Meteor Orbits Research Articles

THE RETURN OF THE ANDROMEDIDS METEOR SHOWER

The Andromedid meteor shower underwent spectacular outbursts in 1872 and 1885, producing thousands of visual meteors per hour and described as `stars fell like rain' in Chinese records of the time. The shower originates from comet 3D/Biela whose disintegration in the mid-1800's is linked to the outbursts, but the shower has been weak or absent since the late 19th Century. This shower returned in December 2011 with a zenithal hourly rate of approximately 50, the strongest return in over a hundred years. Some 122 probable Andromedid orbits were detected by the Canadian Meteor Orbit Radar. The shower outburst occurred during 2011 Dec 3-5. The radiant at RA +$18\degree$ and Dec +$56\degree$ is typical of the `classical' Andromedids of the early 1800's, whose radiant was actually in Cassiopeia. The orbital elements indicate that the material involved was released before 3D/Biela's breakup prior to 1846. The observed shower in 2011 had a slow geocentric speed (16 km s$^{-1}$) and was comprised of small particles: the mean measured mass from the radar is $\sim5 \times 10^{-7}$ kg corresponding to radii of 0.5 mm at a bulk density of 1000 kg/m$^3$. Numerical simulations of the parent comet indicate that the meteoroids of the 2011 return of the Andromedids shower were primarily ejected during 3D/Biela's 1649 perihelion passage. The orbital characteristics, radiant, timing as well as the absence of large particles in the streamlet are all consistent with simulations. Predictions are made regarding other appearances of the shower in the years 2000-2047 based on our numerical model. We note that the details of the 2011 return can, in principle, be used to better constrain the orbit of 3D/Biela prior to the comets first recorded return in 1772.

Meteor Showers: which ones are real and where do they come from?

AbstractThe IAU Meteor Shower Working List contains 369 showers, of which only 64 are considered established (per February 28, 2012). In this invited review, we will give an overview of international efforts to validate the remaining showers. We report on the showers that were validated in this triennium and proposed to receive the predicate “established" at the present General Assembly. The meteoroid orbit surveys characterize the meteoroid streams in terms of orbital elements and their dispersions, which is ground truth for efforts to identify their parent comets, study the fragmentation history of the (mostly dormant) comet population in the inner solar system, and understand the origin of the zodiacal cloud.

CCD modification to obtain high-precision orbits of meteoroids

Few high-resolution video cameras have been used for observing meteors, so the orbits obtained have high uncertainty. Precise orbits are necessary so that the meteors can be integrated backwards in time and be identified with their parent body. Also, by comparing these orbits with a theoretical evolution model, the meteors can be associated with a particular dust trail. An electronic shutter system has been developed to enhance the temporal resolution for large CCD sensors. For the first time, an LH100 camera with an electronic shutter system has been tested for observing meteors. This new innovational technique has removed the theoretical upper limit – resulting from slow frame rates – to the size of CCD that can be used for the detection of meteors. Three such cameras will be installed in southern France to create a network for determining the orbits of meteors; this will be called the CAmera for BEtter Resolution NETwork (CABERNET). Here, we present preliminary results from the Geminid test campaign, which made use of this camera.

Simultaneous radar and video meteors—I: Metric comparisons

Simultaneous radar and video measurements were made using the Canadian Meteor Orbit Radar (CMOR) and several Gen-III image-intensified CCD cameras to observationally validate metric instrument errors determined through Monte Carlo modelling. We find that our radar interferometry accuracy is ∼0.8° using multiple independent techniques validated with video data. Our average radar–video radiant difference is 3.4°, suggesting that radiant errors for CMOR are dominated by errors in time-of-flight lag time determinations. Our video speeds were found to be consistently lower for slower speed meteors, with our modelled video speed errors following the relation log10δv=−1.64+0.02v. Our modelled video radiant errors had error distributions of 0.73°±0.51°. Errors in the fiducial picks for video meteors were found to be anisotropic, with errors along the meteor trail being larger than those perpendicular to the trail, primarily affecting the fit speed. We also find that the majority of our radar detections occur near the end of the observed video height interval. Our average video speeds are higher than our radar speeds, consistent with decelerations and specular reflections occurring preferentially near the end of trails. Range comparisons show our radar determined specular ranges to be systematically +0.32km farther in range, although this is smaller than the statistical spread. We find 7%±3% of our video events are simultaneously detected by our radar system. This is above the expected 2%–5% range determined through modelling, suggesting our observations are biased towards larger, non-fragmenting meteoroids.

