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

<p>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<sup>th</sup> 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.</p> <p>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<sup>th</sup> July and 12<sup>th</sup> 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.  </p> <p>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. </p>

Satellite observation of the dust trail of a major bolide event over the Bering Sea on December 18, 2018

Context. One of the most energetic bolide events in recent decades was detected by the US Government sensors (USGS) over remote areas of the Bering Sea on December 18, 2018, 23:48 UT. No ground-based optical observations exist. Aims. Using the satellite imagery of the dust trail left behind by the bolide, we tried to reconstruct the bolide trajectory. In combination with the bolide speed reported by the USGS, we computed the pre-atmospheric orbit. Observations in various spectral bands from 0.4 to 13.3 μm enabled us to study the dust properties. Methods. Images of the dust trail and its shadow obtained from various angles by the Multi-angle Imaging SpectroRadiometer (MISR) on board the Terra polar satellite and geostationary satellites Himawari-8 and Geostationary Operational Environmental Satellite 17 (GOES-17) were used. The initial position and orientation of the trail was varied, and its projections into the geoid coordinate grid were computed and compared with real data. Trail motion due to atmospheric wind was taken into account. Radiances and reflectances of selected parts of the dust trail were taken from the Moderate-resolution Imaging Spectroradiometer (MODIS) on board Terra. Reflectance spectra were compared with asteroid spectra. Results. The bolide radiant was found to be 13° ± 9° from that reported by the USGS, at azimuth 130° (from south to west) and zenith distance 14°. The bolide position was confirmed, including the height of maximum dust deposition around 25 km. The incoming asteroid had to be quite strong to maintain a high speed down to this height. The speed of 32 km s−1, reported by the USGS, was found to be plausible. The orbit had a high inclination of about 50° and a perihelion distance between 0.95–1 AU. The semimajor axis could not be restricted well but was most probably between 1–3 AU. The dust reflectance was much lower in the blue than in the red, consistent with the material of A- or L-type asteroid. The absorption at 11 μm confirms the presence of crystalline silicates in the dust.

Dynamical and physical features of Perseid meteoroids from Tajikistan fireball network observations

ABSTRACT We present the results of a study of the dynamical and physical properties of large-sized Perseid meteoroids based on optical observations. Photographic observations of the Perseid meteor shower were carried out during the maximum of its activity in 2007–2011 using the Tajikistan fireball network. Multistation images of 29 Perseids recorded during this period were processed. The atmospheric trajectories, velocities, radiants, orbits, photometric masses and densities of the meteoroids were determined using the astrometric and photometric reduction of fireball images. The initial masses of meteoroids that produced fireballs range from several to 20 g. The observed light-curves of the Perseids and the mean bulk density of most meteoroids of ~0.4 g cm−3 are typical for cometary matter. According to the radiants, velocities and orbits, the captured Perseids are related both to the annual component of the stream and to the dust trail ejected by the parent comet 109P/Swift–Tuttle during its last perihelion passage in 1992.

Parker Solar Probe Observations of a Dust Trail in the Orbit of 3200 Phaethon

<p>We present details on the first white-light detection of a dust trail following the orbit of asteroid 3200 Phaethon, seen in images recorded by the Wide-field Imager for Parker Solar Probe (WISPR) instrument on the NASA Parker Solar Probe (PSP) mission. In this talk we will present a brief introduction to the PSP mission and the WISPR instrument. We will then show observations returned by WISPR in multiple perihelion 'encounters' that clearly show a diffuse dust trail perfectly aligned with the perihelion portion of the orbit of 3200 Phaethon, recorded while the asteroid itself was near aphelion. We will discuss the physical parameters that we have derived for the dust trail, including its visual magnitude, surface brightness and mass. We also speculate on the relationship of this trail to the Geminid meteor shower, of which Phaethon is assumed to be the parent, and demonstrate why the trail has not been detected visually until now, despite a number of dedicated observing campaigns. We also hope to present initial analyses of the most recent set of WISPR observations (January 2020), where we anticipate the trail should again be visible in the WISPR observations.</p>

Characterisation of the Perseid meteoroid stream through SPOSH observations between 2010–2016

We have characterised the Perseid meteoroid stream from data acquired in a series of observing campaigns between 2010 and 2016. The data presented in this work were obtained by the Smart Panoramic Optical Sensor Head (SPOSH), an all-sky camera system designed to image faint transient noctilucent phenomena on dark planetary hemispheres. For the data reduction, a sophisticated software package was developed that utilises the high geometric and photometric quality of images obtained by the camera system. We identify 934 meteors as Perseids, observed over a long period between late July (~124°) and mid-to-late August (~147°). The maximum meteor activity contributing to the annual shower was found at λ⊙ = 140°.08 ± 0°.07. The radiant of the shower was estimated at RA = 47°.2 and Dec = 57°.5 with a median error of 0°.6 and 0°.2, respectively. The mean population index of the shower between solar longitudes of 120°.68 and 145°.19 was r = 2.36 ± 0.05, showing strong temporal variation. A predicted outburst in shower activity for the night of August 11–12, 2016 was confirmed, with a peak observed 12.75 hr before the annual maximum at 23:30 ± 15′ UT. We measure a peak flux of 6.1 × 10−4 km−2 hr−1 for meteoroids of mass 1.6 × 10−2 g or more, appearing in the time period between 23:00 and 00:00 UT. We estimate the measured flux of the outburst meteoroids to be approximately twice as high as the annual meteoroid flux of the same mass. The population index of r = 2.19 ± 0.08, computed from the outburst Perseids in 2016, is higher than the value of r = 1.92 ± 0.06 derived from meteors observed in 2015 belonging to the annual Perseid shower which was active near the time of the outburst. A dust trail with an unusually high population index of r = 3.58 ± 0.24 was encountered in 2013 between solar longitudes 136°.261 and 137°.442. The relatively high r-value implies an encounter with a dust trail rich in low-mass particles.