Solution: Planetary Physics with Enums

public class PlanetarySystem {
    public enum Planet {
        MERCURY(3.303e+23, 2.4397e6),
        EARTH(5.976e+24, 6.37814e6),
        JUPITER(1.9e+27, 7.1492e7);
        private final double mass;   // in kilograms
        private final double radius; // in meters
        // Universal Gravitational Constant
        public static final double G = 6.67300E-11;
        // Constructor
        Planet(double mass, double radius) {
            this.mass = mass;
            this.radius = radius;
        }
        // Calculate surface gravity (g)
        public double surfaceGravity() {
            return (G * mass) / (radius * radius);
        }
        // Calculate weight (Force = mass * g)
        public double surfaceWeight(double otherMass) {
            return otherMass * surfaceGravity();
        }
    }
    public static void main(String[] args) {
        double roverMass = 100.0; // kg
        System.out.println("Rover Mass: " + roverMass + "kg");
        System.out.println();
        for (Planet p : Planet.values()) {
            System.out.println("Weight on " + p + ": " + p.surfaceWeight(roverMass) + " N");
        }
    }
}