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dukesdj t1_iy1h5p6 wrote

Star mass only really effects the probability of a planet of a certain mass being formed.

 

We expect that lower mass objects are more common and so there is no theoretical reason to believe and star has a lower mass limit. At the opposite end of the spectrum, we have observed giant planets around M class stars. So we know that even the lower mass stars can form the more massive planets. With the exception of massive stars, we have observed giant planets around all stellar classifications of type A (from memory) or lower mass. However, we do not expect the most massive stars to have any real difference in the mass of planets that can form around them. The reason we do not observe them is simply because it is harder (the stars are very bright and the planets would need to have wider long period orbits). So we expect that all stars can host planets covering the full spectrum of planetary masses (up to 14 Jupiter masses where the classification of brown dwarf begins). What will be affected is the occurrence rate of certain planetary masses as a function of the stellar mass (for example we expect to see less giant planets around low mass stars, although metalicity also seems to play a role).

 

There is a slight caveat to this which is when one considers the grey area of brown dwarfs. Currently, despite what the IAU says, we are not sure if brown dwarfs should be classified as stars, planets, or something separate. At the heart of this issue is the fact that brown dwarfs can form through planetary formation pathways as well as stellar formation pathways (Jeans instability of an interstellar cloud). In particular, gravitational instability of the protoplanetary disc is a planetary formation pathway which can lead to the formation of the most massive brown dwarfs. The requirement for gravitational instability is that the disc is massive which would only be expected around the most massive stars. So if we define brown dwarfs as planets if they follow a planetary formation pathway, then the most massive planets could only form around massive stars.

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nicolasknight t1_ixzvuw7 wrote

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.

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dukesdj t1_iy1f42g wrote

> 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.

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