system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Perfect silicon spheres were developed to redefine the kilogram because the platinum kilogram was changing in weight even in extremely strictly controlled physical conditions. If dust can ruin the platinum kilogram, why are people allowed to touch the silicon version?

How is it that the sphere doesn't become 'contaminated' with extra atoms from skin, clothes or even breath? Or is it just that these contaminants are very easy to clean off afterwards?
gpt
Not sure about silicon spheres, but the kilogram is now defined in terms of fundamental constants rather than a lump of something.

The definition is in terms of the Planck constant, the speed of light and the atomic transition frequency.

A lump of something is simpler, but as you note, is prone to changing over time.