Limits on the size and orbit distribution of main belt comets

October 2011 • 2011Icar..215..534S

Authors • Sonnett, Sarah • Kleyna, Jan • Jedicke, Robert • Masiero, Joseph

Abstract • The first of a new class of objects now known as main belt comets (MBCs) or "activated asteroids" was identified in 1996. The seven known members of this class have orbital characteristics of main belt asteroids yet exhibit dust ejection like comets. In order to constrain their physical and orbital properties we searched the Thousand Asteroid Light Curve Survey (TALCS; Masiero, J.R., Jedicke, R., Durech, J., Gwyn, S., Denneau, L., Larsen, J. [2009]. Icarus 204, 145-171) for additional candidates using two diagnostics: tail and coma detection. This was the most sensitive MBC survey effort to date, extending the search from MBCs with H ∼ 18 ( D ∼ 1 km) to MBCs as small as H ∼ 21 ( D ∼ 150 m). We fit each of the 924 objects detected by TALCS to a PSF model incorporating both a coma and nuclear component to measure the fractional contribution of the coma to the total surface brightness. We determined the significance of the coma detection using the same algorithm on a sample of null detections of comparable magnitude and rate of motion. We did not identify any MBC candidates with this technique to a sensitivity limit on the order of cometary mass loss rate of about 0.1 kg/s. Our tail detection algorithm relied on identifying statistically significant flux in a segmented annulus around the candidate object. We show that the technique can detect tail activity throughout the asteroid belt to the level of the currently known MBCs. Although we did not identify any MBC candidates with this technique, we find a statistically significant detection of faint activity in the entire ensemble of TALCS asteroids. This suggests that many main belt asteroids are active at very low levels. Our null detection of MBCs allows us to set 90% upper confidence limits on the number distribution of MBCs as a function of absolute magnitude, semi-major axis, eccentricity, and inclination. There are ≲400,000 MBCs in the main belt brighter than H_V = 21 (∼150-m in diameter) and the MBC:MBA ratio is ≲1:400. We further comment on the ability of observations to meaningfully constrain the snow line's location. Under some reasonable and simple assumptions we claim 85% confidence that the contemporary snow line lies beyond 2.5 AU.

Links

• PREPRINT http://arxiv.org/abs/1108.3095
• ELECTR https://doi.org/10.1016%2Fj.icarus.2011.08.001