Terrestrial planets: Definition & facts about the inner planets and beyond

I note this in the article, "In our solar system, there are four terrestrial planets, which also happen to be the four closest to the sun: Mercury, Venus, Earth and Mars. During the formation of the solar system, there were likely more terrestrial planetoids, but they either merged with each other or were destroyed."

This is a condition that develops from the many different computer simulations over the years for assembling the terrestrial planets using accretion processes, theoretical calculations. See this discussion on the forums, much has changed over the years since the 1977 MMSN was published. https://forums.space.com/threads/the-sun-used-to-have-rings-like-saturn.53464/

By comparing the TRAPPIST-1 system to the 4 terrestrial planets in our solar system orbiting a one solar mass star vs. 0.08 solar mass red dwarf with 7 exoplanets orbiting much closer than where Mercury is today around the Sun, points to some very real differences that took place during their origins.
 

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