Mass Distribution Of Meteoroids Research Articles

Learning about comets from the study of mass distributions and fluxes of meteoroid streams

ABSTRACT Meteor physics can provide new clues about the size, structure, and density of cometary disintegration products, establishing a bridge between different research fields. From meteor magnitude data we have estimated the mass distribution of meteoroids from different cometary streams by using the relation between the luminosity and the mass obtained by Verniani. These mass distributions are in the range observed for dust particles released from comets 1P/Halley and 81P/Wild 2 as measured from spacecraft. From the derived mass distributions, we have integrated the incoming mass for the most significant meteor showers. By comparing the mass of the collected interplanetary dust particles (IDPs) with that derived for cometary meteoroids a gap of several orders of magnitude is encountered. The largest examples of fluffy particles are clusters of IDPs no larger than 100 μm in size (or 5 × 10–7 g in mass) while the largest cometary meteoroids are centimeter-sized objects. Such gaps can be explained by the fragmentation in the atmosphere of the original cometary particles. As an application of the mass distribution computations we describe the significance of the disruption of fragile comets in close approaches to Earth as a more efficient (and probably more frequent) way to deliver volatiles than direct impacts. We finally apply our model to quantify the flux of meteoroids from different meteoroid streams, and to describe the main physical processes contributing to the progressive decay of cometary meteoroids in the interplanetary medium.

Measuring fluxes of meteor showers with the NASA All-Sky Fireball Network

We present an algorithm developed to measure the fluxes of major meteor showers as observed in NASA’s All-Sky Fireball Network cameras. Measurements of fluxes from the All-Sky cameras not only improve the Meteoroid Environment Office’s (MEO’s) ability to provide accurate risk assessments from major showers, but also allows the mass distribution of meteoroids within the shower to be constrained. This algorithm accounts for the shower-specific and event-specific exposure time and collecting area of the sky for nights where sufficiently large samples of shower meteors (~30 or more from the shower) are observed. The fluxes derived from the All-Sky Fireball Network for the 2015 Geminid, 2016 Perseid and Quadrantid, 2017 Orionid, and 2018 Leonid shower peaks are calculated. All five of these shower fluxes show excellent agreement with expectations from independent measurements at different mass and luminosity limits. For four of these five showers, the measured mass indices are significantly shallower than what is currently assumed by the NASA Meteoroid Environment Office’s (MEO’s) annual meteor shower forecast. A direct comparison between forecasted and measured fluxes at limiting masses of ~1g shows good agreement for the three showers for which the observations took place near their peak activity.

A Decade of Sporadic Meteoroid Mass Distribution Indices in the Southern Hemisphere Derived from SAAMER’s Meteor Observations

Abstract We present determinations of the meteoroid differential mass index, s, using over a decade of meteor observations from the Southern Argentina Agile MEteor Radar (SAAMER). For this, we employ an autonomous statistical technique to determine this parameter from the measured radar echo amplitudes. Unlike previous studies, we examine the role of the system noise in the determination of this parameter and found that if not taken into account appropriately, the results can yield significant over estimations of the mass index. In general we found that a value of s = 2.0 represents SAAMER’s results in general agreement with recent studies performed in the northern hemisphere. We explore both the index interannual and seasonal variability and, unlike previous studies, we found them to be constant, except during the presence of the Southern δ Aquariids meteor shower which is so strong that it dominates the meteor counts when present. Our study suggests that using the maximum echo amplitude for these studies is not ideal as it can be biased by many factors which make the inaccuracies larger than the precision estimated by the fitting routine. A method that results in a more direct estimate of the electron line density would be required which takes into account range, gain pattern, system noise, etc.

Determination of the meteor limiting magnitude

We present our method to calculate the meteor limiting magnitude. The limiting meteor magnitude defines the faintest magnitude at which all meteors are still detected by a given system. An accurate measurement of the limiting magnitude is important in order to calculate the meteoroid flux from a meteor shower or sporadic source. Since meteor brightness is linked to meteor mass, the limiting magnitude is needed to calculate the limiting mass of the meteor flux measurement. The mass distribution of meteoroids is thought to follow a power law, thus being slightly off in the limiting magnitude can have a significant effect on the measured flux. Sky conditions can change on fairly short timescales; therefore one must monitor the meteor limiting magnitude at regular intervals throughout the night, rather than just measuring it once. We use the stellar limiting magnitude as a proxy of the meteor limiting magnitude. Our method for determining the stellar limiting magnitude and how we transform it into the meteor limiting magnitude is presented. These methods are currently applied to NASA's wide-field meteor camera network to determine nightly fluxes, but are applicable to other camera networks.

