<p>Whether or not gas giants form is largely to do with whether rocky/icy cores are able to accrete large quantities of hydrogen and helium, which dominate the mass of the protostellar disc. </p>

<p>Terrestrial planets form from the tiny fraction of the disc that is able to form solids.</p>

<p>There is no indication that systems without gas giants have more "solids" and most of the raw material in the disc is either accreted onto the star or expelled from the system in either case.</p>

CC BY-SA 4.0
2019-09-29T09:32:08.287Z
2019-09-29T09:32:08.287Z
ProfRob
<p>So, most of the mass of the solar system (that isn't inside the sun) is inside Jupiter. And most of whats left after THAT is inside Saturn. So, all the rocky planets, moons, and asteroids in our solar system are a tiny minority of the mass. </p>

<p>Now, we're looking at other solar systems for Exoplanets, and mostly finding gas giants. But not every system has one that we can detect- even some of the nearby systems. Which implies that there are plenty of systems without a Gas Giant.</p>

<p>Unless I'm misunderstanding things, the amount of raw material in those systems should be fairly similar to ours. So what, realistically, would those systems have in terms of planets? Without the massive gas giants to suck up all the mass, they'd presumably have lots of smaller objects, right? Massive asteroid belts, large numbers of small planetoids? Are there any models of what those systems are likely to look like?</p>

CC BY-SA 4.0
2019-09-29T00:10:26.007Z
"and mostly finding gas giantsand mostly finding gas giantsand mostly finding gas giants" wrong, only 0.5% of all stars host gas giants. They are a stark minority, most systems dont form them.
AtmosphericPrisonEscape
CC BY-SA 4.0
2019-09-29T01:11:57.993Z
Sorry. When I wrote 'And mostly finding gas giants', I didn't mean 'found gas giants everywhere', I meant 'most of the planets we could see are gas giants (because with our telescopes, those are the easiest to see)'
Doug
CC BY-SA 4.0
2019-09-29T02:45:49.653Z
Bear in mind that most of the mass in gas giants is hydrogen & around 10% helium (by mass). Hydrogen liquifies at around 20 K, and it doesn't solidify without pressure. You can't make asteroids or planetisimals out of that stuff. True, at more reasonable temperatures you can make solid bodies from hydrogen compounds like methane, ammonia, and water, if you have enough carbon, nitrogen, or oxygen to make those compounds.
PM 2Ring
<exoplanet><planetary-formation><proto-planetary-disk>
Exoplanets, Protoplanets, and planetesimals
Doug
# Exoplanets, Protoplanets, and planetesimals

(Asked by: username_0 on 2019-09-28)

So, most of the mass of the solar system (that isn't inside the sun) is inside Jupiter. And most of whats left after THAT is inside Saturn. So, all the rocky planets, moons, and asteroids in our solar system are a tiny minority of the mass.

Now, we're looking at other solar systems for Exoplanets, and mostly finding gas giants. But not every system has one that we can detect- even some of the nearby systems. Which implies that there are plenty of systems without a Gas Giant.

Unless I'm misunderstanding things, the amount of raw material in those systems should be fairly similar to ours. So what, realistically, would those systems have in terms of planets? Without the massive gas giants to suck up all the mass, they'd presumably have lots of smaller objects, right? Massive asteroid belts, large numbers of small planetoids? Are there any models of what those systems are likely to look like?

**Tags:** exoplanet, planetary-formation, proto-planetary-disk

> **Comments:**
> **username_1**: "and mostly finding gas giantsand mostly finding gas giantsand mostly finding gas giants" wrong, only 0.5% of all stars host gas giants. They are a stark minority, most systems dont form them.  
> **username_0**: Sorry. When I wrote 'And mostly finding gas giants', I didn't mean 'found gas giants everywhere', I meant 'most of the planets we could see are gas giants (because with our telescopes, those are the easiest to see)'  
> **username_2**: Bear in mind that most of the mass in gas giants is hydrogen & around 10% helium (by mass). Hydrogen liquifies at around 20 K, and it doesn't solidify without pressure. You can't make asteroids or planetisimals out of that stuff. True, at more reasonable temperatures you can make solid bodies from hydrogen compounds like methane, ammonia, and water, if you have enough carbon, nitrogen, or oxygen to make those compounds.  

---

## 1 answers

### Answer by username_3 on 2019-09-29. Score: 3

Whether or not gas giants form is largely to do with whether rocky/icy cores are able to accrete large quantities of hydrogen and helium, which dominate the mass of the protostellar disc.

Terrestrial planets form from the tiny fraction of the disc that is able to form solids.

There is no indication that systems without gas giants have more "solids" and most of the raw material in the disc is either accreted onto the star or expelled from the system in either case.


---

