ALBERT

Description: We measure the activity and orbital characteristics of the -Aquariid meteor shower appropriate to meteoroids of 200 μm size (mass 5–10 μg) based on ~4 10 4 stream orbits measured by the Canadian Meteor Orbit Radar during the years 2002–2014. Significant activity from the stream is found to last from April 25–May 21 (  = 35°–60°) with the shower detectable approximately one week on either side of these dates just above the median background. The radiant at peak activity (  = 45 $_{.}^{\circ}$ 5) is located at α g  = 337 $_{.}^{\circ}$ 8, g  = –0 $_{.}^{\circ}$ 6 and shows a consistent drift of α g  = +0 $_{.}^{\circ}$ 69, g  = +0 $_{.}^{\circ}$ 60. The velocity of the stream throughout its active period remains within 1 km s –1 of V g = 64.3 km s –1 found at the peak; however, there are indications this is an underestimate due to undercorrection for stream meteoroids having larger than average deceleration. The activity profile shows no mass dependence between μg to mg sizes, but a clear asymmetry with the slope of the ascending branch having B + = 0.135 ± 0.003 and the descending branch B – = 0.078 ± 0.003. The average yearly equivalent radar-measured peak Zenithal Hourly Rate (ZHR) is 50–80 from 2002–2014, with outbursts in 2004 and 2013 exceeding ZHRs of 100. The mass index shows a minimum at the time of the flux maximum with 1.8 ≤  s ≤ 1.9.

Description: The optical trail widths of 30 faint meteors (average magnitude ~+3, m  ~ 10 –4 kg) were resolved and measured using the Canadian Automated Meteor Observatory (CAMO). CAMO is an automated, high-resolution intensified digital video system capable of detecting meteors as faint as magnitude +5. The observatory's two stations, separated by a baseline of 50 km, and each comprised of a narrow- and wide-field camera, observed the meteors for this survey. Data from the wide-field cameras were used to derive a trajectory solution for each meteor with the software package metal , while data from the narrow-field cameras were used to measure trail widths with the image analysis software imagej . Raw widths were measured as a function of distance along the meteor trail for each frame of the video. To ensure that instrumental bloom did not artificially increase trail widths, the width of a star imaged with the narrow-field camera, with equivalent brightness to the meteor trail at the point of measurement, was subtracted from each observed raw width. Corrected trail widths up to 100 m at heights above 110 km were observed, varying with height as the inverse of atmospheric density. 14 of the 30 events were observed with both narrow-field cameras and each showed good agreement of trail width values after bloom correction. This suggested that the widths were true physical sizes, and not instrumental artefacts. Preliminary investigation suggests collisional de-excitation of energetic atoms is a plausible process for the formation of these wide trails.

Description: Dormant comets in the near-Earth object (NEO) population are thought to be involved in the terrestrial accretion of water and organic materials. Identification of dormant comets is difficult as they are observationally indistinguishable from their asteroidal counterparts, however, they may have produced dust during their final active stages which potentially are detectable today as weak meteor showers at the Earth. Here we present the result of a reconnaissance survey looking for dormant comets using 13 567 542 meteor orbits measured by the Canadian Meteor Orbit Radar (CMOR). We simulate the dynamical evolution of the hypothetical meteoroid streams originated from 407 near-Earth asteroids in cometary orbits that resemble orbital characteristics of Jupiter-family comets (JFCs). Out of the 44 hypothetical showers that are predicted to be detectable by CMOR, we identify five positive detections that are statistically unlikely to be chance associations, including three previously known associations. This translates to a lower limit to the dormant comet fraction of 2.0 ± 1.7 per cent in the NEO population and a dormancy rate of ~10 –5 yr –1 per comet. The low dormancy rate confirms disruption and dynamical removal as the dominant end state for near-Earth JFCs. We also predict the existence of a significant number of meteoroid streams whose parents have already been disrupted or dynamically removed.

Description: The quantitative evidence of human impacts on the Earth System has produced new calls for planetary stewardship. At the same time, numerous scholars reject modern social sciences by claiming that the Anthropocene fundamentally changes the human condition. However, we cannot simply dismiss all previous forms of cultural learning or transmission. Instead, this paper examines ethics in the Anthropocene, and specifically what it implies for: (1) reassessing our normative systems in view of human impacts on the Earth System; (2) identifying novel ethical problems in the Anthropocene; and (3) repositioning traditional issues concerning fairness and environmental ethics. It concludes by situating ethics within the challenge of connecting multiple social worlds to a shared view of human and Earth histories and calls for renewed engagement with ethics.

