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NASA NTRS2016

Performance of D-Parameters in Isolating Meteor Showers from the Sporadic Background

It is often necessary to draw a division between meteor showers and the sporadic meteor complex in order to study these components of the meteoroid environment. Meteor showers persist for less than a season and are composed of members with a greater-than-average degree of orbital similarity. The level of orbital similarity is often quantified using so-called D-parameters; a D-parameter cutoff may be employed to define or extract a shower. Depending on the study, this cutoff value may be chosen based on the size of the data-set, the percentage of sporadic meteors within the data-set, or the inclination of the shower in question. We argue that the cutoff value should also reject the strength of the shower compared to the local sporadic background. We therefore present a method for determining, on a per-shower basis, the D-parameter cutoff that limits the false-positive rate to an acceptable percentage. If the false-positive rate exceeds this percentage regardless of cutoff value, we deem the shower to be undetectable in our data. We apply this method to optical meteor observations from the NASA All-Sky and Southern Ontario Meteor Networks and present the detectable meteor showers and their characteristics.

Moorhead, Althea↗
NASA NTRS2016

Determination of the Meteor Limiting Magnitude

The limiting meteor magnitude of a meteor camera system will depend on the camera hardware and software, sky conditions, and the location of the meteor radiant. Some of these factors are constants for a given meteor camera system, but many change between meteor shower or sporadic source and on both long and short timescales. Since the limiting meteor magnitude ultimately gets used to calculate the limiting meteor mass for a given data set, it is important to have an understanding of these factors and to monitor how they change throughout the night, as a 0.5 magnitude uncertainty in limiting magnitude translates to a uncertainty in limiting mass by a factor of two.

Kingery, A.↗
NASA NTRS2017

The 2017 Meteor Shower Activity Forecast for Earth Orbit

Most meteor showers will display typical activity levels in 2017. Perseid activity is expected to be higher than normal but less than in 2016; rates may reach 80% of the peak ZHR in 2016. Despite this enhancement, the Perseids rank 4th in flux for 0.04-cm-equivalent meteoroids: the Geminids (GEM), Daytime Arietids (ARI), and Southern delta Aquariids (SDA) all produce higher fluxes. Aside from heightened Perseid activity, the 2017 forecast includes a number of changes. In 2016, the Meteoroid Environment Office used 14 years of shower flux data to revisit the activity profiles of meteor showers included in the annual forecast. Both the list of showers and the shape of certain major showers have been revised. The names and three-letter shower codes were updated to match those in the International Astronomical Union (IAU) Meteor Data Center, and a number of defunct or insignificant showers were removed. The most significant of these changes are the increased durations of the Daytime Arietid (ARI) and Geminid (GEM) meteor showers. This document is designed to supplement spacecraft risk assessments that incorporate an annual averaged meteor shower flux (as is the case with all NASA meteor models). Results are presented relative to this baseline and are weighted to a constant kinetic energy. Two showers - the Daytime Arietids (ARI) and the Geminids (GEM) - attain flux levels approaching that of the baseline meteoroid environment for 0.1-cm-equivalent meteoroids. This size is the threshold for structural damage. These two showers, along with the Quadrantids (QUA) and Perseids (PER), exceed the baseline flux for 0.3-cm-equivalent particles, which is near the limit for pressure vessel penetration. Please note, however, that meteor shower fluxes drop dramatically with increasing particle size. As an example, the Arietids contribute a flux of about 5x10(exp -6) meteoroids m(exp -2) hr-1 in the 0.04-cm-equivalent range, but only 1x10(exp -8) meteoroids m(sub -2) hr-1 for the 0.3-cmequivalent and larger size regime. Thus, a PNP risk assessment should use the flux and flux enhancements corresponding to the smallest particle capable of penetrating a component, because the flux at this size will be the dominant contributor to the risk.