Do Meteoroids Originating from Near-Earth Asteroid (25143) Itokawa Exist?

Abstract Making a survey of Itokawids, i.e., meteor(oid)s originating from Apollo-type near-Earth Asteroid (25143) Itokawa, from among the multiple-station optical meteor orbit data, and employing several orbital similarity criteria, we found five Itokawid candidates. Furthermore, we classified the Itokawid candidates in meteorite types according to their physical data. The physical analyses indicate that all of the candidates evidently belong to not cometary, but asteroidal, meteoroids. Especially, the fireball, MORP 172, is the one candidate that is classified among ordinary/carbonaceous chondrites, as against the four other at carbonaceous chondrites. Hence, the classified meteoritic matter of MORP 172 shows more similarities to Itokawa's surface composition of an LL chondrite analogue than those of the other candidates. Therefore, the fireball is considered to be the strongest of the Itokawid candidates.

DYNAMICAL MODEL FOR THE ZODIACAL CLOUD AND SPORADIC METEORS

The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving to the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer (>10^5 yr at 1 AU) than postulated in the standard collisional models (10^4 yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite (IRAS) to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5)x10^11 km^2 and 4x10^19 g, respectively, in a good agreement with previous studies. The mass input required to keep the Zodiacal Cloud (ZC) in a steady state is estimated to be 10^4-10^5 kg/s. The input is up to 10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes, and need to be supplied at a faster rate.

CAMS: Cameras for Allsky Meteor Surveillance to establish minor meteor showers

First results are presented from a newly developed meteoroid orbit survey, called CAMS – Cameras for Allsky Meteor Surveillance, which combines meteor detection algorithms for low-light video observations with traditional video surveillance tools. Sixty video cameras at three stations monitor the sky above 31° elevation. Goal of CAMS is to verify meteor showers in search of their parent comets among newly discovered near-Earth objects. This paper outlines the concept of operations, the hardware, and software methods used during operation and in the data reduction pipeline, and accompanies the data release of the first batch of meteoroid orbits. During the month of November 2010, 2169 precisely reduced meteoroid trajectories from 17 nights have an error in the apparent radiant of the trajectory <2° and error in speed <10%. Median values of the error are 0.31° and 0.53 km/s, respectively, sufficient to resolve the intrinsic dispersion of annual meteor showers and resolve minor showers from the sporadic background. The limiting visual magnitude of the cameras is +5.4, recording meteors of +4 magnitude and brighter, bright enough to stand out from the mostly fainter sporadic meteors detected as under dense radar echoes. CAMS readily detected all established showers (6) active during the clear nights in November. Of the showers that needed confirmation, we confirm the theta Aurigids (THA, IAU#390), the chi Taurids (CTA, IAU#388), and the omicron Eridanids (OER, IAU#338). We conclude that the iota November Aurigids (IAR, IAU#248) are in fact the combined activity of the theta Aurigids and chi Taurids, and this shower should be dismissed from the list. Finally, there is also a clustering consistent with the zeta Cancrids (ZCN, IAU#243), but we cannot exclude that this is lower perihelion dust belonging to the Orionid shower. Data are submitted to the IAU Meteor Data Center on a semi-regular basis, and can be accessed also at http://cams.seti.org.

