[chris (OP)]

Donald is wondering:

Most solar systems have two suns. How much larger would Jupiter have to be to begin nucleosynthesis? Would this size change the orbit of the earth? And how big would Jupiter have to get before it would eject the earth from the solar system. No, I am not planning anything, nothing to see here, nothing suspicious at all!

What do you think?

[puppypower]

Donald is wondering:

Most solar systems have two suns. How much larger would Jupiter have to be to begin nucleosynthesis? Would this size change the orbit of the earth? And how big would Jupiter have to get before it would eject the earth from the solar system. No, I am not planning anything, nothing to see here, nothing suspicious at all!

What do you think?

There is a wild card that is not often considered. Under the extremes pressures of Jupiters core, hydrogen and water both become metallic solids. As metals, the properties of hydrogen and water change allowing them to conduct electricity like metals. What that potentially means is, Jupiter's core can conceptually induced currents, through this metallic medium. If you can get enough volts, you can generate limited local nuclear synthesis.

Research at one of the National laboratories in the USA, have shown that metallic water can be generated at lower pressures and temperatures than originally thought. In fact, the core the earth has conditions sufficient to generate metallic water. Such water could be form an amalgam with the iron in the core and be a very good conductor of electricity.

Water is well known for its astonishing range of unusual properties, and now Thomas Mattsson and Michael Desjarlais of Sandia National Laboratories in New Mexico have suggested yet another one. They found that water should have a metallic phase at temperatures of 4000 K and pressures of 100 Gpa, which are a good deal more accessible than earlier calculations had indicated.

The core of earth exists at about 5700K snd about 360 Gpa.

[evan_au]

how big would Jupiter have to get before it would eject the earth from the solar system?

It is quite large enough already - and may have already ejected planets from the Solar System.

Astronomers were surprised at the number of "Hot Jupiters" seen in orbit around other stars - gas giants like Jupiter that were in close orbit around their star; current theories suggest they should have formed much farther from their parent star.

One way they could have reached their current position is by ejecting inner planets from their planetary system, losing angular momentum and moving inwards and then ejecting the next one, etc.

Perhaps it is the presence of the asteroid belt that has prevented Jupiter from ejecting Mars and then Earth?
But it could still happen - on long timescales (hundreds of millions of years), the solar system orbits could become chaotic, and eject more planets.

How much larger would Jupiter have to be to begin nucleosynthesis?

Fusion of ordinary Hydrogen requires a mass of around 70 times the mass of Jupiter.
The matter from which stars condensed has tiny concentrations of Deuterium, and it is thought that planets as small as 13 times the mass of Jupiter could produce a small amount of energy from Deuterium fusion - a "Brown Dwarf".
To become a red dwarf star, a planet would need to be at least 70 times the mass of Jupiter.
See: https://en.wikipedia.org/wiki/Brown_dwarf

larger

It is interesting that as the mass of a Jupiter-sized planet grows to become a brown dwarf, it does not get significantly larger.
The extra mass causes a stronger surface gravity, which crushes all the extra gas into basically the same volume.

Jupiter has a diameter of 143,000km, while Proxima Centauri (a red dwarf which has the distinction of being the closest star to the Sun) has a diameter of only 200,000km. So it's not much larger physically, even though the mass is 100 times greater.

See: https://en.wikipedia.org/wiki/Brown_dwarf#Low-mass_brown_dwarfs_versus_high-mass_planets
 

Would this size change the orbit of the earth?

The Solar system is relatively stable because the Sun is the dominant gravitational attraction. Jupiter has only 0.1% the mass of the Sun.

If Jupiter were 100 times larger (10% the mass of the Sun), only planets that are very close to the Sun or moons that were very close to Jupiter would have stable orbits. Other planets would have unstable orbits and would be thrown out of the system, or crash into one of the larger bodies.

[chris (OP)]

This is slightly off-topic but it's an interesting relevant observation, published in 2009, about the behaviour of Jupiter during its evolution.

This is a transcript of an interview I did with David Minton, who was studying Kirkwood Gaps in the asteroid belt. I regret that I cannot immediately locate the original interview audio (I'll have to poke about a bit), but this is what he said:

Chris Smith: Between Mars and Jupiter is a very large field of orbiting debris, but it contains holes called Kirkwood Gaps where the material that would have sat there has been dislodged by the gravity of giant planets like Jupiter. But when a research duo in the US ran a computer simulation they found more holes than the present theory could account for, and what these empty spaces are actually revealing is how the planets migrated to their present positions when the solar system was very young. Here's David Minton.

David Minton: The asteroid belt is basically a belt of loose debris and rocks that orbits the sun between the orbits of Mars and Jupiter. What it is, is the leftovers of planet formation, it was a region that, because of Jupiter's gravity, was too unstable to form planets so all the stuff that went into making a planet elsewhere in the solar system sort of got kicked out and that's one unstable region and we're sort of left with the debris at a place where planet formation never really got past a certain stage.

Chris Smith: And is all the debris in that region just uniformly scattered through space, or are there hot spots where there's more of it and cold spots where there's less of it?

David Minton: In some ways it's almost uniformly scattered but there are these gaps, and these gaps were actually noticed about 150 years ago by a scientist and astronomer named Daniel Kirkwood and since then named the Kirkwood Gaps. And they are specific locations where there is, what is called, a resonance with Jupiter.

