The dust tail gap of C/2014 Q1 (PanSTARRS)

A dust tail ‘gap’ was discovered in amateur images of the dust tail of C/2014 Q1 (PanSTARRS), which appeared around the comet’s most recent perihelion on 6^th July 2015. This gap presented itself as a wedge-shaped region devoid of dust, with the comet’s dust tail appearing to be normal on either side of this dark zone.

The results of the C/2014 Q1 study, employing Finson-Probstein modelling of the dust tail, show that none of the dust lay along the comet’s orbital path, confirming that both sections of dust were part of the dust tail and not a typical separation between dust tail and dust trail. A gap, devoid of dust, separates these two sections. The edges of this gap are bounded fairly accurately by lines of constant dust ejection time, corresponding to dust that should have been ejected between 6^th July and 12^th July. This suggests that cometary activity between these two dates was drastically reduced, although the cause of this is still unknown. The gap was visible throughout July and August 2015, and its shape and structure remained constant in the context of expected dust tail behaviour.  

The limited dataset for C/2014 Q1 meant that the formation mechanism of this gap could not be fully investigated.  However, a subsequent survey of amateur and professional comet images revealed the presence of similar gaps in the dust tails of several other comets. Analysis of these comets show many similarities with the results of the C/2014 Q1 study, including that these dust gaps observed all form during the comets’ perihelia. We present the results of individual analyses and cross-comparison of these comets, and summarize what we believe are the most likely scenarios for the formation of these perplexing features.