Answer:
The mass of an object remains same everywhere
Explanation:
The mass of an object is equal to amount of matter contained in it and therefore it remains constant everywhere.
However, it is the weight of an object that varies with the gravity.
Weight of an object 
Where "M" represents the mass of an object in Kg
and "g" represents the acceleration due to gravity in 
Now, if on earth mass of an object is 100 Kg, then its mass on neptune will also be 100 Kg.
But weight of the same object on earth would be

Since gravity of Neptune is
times the gravity of earth, its gravitational constant g would be equal to 
Therefore, weight of this object on Neptune will be equal to 