Comparison of the structures of meteor streams of cometary and possible asteroidal origin

The structures of the meteor streams of cometary origin—Draconids, Ursids, Perseids, and Lyrids—and the streams presumably connected with asteroids—Taurids and α-Capricornids—are compared. The comparative analysis was performed by the mass distribution of meteoroids in the stream and the activity profile for the meteors with the maximum recorded stellar magnitude +3 m and brighter. Visual observations of 1987–2008 from the database of the International Meteor Organization (IMO) and earlier sources were considered. It has been shown that the structures of the meteor streams of cometary and, presumably, asteroidal origin differ somewhat by the activity profile and the mass distribution of meteoroids in the cross-section of a stream along the Earth’s orbit.

Mass distribution of lyrid meteoroids

Long-term visual observations of the Lyrid meteoroid shower have been analyzed to determine the mass distribution of Lyrid meteoroids. The value of the parameter S has been confirmed to be less than 1.8, which is normally assumed for meteoroid streams. The inclination of the descending and ascending branches of the S curve, depending on the longitude of the Sun, does not seem to exceed 3°. Observations carried out from 1987 until 2007 reveal that the minimum value of S corresponding to the longitude of the Sun 32.19 ± 0.04° is equal to 1.54 ± 0.02 (2000.0). The analysis of the S parameter derived from visual observations did not discover any particularities in the mass distribution of the meteoroids in the stream connected with the assumed 12-year enhancement period in the activity of the Lyrids.

Mass distribution of Perseid meteoroids

An analysis of the Perseid meteoroid mass distribution is given. It is shown that particle mass distributions are qualitatively the same along the entire orbit of the stream. The extra minima in the cross sections of the stream at the ascending and descending branches of the curve of the parameter S indicate a jetlike nature of the stream. The variations of the nodal longitudes of maximum stream activity versus the minimum observed mass of meteoroids are found along the entire orbit of the stream. The positions of maximum activity for particles with minimum detectable masses larger than 1 and 10−3 g are shifted by 1.4 degrees in solar longitude, with larger longitudes for smaller particles.

MASS FLUX OF ASTEROIDAL ORIGIN METEOROIDS ON PERIODIC COMET NUCLEI

We examine the potential contamination of cometary nuclei through impacts from asteroidal origin meteoroids. The paper uses a simple model and has the goal of determining whether asteroidal contamination is potentially significant. We assume a meteoroid power law mass distribution with index values in the range from s=1.83 to s=2.09. We used maximum and minimum models which we believe will bracket the true meteoroid mass distribution. We identify those comets which are expected to be most significantly contaminated, and find values of up to 3.6 kg of asteroidal meteoroid impact per square meter of the cometary surface per orbital revolution. This is less than the expected mass loss per perihelion passage for most comets. Therefore any remnant effects of the contamination will depend on the penetration depth of the meteoroids in the cometary nucleus, and possibly on the distribution of active and inactive areas on cometary nuclei. We present a simple model which suggests that even small meteoroids will embed relatively deeply into a cometary nucleus.

Meteor44 Video Meteor Photometry

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The photometric range of the (8 bit) video data is extended from a visual magnitude range of from 8 to 3 to from 8 to −8 for both meteors and stellar images using saturation compensation. Camera and lens specific saturation compensation coefficients are derived from artificial variable star laboratory measurements. Saturation compensation significantly increases the number of meteors with measured intensity and improves the estimation of meteoroid mass distribution. Astrometry is automated to determine each image’s plate coefficient using appropriate star catalogs. The images are simultaneously intensity calibrated from the contained stars to determine the photon sensitivity and the saturation level referenced above the atmosphere. The camera’s spectral response is used to compensate for stellar color index and typical meteor spectra in order to report meteor light curves in traditional visual magnitude units. Recent efforts include improved camera calibration procedures and long focal length “treak” meteor photometry. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers.

A Direct Measurement of the Terrestrial Mass Accretion Rate of Cosmic Dust

The mass of extraterrestrial material accreted by the Earth as submillimeter particles has not previously been measured with a single direct and precise technique that samples the particle sizes representing most of that mass. The flux of meteoroids in the mass range 10(-9) to 10(-4) grams has now been determined from an examination of hypervelocity impact craters on the space-facing end of the Long Duration Exposure Facility satellite. The meteoroid mass distribution peaks near 1.5 x 10(-5) grams (200 micrometers in diameter), and the small particle mass accretion rate is (40 +/- 20) x 106 kilograms per year, higher than previous estimates but in good agreement with total terrestrial mass accretion rates found by geochemical methods. This mass input is comparable with or greater than the average contribution from extraterrestrial bodies in the 1-centimeter to 10-kilometer size range.

