Geminid Meteoroids Research Articles

Mechanical strength distribution in Geminid meteoroids derived via fireball modeling

Context. Geminids are the most active annual meteor shower observed on Earth. Their parent is an active asteroid, (3200) Phaethon, which is a target of the planned DESTINY+ mission of the Japan Aerospace Exploration Agency (JAXA). The exact physical nature of (3200) Phaethon and Geminids is still debated. Aims. This paper is devoted to fragmentation modeling of bright Geminid fireballs, which should reveal information about the structure of centimeter-sized Geminid meteoroids. These fireballs were observed by the European Fireball Network (EN) over the past few years. We aim to describe their disintegration cascade in the atmosphere and their mechanical properties, and to derive their precise initial masses and velocities. Methods. We used a semi-empirical fragmentation model that employs an automatic procedure based on parallel genetic algorithms to determine the aerodynamic pressures at which a meteoroid and its parts fragment. This serves as a proxy for the mechanical strength of the body and its subsequent fragments. It enabled us to derive the minimum, median, and maximum mechanical strength and the strength distribution inside the meteoroid and reveal its internal structure. Results. We find that the Geminids begin to crumble at pressures 1–100 kPa, with the strongest parts reaching pressures of between 0.4 and 1.55 MPa before fragmenting. Knowing the spectral type of (3200) Phaethon (a B-type asteroid, part of the C complex), we conclude that the Geminids are made of compact and coherent carbonaceous material. We also find that the minimum aerodynamic pressure that causes the fragmentation of Geminids increases with increasing entry mass of Geminids. In contrast, the median aerodynamic pressure decreases as their entry mass increases. The spectra of all the observed Geminid fireballs show normal content and little variation in terms of sodium.

Investigating the Relationship between (3200) Phaethon and (155140) 2005 UD through Telescopic and Laboratory Studies

Abstract The relationship between the near-Earth objects (3200) Phaethon and (155140) 2005 UD is unclear. While both are parents to meteor showers (the Geminids and Daytime Sextantids, respectively) and have similar visible-wavelength reflectance spectra and orbits, dynamical investigations have failed to find any likely method to link the two objects in the recent past. Here we present the first near-infrared reflectance spectrum of 2005 UD, which shows it to be consistently linear and red-sloped, unlike Phaethon’s very blue and concave spectrum. Searching for a process that could alter some common starting material to both of these end states, we hypothesized that the two objects had been heated to different extents, motivated by their near-Sun orbits, the composition of Geminid meteoroids, and previous models of Phaethon’s surface. We thus set about building a new laboratory apparatus to acquire reflectance spectra of meteoritic samples after heating to higher temperatures than available in the literature to test this hypothesis and were loaned a sample of the CI chondrite Orgueil from the Vatican Meteorite Collection for testing. We find that while Phaethon’s spectrum shares many similarities with different CI chondrites, 2005 UD’s does not. We thus conclude that the most likely relationship between the two objects is that their similar properties are only by coincidence as opposed to a parent-fragment scenario, though the ultimate test will be when JAXA’s DESTINY+ mission visits one or both of the objects later this decade. We also discuss possible paths forward to understanding Phaethon’s properties from dynamical and compositional grounds.

Sodium variation in Geminid meteoroids from (3200) Phaethon

Sodium is a perfect indicator to investigate the volatility within meteoroid composition. Spectroscopic observations of the Geminid meteors were carried out using modern high sensitive large format CMOS cameras. 149 visible spectra of the Geminid meteors observed in 2017 and 2018 were analyzed by a newly developed procedure. The variation of Na, Mg and Fe during meteor ablation in the atmosphere has been studied. Although sodium is depleted in ~80% of the Geminids, statistically significant variations of sodium in the Geminid meteors were found. It should be noted that Na depletion in the Geminid meteors increased with decreasing meteoroid size. A yearly variation of Na in the Geminid meteor streams was also found. Solar-heating age across the different parts of the meteoroids stream ejected from a parent active asteroid (3200) Phaethon having 0.14 AU small perihelion distance seems to the most likely explanation for the sodium variation and depletion. Surprisingly, three iron Geminid meteors were detected across the maximum of 2018 Geminids.

