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One of the major puzzles in the study of stellar evolution is the formationprocess of bipolar and multi-polar planetary nebulae. There is growingconsensus that collimated jets create cavities with dense walls in theslowly-expanding (10--20 ~km~s$^{-1}$) envelope ejected in previousevolutionary phases, leading to the observed morphologies. However, thelaunching of the jet and the way it interacts with the circumstellar materialto create such asymmetric morphologies have remained poorly known. Here wepresent for the first time CO emission from the asymptotic giant branch starW43A that traces the whole stream of a jet, from the vicinity of its drivingstellar system out to the regions where it shapes the circumstellar envelope.We found that the jet has a launch velocity of 175~km~s$^{-1}$ and deceleratesto a velocity of 130~km~s$^{-1}$ as it interacts with circumstellar material.The continuum emission reveals a bipolar shell with a compact bright dot in thecentre that pinpoints the location of the driving source of the jet. Thekinematical ages of the jet and the bipolar shell are equal,$\tau$$\sim$60~years, indicating that they were created simultaneously,probably by a common underlying mechanism, and in an extremely short time.These results provide key initial conditions for the theoretical models thataim to explain the formation of bipolar morphologies in the circumstellarenvelopes of low and intermediate mass stars.

Shaping the envelope of the asymptotic giant branch star W43A with a collimated fast jet