Meteoric ion production near Jupiter

The effects of meteoroids on the Jovian ionosphere are explored through model calculations of the Fe+ production rates associated with these particles. Dohnanyi's meteoroid mass distribution law appropriate to the near‐earth environment is extrapolated to Jupiter. For a possible meteoroid spatial density at Jupiter 10 times that at the earth, gravitational focusing could produce a cumulative meteoroid flux into the Jovian atmosphere nearly 3 orders of magnitude greater than that in the earth's atmosphere. The spatial density at Jupiter may also be down to an order of magnitude smaller. For this maximum meteoroid flux, assuming chondritic characteristics and using an ionization probability for Fe impacting H2 estimated as 0.3 times that for measured interactions with air, the ablation and impact ionization rates for Fe and Fe+ were computed. The Fe+ impact ionization rate within the Jovian atmosphere peaks above the mesopause with a magnitude ∼0.5 cm−3 s−1 and is much less than the ambient ionosphere photoionization rates near the late afternoon Pioneer 10 ionosphere occultation. Charge exchange of the ablated neutral Fe atoms with ambient ions can result in an Fe+ production rate of ∼10 cm−3 s−1 which is comparable to the ambient rates. Photoionization of metallic atoms is ignorable compared to charge exchange as a source of Fe+. Ignoring transport, steady state Fe+ density maxima of ∼104 or 106 cm−3 can be maintained when Fe+ loss is through radiative association or radiative recombination, respectively. Even if one uses an estimated lower limit to the incident meteoroid flux based on a meteoroid spatial density which does not vary with distance from the sun, the corresponding Fe+ peak densities are ∼10³ and 5 × 105 cm−3, respectively. Hence meteoric ion densities may be significant in the lower ionosphere of Jupiter.

Mass distribution of massive meteoroids determined by occurrence of brilliant fireballs

DETERMINATION of the mass distribution function of bodies is of prime importance for an understanding of the evolutionary processes that determine the population of the Solar System. We report here a method for measuring mass distribution of meteoroids, by determining the occurrence frequency of very brilliant fireballs. In a certain mass regime the number distribution can be described by a power law dn = (const.)m−s dm where dn is the number of particles having a mass between m and m+dm and s is the mass distribution index. s is a slowly varying function of mass, and values of s have been well established for meteoroid particles 10−12< m ≲ 101 g by various techniques, and reasonable estimates are available for large bodies m ≳ 105 g (meteorites and asteroids). There is, however, a lack of information in the mass range 101 ≲ m ≲ 105 g corresponding1 to meteoroids which yield meteors of visual magnitude − 2 ≳ Mv □ − 12 ranging from bright visual objects to very brilliant fireballs (the term fireball generally refers to any meteor brighter than Venus, Mv ≃ −4). The problem is one of sampling: while meteor (radar, visual, optical) counts over periods of hours at a single station are suitable for estimates of s for m ≲ 1 g (Mv ≳ 0), such a procedure yields a prohibitively low count for larger objects. This difficulty would be overcome by observing over a large area of the Earth's surface for many years. We determine here the occurrence frequency of very brilliant fireballs, as a method of s measurement. A fireball of magnitude equal to that of the full Moon is an outstanding spectacle likely to be well reported in an area with a high population density. With good communications and active research groups analysing reports and recording data, a reliable estimate of the influx of such large objects could be secured. In the British Isles, extensive records of fireball events covering more than 40 yr, are available2,3. Most observers' estimates were based on the great illumination produced on the landscape or inside buildings, and the personnel analysing the reports were experienced workers in the field. A detailed examination of the reports reveals a consistent rate of about two lunar fireballs (apparent visual magnitude equal to or brighter than that of the full Moon) seen in the British Isles per year. Specifically, in the period 1900–36 the average occurrence frequency was 2.4 yr−1. This frequency can be compared with that of visual meteors to obtain an estimate of s.

Variation in the number of meteoroid impacts on the Moon with lunar phase

Data from the ALSEP 12 and 14 seismometers of the Apollo Passive Seismic Experiment Network are used to determine the statistics of the mass distribution of meteoroids and their direction of approach in near earth space. The cumulative number of meteoroid impacts detected is analyzed as a function of phase of the moon, taking into account the sensitivity of the seismometer and the seismic wave propagation characteristics of the moon. We conclude that, in the mass range studied (&gt;5 kg), (a) most meteoroid orbits lie near the plane of the ecliptic, (b) the orbits have aphelia between 2 and 5 a.u., and (c) the mass distribution statistics are described by the relation log10 n = B + G log10 m, where n = number of meteoroids of mass m grams or greater, B ∼ 0.9 and G = −1.5.