The Geminid meteoroid stream as a potential meteorite dropper: a case study

A Geminid fireball with an absolute magnitude of -13 was observed over the south of Spain on Dec. 15, 2009. This extraordinarily bright event (the brightest Geminid ever recorded by our team) was imaged from two meteor observing stations operated by the SPanish Meteor Network (SPMN). The bolide exhibited fast and quasi-periodic variations in brightness, a behaviour typically associated to the rotation of the parent meteoroid. The inferred tensile strength of this particle was found to be significantly higher that the typical values obtained for Geminid meteoroids. The fireball penetrated in the atmosphere till a final height of about 25 km above the ground level and a non-zero terminal mass was calculated at the ending point of the luminous trajectory. In this way, the observational evidence points to the existence of a population of meteoroids in the higher end of the Geminid mass distribution capable of producing meteorites. From the relative chemical abundances inferred from the emission spectrum of this bolide we conclude that the Geminid-forming materials are similar to some primitive carbonaceous chondrite groups. Then, we conclude that in meteorite collections from cold deserts, capable to preserve meteorites of few tens of grams, some rare groups of carbonaceous chondrites could be coming from the Geminid parent body: (3200) Phaeton.

THE DUST TAIL OF ASTEROID (3200) PHAETHON

We report the discovery of a comet-like tail on asteroid (3200) Phaethon when imaged at optical wavelengths near perihelion. In both 2009 and 2012, the tail appears >=350" (2.5x10^8 m) in length and extends approximately in the projected anti-solar direction. We interpret the tail as being caused by dust particles accelerated by solar radiation pressure. The sudden appearance and the morphology of the tail indicate that the dust particles are small, with an effective radius ~1 micrometer and a combined mass ~3x10^5 kg. These particles are likely products of thermal fracture and/or desiccation cracking under the very high surface temperatures (~1000 K) experienced by Phaethon at perihelion. The existence of the tail confirms earlier inferences about activity in this body based on the detection of anomalous brightening. Phaethon, the presumed source of the Geminid meteoroids, is still active.

On the shape of meteor light curves, and a fully analytic solution to the equations of meteoroid ablation

The shape and characteristics (beginning and end heights, and height of maximum brightness) of meteor light curves are investigated under the constraint that the surface area S that a meteoroid presents to the oncoming air flow varies as a power law in the meteoroid mass m such that S ~ m α . We investigate the meteoroid ablation for a range of values of α, and find that the α = 1 condition allows for a fully analytic solution to the coupled differential equations of meteoroid ablation when the density profile is that of an isothermal atmosphere. The possible geometrical properties of Geminid meteoroids are discussed in terms of the α = 1 ablation model and it is shown that they are consistent with being derived from an asteroidal, rather than cometary, parent body.

Quantitative model of the release of sodium from meteoroids in the vicinity of the Sun: Application to Geminids

A considerable depletion of sodium was observed in Geminid meteoroids. To explain this phenomenon, we developed a quantitative model of sodium loss from meteoroids due to solar heating. We found that sodium can be lost completely from Geminid meteoroids after several thousands of years when they are composed of grains with sizes up to ∼100 μm. The observed variations of sodium abundances in Geminid meteor spectra can be explained by differences in the grain sizes among these meteoroids. Sodium depletions are also to be expected for other meteoroid streams with perihelion distances smaller than ∼0.2 AU. In our model, the meteoroids were represented by spherical dust-balls of spherical grains with an interconnected pore space system. The grains have no porosity and contain usual minerals known from meteorites and IDP's, including small amount of Na-bearing minerals. We modeled the sequence of three consecutive processes for sodium loss in Geminid meteoroids: (i) solid-state diffusion of Na atoms from Na-bearing minerals to the surface of grains, (ii) thermal desorption from grain surfaces and (iii) diffusion through the pore system to the space. The unknown material parameters were approximated by terrestrial analogs; the solid-state diffusion of Na in the grains was approximated by the diffusion rates for albite and orthoclase.

Densities and porosities of meteoroids

Using a physical theory of meteors and on the basis of the results of double-station photographic observations of meteors in Dushanbe (Tajikistan), Kiev, and Odessa (Ukraine), the mean mineralogical and bulk densities of meteoroids belonging to nine meteoroid streams and sporadic background are determined. The mean mineralogical densities of meteoroids range from 2.2 g cm-3 (Perseids) to 3.4 g cm-3 (Quadrantids, δ -Aquarids, and α -Capricornids). The meteoroid bulk densities δ , which were determined according to the theory of quasi-continuous fragmentation of meteoroids in the Earth's atmosphere, vary from 0.4 g cm-3 (Leonids) to 2.9 g cm-3 (Geminids). Using the relation between bulk density and mineralogical density the porosity of meteoroids was estimated. The Geminid meteoroids are found to have the lowest porosity, while the Leonid and Draconid meteoroids have the most porous structure (83%). These results confirm the porous-structure nature of meteoroids' parent bodies i.e. comets and asteroids.

