New Active Asteroid 313P/Gibbs

TL;DR

This paper reports initial observations of active asteroid 313P/Gibbs, revealing continuous dust ejection likely caused by ice sublimation, with no evidence of impact or secondary nuclei, indicating the presence of ice in the outer asteroid belt.

Contribution

First detailed characterization of 313P/Gibbs showing dust ejection driven by sublimation, supporting the presence of ice in outer asteroid belt objects.

Findings

Mass-loss rate of 0.2 to 0.4 kg/s

Dominance of large dust particles (~50-100 μm)

No gas detected, but dust emission suggests sublimation

Abstract

We present initial observations of the newly-discovered active asteroid 313P/Gibbs (formerly P/2014 S4), taken to characterize its nucleus and comet-like activity. The central object has a radius $\sim$0.5 km (geometric albedo 0.05 assumed). We find no evidence for secondary nuclei and set (with qualifications) an upper limit to the radii of such objects near 25 m, assuming the same albedo. Both aperture photometry and a morphological analysis of the ejected dust show that mass-loss is continuous at rates $\sim$0.2 to 0.4 kg s$^{-1}$, inconsistent with an impact origin. Large dust particles, with radii $\sim$50 to 100 $\mu$m, dominate the optical appearance. At 2.4 AU from the Sun, the surface equilibrium temperatures are too low for thermal or desiccation stresses to be responsible for the ejection of dust. No gas is spectroscopically detected (limiting the gas mass loss rate to $<$1.8 kg s$^{-1}$). However, the protracted emission of dust seen in our data and the detection of another episode of dust release near perihelion, in archival observations from 2003, are highly suggestive of an origin by the sublimation of ice. Coincidentally, the orbit of 313P/Gibbs is similar to those of several active asteroids independently suspected to be ice sublimators, including P/2012 T1, 238P/Read and 133P/Elst-Pizarro, suggesting that ice is abundant in the outer asteroid belt.