Context : Comet 17P/Holmes underwent a dramatic outburst in October 2007 , caused by the sudden fragmentation of its nucleus and the production of a large quantity of grains scattering sunlight .

Aims : We report on 90 GHz continuum observations carried out with the IRAM Plateau de Bure interferometer on 27.1 and 28.2 October 2007 UT , i.e. , 4–5 days after the outburst .
These observations probed the thermal radiation of large dust particles , and therefore provide the best constraints on the mass in the ejecta debris .

Methods : The thermal emission of the debris was modelled and coupled to a time-dependent description of their expansion after the outburst .
The analysis was performed in the Fourier plane .
Visibilities were computed for the two observing dates and compared to the data to measure their velocity and mass .
Optical data and 250-GHz continuum measurements published in the literature were used to further constrain the dust kinematics and size distribution .

Results : Two distinct dust components in terms of kinematic properties are identified in the data .
The large-velocity component , with typical velocities V _ { 0 } of 50–100 m s ^ { -1 } for 1 mm particles , displays a steep size distribution with a size index estimated to q = –3.7 ( \pm 0.1 ) , assuming a minimum grain size of 0.1 \mu m. It corresponds to the fast expanding shell observed in optical images .
The slowly-moving ” core ” component ( V _ { 0 } = 7–9 m s ^ { -1 } ) detected near the nucleus has a size index |q| < 3.4 and contains a higher proportion of large particles than the shell .
The dust mass in the core is in the range 0.1–1 that of the shell .
Using optical constants pertaining to porous grains ( 50 % porosity ) made of astronomical silicates mixed with water ice ( 48 % in mass ) , the total dust mass M _ { dust } injected by the outburst is estimated to 4–14 \times 10 ^ { 11 } kg , corresponding to 3–9 % the nucleus mass .

Conclusions :