Mahesh Godavarti

Hi Shubhanan, the gravitational force between Josh and Mars is given by \frac{G m M}{r^2} where m is Josh's mass and M is Mars'.

Essentially, the weight is the force acting on Josh which is the gravitational force. If the mass of Mars increased suddenly then the gravitational force given by \frac{G m M}{r^2} would increase as well. Therefore, the scale will suddenly read higher even though Josh's mass didn't increase at all.