It was once thought that there was a planet closer to the Sun than Mercury. It was a planet they called Vulcan.
Tilt a Whirl
As a star forms, a protoplanetary disk also forms, out of which the planets coalesce. Since the protoplanetary disk is generally aligned with the equator of the star, the planets form with that same basic orientation. This is what we see in our solar system and in many exoplanetary systems. But not all systems follow this rule.
Pattern Recognition
Looking for patterns in data is useful because such patterns are often caused by a simple underlying principle, but this isn’t always the case. As an example, consider the story of the the Titus-Bode law.
Point of Origin
Because of their gradual evaporation, periodic comets don’t last long on a geologic scale. Over time they will disappear. So it’s generally thought that periodic comets were once non-periodic ones that were perturbed by Jupiter or other planets into a short periodic orbit. Of course that raises the question: from where do the non-periodic comets come?
Close Encounters
Just how stable is the solar system against close encounters with stray planets? Pretty stable, and we can show that with a bit of computational physics.
Connected
The atoms in our body appear in about same relative abundance as they do in the solar system.