Dust counter and mass analyser (DUCMA) measurements of comet Halley's coma from Vega spacecraft

The Vega encounters with comet Halley allowed the first direct measurements of the spatial and temporal distributions of the masses and fluxes of dust particles originating from the comet nucleus. These data are fundamental for establishing the physical processes of dust emission from the nucleus, their propagation to form a coma, and the behaviour of dust jets. The measurements reported here were made with instruments employing a new principle of dust detection^1,2, which have a high time-resolution (~4µs) over a large range of dust fluxes and masses. The dust coma, whether quiescent (as seen by Vega 2) or containing a major jet structure (as seen by Vega 1), displays large, short-term variations throughout, which are at times quasi-periodic. The integral mass spectra increase in intensity to the lowest masses measured (contrary to some theoretical models), and the flux levels lie approximately in the ranges estimated previously from ground-based observations⁶. The coma is highly dynamical on all spatial and temporal scales, suggesting a complex structure of localized regions of dust emission from the nucleus.