Sporadic Background Research Articles

Statistical equivalence of metrics for meteor dynamical association

Meteor showers, originating as a result of the activity of comets or the disruption of large objects, provide a unique window into the composition and dynamics of our Solar System. While modern meteor detection networks have amassed extensive data, distinguishing sporadic meteors from those belonging to specific meteor showers remains challenging. In this study, we statistically evaluate and compare four orbital similarity criteria within five-dimensional parameter space (DSH,DD,DH, and ϱ2) to study dynamical associations using the already classified meteors (manually by a human) in CAMS database as a benchmark. In addition, we assess various distance metrics typically used in Machine Learning with two different vectors: ORBIT, grounded in heliocentric orbital elements, and GEO, predicated on geocentric observational parameters. To estimate their degree of correlation and efficacy, the Kendall rank correlation coefficient and the Top-k accuracy are employed. The statistical equivalence of the Top-1 results is examined using the Kolmogorov–Smirnov test and the percentage of Top-1 agreement is calculated on an event-by-event basis. Additionally, we compute the optimal cut-offs for all methods for distinguishing sporadic background events. Our findings demonstrate the superior performance of the sEuclidean metric in conjunction with the GEO vector. Within the scope of D-criteria, DSH emerged as the preeminent metric, closely followed by ϱ2. The Bray-Curtis metric displayed an advantage compared to the other distance metrics when paired with the ORBIT vector for Top-k accuracy, however, the Cityblock metric is more effective when considering the sporadic background. ϱ2 stands out as the most equivalence to the distance metrics when utilizing the GEO vector and the most compatible with GEO and ORBIT simultaneously, whereas DD aligns more closely when using the ORBIT vector. The stark contrast in DD’s behavior compared to other D-criteria highlights potential inequivalence. Our results suggest that geocentric features provide a more robust basis than orbital elements for meteor dynamical association. Most distance metrics associated with the GEO vector surpass the D-criteria when differentiating the meteoroid background. Accuracy displayed a dependence on solar longitude with a pronounced decrease around 180° matching an apparent increase in the meteoroid background activity, tentatively associated with the transition from the Perseids to the Orionids. Considering lately identified meteor showers, ∼27% of meteors in CAMS would have different associations. This work unveils that Machine Learning distance metrics can rival or even exceed the performance of tailored orbital similarity criteria for meteor dynamical association.

Gardenia blue is not carcinogenic in the rasH2 mouse

Introduction Gardenia blue is currently being considered as a naturally derived food colorant for use in the global marketplace. Methods To assess its carcinogenic potential, 100 female and 100 male CByB6F1-Tg (HRAS)2Jic (rasH2) mice were allocated to four dose groups and exposed to gardenia blue in the diet for 26 weeks at dose levels of 0.0% (control), 0.5%, 2.5%, or 5.0% (corresponding to 0.0, 664.8, 3341.0, and 6623.2 mg/kg/day in male mice and 0.0, 1182.7, 5561.1, and 10,440.3 mg/kg/day in female mice, respectively). An additional group of 10 males and 10 females was administered intraperitoneal N-methyl-N-nitrosourea (MNU) as a positive control. Clinical observations, body and organ weights, clinical chemistry, hematology, and hormone analyses were performed in addition to urinalysis and histopathology. Results The positive control elicited expected responses specific to rasH2 mice. There were sporadic background non-dose-related findings in clinical pathology parameters and anatomic pathology common to rasH2 mice in the absence of any gardenia blue induced dose-related changes. Discussion Under these study conditions, the no-observed-adverse-effect level was 5% gardenia blue (6623.2 mg/kg/day in male mice and 10,440.3 mg/kg/day in female mice). Conclusions Based on this study a high dietary level of gardenia blue was negative for carcinogenicity in the rasH2 mouse test system.

