Context :

Aims : We measure the mass and kinematics of the massive molecular torus in the planetary nebula NGC 6302 .
The nebula is the proto-typical butterfly nebula .
The origin of the wing-like morphology is disputed : determining the mass-loss history of the confining torus is an important step in understanding the formation of this structure .

Methods : We performed submillimeter observations with JCMT and the SMA interferometer .
The continuum emission as well as the J=2–1 and 3–2 transitions of ^ { 12 } CO and ^ { 13 } CO are analysed at arcsecond resolution .

Results : The CO emission indicates a mass of the torus of \sim 2 M _ { \odot } \pm 1 M _ { \odot } .
The ^ { 12 } CO and ^ { 13 } CO emission matches the dark lane seen in absorption in the H { \alpha } image of the object .
The CO torus is expanding with a velocity of \sim 8 km s ^ { -1 } , centred at V _ { lsr } = -31.5 km s ^ { -1 } .
The size and expansion velocity of the torus indicates that the torus was ejected from \sim 7500 yr to 2900 yr ago , with a mass-loss rate of 5 \times 10 ^ { -4 } M _ { \odot } yr ^ { -1 } .
We also see a ballistic component in the CO images with a velocity gradient of 140 km s ^ { -1 } pc ^ { -1 } .

Conclusions : The derived mass-loss history of the torus favours binary interaction as the cause of the ejection of the torus .
We predict the existence of a companion with an orbital period { { { { P \mathrel { \mathchoice { \lower 0.5 pt \vbox { \halign { \cr } $ \displaystyle \hfil < $ \cr$% \displaystyle \hfil \sim$ } } } { \lower 0.5 pt \vbox { \halign { \cr } $ \textstyle \hfil < $ \cr% $ \textstyle \hfil \sim$ } } } { \lower 0.5 pt \vbox { \halign { \cr } $ \scriptstyle \hfil < $ \cr% $ \scriptstyle \hfil \sim$ } } } { \lower 0.5 pt \vbox { \halign { \cr } $ \scriptscriptstyle% \hfil < $ \cr$ \scriptscriptstyle \hfil \sim$ } } } } 1 month .