How Special Is the Solar System?

TL;DR

This paper investigates whether the solar system is unique by comparing it to exoplanetary systems, highlighting its lack of super-Earths and close-in planets, and discussing implications for life's emergence.

Contribution

It identifies key features that distinguish the solar system from other systems and analyzes their implications for planetary formation and the emergence of life.

Findings

Solar system lacks super-Earths and close-in planets.

Models suggest formation and evolution differences impact habitability.

Reevaluation of the rarity of intelligent civilizations.

Abstract

Given the fact that Earth is so far the only place in the Milky Way galaxy known to harbor life, the question arises of whether the solar system is in any way special. To address this question, I compare the solar system to the many recently discovered exoplanetary systems. I identify two main features that appear to distinguish the solar system from the majority of other systems: (i) the lack of super-Earths, (ii) the absence of close-in planets. I examine models for the formation of super-Earths, as well as models for the evolution of asteroid belts, the rate of asteroid impacts on Earth, and of snow lines, all of which may have some implications for the emergence and evolution of life on a terrestrial planet. Finally, I revisit an argument by Brandon Carter on the rarity of intelligent civilizations, and I review a few of the criticisms of this argument.