A comet model. I. The acceleration of Comet Encke
A new comet model is presented that resolves the chief problems of abnormal cometary motions and accounts for a number of other cometary phenomena. The nucleus is visualized as a conglomerate of ices, such as H,O, NH3, CH4, CO, or CO, (C,N,?), and other possible materials volatile at room temperature, combined in a conglomerate with meteoric materials, all initially at extremely low temperatures (<50 K). Vaporization of the ices by externally applied solar radiation leaves an outer matriz of nonvolatile insulating meteoric material. Quantitative and qualitative study shows that heat transfer through tiiin meteoric layers in a vacuum is chiefly by radiation, that the heat transfer is inversely proportional to the effective number of layers, and that an appreciable time lag in heat transfer can occur for a rotating cometary nucleus. Because of the time lag, such a cometary nucleus rotating in the "forward" sense will emit its vaporized ices with a component toward the antapex of motion. The momentum transfer from the kinetic velocity of the emitted gas will propel the nucleus in the forward sense, reduce the mean motion, and increase the eccentricity of the orbit. Such orbital effects occur for Comet D'Arrest; the mean daily motion of Comet Wolf I also appears to be decreasing. Retrograde rotation can produce an acceleration in mean motion and a decrease in eccentricity, as observed for Comet Encke. If the decelerating force component is taken as its maximum theoretical value, the present observed acceleration in the mean motion of Comet Encke can be produced by a loss of 0.002 of its mass per revolution. The corresponding mass loss for Comet D'Arrest is 0.005. For both comets the observed changes in eccentricity are obtained if the force acts proportionately to the solar energy flux but is cut off at a solar distance of about 2 A.U. A second paper (Part II) soon forthcoming will be concerned with the physical problems of comet structure, loss of meteoric and gaseous material, and correlations with observed meteoric phenomena.
The Astrophysical Journal
- Pub Date:
- March 1950