A numerical comparison with the Ceplecha analytical meteoroid orbit determination method

Abstract– Analytic methods by Ceplecha have long been used for the determination of meteoroid heliocentric orbits. These methods include both the derivation of an initial atmospheric contact position and velocity state, and the calculation of an orbit at infinity based on zenithal attraction assumptions. Herein, we describe a numerical integration‐based verification for a portion of the Ceplecha methods, a verification driven by the need for an accurate meteoroid ephemeris in the hours before atmospheric contact. We show a close correspondence in analytic and numerical results, with a previously undocumented minor correction to a meteoroid’s longitude of the ascending node.

Interstellar Meteoroids in the Japanese tv Catalogue

The present work is based on an analysis of the 14763 precise determined meteor orbits collected in the Japanese tv catalogue (SonotaCo (2009)), with the aim of determining the real proportion of interstellar meteors in this database. If interstellar meteors are present among the registered meteor orbits, the distribution of the excesses of their heliocentric velocities should correspond to the distribution of the radial velocities of close stars. For the velocity $v_i$$=$ 20 km s$^{-1}$ of an interstellar meteor, with respect to the Sun, we obtain a heliocentric velocity of $v_H$$=$ 46.6 km s$^{-1}$ of an interstellar meteor arriving at Earth. Any error in the determination of $v_H$, especially near the parabolic limit, can create an artificial hyperbolic orbit that does not really exist. The analysis of the data did not produce any convincing arguments in favour of the existence of true hyperbolic meteors in the catalogue. It was shown that the vast majority of the 484 hyperbolic orbits has been caused by an overestimation of their velocity, and approximately 50% of them belong to meteor showers. Furthermore, the hyperbolic excesses of the velocities in all cases are very low, about one order less than the velocity distribution of neighbouring stars suggest. The upper limit of the proportion of possible interstellar meteors to interplanetary ones among all investigated meteor orbits in the database is 1.3 $\times$ 10$^{-3}$.

A meteoroid stream survey using the Canadian Meteor Orbit Radar - III. Mass distribution indices of six major meteor showers

The mass distribution index of the Geminid, Quadrantid, Arietid, Eta Aquariid, Orionid and South Delta Aquariid meteor showers have been measured using data from 2007 to 2010 from the Canadian Meteor Orbit Radar (CMOR). Single-station data from the 29.85-MHz system were used to find mass index as a function of solar longitude, and to compare separate years of showers. The variation in mass index with solar longitude can provide information on the structure of the stream and how the structure changes with time. The Geminids and Quadrantids were the most prominent showers seen by CMOR, and had peak mass indices of 1.65 and 1.55, respectively. They had clear, strong peaks and little year-to-year variation. The other showers had slightly higher peak mass indices and a greater variability, even though a more sporadic contamination, which might have affected the results.

The Daytime Craterids, a radar-detected meteor shower outburst from hyperbolic comet C/2007 W1 (Boattini)

We report a new daytime meteor shower detected with the Canadian Meteor Orbit Radar (CMOR). This shower has a radiant in the southern constellation Crater. The Daytime Craterid shower was observed in 2003 and 2008 but not in any of the other years in the 2002–09 interval. The strength of this shower in the years observed is equivalent to a daily averaged zenithal hourly rate (ZHR) over 30, with a peak ZHR likely much higher at the time of the outburst. The orbital elements of the shower closely match those of Comet C/2007 W1 (Boattini), which passed perihelion in 2007. The orbit of C/2007 W1 is nominally hyperbolic orbit making this the first meteor shower detected from a clearly unbound comet. The 2003 outburst of the Daytime Craterid shower indicates that this comet must have recently been transferred to an unbound orbit from a bound one, likely through a close encounter with a giant planet. As a result we conclude that this shower provides us with one of the few examples of showers originating from the population of nearly isotropic comets. The stream is difficult to model owing to its proximity to the orbits of Jupiter, Saturn and the Earth. However, the intermittent nature of the shower can be largely understood from numerical simulations. No outbursts of similar strength are expected in the next decade, with the possible exception of 2015.