Moorhead, Althea↗
NASA NTRS2017

An Orbital Meteoroid Stream Survey Using the Southern Argentina Agile Meteor Radar (SAAMER) Based on a Wavelet Approach

Over a million individually measured meteoroid orbits were collected with the Southern Argentina Agile MEteor Radar (SAAMER) between 2012-2015. This provides a robust statistical database to perform an initial orbital survey of meteor showers in the Southern Hemisphere via the application of a 3D wavelet transform. The method results in a composite year from all 4 years of data, enabling us to obtain an undisturbed year of meteor activity with more than one thousand meteors per day. Our automated meteor shower search methodology identified 58 showers. Of these showers, 24 were associated with previously reported showers from the IAU catalogue while 34 showers are new and not listed in the catalogue. Our searching method combined with our large data sample provides unprecedented accuracy in measuring meteor shower activity and description of shower characteristics in the Southern Hemisphere. Using simple modeling and clustering methods we also propose potential parent bodies for the newly discovered showers.

Meteor showers↗
NASA NTRS2017

Results of the First Continuous Meteor Head Echo Survey at Polar Latitudes

We present the first quasi continuous meteor head echo measurements obtained during a period of over two years using the Middle Atmosphere ALOMAR Radar System (MAARSY). The measurements yield information on the altitude, trajectory, vector velocity, radar cross section, deceleration and dynamical mass of every single event. The large statistical amount of nearly one million meteor head detections provide an excellent overview of the elevation, altitude, velocity and daily count rate distributions during different times of the year at polar latitudes. Only 40 percent of the meteors were detected within the full width half maximum of the specific sporadic meteor sources. Our observation of the sporadic meteors are compared to the observations with other radar systems and a meteor input function (MIF). The best way to compare different radar systems is by comparing the radar cross section (RCS), which is the main detection criterion for each system. In this study we aim to compare our observations with a MIF, which provides information only about the meteoroid mass. Thus, we are using a statistical approach for the elevation and velocity dependent visibility and a specific mass selection. The predicted absolute count rates from the MIF are in a good agreement with the observation when it is assumed that the radar system is only sensitive to meteoroids with masses higher than one microgram. The analysis of the dynamic masses seems to be consistent with this assumption since the count rate of events with smaller masses are low and decrease even more by using events with relatively small errors.

Interplanetary dust↗
NASA NTRS1975

SEC Vidicon spectra of Geminid meteors, 1972

The SEC Vidicon, a low light level closed circuit television system, was used to obtain 137 spectrographic records of meteors at Mt. Hopkins, Arizona, during the Geminid meteor shower in December 1972. Seven of the best Geminid meteor spectra are studied here in detail. The near infrared, out to wavelengths near 9000 A, is recorded for the first time for Geminids. The spectra, in general, exhibit the elements previously found in photographic records of this shower but show a surprising frequency of occurrence of the forbidden green line of O I at 5577 A. This line is normally absent from meteors moving as slowly as the Geminids (36 km/sec) and its presence in these records may be due to the added sensitivity available with the SEC Vidicon. The average green line duration in Geminid meteors with a luminosity near zero absolute visual magnitude is 0.73 sec at a mean height of 95 km, 11 km lower than the green line peak in Perseid meteors of the same luminosity.

Millman, P. M.↗
NASA NTRS1975

Southern Hemisphere meteor stream determinations

Meteor orbits have been deduced from radio observations of meteor trails carried out at Adelaide, Australia, using a combined multistation CW and pulse radar system operating at 27 MHz. The orbits of 1667 meteors have been determined down to a limiting radio magnitude of +8. The data have been systematically searched for stream meteors, and the significance of minor associations has been appraised. Altogether, 40.4% of the orbits were found to be associated with at least one other orbit, and 29.8% with two or more. Numerous minor streams with high inclination and low eccentricity have been found at deep southern declinations from December to March, with little activity in this quarter during June and October. In addition to confirming several previously established cometary associations, a comprehensive search has indicated that 34 of the meteor associations may be related to 17 comets. Associations between several long-period comets and low-eccentricity high-inclination streams appear to be indisputable, and they confirm the origin of at least some of the 'toroidal group' meteors.

