What is the best way to store data about a GameObject?

I am new to unity, but not new to programming. In other languages, I would do something like this to store data about an object:

 class Earth extends Planet {
     private float defenseValue = 100;
 
     public setDefenseValue(float value) {
         this.defenseValue = value;
     }
 
     public getDefenseValue() {
         return this.defenseValue;
     }
 }

But I don't see much in the way of classes like this in Unity. I am probably missing something, but I wanted to be sure. Aside from creating a new script and attaching it to the object with public variables, is there a way to make a class like above and attach it to a game object?

I hope I made sense. Thanks in advance!