others.

None of which, of course, really helps clear up whether it's a fusion followed by a fission, or one big transmogrification all at once. :-?

As is so often the case in quantum mechanics, the answer to your question is likely to be "yes". :)

Drakheim
2004-Mar-11, 09:53 PM
Thank you all for the info that you provided... It was quite helpful in swaying a few people over at GLP away from Nancy's side, but alas...

Now she is claiming


We say PX is a brown dwarf because you humans do not have the scientific capability to understand its true form.

So it went from being a Brown Dwarf, to a Planet, to a Brown Dwarf that doubles as a planet... to something we cannot understand. #-o

** goes to look for some other way to help paint her further into the corner. **

Rc2000
2004-Mar-12, 04:01 AM
Whatever you throw at her, she'll most likely come up with some off the wall metaphysical mess to get out of it or just spout off about human knowledge is incorrect. Or that only the TRUE BELIEVERS can see and understand all that's happening. :roll:

Rc

Drakheim
2004-Mar-12, 01:48 PM
Whatever you throw at her, she'll most likely come up with some off the wall metaphysical mess to get out of it or just spout off about human knowledge is incorrect. Or that only the TRUE BELIEVERS can see and understand all that's happening. :roll:

Rc

** nods ** I gave up on trying to help Nancy see the error of her ways after I read the 1st two sentences of zetatalks homepage.

I'm mainly doing it to try and keep the gullible and "fenced" people from swaying her way. 8)