Every object in the universe has mass. Mass is determined by the
amount of matter in an object and how much space it takes up or occupies. No matter where an
object is in the universe, its mass will never change. However its weight will always change
with its location in the universe. Every planet or heavenly body has a core that exerts a
gravitational pull on any object on or near its surface.
The weight of an object is determined by the amount of
gravitational pull on an object. This gravity changes in amounts because
of the size or difference in mass of the objects and the distance between objects. The farther
away an object is from the earth's or any planet's surface, the less gravitational force or pull
the earth or planet has on it. For example, if you had two people of equal weight, one at a
mountain top, and one at the foot of that mountain, the person at the top would weigh less
because she is farther away from the earth's surface.
The reason you seem to experience
weightlessness or zero gravity in space is because there is extremely little gravitational pull
being exerted on you by planets or heavenly bodies because you are far enough away from any
planet or heavenly body to not be pulled in or attracted to it.