This is my (Squirrel719's) theory of how the solar system looked like 3.5-4.0 BYA:

Planets & Dwarf & Proto-Planets

  • A Hot Jupiter planet - Short-lived hot jupiter planet that was absorbed by the sun
  • Mercury - Earth-Sized hot planet until solar winds blew much of the planet away (Explaining the large core)
  • Venus - Proto-Venus, Plate-Techtonics never formed and water never formed (No carbon recycling) which turned it like it is.
  • Proto Earth - Unable to support life yet, probably was closer to the Sun slightly
  • Theia - Unstablish orbit around 1AU due to Jupiter and Mars.
  • Mars - Smaller due to Jupiter pulling the astroid belt away from Mars. Could have been 2-3 AU.
  • Triton, Calisto, Greymade, IO, Europa, Titan and possibly outer dwarf planets - Proto-Planets in the astroid belt before being captured by Jupiter/Ejected then captured by other outer planets.
  • Jupiter - In a gravitational sync with the sun, fluctuating it's orbit which effects pretty much every other planet.
  • Saturn - Closer to the sun
  • Proto Uranus - A smaller stable gas giant, much closer to the sun
  • Proto Uranus 2 - A smaller unstable gas giant which crashed into Uranus eventually, creating it's huge tilt
  • Planet Nine - Ejected by Jupiter, but then recaptured by the Sun, creating a really far orbit around the sun
  • Neptune - MUCH closer to the sun, pretty much normal.