1 billion year old system?

[EDG]

I have a fictional system that is just under a billion years old, with a large metal-rich asteroid belt, two big jovian planets, a rocky Mars-like world, and a large icebal in the outermost orbit (no habitable worlds here). The star itself is an evolved A V star, now a K III giant in its Horizontal Branch stage.

What I'm a little stuck on is the amount of debris in the system. I suspect that after 986 million years most of the planet-forming is finished, and all the dust has been long since blown away by the stellar wind. In our own system the Heavy Bombardment stage took up roughly the first 500 million years after formation, right?

So would it be reasonably realistic to say that the system would be fairly stable (gravitationally) and that most of the asteroids and debris in dangerous planet-crossing orbits have either hit planets or been ejected from the system already? Or would there still be a lot of junk flying around? I just don't really have much of a clue what a one billion year old system would be like - data from our own system at that time is a bit sketchy .

[timb]

I have a fictional system that is just under a billion years old, with a large metal-rich asteroid belt, two big jovian planets, a rocky Mars-like world, and a large icebal in the outermost orbit (no habitable worlds here). The star itself is an evolved A V star, now a K III giant in its Horizontal Branch stage.

What I'm a little stuck on is the amount of debris in the system. I suspect that after 986 million years most of the planet-forming is finished, and all the dust has been long since blown away by the stellar wind. In our own system the Heavy Bombardment stage took up roughly the first 500 million years after formation, right?

So would it be reasonably realistic to say that the system would be fairly stable (gravitationally) and that most of the asteroids and debris in dangerous planet-crossing orbits have either hit planets or been ejected from the system already? Or would there still be a lot of junk flying around? I just don't really have much of a clue what a one billion year old system would be like - data from our own system at that time is a bit sketchy .

There are considerably older systems with more dust than the Solar system. A heavy asteroid belt can continue to produce large amounts of dust for a long time, particularly if it is continually "stirred" by a giant planet. In theory there's no time after which a system is guaranteed to be stable, but the chances of catastrophic instability decrease with time. For example, it is hypothesized that the amount of warm dust in the tau Ceti system is due to a relatively recent disturbance of the outer icy debris disk. tau Ceti is considerably older than the Sun.

[Cougar]

In our own system the Heavy Bombardment stage took up roughly the first 500 million years after formation, right?

I think that's about right. And some sort of rudimentary form of life took hold shortly after that. But it took another 3 billion years to go from single-cellular to multi-cellular organisms.

So would it be reasonably realistic to say that the system would be fairly stable (gravitationally) and that most of the asteroids and debris in dangerous planet-crossing orbits have either hit planets or been ejected from the system already? Or would there still be a lot of junk flying around?

Seems perfectly reasonably realistic to me, particularly since that seems to be something like what happened here. Apparently there is a "good" place for an asteroid belt to be so that tidal forces don't turn it into a grinding pepper mill....

[Nowhere Man]

The latest issue of Science News magazine (2 Feb 2009) has an article about the timing and probable sequence of events which lead to the late heavy bombardment. It describes the LHB as taking place between about 3.9 and 3.8 billion years ago. Only about 100-200 million years in duration.

Fred

[EDG]

The latest issue of Science News magazine (2 Feb 2009) has an article about the timing and probable sequence of events which lead to the late heavy bombardment. It describes the LHB as taking place between about 3.9 and 3.8 billion years ago. Only about 100-200 million years in duration.

Fred

Are they still thinking that Uranus and Neptune's formation/migration had something to do with the late heavy bombardment? Last I heard, that might have stirred up some comets and sent them into the inner system.

[EDG]

Seems perfectly reasonably realistic to me, particularly since that seems to be something like what happened here. Apparently there is a "good" place for an asteroid belt to be so that tidal forces don't turn it into a grinding pepper mill....

The belt is between about 0.75 and 1.3 AU from the star. However, since it's always been within the star's habitable zone (even when it was an A V star) I'm figuring that it's mostly going to be metallic and stony asteroids.

Which reminds me... would metallic asteroids form in situ there, or are they "second generation" bodies (i.e. would you form a big asteroid first, which differentiates into a metal core and rocky mantle, and that then gets shattered and the core fragments become metallic asteroids?). I figure the temperature in which the belt was forming was so high (because it's so close to a hot star) that maybe only refractory materials were available to form the asteroids?

[Nowhere Man]

Are they still thinking that Uranus and Neptune's formation/migration had something to do with the late heavy bombardment? Last I heard, that might have stirred up some comets and sent them into the inner system.