Gartrell, G.↗
NASA NTRS1980

Flux of optical meteors down to M sub pg = +12

Observations of the flux of optical meteors down to photographic magnitudes of +12 are reported. The meteors were detected by photometry using a 10-m optical reflector from December 12-15, 1974, during the Geminid shower. A total of 2222 light pulses is identified as coming from meteors within the 1 deg field of view of the detector, most of which correspond to sporadic meteors traversing the detector beam at various angles and velocities and do not differ with the date, indicating that the Geminid contribution at faint luminosities is small compared to the sporadic contribution. A rate of 1.1 to 3.3 x 10 to the -12th meteors/sq cm per sec is obtained together with a power law meteor spectrum which is used to derive a relationship between cumulative meteor flux and magnitude which is linear for magnitudes from -2.4 through +12. Expressions for the cumulative flux upon the earth's atmosphere and at a test surface at 1 AU far from the earth as a function of magnitude are also obtained along with an estimate of the cumulative number density of particles.

Cook, A. F.↗
NASA NTRS1984

MENTOR: Adding an outlying receiver to an ST radar for meteor-wind measurement

Radar scattering from ionized meteor trails has been used for many years as a way to determine mesopause-level winds. Scattering occurs perpendicular to the trails, and since the ionizing efficiency of the incoming meteoroids depends on the cosine of the zenith angle of the radiant, echoes directly overhead are rare. Stratosphere-troposphere (ST) radars normally sample within 15 deg of the vertical, and thus receive few meteor echoes. Even the higher powdered mesosphere-stratosphere-troposphere (MST) radars are not good meteor radars, although they were used to successfully retrieved meteor winds from the Poker Flat, Alaska MST radar by averaging long data intervals. It has been suggested that a receiving station some distance from an ST radar could receive pulses being scattered from meteor trails, determine the particular ST beam in which the scattering occurred, measure the radial Doppler velocity, and thus determine the wind field. This concept has been named MENTOR (Meteor Echoes; No Transmitter, Only Receivers).

Roper, R. G.↗
NASA NTRS2000

Observations of Leonid Meteors Using a Mid-Wave Infrared Imaging Spectrograph

We report broadband 3-5.5 micrometer detections of two Leonid meteors observed during the 1998 Leonid Multi-Instrument Aircraft Campaign. Each meteor was detected at only one position along their trajectory just prior to the point of maximum light emission. We describe the particular aspects of the Aerospace Corp. Mid-wave Infra-Red Imaging Spectrograph (MIRIS) developed for the observation of short duration transient events that impact its ability to detect Leonid meteors. This instrument had its first deployment during the 1998 Leonid MAC. We infer from our observations that the mid-infrared light curves of two Leonid meteors differed from the visible light curve. At the points of detection, the infrared emission in the MIRIS passband was 25 +/- 4 times that at optical wavelengths for both meteors. In addition, we find an upper limit of 800 K for the solid body temperature of the brighter meteor we observed, at the point in the trajectory where we made our mid-wave infrared detection.

Rossano, G. S.↗
NASA NTRS2004

Meteor44 Video Meteor Photometry

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The dynamic range of the (8bit) video data is extended by approximately 4 magnitudes 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, long focal length 'streak' meteor photometry and two-station track determination. Meteor44 has been used to analyze data from the 2001, 2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers. The software is interactive and can be demonstrated using data from recent Leonid campaigns.

Swift, Wesley R.↗
NASA NTRS2004

Meteor44 Video Meteor Photometry

Meteor44 is a software system developed at MSFC for the calibration and analysis of video meteor data. The dynamic range of the (8bit) video data is extended by approximately 4 magnitudes 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, long focal length "streak" meteor photome&y and two-station track determination. Meteor44 has been used to analyze data from the 2001.2002 and 2003 MSFC Leonid observational campaigns as well as several lesser showers. The software is interactive and can be demonstrated using data from recent Leonid campaigns.