Present-day model of lunar meteoroids and their impact flashes for LUMIO mission

The Lunar Meteoroid Impacts Observer (LUMIO) is a CubeSat mission to observe, quantify, and characterize the meteoroid impacts by detecting their flashes on the lunar farside. It complements lunar nearside observations performed by ground-based observatories to yield global information synthesis on the lunar meteoroid environment. Predicting LUMIO’s scientific outcome involves devising a methodology to model the meteoroid environment. We propose a method where numerous known meteoroid streams, as well as sporadic collisions with the lunar surface, are modeled. Impacts are generated with a stochastic approach based on experimental observations of fireballs, impact flashes, and meteors. A catalog collecting data of both meteoroid streams and sporadic background is made available to the community. Sample scenarios are reproduced to show the capabilities of our method. A synthesis of the statistical analysis performed on the collision dynamics is presented. Results show that a typical scenario counts almost 2 million impacts with impact kinetic energy larger than 10−7 kton TNT Equivalent, out of which approximately 200.000 fall in the energy range of interest for the LUMIO mission. For that subset, the equivalent black body temperature is estimated to range in 1510-2290K, the average impact flash duration is expected to be approximately 15ms, and the average plume area is predicted to be roughly 70m2.

Formation of the Lunar Dust Ejecta Cloud

Abstract The Lunar Dust Experiment (LDEX) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission orbited the Moon from 2014 September to 2015 April and observed a dynamic, permanently present dust cloud produced by continual meteoroid bombardment. For the latitudes observed by LDEX, the sporadic background contribution to the impacting dust flux is dominated by helion (HE), apex (AP), and antihelion (AH) sources oscillating with lunar phase. Using improved impact ejecta distributions, a three-dimensional model was implemented to estimate the inner and outer ejecta cone angles from LDEX plume measurements. Expanding upon this single-plume model and the derived ejecta cone angles, we implemented a global lunar model fitted to LDEX measurements of the sporadic background to constrain the product of meteoroid impactor fluxes and ejecta mass yield per source. We use the observed asymmetry between sunward and antisunward impactor fluxes to discuss the possible contributions of β-meteoroids, in addition to the HE and AH sporadic meteoroid sources. We find that if β-meteoroids are responsible for the day/night asymmetry, they must have an impact ejecta yield of at least 103.

Spontaneous Necrotizing Hepatic Arteriopathy in Male Sprague-Dawley Rats.

Differentiating test article-related vascular changes from spontaneous findings is important for microscopic interpretation in drug safety evaluation studies intended for regulatory submission. Here, we report background spontaneous hepatic artery degeneration and necrosis in up to 20% of 3- to 9-month-old control male Sprague-Dawley rats in 23 individual safety studies. The vascular degeneration occurred in one cross section of a medium-sized hepatic artery near the hilus and ranged from acute intramural hemorrhage and fibrinoid necrosis to chronic fibrosis of the vascular wall with perivascular edema, hemorrhage, and inflammatory cell infiltrates. The cause was uncertain. Many microscopic features were consistent with systemic necrotizing arteriopathy (SNA) or polyarteritis; however, there was no change in arteries commonly affected in SNA/polyarteritis (mesenteric, pancreatic, or testicular arteries) and hepatic artery degeneration/necrosis occurred in younger rats which is unusual for SNA/polyarteritis. Spontaneous hepatic artery degeneration/necrosis represents a sporadic background finding that may be confused with a test article's toxicologic effect.

