Our solar system planets migrate toward the sun 4.6 gyr ago?

[neilsox]

Since we have established that some alien planets move toward their sun = migrate, Why do we assume this did not happen in our solar system, about 4.6 billion years ago? Neil

 

[MeteorWayne]

The outer planets have midgrated quite a bit, but the inner planets appear not to have.

I've looked over the wiki article on planetary migration, it summarizes current theories and models quite well.

http://en.wikipedia.org/wiki/Planetary_migration

 

[3488]

Also there was evidence from the Jupiter Galileo Atmospheric entry probe, also suggested that Jupiter has migrated inwards, due to the over abundance of Argon, Neon & Krypton found in the Jovian atmosphere. These elements are easily driven off, hense thay are not expected to be found in the quantities found in Jupiter's atmosphere, if Jupiter formed within 40 AU of the Sun??????

A November 1999 SDC article.

Spaceref article.

Also Uranus & Neptune may have swapped places.

There is no evidence as Wayne says that the inner planets have moved inwards, Mercury to Mars appear to be in the same order as always & more or less at the same distance from the Sun since formation.

Andrew Brown.

 

[roj2003]

I checked the wiki ref but did not really understand the difference between Type I & II migration:-
Type I migration
Terrestrial mass planets drive spiral density waves in the surrounding gas or planetesimal disk. .... This causes the planet to lose angular momentum and the planet then migrates inwards on timescales that are short relative to the million-year lifetime of the disk.
[edit] Type II migration
Planets of more than about 10 Earth masses clear a gap in the disk, ending Type I migration. However, material continues to enter the gap on the timescale of the larger accretion disk, moving the planet and gap inward on the accretion timescale of the disk.

What is this 'timescale of the larger accretion disc', how is material entering the 'gap' (doesn't the protosun/T Tauri clear this or is accretion still running under gravity from the centre? Surely for migration (Type II) to occur, gas density HAS to be high so inflow should be equally 'high'?
Can you explain, please?
roj