Planets:

* Orbit a star: Planets are celestial bodies that orbit a star.

* Have enough gravity to be round: Planets have enough gravity to pull themselves into a nearly round shape.

* Cleared their orbital neighborhood: Planets have cleared most of the other objects from their orbital path.

* There are eight planets in our Solar System: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Asteroids:

* Smaller than planets: Asteroids are much smaller than planets.

* Rocky or metallic: Asteroids are made up of rock, metal, or both.

* Orbit the Sun: Asteroids orbit the Sun, mostly in a belt between Mars and Jupiter.

* Some are irregularly shaped: Unlike planets, asteroids can have very irregular shapes.

* Can be dangerous: Some asteroids can pose a threat to Earth if they impact our planet.

Similarities:

* Both orbit a star: Both planets and asteroids orbit the Sun.

* Both are part of the solar system: Both are members of our solar system.

Key Difference:

* Gravity and shape: Planets have enough gravity to pull themselves into a round shape, while asteroids are much smaller and have less gravity, resulting in irregular shapes.

Let me know if you'd like to learn more about specific planets or asteroids!