Description: A strong outburst of the October Draconid meteor shower was predicted for 2011 October 8. Here we present the observations obtained by the Canadian Meteor Orbit Radar (CMOR) during the 2011 outburst. CMOR recorded 61 multistation Draconid echoes and 179 single-station overdense Draconid echoes (covering the magnitude range of +3 ≤  M V  ≤ +7) between 16 and 20 h ut on 2011 October 8. The mean radiant for the outburst was determined to be α g  = 261 $_{.}^{\circ}$ 9 ± 0 $_{.}^{\circ}$ 3, g  = +55 $_{.}^{\circ}$ 3 ± 0 $_{.}^{\circ}$ 3 (J2000) from observations of the underdense multistation echoes. This radiant location agrees with model predictions to ~1°. The determined geocentric velocity was found to be ~10–15 per cent lower than the model value (17.0–19.1 km s –1 versus 20.4 km s –1 ), a discrepancy we attribute to undercorrection for atmospheric deceleration of low-density Draconid meteoroids as well as to poor radar radiant geometry during the outburst peak. The mass index at the time of the outburst was determined to be ~1.75 using the amplitude distribution of underdense echoes, in general agreement with the value of ~1.72 found using the diffusion-limited durations of overdense Draconid echoes. The relative flux derived from overdense echo counts showed a similar variation to the meteor rate derived from visual observations. We were unable to measure the peak flux due to the high elevation of the radiant (and hence low elevation of specular Draconid echoes). Using the observed speed and electron line density measured by CMOR for all underdense Draconid echoes as a function of height as a constraint, we have applied the ablation model developed by Campbell-Brown & Koschny. From these model comparisons, we find that Draconid meteoroids at radar sizes are consistent with a fixed grain number n grain  = 100 and a variable grain mass m grain between 2 10 –8 and 5 10 –7 kg, with bulk and grain density of 300 and 3000 kg m –3 , respectively. One particular Draconid underdense echo displayed well-defined Fresnel amplitude oscillations at four stations. The internal synchronization allowing us to measure absolute length as a function of time by combining the absolute timing offsets between stations. This event showed clear deceleration and modelling suggests that the number of grains for this meteoroid was of the order of 1000 with grain masses between 10 –10 and 10 –9  kg, and a total mass of 2 10 –6  kg.

Description: An unexpected intense outburst of the Draconid meteor shower was detected by the Canadian Meteor Orbit Radar on 2012 October 8. The peak flux occurred at ~16:40 ut on October 8 with a maximum of 2.4 ± 0.3 h –1 km –2 (appropriate to meteoroid mass larger than 10 –7 kg), equivalent to a ZHR max 9000 ± 1000 using 5-min intervals, using a mass distribution index of s  = 1.88 ± 0.01 as determined from the amplitude distribution of underdense Draconid echoes. This makes the outburst among the strongest Draconid returns since 1946 and the highest flux shower since the 1966 Leonid meteor storm, assuming that a constant power-law distribution holds from radar to visual meteoroid sizes. The weighted mean geocentric radiant in the time interval of 15–19 h ut , 2012 October 8, was α g = 262 $_{.}^{\circ}$ 4 ± 0 $_{.}^{\circ}$ 1, g = 55 $_{.}^{\circ}$ 7 ± 0 $_{.}^{\circ}$ 1 (epoch J2000.0). Visual observers also reported increased activity around the peak time, but with a much lower rate (ZHR ~ 200), suggesting that the magnitude–cumulative number relationship is not a simple power law. Ablation modelling of the observed meteors as a population does not yield a unique solution for the grain size and distribution of Draconid meteoroids, but is consistent with a typical Draconid meteoroid of m total between 10 –6 and 10 –4 kg being composed of 10–100 grains. Dynamical simulations indicate that the outburst was caused by dust particles released during the 1966 perihelion passage of the parent comet, 21P/Giacobini-Zinner, although there are discrepancies between the modelled and observed timing of the encounter, presumably caused by approaches of the comet to Jupiter during 1966–1972. Based on the results of our dynamical simulation, we predict possible increased activity of the Draconid meteor shower in 2018, 2019, 2021 and 2025.