Swift, Wesley R.↗
NASA NTRS2004

Hydrogen emission in meteors as a potential marker for the exogenous delivery of organics and water

We detected hydrogen Balmer-alpha (H(alpha)) emission in the spectra of bright meteors and investigated its potential use as a tracer for exogenous delivery of organic matter. We found that it is critical to observe the meteors with high enough spatial resolution to distinguish the 656.46 nm H(alpha) emission from the 657.46 nm intercombination line of neutral calcium, which was bright in the meteor afterglow. The H(alpha) line peak stayed in constant ratio to the atmospheric emissions of nitrogen during descent of the meteoroid. If all of the hydrogen originates in the Earth's atmosphere, the hydrogen atoms are expected to have been excited at T = 4400 K. In that case, we measured an H(2)O abundance in excess of 150 +/- 20 ppm at 80-90 km altitude (assuming local thermodynamic equilibrium in the air plasma). This compares with an expected <20 ppm from H(2)O in the gas phase. Alternatively, meteoric refractory organic matter (and water bound in meteoroid minerals) could have caused the observed H(alpha) emission, but only if the line is excited in a hot T approximately 10000 K plasma component that is unique to meteoric ablation vapor emissions such as Si(+). Assuming that the Si(+) lines of the Leonid spectrum would need the same hot excitation conditions, and a typical [H]/[C] = 1 in cometary refractory organics, we calculated an abundance ratio [C]/[Si] = 3.9 +/- 1.4 for the dust of comet 55P/Tempel-Tuttle. This range agreed with the value of [C]/[Si] = 4.4 measured for comet 1P/Halley dust. Unless there is 10 times more water vapor in the upper atmosphere than expected, we conclude that a significant fraction of the hydrogen atoms in the observed meteor plasma originated in the meteoroid.

Water↗
NASA NTRS2004

Meteors do not break exogenous organic molecules into high yields of diatomics

Meteoroids that dominate the Earth's extraterrestrial mass influx (50-300 microm size range) may have contributed a unique blend of exogenous organic molecules at the time of the origin of life. Such meteoroids are so large that most of their mass is ablated in the Earth's atmosphere. In the process, organic molecules are decomposed and chemically altered to molecules differently from those delivered to the Earth's surface by smaller (<50 microm) micrometeorites and larger (>10 cm) meteorites. The question addressed here is whether the organic matter in these meteoroids is fully decomposed into atoms or diatomic compounds during ablation. If not, then the ablation products made available for prebiotic organic chemistry, and perhaps early biology, might have retained some memory of their astrophysical nature. To test this hypothesis we searched for CN emission in meteor spectra in an airborne experiment during the 2001 Leonid meteor storm. We found that the meteor's light-emitting air plasma, which included products of meteor ablation, contained less than 1 CN molecule for every 30 meteoric iron atoms. This contrasts sharply with the nitrogen/iron ratio of 1:1.2 in the solid matter of comet 1P/Halley. Unless the nitrogen content or the abundance of complex organic matter in the Leonid parent body, comet 55P/Tempel-Tuttle, differs from that in comet 1P/Halley, it appears that very little of that organic nitrogen decomposes into CN molecules during meteor ablation in the rarefied flow conditions that characterize the atmospheric entry of meteoroids approximately 50 microm-10 cm in size. We propose that the organics of such meteoroids survive instead as larger compounds.

Meteoroids↗
NASA NTRS2011

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 (approx. > 10(exp 5) yr at 1 AU) than postulated in the standard collisional models (approx 10(exp 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) 10(exp 11) sq km and approx. 4 10(exp 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 approx. 10(exp 4)-10(exp 5) kg/s. The input is up to approx 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. The total mass accreted by the Earth in particles between diameters D = 5 micron and 1 cm is found to be approx 15,000 tons/yr (factor of 2 uncertainty), which is a large share of the accretion flux measured by the Long Term Duration Facility (LDEF). Majority of JFC particles plunge into the upper atmosphere at <15 km/s speeds, should survive the atmospheric entry, and can produce micrometeorite falls. This could explain the compositional similarity of samples collected in the Antarctic ice and stratosphere, and those brought from comet Wild 2 by the Stardust spacecraft. Meteor radars such as CMOR and AMOR see only a fraction of the accretion flux (approx 1- 10% and approx 10-50%, respectively), because small particles impacting at low speeds produce ionization levels that are below these radars detection capabilities.

