Erosion Model for the Sungrazing Comets Observed with the Solar and Heliospheric Observatory

Abstract

The objectives of this study are to model and interpret quantitatively the brightness variations of 27 Solar and Heliospheric Observatory (SOHO) sungrazers. The light curves, published by Uzzo et al. and by Biesecker et al., are shown to provide information on a proposed erosion process, which consists of continuous, progressive bulk fragmentation and sublimation of these minicomets on their approach to the Sun. The erosion rate and the time of peak signal are determined primarily by an effective latent energy of erosion (analogous to a sublimation heat), which is found to have a bimodal distribution with sharp peaks near 34,000-35,000 and 40,000-41,000 cal mol À1 for the main components of the 27 objects. Their derived initial diameters are between 17 and 200 m. With the given range of erosion energies, a sungrazer that is to survive its return to the Sun needs to be more than 1-1.4 km in diameter, depending on its perihelion distance. The shape of the light curves at heliocentric distances smaller than 7 R is interpreted to indicate the existence of fairly sizable, but unresolved, close companions, which appear to have split off from their parent bodies shortly before, if not during, observation. All subfragments that survived longer than the main components had erosion energies significantly higher than the average, between 45,000 and nearly 90,000 cal mol À1. There is also evidence for subfragments with erosion energies lower than 34,000 cal mol À1. Because the erosion process is believed to be dominated by continual fragmentation, the existence of such subfragments should not be surprising. The brightness of the SOHO sungrazers at peak signal is mass diagnostic, and their cumulative distribution varies inversely as the initial mass to a power of 0.56-0.68. Thus, much of the total mass is still locked in the most massive fragments, and the Kreutz system is apparently in an early phase of its evolution.