Re: Heavy science
The kilogram(kg) is not a measure of weight. The Newton(N) is.
"...yet is presently defined by a weight."
The weight (object) you refer to has a mass of exactly one kilogram, since it is the reference for that. It will still have that same mass, wherever it happens to be.
On Earth's surface, the weight (force of gravity) of a weight (object) with a mass of 1kg will be approximately 9.81N give-or-take depending where and when you measure it.