That's what the article says. Here is a link. Uranus and Neptune were much closer to the Sun, with Neptune closer in. Jupiter ans Saturn eventually reached a 2:1 resonance, which sent the outer two into a large cloud of debris, sending stuff everywhere and eventually clearing most of the small stuff out. Neptune wandered out beyond Uranus during this period.

How they figured that Uranus and Neptune switched places beats me. But plowing into that debris could explain Uranus's tilt and their oddball satellites.

Fred

[EDG]

Oo, thanks for the link! Very interesting stuff.

[RalofTyr]

What would a 1 billion year old system be like?
I have a fictional system that is just under a billion years old, with a large metal-rich asteroid belt, two big jovian planets, a rocky Mars-like world, and a large icebal in the outermost orbit (no habitable worlds here). The star itself is an evolved A V star, now a K III giant in its Horizontal Branch stage.

What I'm a little stuck on is the amount of debris in the system. I suspect that after 986 million years most of the planet-forming is finished, and all the dust has been long since blown away by the stellar wind. In our own system the Heavy Bombardment stage took up roughly the first 500 million years after formation, right?

So would it be reasonably realistic to say that the system would be fairly stable (gravitationally) and that most of the asteroids and debris in dangerous planet-crossing orbits have either hit planets or been ejected from the system already? Or would there still be a lot of junk flying around? I just don't really have much of a clue what a one billion year old system would be like - data from our own system at that time is a bit sketchy .

What's the mass of your Mar's world? Because Mars was "Earthlike" for about 800MY, if it's a little more massive, it may still be Earth like, but extremely hot due to the red giant. In fact, it may be more Venus like than Mars like.

There's be a lot more junk in the system. First, there's a massive amount of material that gets quickly absorbed or ejected, than a gradual winding down of debris. The late heavy bombardment was an event unique to the solar system and not necessarily standard in system evolution.

Check this system out

http://www.solstation.com/stars/eps-erid.htm

That's what the article says. Here is a link. Uranus and Neptune were much closer to the Sun, with Neptune closer in. Jupiter ans Saturn eventually reached a 2:1 resonance, which sent the outer two into a large cloud of debris, sending stuff everywhere and eventually clearing most of the small stuff out. Neptune wandered out beyond Uranus during this period.

How they figured that Uranus and Neptune switched places beats me. But plowing into that debris could explain Uranus's tilt and their oddball satellites.

Fred

Just who big was the object that his Uranus that tilted it? Could it have been another gas giant?

[Nowhere Man]

Who knows? It may have taken several collisions. We have no evidence for exactly what the solar system looked like back then. This model is, I presume, based on observations of other developing planetary systems.

Granted our observations are still from a great distance, so there is a lot of guesswork here. The original paper should spell out the assumptions that were made.

Fred

[EDG]

Generally speaking though, I think it's fair to say that most of the impacts (especially planet-smashing ones) would have been over and done with after a billion years. The surface environments of any rocky worlds may have to deal with somewhat more frequent impacts than Earth today, but they're not going to be big enough or frequent enough to wipe the slate clean so to speak.

[EDG]

Hm, run into a slight problem - the asteroid belt that's close to the star (0.8-1.3 AU) is going to be suffering when the star is in its RGB phase. In this era, the black body temperature at that distance is between 1000-1500K - hot enough to melt rock! Does that mean the asteroids will literally evaporate away (there's no way they'd be big enough to hold onto rock vapour is there?). Or will their surfaces just melt and they'll become smooth, rounded balls of rock and iron?

[RalofTyr]

Hm, run into a slight problem - the asteroid belt that's close to the star (0.8-1.3 AU) is going to be suffering when the star is in its RGB phase. In this era, the black body temperature at that distance is between 1000-1500K - hot enough to melt rock! Does that mean the asteroids will literally evaporate away (there's no way they'd be big enough to hold onto rock vapour is there?). Or will their surfaces just melt and they'll become smooth, rounded balls of rock and iron?

The smaller asteroids, yes. The larger ones, perhaps the ones large enough with enough gravity to be spherical, will have a molten surface.


Also, a Late Heavy Bombardment can happen at any time. Tau Ceti is close ten billion years old and it has a large disk of cometary material. If it came close enough to another system that disturbed that belt, it would cause massive bombardments.

Perhaps that's what happened to our large cometary belt. The LHB took care of that.