Comet 108P/Ciffreo: The Blob

TL;DR

This study investigates the peculiar double morphology of comet 108P/Ciffreo, revealing that the co-moving blob is an artifact caused by the dynamics of particles ejected from the nucleus, rather than a secondary object.

Contribution

The paper provides new Hubble and Nordic Telescope observations and models the particle dynamics to explain the comet's unusual morphology as an ejected particle artifact.

Findings

The blob is not a secondary object but an artifact of particle dynamics.

The morphology is explained by particles turning around after being sunward ejected.

The rarity of the blob appearance is due to specific ejection directions.

Abstract

Short-period comet 108P/Ciffreo is known for its peculiar double morphology, in which the nucleus is accompanied by a co-moving, detached, diffuse 'blob'. We report new observations of 108P/Ciffreo taken with the Hubble Space Telescope and the Nordic Optical Telescope and use them to determine the cause of this unusual morphology. The separation and the longevity of the blob across several orbits together rule out the possibility of a single, slow-moving secondary object near the primary nucleus. We use a model of coma particle dynamics under the action of solar gravity and radiation pressure to show that the blob is an artifact of the turn-around of particles ejected sunward and repelled by sunlight. Numerical experiments limit the range of directions which can reproduce the morphology and explain why the co-moving blob appearance is rare.