Hyperactivity in 103P/Hartley 2: Chunks from the sub-surface in Type IIa jet regions

TL;DR

This study models the distribution and dynamics of water-ice particles in comet 103P/Hartley 2's jet, revealing that large chunks contribute to hyperactivity but are not observed at higher altitudes.

Contribution

It introduces a CO2-driven jet model explaining water-ice particle distribution and suggests large chunks are key to hyperactivity but escape before reaching higher altitudes.

Findings

Mass flow of water is 40 times greater than previous models.

Particle speeds are increased by up to 20 times compared to earlier estimates.

Large chunks are responsible for hyperactivity but leave the jet region early.

Abstract

We analyze the observed radial distribution of column densities of water-ice particulates embedded in the primary jet region of 103Ps inner coma at altitudes between 439 and 1967 m (Protopapa et al, 2014) and determine the speed and acceleration of particles and their mass flow within the filaments of the jet. This is done by applying a CO2 driven type IIa jet model proposed by Belton (2010) The model utilizes water-ice particles dislodged in the source regions of the jet filaments and accelerated by CO2 to explain the radial distribution of water-ice particulates. We provide an explanation for the remarkably different radial distribution of refractory dust particles by hypothesizing that the majority of the dust originates directly from the nucleus surface in interfilament regions of the jet complex and is accelerated by H2O. Our model provides a mass-flow of water from the J1 jet complex that is 40 times greater than the constant speed sublimation model discussed by Protopapa et al. but is still too small to explain the hyperactivity of the comet. Speeds in the flow are increased by a factor up to 20 over those found by Protopapa et al. To account for the hyperactivity, most of the mass dislodged in the filament source regions must be in weakly accelerated large chunks that achieve only low speeds en route to the region of observation. These chunks soon leave the filamentary jet structure due to the rotation of the nucleus and do not contribute to the column densities observed at higher altitudes in the jet filaments.