Gravity is a fundamental force of nature that exists everywhere in the universe. It is a property of mass, and all objects with mass have gravity.

Here's why:

* Newton's Law of Universal Gravitation: This law states that every particle in the universe attracts every other particle with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

* Planets are massive objects: Planets are composed of vast amounts of matter, meaning they have a significant amount of mass.

* Gravity is essential for planet formation: Gravity pulls together gas and dust in space, forming the core of planets.

Even though gravity might seem weaker on smaller celestial bodies like asteroids or comets, it is still present.

So, while the strength of gravity can vary depending on the mass and size of an object, it is impossible for a planet to exist without it.