Physics – Geophysics
Scientific paper
May 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003dps....35.4706w&link_type=abstract
American Astronomical Society, DPS meeting #35, #47.06; Bulletin of the American Astronomical Society, Vol. 35, p.1012
Physics
Geophysics
3
Scientific paper
Both long- and short-period comets have been observed to randomly disrupt (split) during passage through the planetary region. These disruption events range from small fragments separating from the primary nucleus to complete disruption and disintegration of the nucleus. These events do not show any correlation with time from perihelion passage or distance above or below the ecliptic plane (Weissman, A&A 85, 191, 1980). A variety of mechanisms have been proposed to explain disruption events, including: impacts, gas release from volatile pockets, the amorphous-crystalline water ice phase transition, and rotational spin-up. We believe the last mechanism may provide the most plausible explanation for nucleus disruption events. This view is supported by the rotation period versus axial ratio plot of Lowry & Weissman (Icarus, in press, 2003), which shows an apparent lack of nuclei with rotation periods < 5 hours, corresponding to a bulk density lower limit of ˜ 0.6 g cm-3 for strengthless rubble piles. We have investigated this problem using two different methods. First we developed an analytic model of the expected rotational spin-up (and spin-down) of typical cometary nuclei due to asymmetric forces from jetting of volatiles on the nucleus surface. Next, we modeled the spin-up of rubble-pile nuclei with discrete active surface areas, using an N-body code, pkdgrav (Richardson et al., Icarus 143, 45, 2000). The code treats gravity and impacts between particles as hard-sphere interactions with adjustable collisional dissipation. The jets are modeled as an optionally varying force acting on one or more particles. Results will be reported. This work was funded in part by the NASA Planetary Geology & Geophysics and Origins programs.
Bottke William F.
Richardson Chris D.
Weissman Paul R.
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