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  2. MARIAN IS BACK!

MARIAN IS BACK!

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Cheers, all.  I know you missed me… admit it.  Sorry for the sudden abandonment, but hopefully life has returned to normal for me.   I believe I owe Dwight a post about planetary development.  So without further ado:

The most generally accepted theory on planetary development is that they come together through accretion of matter.  That’s when particles “stick together” due to the forces of gravity.  This works for gas giants, also, in that the gas particles come together through gravity, and as the matter builds up, the particles in the center of the mass are compressed closer and closer together.

The formation of planets, and indeed solar systems, is cyclical in nature.  It all starts with a star.

Close Up of Ancient, White Dwarf Stars in the Milky Way Galaxy
Credit:  Hubble/NASA  Ancient white-dwarf stars in the Milky Way
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As a star ages, it burns up its primary fuel source through the nuclear fusion of hydrogen to helium.  Fusion is the joining together of atoms to form “heavier” matter.  This is different from what happens in nuclear fission (as in atomic bombs), where heavier matter is blasted apart.  Okay, as the star ages, it begins to “burn” (fuse) the heavier fuel; helium to carbon to neon to oxygen to silicon to iron (if I remember the sequence correctly).  This is the process by which all the elements are created, in the burning furnace of stars.

At the end of a star’s life, it will blow off the elements in many spectacular ways, creating a “cloud” of matter, sometimes several hundred light years across.
A Giant Hubble Mosaic of the Crab Nebula
Hubble/NASA  Crab Nebula Supernova remnant
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This is believed to be the most powerful, catastrophic event in nature.  What can compete with the complete destruction of a star?  The shock-wave of a supernova, besides throwing out all the elements needed for absolutely everything else, also triggers the birth of new stars.

We’ll save stellar evolution for another post.  Just trust me here, they do form.  Once the forming star reaches the point of stellar ignition (which must be absolutely spectacular to watch), the shock of ignition blows matter out away from it, forming the spatial relationship of and within the protoplanetary disc, or proplyd, which is all the matter left over.  The matter begins to clump together.

Lather; rinse; repeat.
File:M42proplyds.jpg
Hubble/NASA (of course) Orion Nebula showing M42 Proplyds
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Now, why are they arranged the way they are?  Why didn’t Jupiter form where Mercury is located?  That’s easy…

It couldn’t.

No way.  It would have been blown apart by the stellar wind before it ever got massive enough to hold its gasses together.  We now know that hot Jupiters are there because they spiral inward toward the sun after they have already become so massive as to withstand the force of the solar wind.  Some of them can even hold on to their atmospheres, at least for a while, but they’re being blown off at an enormous rate.  Just think a moment about how powerful a star really is.  Don’t think so?  You go stand outside for a few hours in the summer without protection, then come explain to me how you didn’t just get partially cooked by something burning over 93 million miles away from you.

Planets don’t actually form as “twins”, they just seem so similar because of their location.  We don’t sit next to a gas giant because it couldn’t have formed, and by the time one gets to this location, we’ll be long gone.

And I don’t want anyone to come up with a rocky core to a gas giant.  That’s not a gas giant.  That’s a small rocky planet with a very thick atmosphere.

Thanks for the fun, Dwight.

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  1. Astronomy
  2. MARIAN IS BACK!