For instance, there's a two to one Kirkwood Gap, which is a place where, if you stuck an asteroid there, it would orbit the sun two times exactly for every one time Jupiter orbited, and because of this resonance it's a very unstable orbit and it's a very unstable place so an asteroid doesn't last in that particular place for very long. And so these specific locations, and there are a multiple of them for different resonance locations, get emptied out of asteroids and so there are currently gaps. What we wanted to ask was: how much of the asteroid belt is shaped by the gravity of Jupiter and Saturn?

Chris Smith: So how are you actually doing that?

David Minton: Well it turned out to be a trickier problem than we first imagined, and took a whole lot of computing power because what we ended up doing was we sort of built a computer simulated solar system and in our computer simulation we filled up the asteroid belt region, the sort of region stretching between Mars and Jupiter, with a whole bunch of computer asteroids and then just let it go, let these computer planets orbit the sun and let these computer asteroids orbit and just let the whole belt be shaped by the gravity of the solar system. And after four billion computer years we were left with an asteroid belt that looked a little bit different than the asteroid belt we see today. There are places specifically around some of these gaps, around these Kirkwood Gaps, where the sunward facing side of the Kirkwood Gap had lots of asteroids but the Jupiter-facing side of the Kirkwood Gap seemed to be depleted in asteroids, like there weren't as many there as there could have been.

Chris Smith: So what do you think's going on, how would you explain those missing lumps?

David Minton: Well the explanation that we've come up with is that this is a record of this migration of the giant planets.

Chris Smith: So are you saying then that the planet configurations we see today aren't where the planets formed, they didn't form in that situation, they started somewhere else and they moved and as they moved they effectively made holes in the asteroid belt?

David Minton: Exactly, so the planets formed probably in a tighter configuration, like Jupiter was a little further away from the sun, the other three gas giant planets, Saturn, Uranus and Neptune, when they were first born they were closer to the sun, so all four of these giant planets were in a much closer position to each other than they are now.

And at some point the giant planets began to migrate, and probably due to interactions with a more massive Kuiper belt, which is this icy belt of objects where Pluto lives. And that ancient Kuiper belt actually fuelled this migration and all four of the giant planets started to move from their original location, where they formed, to where find them today. And during that migration, the locations of these resonances in the asteroid belt which sculpts the Kirkwood Gaps, they had themselves also moved and as they moved they tossed asteroids out along the way, and so what we see today in the distribution of asteroids, is almost the footprint of the migration of these planets.

Chris Smith: And is this process, perish the thought, still happening today?

David Minton: No, what happened was that the Kuiper belt which was fuelling all this migration eventually ran out of mass, so the Kuiper belt we have today is like Pluto and Ares and some of these objects that themselves have been causing some controversy, they're sort of the remnants of this ancient more massive disc and there's almost nothing left out there, so there's nothing to fuel the migration of the planets any more. And this migration probably happened over a very short period of time, it was probably very brief. It was probably very violent, you wouldn't have wanted to have been on the earth when this was going on because all these asteroids when they were kicked out of the asteroid belt had to go somewhere, Earth would have been a major target for some of these objects. But that all ended fairly briefly and a very, very long time ago, probably about four billion years ago.

[yor_on]

I definitely think I'm feeling suspicious reading "And how big would Jupiter have to get before it would eject the earth from the solar system. No, I am not planning anything, nothing to see here, nothing suspicious at all!

What do you think?"

Defcon one, anyone?

[Colin2B]

Defcon one, anyone?

Definitely a 4.
Any space under that table?

[yor_on]

sure :)

[puppypower]

Donald is wondering:

How much larger would Jupiter have to be to begin nucleosynthesis?
What do you think?

The question should be how much larger would Jupiter be to begin nucleosynthesis using standard assumptions. There are other assumptions, not mass dependent, which would also allow nucleosynthesis, using much less mass, than standard assumptions. In my last post, I alluded to one such theoretical technique that appears to exist in the earth, which may also exist in surface active planets like Jupiter.

Under the pressure and temperature of the earth's core, water would exist as a exotic metallic phase and have a density about 3-4 times what it does on the surface. As a metal, water could form an amalgam with the iron in the core of the earth. We know the earth has a strong magnetic field, implying moving electric currents, which can easily flow within the highly conducting metallic core, even if it contained metallic water.

In terms of water, if we reduce the pressure and temperature, away from the core conditions; outward to the outer core and lower mantle, water will change phase from being metallic water into being ionic water. These two different phases of water have totally different physical parameters.

What this phase change does is change the highly conducting metallic water of the core, into a nonconducting ionic phase of water. Essentially, the ionic water phase becomes a huge resistor, where currents can't flow to the surface, but are turned into heat. The currents within the core never reach the surface, rather we only observe the magnetic field. Conceptually, this water phase transition, resistor, would turn high energy electric currents, into heat, which could  ignite small scale fusion, using the hydrogen of the ionic water.

One observation that suggests this scenario possible is the observation that the core of the earth spins faster than the surface of the earth. For that to occur and perpetuate, there needs to be a way to limit the friction between the spinning core and the viscoelastic mantle material beyond. Nuclear fusion at the metallic-ionic water phase boundary would create conditions where chemistry breaks down due to the fusion heat. This would eliminate chemical based friction allowing the core to spin faster, for centuries and beyond.

http://www.columbia.edu/cu/record/archives/vol22/vol22_iss1/Core_Spin.html