Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979aj.....84.1894w&link_type=abstract
Astronomical Journal, vol. 84, Dec. 1979, p. 1894-1909.
Astronomy and Astrophysics
Astronomy
47
Astronomical Models, Celestial Mechanics, Comet Nuclei, Light Curve, Oblate Spheroids, Orbits, Precession, Rotating Bodies, Sublimation, Comets, Encke Comet, Spin, Axis, Motion, Sublimation, Lightcurves, Precession, Rotation, Data, Revolutions, Period, Density, Mass, Gradient, Models, Nucleus, Jupiter, Perturbations, Evolution, Parameters, Outgassing, Data Reduction, Comparisons, Momentum, Wobble
Scientific paper
From the observed light curve of P/Encke the jet force from sublimation is calculated both as a (precessing) torque and as a (perturbing) force transverse to the radius vector. An integral iteration is carried out over 59 perihelion passages, 1786-1977, to fit the previously determined nongravitational transverse force and to derive the precession of the spin axis. It is shown that the spin axis turned more than 100 degrees in longitude and almost 30 degrees in latitude from 1786 to 1977, but appears to have been almost fixed in direction for hundreds of revolutions before 1700. It is suggested that ejected meteoroidal debris accumulated on the currently less active hemisphere, insulating it to maintain a low activity level. A tentative rotation period of 6 h 33 min is derived, using Whipple's halo method. The suggested spinup rate is 21 min/century, while the current rate of relative mass loss by sublimation is 0.09% of the comet's mass per revolution. Moreover, the mass of the nucleus is estimated at less than 10 to the 16th grams, and its oblateness at less than 4%.
Sekanina Zdenek
Whipple Fred L.
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