The massive expanding molecular torus in the planetary nebula NGC 6302

Aims. We measure the mass and kinematics of the massive molecular torus in the the proto- typical butterfly planetary nebula NGC 6302. Determining the mass- loss history of the source is an important step in understanding the origin and formation of the wing- like morphology. Methods. Using the SMA interferometer we have imaged both the continuum emission and the J = 2 - 1 transitions of (CO)-C-12 and (CO)-C-13 at arcsecond resolution. These data are analysed in combination with observations of both the J = 2 - 1 and J = 3 - 2 transitions of (CO)-C-12 and (CO)-C-13 made with JCMT. Results. The (CO)-C-12 and (CO)-C-13 emission match the dark lane seen in absorption in the Ha image of the object and trace an expanding torus of material. The CO indicates a mass of the torus of similar to 2 M-circle dot +/- 1 M-circle dot. The torus is expanding with a velocity of similar to 8kms(-1), centred at V-1st = - 31.5 km s(-1). The size and expansion velocity of the torus indicates that it was ejected from similar to 7500 yr to 2900 yr ago, with a mass- loss rate of 5 x 10(-4) M-circle dot yr(-1). In addition we detect a ballistic component in the CO images which has 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 and we predict the existence of a companion with an orbital period P <= 1month.