How do you measure a comet's weight?

Scientists have calculated that the comet at the centre of the Rosetta mission weighs 10 trillion kilograms.

How the figure was worked out seems almost as amazing as the fact we spent a decade chasing the comet 67P/Churyumov-Gerasimenko in the first place.

Onboard kit is sending back a flood of data about the comet to a team of scientists on the ground.