Optical and Dynamical Characterization of Comet-Like Main-Belt Asteroid (596) Scheila

TL;DR

This study characterizes the physical and dynamical properties of asteroid (596) Scheila, concluding its comet-like appearance is due to an impact event rather than sublimation, and confirms its stable orbit within the main belt.

Contribution

It provides detailed observational data and dynamical analysis, demonstrating that Scheila's dust features result from an impact, not cometary activity, and confirms its stable main-belt orbit.

Findings

Dust cloud has a scattering cross-section 1.4 times larger than the nucleus.

No significant CN or H2O emission detected, indicating low activity.

Dynamically stable for over 100 million years, likely native to its current location.

Abstract

We present observations and a dynamical analysis of the comet-like main-belt object, (596) Scheila. V-band photometry obtained on UT 2010 December 12 indicates that Scheila's dust cloud has a scattering cross-section ~1.4 times larger than that of the nucleus, corresponding to a dust mass of M_d~3x10^7 kg. V-R color measurements indicate that both the nucleus and dust are redder than the Sun, with no significant color differences between the dust cloud's northern and southern plumes. We also undertake an ultimately unsuccessful search for CN emission, where we find CN and H2O production rates of Q(CN) < 9x10^23 s^-1 and Q(H2O) < 10^27 s^{-1}. Numerical simulations indicate that Scheila is dynamically stable for >100 Myr, suggesting that it is likely native to its current location. We also find that it does not belong to a dynamical asteroid family of any significance. We consider sublimation-driven scenarios that could produce the appearance of multiple plumes of dust emission, but reject them as being physically implausible. Instead, we concur with previous studies that the unusual morphology of Scheila's dust cloud is most simply explained by a single oblique impact, meaning this object is likely not a main-belt comet, but is instead the second disrupted asteroid after P/2010 A2 (LINEAR) to be discovered.