R. J. Weryk

A brief visit from a red and extremely elongated interstellar asteroid

None of the approximately 750,000 known asteroids and comets in the Solar System is thought to have originated outside it, despite models of the formation of planetary systems suggesting that orbital migration of giant planets ejects a large fraction of the original planetesimals into interstellar space. The high predicted number density of icy interstellar objects (2.4 × 10−4 per cubic astronomical unit) suggests that some should have been detected, yet hitherto none has been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of the Solar System today, but there has been no way of telling whether the Solar System is typical of planetary systems. Here we report observations and analysis of the object 1I/2017 U1 (‘Oumuamua) that demonstrate its extrasolar trajectory, and that thus enable comparisons to be made between material from another planetary system and from our own. Our observations during the brief visit by the object to the inner Solar System reveal it to be asteroidal, with no hint of cometary activity despite an approach within 0.25 astronomical units of the Sun. Spectroscopic measurements show that the surface of the object is spectrally red, consistent with comets or organic-rich asteroids that reside within the Solar System. Light-curve observations indicate that the object has an extremely oblong shape, with a length about ten times its width, and a mean radius of about 102 metres assuming an albedo of 0.04. No known objects in the Solar System have such extreme dimensions. The presence of ‘Oumuamua in the Solar System suggests that previous estimates of the number density of interstellar objects, based on the assumption that all such objects were cometary, were pessimistically low. Planned upgrades to contemporary asteroid survey instruments and improved data processing techniques are likely to result in the detection of more interstellar objects in the coming years.

The 2005 Draconid outburst

Aims. We report the flux profile and mean orbit for meteoroids associated with an unexpected activity outburst from the Draconid meteor shower on 8 October, 2005. The primary aim is to define the characteristics of the outburst and establish the age of the associated meteoroids. Methods. Radar data from the outburst are used to define the flux profile and mass distribution for Draconid meteoroids at small meteoroid masses, while visual data are used to define the ZHR profile at larger masses. The radar recorded both single station and orbital data permitting orbits for many individual Draconid radar echoes as well as determination of a mean shower radiant. Results. The peak activity was centered at 16.1 hrs UT, (/to = 195°42 (J2000) solar longitude) with noticeably heightened radar activity lasting for a total of more than three hours. Based on the distribution of amplitudes for underdense Draconid echoes, the mean mass distribution index at masses of 10 -6 kg was found to be 2.0 ± 0.1. The equivalent hourly-binned radar ZHR was in excess of 150, while visual observations in the same intervals produced ZHRs of 40. The apparent radiant of the outburst was α = 256.9 ± 2.2°, δ = +56.6 ± 1.8°. Numerical modelling of radar-sized Draconids show that a significant number of meteoroids from the 1946 perihelion passage of 21 P/Giacobini-Zinner encountered the Earth over the interval 195°.23 λ ⊙ < 196°0 in 2005, centred about 195°50 Conclusions. The shower was rich in faint meteors, and therefore showed higher activity in radar data than in visual data alone. The duration of the outburst was very similar to past returns, while the mean radar stream orbit was somewhat different than previous measurements (the radiant differed by 6° in right ascension and 2° in declination) and also from the expected distribution of orbital elements for modelled 1946 meteoroids encountered in 2005.

Radar Observations of the 2011 October Draconid Outburst

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 singlestation overdense Draconid echoes (covering the magnitude range of +3 ≤ MV ≤+ 7) between 16 and 20 h UT on 2011 October 8. The mean radiant for the outburst was determined to be αg = 261. 9 ± 0. ◦ 3, δg =+ 55. 3 ± 0. 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 ngrain = 100 and a variable grain mass mgrain 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.

Photometric and ionization masses of meteors with simultaneous EISCAT UHF radar and intensified video observations

There are significant uncertainties in the calculation of photometric and ionization masses of meteors, particularly those derived from meteor head echoes observed by high power, large aperture rad ...

The unexpected 2012 Draconid meteor storm

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

The return of the Andromedids meteor shower

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Physical characteristics of very small meteoroids

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Global Ground-Based Electro-Optical and Radar Observations of the 1999 Leonid Shower: First Results

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The Pan-STARRS search for Near Earth Objects

1, δ g = 55

A meteoroid stream survey using the Canadian Meteor Orbit Radar: I. Methodology and radiant catalogue

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