Context : Understanding the formation of collimated outflows is one of the most debated and controversial topics in the study of the late stages of stellar evolution .

Aims : M~2–9 is an outstanding representative of extreme aspherical flows .
It presents unique features such as a pair of high-velocity dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes .
Their study provides important information on the nature of the poorly understood central source of M~2–9 and its nebula .

Methods : Imaging monitoring at sub-arcsec resolution of the evolution of the nebula in the past decade is presented .
Spectroscopic data provide complementary information .

Results : We determine the proper motions of the dusty blobs , which infer a new distance estimate of 1.3 \pm 0.2 kpc , a total nebular size of 0.8 pc , a speed of 147 km s ^ { -1 } , and a kinematical age of 2500 yr .
The corkscrew geometry of the inner rotating pattern is confirmed and quantified .
Different recombination timescales for different ions explain the observed surface brightness distribution .
According to the images taken after 1999 , the pattern rotates with a period of 92 \pm 4 years .
On the other hand , the analysis of images taken between 1952 and 1977 measures a faster angular velocity .
If the phenomenon were related to orbital motion , this would correspond to a modest orbital eccentricity ( e = 0.10 \pm 0.05 ) , and a slightly shorter period ( 86 \pm 5 years ) .
New features have appeared after 2005 on the west side of the lobes and at the base of the pattern .

Conclusions : The geometry and travelling times of the rotating pattern support our previous proposal that the phenomenon is produced by a collimated spray of high velocity particles ( jet ) from the central source , which excites the walls of the inner cavity of M~2–9 , rather than by a ionizing photon beam .
The speed of such a jet would be remarkable : between 11 000 and 16 000 km s ^ { -1 } .
The rotating-jet scenario may explain the formation and excitation of most of the features observed in the inner nebula , with no need for additional mechanisms , winds , or ionization sources .
All properties point to a symbiotic-like interacting binary as the central source of M~2–9 .
The new distance determination implies system parameters that are consistent with this hypothesis .