Latitudinal difference in meteor trail ionization heights and identification of meteor showers

The ionization heights of meteor trails are strongly dependent on local atmospheric conditions in the mesosphere and lower thermosphere (MLT)-region. We present here latitudinal difference in ionization heights of meteor trails at two distinct latitudes, Thumba (8.5∘N, 77∘E), India and Eureka (80∘N, 85.8∘W), Canada. There is a large seasonal variation in meteor count at high latitude as compared to low latitude. Similarly, there is a large variation in meteor trail ionization heights at high latitudes, but not at low latitudes. However, it noticed that the trail ionisation heights at low latitude are found to be about 2 km higher. The latitudinal differences are probably related to changes in electron line densities at local MLT-regions. The identification of meteoroid streams in the sporadic background is still a noteworthy problem to pursue. By considering ionisation heights of meteor trails as a simple but robust metric, we identified shower meteors from the background sporadic activity, as the ionization heights of shower meteors are different from the sporadic meteors. We apply this shower detection technique on long-term data set at two different latitudes and compared with existing shower calendars. By using the median height of meteor trails and their corresponding upper and lower quartiles (Uq and Lq) as a metric, we unambiguously identified all northern hemisphere showers with a zenithal hourly rate larger than 20, which are in good agreement with the known showers.

Recognition of Meteor Showers From the Heights of Ionization Trails

AbstractMeteoroids constantly enter the Earth's atmosphere, collide with atmospheric molecules, and heat and ablate in the sufficiently dense atmospheric layers at heights between 70 and 110 km. It is still a problem to recognize properties of the meteor streams among the sporadic background. The meteor radar observations at Sodankylä Geophysical Observatory (67°22′N, 26°38′E, Finland) during 2008–2017 show that meteoroids of some showers produce ionization trails at altitudes noticeably exceeding those of sporadic meteors. Using the median height of meteor trails and corresponding upper and lower quartiles as a metric, we unambiguously distinguish all northern hemisphere meteor showers with a zenithal hourly rate larger than 12, namely, the Quadrantids, Lyrids, Eta Aquariids, Arietids (or/and Daytime Zeta Perseids), Perseids, Orionids, Leonids, and Geminids. Additionally, signatures of a possible meteor stream during 26–30 January were detected, although identification of this stream is still under question. This new analysis indicates that the origin of the shower meteor trails at higher altitudes is likely due to higher speed and probably lighter or less dense meteoroids belonging to the showers.

First determination of the temperature of a lunar impact flash and its evolution

We report the first analysis of a flash produced by the impact of a meteoroid on the lunar surface and recorded both in the near-infrared and in the visible. Despite the fact that similar data have been recently published by other team during the refereeing process of our manuscript (Bonanos et al. 2018), our result still forms the first measurement of the temperature of a telescopic lunar impact flash (Madiedo and Ortiz 2016, 2018). The flash exhibited a peak magnitude of 5.1 $\pm$ 0.3 in the near-infrared I band and 7.3 $\pm$ 0.2 in the visible, and the total duration of the event in these bands was 0.20 s and 0.18 s, respectively. The origin of the meteoroid was investigated, and we inferred that the most likely scenario is that the impactor that belonged to the sporadic background. The analysis of this event has provided for the first time an estimation of the emission efficiency in the near-infrared {\eta}I for sporadic meteoroids impacting the Moon. We have determined that this efficiency is around 56% higher than in the visible band and we have found a maximum impact plume temperature of ~4000 K at the initial phase followed by temperatures of around 3200 K after the peak brightness. The size of the crater produced as a consequence of this impact is also calculated.

Performance ofD-criteria in isolating meteor showers from the sporadic background in an optical data set

Separating meteor showers from the sporadic meteor background is critical for the study of both showers and the sporadic complex. The linkage of meteors to meteor showers, to parent bodies, and to other meteors is done using measures of orbital similarity. These measures often take the form of so-called D-parameters and are generally paired with some cutoff value within which two orbits are considered related. The appropriate cutoff value can depend on the size of the data-set (Southworth & Hawkins 1963), the sporadic contribution within the observed size range (Jopek 1995), or the inclination of the shower (Galligan 2001). If the goal is to minimize sporadic contamination of the extracted shower, the cutoff value should also reflect the strength of the shower compared to the local sporadic background. In this paper, we present a method for determining, on a per-shower basis, the orbital similarity cutoff value that corresponds to a chosen acceptable false-positive rate. This method also assists us in distinguishing which showers are significant within a set of data. We apply these methods to optical meteor observations from the NASA All-Sky and Southern Ontario Meteor Networks.

