So by that they are referring to how much energy is contained in that mass. They could have more easily said 'the energy that is contained in a 700 kilo object'. By that they are referring to the equation E=mc^2 which tells you how much energy is contained in an amount of mass. So from E=mc^2 we can see that 1 kilo has 300,000^2 (300,000 is the speed of light in kilometers per second) joules of energy.
So, if the Voyager is 722 kg, it would represent 6.5 x 10^13 joules of energy? So, it'd be less than 1 nuclear explosion (since I read on a random website that that would be 10^17 joules)?