Pioneer 11 Meteoroid Detection Experiment: Preliminary Results

The concentration of meteoroids of mass ~ 10(-8) gram in interplanetary space, in the asteroid belt, and near Jupiter has been measured. The data confirm the Pioneer 10 observation that the asteroid belt is not highly populated with small meteoroids, suggest that the high concentration of small particles around Jupiter is the result of gravitational focusing, and provide an indication of the mass distribution of meteoroids in interplanetary space.

Current Evolution of Meteoroids

The observed mass distribution of meteoroids at 1 AU from the Sun is briefly reviewed in a survey that ranges over the bulk of the mass spectrum from micrometeoroids to meteorite parent objects. The evolution of meteoroids under the influence of collisions, planetary perturbations, the Poynting-Robertson effect and radiation pressure is then discussed.Most micrometeoroids are expelled from the solar system by radiation pressure shortly after their production as secondary ejecta during impact by larger objects or as dust ejected by comets. Particles that survive will eventually be swept out by the Poynting-Robertson effect.Meteoroids in the radio and photographic ranges are destroyed in collisions faster than they can be replaced by the production of secondary fragments during collisions between larger objects. The source of new particles needed to maintain the population of these meteoroids in a stationary distribution may be material expelled by comets.The survival of large objects is limited by gravitational scattering during close planetary encounters and by collisions as well, if they spend sufficient time in the asteroid belt. The observed radiation-exposure ages of chondrites are shown to be consistent with this model.

On the origin and distribution of meteoroids

The influence of collisional and radiative processes on the population of sporadic and shower meteoroids is examined. It is found that the observed distribution of sporadic meteoroids in the photographic and radio ranges is unstable: collisional processes would rapidly change the distribution of these particles if they are not replenished by a source. It is shown that, in order to maintain the distribution of these sporadic meteoroids in a steady-state condition, a source is needed that replaces the sporadic meteoroids destroyed by collisions. The mass distribution of the required source is calculated and found to agree with the distribution of bright radio-shower meteors, provided that the population index α of sporadic meteors (in the photographic and radio ranges) is taken to be α = 13/6. The evolution of the population in a meteor shower under the influence of collisions with sporadic meteoroids is also examined. Since small particles have shorter lifetimes (with respect to collisions) than do larger particles, the population of faint shower meteors is more strongly affected. It is found that the mass distribution of faint radio meteors in the major showers considered here agrees with the results of the analysis, provided that α = 13/6, for sporadic meteors. Taking α = 13/6 therefore provides self-consistency for analysis and observation, thereby providing new evidence favoring the cometary origin of meteors. The rate at which the population of sporadic meteoroids is losing mass is calculated and found to compare favorably with F. L. Whipple's 1967 estimate as well as his estimate of the rate at which comets are injecting meteoritic mass into the solar system. The influence of the Poynting-Robertson effect on the meteoroid mass distribution is found to be minor; collisional processes dominate the evolution of meteoroids in the faint and brighter radio range. The influence of radiation pressure may be profound. By using previous work by Harwit and geometrical optics, it is shown that the smallest masses present in the major meteoroid showers are in the range of 10−6 to 10−10 gram. This is precisely the mass range where a leveling off of the distribution of sporadic meteoroids is indicated by satellite penetration measurements; these measurements are therefore consistent with the cometary origin of sporadic meteoroids. These theoretical results may not apply to particles with masses of 10−12 gram or smaller (i.e., submicron particles, for which details of physical optics become important).

Mass distribution of meteoroids as determined by radar observations of underdense meteor trails

The amplitudes of meteor echoes recorded on high-power radar equipment at Springhill Meteor Observatory have been measured for 57 samples of about 500 meteors each, obtained at various times of day on at least 1 day per month. The number of echoes as a function of echo amplitude is represented by a power law and the exponent in this relation calculated for each sample. Within the limits of error, no strong diurnal or seasonal variations in this exponent have been found. Similarly, there are no significant changes in the exponent when the data are divided into groups according to the height at which the echoes occurred and also according to the distance from the radar to meteor trail.Calibration of the equipment and the methods employed in obtaining and reducing the data are treated in detail. Theory relating the number distribution of echo amplitudes to the distribution of meteoroid masses is reviewed and assessed critically.A best value for the average mass index, s, of the sporadic meteor population in the range from 7th to 10th magnitude is s = 2.3 ± 0.1. The dispersion of individual sample values of s is about ± 0.3.

METEOR RADAR STATISTICS. II

Mean daily values of meteor flux for three categories of meteor echoes are tabulated for the period 1958 to 1962. The variation of echo rate with echo duration is studied. The difficulty of using this relation to determine the mass distribution of meteoroids in interplanetary space is noted.