CAMS newly detected meteor showers and the sporadic background

The Cameras for Allsky Meteor Surveillance (CAMS) video-based meteoroid orbit survey adds 60 newly identified showers to the IAU Working List of Meteor Showers (numbers 427, 445–446, 506–507, and part of 643–750). 28 of these are also detected in the independent SonotaCo survey. In total, 230 meteor showers and shower components are identified in CAMS data, 177 of which are detected in at least two independent surveys. From the power-law size frequency distribution of detected showers, we extrapolate that 36% of all CAMS-observed meteors originated from ∼700 showers above the N=1 per 110,000 shower limit. 71% of mass falling to Earth from streams arrives on Jupiter-family type orbits. The transient Geminids account for another 15%. All meteoroids not assigned to streams form a sporadic background with highest detected numbers from the apex source, but with 98% of mass falling in from the antihelion source. Even at large ∼7-mm sizes, a Poynting–Robertson drag evolved population is detected, which implies that the Grün et al. collisional lifetimes at these sizes are underestimated by about a factor of 10. While these large grains survive collisions, many fade on a 104-y timescale, possibly because they disintegrate into smaller particles by processes other than collisions, leaving a more resilient population to evolve.The meteors assigned to the various showers are identified in the CAMS Meteoroid Orbit Database 2.0 submitted to the IAU Meteor Data Center, and can be accessed also at http://cams.seti.org.

Structure and sources of the sporadic meteor background from video observations

Abstract We investigate and discuss the structure of the sporadic meteor background population in the near-Earth space based on video meteor orbits from the SonotaCo database (SonotaCo 2009, WGN, 37, 55). The selection of the shower meteors was done by the Southworth–Hawkins streams-search criterion (Southworth & Hawkins 1963, Smithson. Contr. Astrophys., 7, 261). Of a total of 117786 orbits, 69.34% were assigned to sporadic background meteors. Our analysis revealed all the known sporadic sources, such as the dominant apex source which is splitting into the northern and southern branch. Part of a denser ring structure about the apex source connecting the antihelion and north toroidal sources is also evident. We showed that the annual activity of the apex source is similar to the annual variation in activity of the whole sporadic background. The antihelion source exhibits a very broad maximum from July until January and the north toroidal source shows three maxima similar to the radar observations by the Canadian Meteor Orbit Radar (CMOR). Potential parent bodies of the sporadic population were searched for by comparison of the distributions of the orbital elements of sporadic meteors, minor planets and comets.

Sungrazing dust particles against the sporadic meteor background

From the results of the statistical study, the genetic relation between some meteors (from −5 m to +5 m ) of the sporadic background and the comets of the Kreutz, Marsden, and Kracht families has been revealed. The radiants of sporadic meteors are concentrated at the geocentric ecliptic latitudes 7°–10° northward and southward of the ecliptic. The radiants of the sungrazing meteoroids, that were detected on their heliocentric orbits “before” and “after” the perihelion passage, are concentrated in the elongation intervals of approximately 120°–165° and 20°–60° from the Sun, respectively. Each of the specified radiant regions, in its turn, breaks up into two groups. The group of radiants with elongations of about 30° and 155° from the Sun belongs to the Marsden and Kracht cometary families, while the group with 50° and 135°, to the Kreutz cometary family. In the distribution by perihelion distance, a sharp decrease of the number of observed dust particles with q < 0.08 AU was found. This corresponds to the heliocentric distances (20–30 R ⊙), where the production of microscopic dust due to sublimation of cometary nuclei, while approaching the Sun, terminates. The number of sporadic sungrazing meteoroids detected after their passage in the vicinity of the Sun is approximately 20 times smaller than the number of similar particles in the preperihelion part of the trajectory. This result is of special importance for studying the thermodesorption effect of meteoroids (i.e., the change in the content of chemical elements in meteoroids as a function of the perihelion distance).

