Planets move in (almost) circular paths around the Sun because gravity keeps pulling them inward while their motion tries to carry them straight ahead, so they end up constantly ā€œfalling aroundā€ the Sun instead of into it. The result is an orbit: a stable, curved path where inward pull and forward motion stay in balance.

Not really a perfect circle

  • Planet paths are actually ellipses , which are slightly stretched circles, with the Sun sitting offā€‘center at one focus.
  • For many planets (like Earth), the ellipse is very close to a circle, so ā€œmoving in a circle around the Sunā€ is a good first approximation.

Gravity as the inward pull

  • The Sun contains about 99.8% of all the mass in the solar system, so its gravity dominates and pulls every planet toward it.
  • That gravitational pull always points roughly toward the Sun and acts as the centripetal force that bends the planetā€™s path into a curve.

Inertia keeps planets from falling in

  • Each planet is moving sideways at enormous speed; its inertia is the tendency to keep going in a straight line at that speed.
  • Gravity keeps tugging the planet inward, but because the planet is always ā€œmissingā€ the Sun due to its sideways motion, it continuously falls around the Sun instead of straight into it.

A common picture is a marble rolling around the inside of a funnel: gravity is like the slope pulling it inward, while the marbleā€™s speed keeps it looping around instead of dropping straight down.

Why the orbit stays stable

  • If a planet were going slower, gravity would win and pull it into a smaller orbit or even into the Sun; if it were going faster, it could escape into a larger orbit or leave the solar system.
  • In the early solar system, planets settled into speeds where their forward motion and the Sunā€™s gravity balanced just right, giving longā€‘lasting orbits that can persist for billions of years.

TL;DR: Gravity pulls planets inward toward the Sun, while their fast sideways motion tries to carry them straight; together these make the planets constantly fall around the Sun in nearly circular paths instead of crashing into it.

Information gathered from public forums or data available on the internet and portrayed here.