A Distribution of Large Particles in the Coma of Comet 103P/Hartley 2

TL;DR

This study analyzes large particles in the coma of comet 103P/Hartley 2, measuring their distribution, composition, and contribution to water production, proposing models involving icy or dusty particles and their dynamics.

Contribution

It provides the first detailed measurements of large particle distributions in the coma and constrains their composition and impact on water production, with updated particle size estimates.

Findings

Particles have steep size distributions with slopes from -6.6 to -4.7.

Icy particles could account for up to 0.5% of water production.

Dark dusty particles are less favored based on mass considerations.

Abstract

The coma of comet 103P/Hartley 2 has a significant population of large particles observed as point sources in images taken by the Deep Impact spacecraft. We measure their spatial and flux distributions, and attempt to constrain their composition. The flux distribution of these particles implies a very steep size distribution with power-law slopes ranging from -6.6 to -4.7. The radii of the particles extend up to 20 cm, and perhaps up to 2 m, but their exact sizes depend on their unknown light scattering properties. We consider two cases: bright icy material, and dark dusty material. The icy case better describes the particles if water sublimation from the particles causes a significant rocket force, which we propose as the best method to account for the observed spatial distribution. Solar radiation is a plausible alternative, but only if the particles are very low density aggregates. If we treat the particles as mini-nuclei, we estimate they account for <16-80% of the comet's total water production rate (within 20.6 km). Dark dusty particles, however, are not favored based on mass arguments. The water production rate from bright icy particles is constrained with an upper limit of 0.1 to 0.5% of the total water production rate of the comet. If indeed icy with a high albedo, these particles do not appear to account for the comet's large water production rate. production rate. Erratum: We have corrected the radii and masses of the large particles of comet 103P/Hartley 2 and present revised conclusions in the attached erratum.