Emission-band and continuum data were obtained of Comet Halley with a CCD camera system at the Perth Observatory during the post-perihelion phase. The image processing techniques which were applied and which revealed jets in the CN band are described. The jets had a spiral shape due to nucleus rotation at a rate which was not precisely determined. Estimates are made of the FWHM and half-width half-maximum spatial extent of the jets. Possible parent molecules of the CN jets are discussed.

Cyanogen jets in comet Halley

The heavy-ion mass spectrum obtained in the inner coma of comet Halley with the PICCA instrument on the Giotto spacecraft has been examined. Short polymer chains of polyoxymethylene and their decay products are identified as the source for the spectrum with six mass peaks between about 45 and 120 atomic mass units. The properties of polyoxymethylene are consistent with many of the unexpected observations in the coma.

https://science.sciencemag.org/content/sci/237/4815/628.full.pdf

First polymer in space identified in comet Halley

The Giotto spacecraft encountered comet Halley on 14 March 1986, approaching to within ∼600km of the nucleus. Its scientific payload comprised ten hardware experiments: a narrow-angle camera, three mass spectrometers (for neutrals, ions and dust), various dust detectors a photopolarimeter and a set of plasma experiments. All experiments performed well and returned a wealth of new scientific results, of which perhaps the most important was the clear identification of the cometary nucleus.

The Giotto encounter with comet Halley

A preliminary evaluation of the mass 28 amu/e signal observed in the neutral mode of the Giotto neutral gas mass spectrometer (NMS) is presented. At 1000 km from the nucleus we obtain for the CO number density n (CO)/n (H2O)≦0.07. The production rate of CO as a parent molecule directly from the nucleus is thus less than 7% of the H2O production rate. However, CO is also produced from an extended source in the inner coma (R < 20 000 km) and at 20 000 km from the nucleus we obtain for the total equivalent CO production rate 0.05≦Q (CO)/Q (H2O)≦0.15. For N2 an upper limit Q (N2)/Q (H2O)≦0.1 is derived. No parent molecule for the CO could be identified which would be in agreement with the NMS measurements. It is proposed that CO or a very short-lived parent is relased in the coma from cometary dust grains, such as the “CHON” particles.

The CO and N2 abundance in comet P/Halley

Analysis of the data from Giotto’s Dust Impact Detection System experiment (DIDSY) is presented These data represent measurement of the size of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on 1986 March 13/14 First detection occurred at some 287000 km distance from the nucleus on the inbound leg; the majority of the DIDSY subsystems remained operational after closest approach (604 km) yielding the last detection at about 202000 km from the nucleus

The dust distribution within the inner coma of comet P/Halley 1982i: encounter by Giotto's impact detectors.

The density and the mass spectrum of the dust near comet Halley have been measured by the Giotto space probe's dust impact detection system. The dust spectrum obtained at 291,000 km from the comet nucleus show depletion in small and intermediate masses; at about 600 km from the nucleus, however, the dust activity rises and the spectrum is dominated by larger masses. Most of the mass striking Giotto is noted to reside in the few large particles penetrating the dust shield. Momentum balances and energy considerations applied to an observed deceleration suggest that a large mass of the spacecraft was detached by an impact.

Dust density and mass distribution near comet Halley from Giotto observations

The Giotto Dust Impact Detection System (DIDSY) consists of six independent subsystems to register the impact of all particulates of significant mass incident on the probe during the post-perihelion encounter with Comet Halley. Mounted on Giotto's front dust shield, the detectors will determine the mass spectrum of the dust, with a limiting sensitivity of 10 to the minus 17th power f, increasing to the largest grain masses encountered along Giotto's trajectory throught the cometary environment with an ultimate spatial resolution of 70 km. An additional detector is located on the rear shield to monitor dust particles that penetrate the from dust shield. An ambient plasma monitor measures the impact plasma generated by dust and gass impacts on the spacecraft.

R. J. L. Grard

Papers

Dust density and mass distribution near comet Halley from Giotto observations

The Giotto dust impact detection system

A dust impact detection system (Didsy) for the Giotto Halley mission