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Samarasinha Nalin H. Mueller Béatrice E. a. Belton Michael J. S. 《Earth, Moon, and Planets》1997,77(3):189-198
We present constraints on the spin state of comet Hale-Bopp based on coma morphology. Three cases of rotational states are
compatible with near perihelion observations: (1) principal-axis rotation, (2) complex rotational state with a small precessional
angle, or (3) complex rotational state with a large ratio between the component periods. For principal axis rotators, images
from 1996 (pre-perihelion) are consistent with a rotational angular momentum vector, M, directed at ecliptic longitude and
latitude (250°, -5°) while images from late 1997 (post-perihelion) indicate (310°, -40°). This may suggest a change in M.
A complex rotational state with small precessional angle requires only a small or no change in M over the active orbital arc.
In this case, M is directed near ecliptic longitude and latitude (270°, -20°). A rotationally excited nucleus with a large
ratio between component periods requires the nucleus to be nearly spherical. The transformation of dust coma morphology from
near-radial jets to bright arcs and then again to near-radial jets is interpreted as a heliocentric and geocentric distance
dependent evolutionary sequence. The spiral structures seen in CN filters near perihelion (in contrast to sunward side arcs
seen in continuum) can be explained if the precursor of CN molecules (likely sub-micron grains) are emitted from the nucleus
at low levels (≈ 10% of the peak daytime emission) during the nighttime. This may be indicative of a nucleus with a CO-rich
active area(s).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献