Physical Observations of 2005 UD: A Mini-Phaethon

Planet-crossing object 2005 UD is dynamically similar to purported Geminid meteor-stream parent 3200 Phaethon, suggesting an association between the two. We present new physical observations taken to characterize 2005 UD when at 1.6 AU from the Sun. Assuming equal albedos, 2005 UD is about 4 times smaller than 3200 Phaethon, with a diameter of ~1.3 ± 0.1 km. The body shows periodic brightness variations of 0.4 mag that are compatible with an aspherical nucleus in rotation with a period near 5.2 hr. At optical wavelengths, 2005 UD is similar to or slightly bluer than the Sun. This property is relatively uncommon among near-Earth objects but is shared by Phaethon, strengthening the association between the two. No evidence for ongoing mass loss at rates as small as 0.01 kg s-1 is found in the surface brightness profile, and we conclude that the fraction of the surface that is losing mass is not greater than 10-4. Overall, we conclude that the dynamical similarities between 2005 UD and 3200 Phaethon are matched by physical similarities between these bodies, except that the former contains only about 2% of the mass of the latter. Phaethon, 2005 UD, and the Geminid meteoroids may be fragments produced by the breakup of a precursor object.

Double station and spectroscopic observations of the Quadrantid meteor shower and the implications for its parent body

Object 2003 EH 1 was recently identified as the parent body of the Quadrantid meteor shower. The origin of this body is still uncertain. We use data on 51 Quadrantid meteors obtained from double-station video observations as an insight on the parent body properties. A data analysis shows that the Quadrantids are similar to other meteor showers of cometary origin in some aspects, but in others to Geminid meteors. Quadrantid meteoroids have partially lost volatile component, but are not depleted to the same extent as Geminid meteoroids. In consideration of the orbital history of 2003 EH 1 , these results lead us to the conclusion that the parent body is a dormant comet.

A survey of meteor spectra and orbits: evidence for three populations of Na-free meteoroids

We present a survey of 97 spectra of mainly sporadic meteors in the magnitude range +3 to −1, corresponding to meteoroid sizes 1–10 mm. For the majority of the meteors, heliocentric orbits are known as well. We classified the spectra according to relative intensities of the lines of Mg, Na, and Fe. Theoretical intensities of these lines for a chondritic composition of the meteoroid and a wide range of excitation and ionization conditions were computed. We found that only a minority of the meteoroids show chondritic composition. Three distinct populations of Na-free meteoroids, each comprising ∼10% of sporadic meteoroids in the studied size range, were identified. The first population are meteoroids on asteroidal orbits containing only Fe lines in their spectra and possibly related to iron–nickel meteorites. The second population are meteoroids on orbits with small perihelia ( q ⩽ 0.2 AU ), where Na was lost by thermal desorption. The third population of Na-free meteoroids resides on Halley type cometary orbits. This material was possibly formed by irradiation of cometary surfaces by cosmic rays in the Oort cloud. The composition of meteoroids on Halley type orbits is diverse, probably reflecting internal inhomogeneity of comets. On average, cometary dust has lower than chondritic Fe/Mg ratio. Surprisingly, iron meteoroids prevail among millimeter-sized meteoroids on typical Apollo-asteroid orbits. We have also found varying content of Na in the members of the Geminid meteoroid stream, suggesting that Geminid meteoroids were not released from their parent body at the same time.

SPECTROSCOPY OF A GEMINID FIREBALL: ITS SIMILARITY TO COMETARY METEOROIDS AND THE NATURE OF ITS PARENT BODY

A detailed analysis of a photographic spectrum of a Geminid fireball obtained in December 14, 1961 at the Ondrejov Observatory is presented. We have computed a synthetic spectrum for the fireball and compared it with the observed spectrum assuming chemical equilibrium in the meteor head. In this way we have determined relative chemical abundances in meteor vapors. Comparing the relative chemical abundances of this Geminid meteoroid with those obtained from meteoroids associated with comets 55P/Tempel-Tuttle and 109P/Swift-Tuttle we found no significant chemical differences in main rock-forming elements. Despite of this similarity, the deepest penetration of the Geminid meteoroids and their ability to reach high rotation rates in space without fragmentation suggest that thermal processing is affecting their physical properties. We suggest that as consequence of space weathering a high-strength envelope is produced around these particles. In this picture, heating processes of the mineral phases could result in the peculiar properties observed during atmospheric entry of the Geminid meteoroids, especially their strength, which is evidenced by its resistance to ablation. Finally, although one meteoroid cannot be obviously considered as representative of the composition of its parent body, we conclude that 3200 Phaethon is able to produce millimetre-size debris nearly chondritic in composition, but the measured slight overabundance of Na would support a cometary origin for this body.