Dynamical resonant structures in meteoroid stream orbits

Herein we use the Canadian Meteor Orbit Radar (CMOR) data set to search for evidence of a resonant swarm in the Taurid meteoroid stream at the 7:2 Jovian resonance. We use a numerical method to estimate the reduction in radar orbit measurement uncertainty required to detect this feature in a data set. This is highly dependent on the proportion of observed particles that are members of the resonant swarm. However, we find that a meteor radar with uncertainties a factor of 10 lower than those of the current CMOR will be sufficient for detection to be possible, if the meteor shower consists of more than 5 per cent resonant particles (considered likely given the results of visual meteor studies). Such an improvement will require accurate removal of deceleration errors from pre-atmospheric meteor velocities, and improvement to the robustness of echo inflection point identification algorithms and interferometric measurements.

Mass distribution indices of sporadic meteors using radar data

The mass distribution index of sporadic meteors and the indices of specific sporadic sources have been measured using data from 2007 to 2010 from the Canadian Meteor Orbit Radar. Single-station data from the 29.85-MHz system were used and the trends throughout the year are examined. We find that the average values for the sources are approximately equal, but the annual variation of each source is unique. We find that the overall average sporadic mass index is 2.17 ± 0.07, less than the frequently cited 2.34. The variation in the mass index throughout the year can provide information about the meteoroid populations that the Earth is encountering at different parts of its orbit.

Seasonal variations in the north toroidal sporadic meteor source

Abstract—Determining the origins of the sporadic meteoroid sources helps determine their current properties. We have analyzed four years of orbital radar data, looking at how the rates, radiants, and orbits of meteoroids in the north toroidal sporadic source change throughout the year. Twelve broad radiant concentrations, separated in either time or radiant location, are identified. Six are broad distributions associated with more focused shower activity, and six are not associated with major showers. Four of the six concentrations not associated with showers have been named Toroidal, Toroidal A, Toroidal B, and Toroidal C, because of their constant location at the north toroidal centre. The other two, which appear close to the north toroidal source and drift toward the helion and antihelion sources respectively, have been named the Helion Arc and the Antihelion Arc. The twelve radiant concentrations generally last for more than ten degrees solar longitude, and those which may have a single parent are likely composed of orbitally evolved material.

A meteoroid stream survey using the Canadian Meteor Orbit Radar: II: Identification of minor showers using a 3D wavelet transform

A 7 year survey using the Canadian Meteor Orbit Radar (CMOR), a specular backscattering orbital radar, has produced three million individually measured meteoroid orbits for particles with mean mass near 10 −7 kg. We apply a 3D wavelet transform to our measured velocity vectors, partitioning them into 1° solar longitude bins while stacking all 7 years of data into a single “virtual” year to search for showers which show annual activity and last for at least 3 days. Our automated stream search algorithm has identified 117 meteor showers. We have recovered 42 of the 45 previously described streams from our first reconnaissance survey (Brown, P., Weryk, R.J., Wong, D.K., Jones, J. [2008]. Icarus 195, 317–339). Removing possible duplicate showers from the automated results leaves 109 total streams. These include 42 identified in survey I and at least 62 newly identified streams. Our large data sample and the enhanced sensitivity of the 3D wavelet search compared to our earlier survey have allowed us to extend the period of activity for several major showers. This includes detection of the Geminid shower from early November to late December and the Quadrantids from early November to mid-January. Among our newly identified streams are the Theta Serpentids which appears to be derived from 2008 KP and the Canum Venaticids which have a similar orbit to C/1975 X1 (Sato). We also find evidence that nearly 60% of all our streams are part of seven major stream complexes, linked via secular invariants.

