Search Publications
Comet P/Halley's nucleus and its activity
Keller, H. U.; Reitsema, H. J.; Delamere, W. A. +2 more
The Halley Multicolour Camera on board ESA's Giotto spacecraft observed the nucleus of comet P/Halley and its environment and returned more than 2000 images. The observations are summarized, their calibration is described, the status of the analysis and the results are discussed. Topographic features on the nuclear surface and areas of activity ar…
To CO and N2 Abundance in Comet p/ Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D. +8 more
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 the authors obtain for the CO number density n(CO)/n(H2O) ≤ 0.07. The production rate of CO as parent molecule directly from the nucleus is thus less than 7% of the…
The dust distribution within the inner coma of comet P/Halley 1982i - Encounter by Giotto's impact detectors
Zarnecki, J. C.; Wallis, M. K.; Sekanina, Z. +12 more
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 287,000 km distance from the nucleus on the inb…
Electron impact ionization in the vicinity of comets
Gombosi, T. I.; Cravens, T. E.; Kozyra, J. U. +2 more
The solar wind interacts very strongly with the extensive cometary coma, and the various interaction processes are initiated by the ionization of cometary neutrals. The main ionization mechanism far outside the cometary bow shock is photoionization by solar extreme ultraviolet radiation. Electron distributions measured in the vicinity of comets Ha…
First Polymer in Space Identified in Comet Halley
Huebner, W. F.
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 polyoxymethyle…
The relationship of active comets, ``extinct'' comets, and dark asteroids
Cruikshank, D. P.; Tholen, D. J.; Hartmann, W. K.
Spectrophotometric data on groups of asteroids in different types of orbits reveal different distributions of spectral properties, depending on whether the orbits are cometary or noncometary. In a list of 10 asteroids frequently suggested on purely dynamical grounds to be extinct or dormant comets, all have properties suggestive of spectral classe…
Evidence for methane and ammonia in the coma of comet P/Halley
Ip, W. -H.; Allen, M.; Yung, Y. +2 more
Methane and ammonia abundances in the coma of Halley are derived from Giotto IMS data using an Eulerian model of chemical and physical processes inside the contact surface to simulate Giotto HIS ion mass spectral data for mass-to-charge ratios (m/q) from 15 to 19. The ratio (m/q) = 19/18 as a function of distance from the nucleus is not reproduced…
On the Evolution and Activity of Cometary Nuclei
Bar-Nun, A.; Prialnik, D.
The thermal evolution of a spherical cometary nucleus (initial radius of 2.5 km), composed initially of very cold amorphous ice and moving in comet Halley's orbit, is simulated numerically for 280 revolutions. It is found that the phase transition from amorphous to crystalline ice constitutes a major internal heat source. This transition does not …
Expansion Velocity and Temperatures of Gas and Ions Measured in the Coma of Comet p/ Halley
Berthelier, J. J.; Eberhardt, P.; Krankowsky, D. +9 more
In situ measurements of flow velocity and temperature in the inner coma were obtained from ram energy spectra of molecules and ions observed by the NMS experiment onboard the Giotto probe to comet Halley. Radial flow speed was (800 ± 50) m s-1 at distances from the nucleus between 1000km and 4000 km. Whereas ions became stagnant just ou…
Giotto magnetic-field results on the boundaries of the pile-up region and the magnetic cavity
Neubauer, F. M.
Data from Giotto's magnetometer collected during the encounter at Comet Halley on March 13/14, 1986, were used to investigate the most conspicuous boundaries in the inner plasma region surronding Comet Halley, i.e., the pile-up boundary and the ionopause. The normal vectors at the boundary crossings were determined using the minimum variance techn…