Tajikistan fireball network and results of photographic observations

The fireball network was created in Tajikistan with the aim of obtaining new data on the near-Earth meteoroid environment concerning large bodies, entering in the Earth’s atmosphere and producing fireballs, as well as new observational data on the activity of known meteor/fireball showers. The network consists of five observational stations equipped with the photographic fireball and digital all-sky cameras. Distances between the stations are from 53 to 184 km and the area covered by monitoring is around 11000 km2. For astrometric reduction of fireball photographs, a technique has been developed that allows positions of object details to be determined at an accuracy of about 1′, which is a sufficiently good result for negatives of this scale. In the method of photometric reduction, a dependence of measured widths of diurnal star trails on their magnitudes is used. As a result of processing of multi-station photographs of more than 200 fireballs, photographed by the fireball network for 2006–2013, the data on their atmospheric trajectories, coordinates of radiants, velocities, decelerations, orbits in the interplanetary space, light curves, photometric masses, and densities, as well as on the nature of origin of meteoroids which produced the fireballs are obtained; membership of the fireballs to the known fireball/meteor showers is determined. A brightness of the majority of fireballs is within the maximum absolute magnitude range from −5 to −8. It is shown that 62% of fireball-producing meteoroids have a cometary origin and the remaining 38% are of an asteroidal nature. The greater part of the photographed fireballs belongs to the known meteor/fireball showers, while the lesser part (almost 30%) relates to the sporadic background. The obtained results will noticeably replenish the world database with new information on fireballs and are required for solving contemporary astronomy problems associated with studying meteoroid environment in the near-Earth space and the asteroidal-cometary hazard as well as for discovering genetic links between small bodies of the Solar System.

MIDAS: Software for the detection and analysis of lunar impact flashes

Since 2009 we are running a project to identify flashes produced by the impact of meteoroids on the surface of the Moon. For this purpose we are employing small telescopes and high-sensitivity CCD video cameras. To automatically identify these events a software package called MIDAS was developed and tested. This package can also perform the photometric analysis of these flashes and estimate the value of the luminous efficiency. Besides, we have implemented in MIDAS a new method to establish which is the likely source of the meteoroids (known meteoroid stream or sporadic background). The main features of this computer program are analyzed here, and some examples of lunar impact events are presented.

Observations of the new Camelopardalids meteor shower using a 38.9 MHz radar at Mohe, China

The Camelopardalids meteor shower was predicted to occur for the first time on 24 May 2014, based on optical observations of the comet 209P/LINEAR. Using a 38.9MHz meteor radar located at Mohe, China, we were able to detect approximately 590 shower meteors originating from an average pre-infall radiant of R.A.=129.1°±9.8°, declination=79.4°±1.6° (J2000) with a geocentric velocity of 16.0±1.6kms−1. Measurements of the shower duration, direction, velocity, and individual meteor detection heights facilitated a detailed analysis of the parent debris stream. Orbital parameters were calculated including a semi-major axis of 2.86AU, eccentricity of 0.659, and inclination of 21.1°. Combining orbital parameters with the shower activity duration FWHM of 5.09h, it was found that the stream has a FWHM of at least 211,000km at 1AU, as measured perpendicular to the direction of orbital motion. A comparison of shower meteor detection heights and diffusion coefficient estimates with the sporadic background is consistent the prediction of Ye and Wiegert (Ye, Q., Wiegert, P. [2014]. Mon. Not. R. Astron. Soc. 437, 3283–3287) that Camelopardalid meteoroids are biased towards larger sizes or that Cameloppardalid meteoroids are less fragile than sporadic background meteoroids.