Nesvorny, David↗
NASA NTRS2014

Collecting Comet Samples by ER-2 Aircraft: Cosmic Dust Collection During the Draconid Meteor Shower in October 2012

Many tons of dust grains, including samples of asteroids and comets, fall from space into the Earth's atmosphere each day. NASA periodically collects some of these particles from the Earth's stratosphere using sticky collectors mounted on NASA's high-flying aircraft. Sometimes, especially when the Earth experiences a known meteor shower, a special opportunity is presented to associate cosmic dust particles with a known source. NASA JSC's Cosmic Dust Collection Program has made special attempts to collect dust from particular meteor showers and asteroid families when flights can be planned well in advance. However, it has rarely been possible to make collections on very short notice. In 2012, the Draconid meteor shower presented that opportunity. The Draconid meteor shower, originating from Comet 21P/Giacobini-Zinner, has produced both outbursts and storms several times during the last century, but the 2012 event was not predicted to be much of a show. Because of these predictions, the Cosmic Dust team had not targeted a stratospheric collection effort for the Draconids, despite the fact that they have one of the slowest atmospheric entry velocities (23 km/s) of any comet shower, and thus offer significant possibilities of successful dust capture. However, radar measurements obtained by the Canadian Meteor Orbit Radar during the 2012 Draconids shower indicated a meteor storm did occur October 8 with a peak at 16:38 (+/-5 min) UTC for a total duration of approximately 2 hours.

Bastien, Ron↗
NASA NTRS2015

The 2014 KCG Meteor Outburst: Clues to a Parent Body

The Kappa Cygnid (KCG) meteor shower exhibited unusually high activity in 2014, producing ten times the typical number of meteors. The shower was detected in both radar and optical systems and meteoroids associated with the outburst spanned at least five decades in mass. In total, the Canadian Meteor Orbit Radar, European Network, and NASA All Sky and Southern Ontario Meteor Network produced thousands of KCG meteor trajectories. Using these data, we have undertaken a new and improved characterization of the dynamics of this little-studied, variable meteor shower. The Cygnids have a di use radiant and a significant spread in orbital characteristics, with multiple resonances appearing to play a role in the shower dynamics. We conducted a new search for parent bodies and found that several known asteroids are orbitally similar to the KCGs. N-body simulations show that the two best parent body candidates readily transfer meteoroids to the Earth in recent centuries, but neither produces an exact match to the KCG radiant, velocity, and solar longitude. We nevertheless identify asteroid 2001 MG1 as a promising parent body candidate.

Moorhead, Althea V.↗
NASA NTRS2015

The Application of New Optical Meteor Flux Routines to the 2014 May Camelopardalid Outburst

NASA's Meteoroid Environment Office (MEO) is charged with monitoring the meteoroid environment in near-Earth space for the protection of satellites and spacecraft. The MEO has recently established eight wide-field meteor cameras, four cameras each at two separate stations to calculate automated meteor fluxes in the millimeter size range. Each camera consists of a 17 mm focal length Schneider lens on a Watec 902H2 Ultimate CCD video camera, producing a 21.7 x 15.5 degree field of view. This configuration has a limiting meteor magnitude of about +5. One station is located at Marshall Space Flight Center in Huntsville, Alabama and the other is 31.8 kilometers away at a school in Decatur, Alabama. Both single-station and double-station fluxes are calculated every morning using data from the previous night. The flux algorithms employed here differ from others currently in use in that they do not assume a single height for all meteors observed in the common camera volume. In the MEO system, the volume is broken up into a set of height intervals, with the collecting areas determined by the position of the active shower or sporadic source radiant. The flux per height interval is calculated and summed to obtain the total meteor flux. As the mass is also computed from the photometry, a mass flux can also be calculated. First, a weather algorithm indicates if sky conditions are clear enough to calculate fluxes, at which point a limiting magnitude algorithm is employed. The limiting magnitude algorithm performs a fit of stellar magnitudes versus camera intensities. The stellar limiting magnitude is derived from this and converted to a limiting meteor magnitude for the active shower or sporadic source. The fluxes are scaled to an average limiting magnitude throughout the night and zenithal hourly rate (ZHR's) are output daily along with flux values. In addition to this process, results will be presented as applied to the 2014 May Camelopardalid outburst, using data from several different optical systems, which looked at May Camelopardalids in different size ranges.

Blaauw, Rhiannon↗