Analysis of the upper limit of the Southworth-Hawkins D criterion for the Pons-Winneckid and Perseid meteoroid streams

The value of the upper limit of the Southworth-Hawkins D criterion for the Pons-Winneckids (June Bootid) and Perseids meteor streams is analyzed on the basis of the comparison of the parent comet orbit with the model orbits of meteoroids ejected at different points of the comet orbit with the most likely ejection velocities. The change of the D values is investigated depending on the dynamic evolution of the streams by integrating forward the orbital elements of the model particles using the Cowell method taking into account the perturbations from all planets. It is shown that after ten rotations, for Pons-Winneckids the upper limit of the D criterion is higher than 0.5 and for Perseids the D criterion does not exceed 0.2.

Study of meteoroid stream identification methods

AbstractWe have tested the reliability of various meteoroid streams identification methods. We used a numerically generated set of meteoroid orbits (a stream component and a sporadic background) that were searched for streams using several methods.

The 2007 Aurigid meteor outburst

A rare outburst of the Aurigid meteor shower was predicted to occur on 2007 September 1 at 11:36 ± 20 min UT due to Earth’s encounter with the one-revolution dust trail of long-period comet C/1911 N1 (Kiess). The outburst was predicted to last ∼1.5 h with peak zenithal hourly rate of ∼200 h −1 , which is ∼20 times higher than the annual Aurigid shower. Three members of Armagh Observatory observed this outburst from the general area of San Francisco, CA, USA, where the shower was anticipated to be best seen. Observed radiant, velocity and activity peak time were consistent with the predictions, whereas the zenithal hourly rate was about half of the predicted value. Five Aurigids were observed by two stations simultaneously, enabling their spatial trajectory to be worked out. The orbits of these double station meteors are in good agreement with that of their parent comet Kiess. The outburst was abundant in bright (− 2t o +1 mag) meteors. The first high-altitude Aurigid, with a beginning height of 137.1 km, was recorded.

The EISCAT meteor code

Abstract. The EISCAT UHF system has the unique capability to determine meteor vector velocities from the head echo Doppler shifts measured at the three sites. Since even meteors spending a very short time in the common volume produce analysable events, the technique lends itself ideally to mapping the orbits of meteors arriving from arbitrary directions over most of the upper hemisphere. A radar mode optimised for this application was developed in 2001/2002. A specially selected low-sidelobe 32-bit pseudo-random binary sequence is used to binary phase shift key (BPSK) the transmitted carrier. The baud-length is 2.4 μs and the receiver bandwidth is 1.6 MHz to accommodate both the resulting modulation bandwidth and the target Doppler shift. Sampling is at 0.6 μs, corresponding to 90-m range resolution. Target range and Doppler velocity are extracted from the raw data in a multi-step matched-filter procedure. For strong (SNR&gt;5) events the Doppler velocity standard deviation is 100–150 m/s. The effective range resolution is about 30 m, allowing very accurate time-of-flight velocity estimates. On average, Doppler and time-of-flight (TOF) velocities agree to within about one part in 103. Two or more targets simultaneously present in the beam can be resolved down to a range separation &lt;300 m as long as their Doppler shifts differ by more than a few km/s.

High resolution radiant distribution and orbits of sporadic radar meteoroids

Five years of meteor orbit data from CMOR (the Canadian Meteor Orbit Radar) are used to study the high-resolution orbital structure of the sporadic meteoroid complex. The large number of high quality orbits (2.35 million) allows the orbital characteristics of meteoroids to be studied not only in the five sporadic sources accessible from the latitude of London, Ontario, Canada, but at a resolution of 2 degrees. The radiant distribution of sporadic meteors is investigated, applying corrections for observing biases, and weighting to a constant limiting mass, and to a constant limiting energy. The orbital distribution of the sporadic sources is compared to other studies. The variation of average geocentric speed, semimajor axis, eccentricity, inclination and perihelion distance with meteoroid radiant is investigated. The source of a ring depleted in meteor radiants at 55 degrees from the apex is attributed to shorter collisional lifetimes inside the ring, due to a higher probability of catastrophic collisions with particles in the zodiacal cloud for the predominantly retrograde meteoroids inside the ring.