Predictions of the effects of Mars's encounter with comet C/2013 A1 (Siding Spring) upon metal species in its ionosphere

AbstractThe infall of dust from the coma of comet C/2013 A1 (Siding Spring) and its subsequent ablation in the atmosphere of Mars has the potential to affect the abundances of metal species in the atmosphere and ionosphere. We develop relationships between properties of the dust population in the coma and densities of metal species in the atmosphere and ionosphere. These can be used to predict the abundances of metal species in the atmosphere and ionosphere during the encounter. Given postencounter observations of the atmosphere and ionosphere, they can also be used to infer relevant cometary properties. Although current predictions suggest that the influx of cometary dust will be comparable to the sporadic background, the higher entry speed involved, which leads to a greater production rate of ions during ablation, means that metal ion abundances may be enhanced during and after the encounter.

DYNAMICAL MODEL FOR THE TOROIDAL SPORADIC METEORS

More than a decade of radar operations by the Canadian Meteor Orbit Radar have allowed both young and moderately old streams to be distinguished from the dispersed sporadic background component. The latter has been categorized according to broad radiant regions visible to Earth-based observers into three broad classes: the helion and anti-helion source, the north and south apex sources, and the north and south toroidal sources (and a related arc structure). The first two are populated mainly by dust released from Jupiter-family comets and new comets. Proper modeling of the toroidal sources has not to date been accomplished. Here, we develop a steady-state model for the toroidal source of the sporadic meteoroid complex, compare our model with the available radar measurements, and investigate a contribution of dust particles from our model to the whole population of sporadic meteoroids. We find that the long-term stable part of the toroidal particles is mainly fed by dust released by Halley type (long period) comets (HTCs). Our synthetic model reproduces most of the observed features of the toroidal particles, including the most troublesome low-eccentricity component, which is due to a combination of two effects: particles' ability to decouple from Jupiter and circularize by the Poynting-Robertson effect, and large collision probability for orbits similar to that of the Earth. Our calibrated model also allows us to estimate the total mass of the HTC-released dust in space and check the flux necessary to maintain the cloud in a steady state.

Search for New Parent Bodies of Meteoroid Streams Among Comets. I. Showers of Comets 126P/1996 P1 and 161P/2004 V2 with Radiants on Southern Sky

We deal with theoretical meteoroid streams the parent bodies of which are two Halley-type comets in orbits situated at a relatively large distance from the orbit of Earth: 126P/1996 P1 and 161P/2004 V2. For two perihelion passages of each comet in the far past, we model the theoretical stream and follow its dynamical evolution until the present. We predict the characteristics of potential meteor showers according to the dynamical properties of theoretical particles currently approaching the orbit of the Earth. Our dynamical study reveals that the comet 161P/2004 V2 could have an associated Earth-observable meteor shower, although no significant number of theoretical particles are identified with real, photographic, video, or radar meteors. However, the mean radiant of the shower is predicted on the southern sky (its declination is about −23°) where a relatively low number of real meteors has been detected and, therefore, recorded in the databases used. The shower of 161P has a compact radiant area and a relatively large geocentric velocity of ∼53 km s−1. A significant fraction of particles assumed to be released from comet 126P also cross the Earth’s orbit and, eventually, could be observed as meteors. However, their radiant area is largely dispersed (declination of radiants spans from about +60° to the south pole) and, therefore, mixed with the sporadic meteor background. An identification with real meteors is practically impossible.

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.

Variation of sporadic meteor background and solar activity

Observations of the sporadic background meteors in 1996-2007 by the Bologna-Lecce-Modra forward-scatter radio system operating along two baselines are analyzed and discussed. The activity curves of sporadic meteor echoes and their variations indicate a direct correlation with the solar activity represented by the sunspot relative number R , as well as with the solar coronal index CI . The mass distribution exponents and its variations in the period of the 23rd solar cycle indicate a relatively stable population of the sporadic background meteoroid population in the surroundings of the Earth’s orbit. Investigation of meteor heights compiled from the IAU MDC catalogue of precise photographic orbits for a period of five solar cycles do not exhibit any pronounced variation consistent with the solar cycle activity.