Search Publications
The photodissociation of water in cometary atmospheres
Crovisier, J.
It is now known from laboratory and theoretical works that following water photodissociation, the OH radical is created in excited states of rotation or vibration. This fact was neglected in previous models of water photodissociation in cometary atmospheres. The goal of the present paper is to update these models. The water life time is not change…
Velocity space diffusion of pickup ions from the water group at Comet Halley
Coates, A. J.; Glassmeier, K. -H.; Wilken, B. +2 more
We have studied the diffusion in velocity space of cometary ions using the distributions of ions measured by the implanted ion spectrometer on Giotto during the inbound pass. The measurements were transformed into a frame comoving with the solar wind and oriented with the magnetic field. The observations show the evolution of the pitch angle distr…
Spectral characteristics of low-frequency plasma turbulence upstream of comet P/Halley
Coates, A. J.; Glassmeier, K. -H.; Neubauer, F. M. +4 more
Spectral characteristics of low-frequency plasma turbulence in a cometary environment have been determined using cross-spectral analyses of magnetic field and plasma measurements made on board the Giotto spacecraft upstream of comet P/Halley. Two upstream regions have been identified, where the mean solar wind magnetic field was approximately para…
The nucleus of comet Halley: Surface structure, mean density, gas and dust production
Rickman, H.
The relation between the mass of a cometary nucleus, its gas production curve, the mean outflow velocity, and the nongravitational delay of the comet is discussed, emphasizing the properties of gaseous outflow from comet Halley. The importance of knowledge about the rotational state of the nucleus is stressed, and it is argued that the likely wobb…
Evaluation of cometary dust parameters from numerical simulations: comparison with an analytical approach and the role of anisotropic emissions.
Fulle, M.
A numerical method is developed which models cometary dust tails by means of sample grains. The orbital motion of the grains is rigorously computed, avoiding any Finson-Probstein hypersonic condition and dust shell geometry approximation. The model is applied to the dust tails of Comet Seki-Lines 1962III and Comet Kohoutek 1973XII. The results sho…
The velocity distributions of cometary protons picked up by the solar wind
Balsiger, H.; Neubauer, F. M.; Fuselier, S. A. +3 more
Velocity space distributions of picked up cometary protons were measured by the ion mass spectrometer on the Giotto spacecraft upstream of the Halley bow shock. Large pitch angle anisotropies were observed at all distances >1.2×106 km from the comet. As expected, pitch angle diffusion was much more rapid than energy diffusion. When t…
Analysis of suprathermal electron properties at the magnetic pile-up boundary of comet P/Halley
Anderson, K. A.; Neubauer, F. M.; Rème, H. +10 more
Among the plasma discontinuities detected by the GIOTTO spacecraft around comet P/Halley, the Magnetic Pile-up Boundary, located at about 135,000 km from the nucleus, has a sharpness which was not foreseen by theoretical models. At this boundary, which marks the beginning of the region where the field lines draped around the nucleus have been pile…
Probable detection of organic-dust-borne aromatic C3H3+ ions in the coma of comet Halley
Anderson, K. A.; Reme, H.; Korth, A. +9 more
The heavy-ion analyser PICCA1,2 on the Giotto spacecraft was used to determine the composition and energy distribution of positively charged ions in the coma of comet Halley. Here we argue that the distinct peak observed at mass 39 AMU is due to the aromatic cation C3H3+ (cyclopropenyl). Laboratory mass …
The colour of Comet P/Halley's nucleus and dust
Keller, H. U.; Thomas, N.
Results are presented on the absolute calibration of the Halley Multicolor Camera (HMC), showing that HMC is 24 less sensitive than previously thought. The results are used to determine the reflectivity of the nuclear surface of the P/Halley comet, its color, and the color of the dust within 300 km of the nucleus. Results showed that the nucleus o…
Observations of a shock and a recombination layer at the contact surface of comet Halley
Schwenn, R.; Altwegg, K.; Balsiger, H. +6 more
Observations in the vicinity of the contact surface (ionopause) of comet Halley obtained by the Giotto ion mass spectrometer (IMS) are reported. Two specific events in this region were observed on the inbound pass. Two seconds before the contact surface was encountered, a burst of energized ions (about 20 eV, much greater than thermal energies) wa…