Analysis of a “flickering” Geminid fireball

Abstract— In the early morning hours of December 13, 2002, a bright Geminid fireball with an absolute magnitude of −9.2 ± 0.5 was observed from Southern Saskatchewan, Canada. The fireball displayed distinct small‐scale oscillations in brightness, or flickering, indicative of the parent meteoroid being both non‐spherical and rotating. Using the light curve derived from a calibrated radiometer, we determine a photometric mass of 0.429 ± 0.15 kg for the meteoroid, and we estimate from its initial rotation rate of some 6 Hz that the meteoroid was ejected from the parent body (3200) Phaethon some 2500 ± 500 years ago. We find that 70% of Geminid fireballs brighter than magnitude −3 display distinct flickering effects, a value that is in stark contrast to the 18% flickering rate exhibited by sporadic fireballs. The high coincidence of flickering and the deep atmospheric penetration of Geminid fireballs are suggestive of Geminid meteoroids having a highly resilient structure, a consequence, we suggest, of their having suffered a high degree of thermal processing. The possibility of Gemind material surviving atmospheric ablation and being sampled is briefly discussed, but the likelihood of collecting and identifying any such material is admittedly very small.

The age of the Geminids: a constraint from the spin-up time-scale

Interpreting fireball flickering in terms of the rotational modulation of the ablation process, the time since ejection into space of three Geminid meteoroids is determined. By estimating the time required to spin-up a meteoroid through non-isotropic photon scattering interactions with the solar radiation field, we find meteoroid ages consistent with ejection times some 1000‐ 4000 yr ago. There appears to be some indication that the stream formation process lasted for at least ∼1000 yr. We also estimate the rotational bursting conditions for the three Geminid meteoroids and find tensile strengths of some 3 × 10 5 Pa. We interpret our results as being supportive of the argument that the parent body to the Geminid stream, (3200) Phaethon, is an aged cometary nucleus.

Dynamic and Probabilistic Relation between Meteoroids and their Parent Bodies

AbstractWe estimate the probability that specific meteoroids were produced by a specific parent body and obtain the ejection velocity and several other conditions of the ejection as a by-product. The duration of cometary activity leading to a meteor stream, or the epoch of a collision can be estimated from the ejection times of meteoroids in the same stream. The level of activity of a comet or probability of asteroid collisions can be estimated from the part of the orbit where ejection took place. We show that Phaethon ejected Geminid meteoroids over at least 3000 years lasting to as recently as ≈ AD 1600. Ejections are predominantly in the direction of the sun, i.e., from Phaethon's day side, and give insights into the ejection process which is suggestive of cometary activity. Our calculations account for the uncertainty in the observational data and include the effects of planetary perturbations, radiation pressure, Poynting-Robertson light drag and solar wind corpuscular drag.

Geminid fireballs and the peculiar asteroid 3200 Phaethon

Twelve long-enduring Geminid fireballs from the camera network in western Canada are studied in an attempt to infer properties of their parent object, 3200 Phaethon. The Geminids decelerate from entry velocities of 36 km sec −1 to lower s limit near 15 km sec −1 and disappear at heights above 38 km. No fragments larger than dust particles appear capable of surviving as meteorites. Dynamic masses are derived for the Geminids from observed decelerations using an assumed shape based on data from the recovered fragments of the Innisfree meteorite fall. The luminosity of each fireball is used to obtain a photometric mass, assuming a luminous efficiency, τ, that is independent of velocity. Since Geminids resist crumbling and fragmentation, the dynamic and photometric masses should agree. It is shown that for reasonable values of τ, between 0.02 and 0.06, the masses agree for particle densities between 0.7 and 1.3 g cm −3. A best value of ρ m = 1.0 with τ = 0.034 is suggested. Geminids commonly exhibit flickering in their light, interpreted as an oscillation of the particle in flight. This may indicate the development of a relatively thin meteoroid during ablation and, in this case, the upper limit for the density could be raised to about 1.7. Eleven other fireballs, including four known or suspected meteorites and two fragile members of the Taurid complex, were studied for comparison with the Geminids. The meteorites penetrate the atmosphere considerably deeper than the Geminids, which in turn survive to lower heights than the more fragile objects. The ablation coefficients, σ, are comparable for Geminids and the meteorites, although σ may become meaningless for the low velocities observed in some meteorite events, due to neglect of the energy loss due to deceleration. Classification parameters suggest the Geminids are not as “tough” as meteorites but are more cohesive than many fireballs. It is concluded that Geminid meteoroids have too low a density to associate them with meteorites or normal asteroids. Frequent exposure to intense solar radiation near perihelion (0.14 AU) may lead to a loss of volatiles and may produce relatively tough meteoroids that resemble the crust of a comet rather than its interior.