nicolasknight t1_ixzvuw7 wrote on November 27, 2022 at 6:17 PM

Not the size but the size and at a certain distance.

The planets are formed when the accretion disk that forms around a star starts the come together.

It's mostly random how it starts but anything 2m from the corona for example will immediately get torn apart both by coronal mass emissions and by gravity.

This pushes out all the smaller planets further out.

Once you get past that point you get to where they will get sand blasted by emissions but not torn apart by gravity.

You can't have gas giants at those distances because their atmospheres will get blasted off.

Smaller planets will form but still lose mass if the sun is big enough.

Once you get far enough from that the size of the planets becomes truly random.

We think with current science that if you don't get gas giants on the outer perimeter you may not get a ton of smaller planets on the inner perimeter because of comets etc... not being blocked but that's still highly theoretical.

A bigger sun would theoretically also attract more objects therefore either have commensurate gas giants which would have increased odds of becoming binary systems if they get big enough OR have smaller planets but only for short periods of time.

dukesdj t1_iy1f42g wrote on November 28, 2022 at 12:35 AM

> It's mostly random how it starts but anything 2m from the corona for example will immediately get torn apart both by coronal mass emissions and by gravity.

It is mostly the stellar wind that results in a pushing of the protoplanetary disc from the host star not magnetic realignment events. More massive stars are hotter and have a stronger wind and hence will mean the minimum distance for planet formation will be further from the star than for a lower mass star. This is not really a random effect as the strength of the wind is a function of the stellar luminosity which in turn is a function of the stellar mass. This inner region where there is no disc is well outside the Roche limit for gravity to cause tidal disruption of a planet during the formation stage.

> You can't have gas giants at those distances because their atmospheres will get blasted off.

This is actually still debated. In-situ formation of Hot Jupiters is not actually conclusively excluded. Indeed, we have observations that are difficult for migration pathways to explain. See Dawson and Johnson 2018 for a good review of Hot Jupiter formation pathways.

> Once you get far enough from that the size of the planets becomes truly random.

I would disagree with this too. The formation of planet mass is not truly random and is determined to first order by the disc density distribution. You simply will not get massive planets forming in regions of low density.

> We think with current science that if you don't get gas giants on the outer perimeter you may not get a ton of smaller planets on the inner perimeter because of comets etc... not being blocked but that's still highly theoretical.

If this is suggesting that gas giants block comets or debris from the outer regions of the system then this too is incorrect. Giant planets cause as much stuff to come into the inner system as they do attract them into their own mass.