The Search for Remnant Cometary Activity in Near - Planetesimals

Details The Search for Remnant Cometary Activity in Near - Planetesimals The Search for Remnant Cometary Activity in Near - Planetesimals

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995phdt........30c&link_type=abstract

Thesis (PH.D.)--UNIVERSITY OF CALIFORNIA, SAN DIEGO, 1995.Source: Dissertation Abstracts International, Volume: 57-02, Section:

Physics

Asteroids

Scientific paper

Among the near-Earth asteroids (NEAs), it is suspected extinct comets may be masquerading as asteroids. Although many short-period comets approach and even cross the Earth's orbit, they populate an orbital region not common with the NEAs. Comet P/Encke is an exception because its orbit is quite similar to the NEAs. A dynamical model developed by Wetherill (1991) describes a plausible evolutionary path for P/Encke and predicts that physical lifetimes of such comets are significantly shorter than their dynamical lifetimes. The implication of his model is that there may be a significant number of extinct comets among the NEAs. To further substantiate this model and investigate evidence that 2201 Oljato and 3200 Phaethon may be weakly -active cometary remnants, observations are made to search for the CN(Delta v=0) band emission at 3880 A. Prior to these observations, comet P/Wilson -Harrington (1949 III) was discovered to be the same object as asteroid 4015 1979 VA. No CN emission feature is detected within 3-sigma for any of these near-Earth objects (NEOs) including 4015 Wilson-Harrington. A Haser model is used to determine the CN production-rate (Q_ {rm CN}) corresponding to 3-sigma CN band-flux upper limits. CN production-rates are < 5 times 10^{22 } molcdot s^{-1} for 4015 Wilson-Harrington, <2 times 1023 molcdot s^{-1} for 2201 Oljato, and <2 times 1023 molcdot s^ {-1} for 3200 Phaethon. These production rates are lower (by as much as an order of magnitude) than those observed in low-activity comets. Upper limits on Q_{rm CN} for 2201 Oljato are an order of magnitude lower than those previously determined. Active surface areas required to produce derived upper limits on Q_{rm CN}, <0.02% for 4015 Wilson-Harrington and < 0.01% for 3200Phaethon, are lower than those derived for most active comets. However, 2201 Oljato's active area, <0.2%, is within the lower end of the active comet range. It is argued that the lack of CN detection is not a conclusive result because a highly evolved comet may be dormant over a significant number of perihelion passages. Finally, I suggest that observations similar to these should be made in the future with the immediate goal of detecting remnant cometary activity and the ancillary goal of finding an observable signature unique to extinct comet nuclei.

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