Results from the AIM-IT Meteor Tracking System

The recent development and data collection results of the Astrobiology Instrumentation for Meteor Imaging and Tracking (AIM-IT) system, has demonstrated an ability to point narrow field-of-view instruments at transient events such as meteors. AIM-IT uses the principle of tracking moving objects via a paired set of relay mirrors along with an integrated hardware/software solution, to acquire and track meteors in real-time. Development of the instrument has progressed from a prototype rocker-box system through more recent use of a fast response mirror system during several meteor shower campaigns. Several narrow field of view instruments have been deployed using AIM-IT including high spatial resolution video, high frame rate video, and meteor spectrographic equipment. Analysis of the imagery shows evidence for meteor fragmentation in as many as 20% of the meteors tracked thus far. The success of the AIM-IT technology in tracking meteors during their luminous flight provides a new tool in enhancing the capabilities and data volume that can be obtained with existing narrow field of view instruments.     

OPTICAL TRAIL WIDTH MEASUREMENTS OF FAINT METEORS

We report results from two station, short-baseline (< 100 m) high resolution measurements of faint meteors (limiting meteor magnitude +9) with the goal of measuring their optical trail widths. Meteors were observed using two 0.40 m Newtonian telescopes (field of view ˜0.4 degrees) equipped with image intensifiers. Both telescopes were vertically oriented in a fixed mount and pointed to the same field of view. One system used a gated image intensified camera allowing the transverse velocity component to be measured. The widest trail captured, out of a total of 34 common events measured by both optical systems, had a full-width to half-maximum of 1.37±0.71 m. The widest trail overall was captured by the gated system only, and was found to have a full-width of ∼ ∼10 m. The brightness variation across this trail was found to be best represented by a Lorentzian. Most trails were smaller than our resolution limit and hence we could only place upper limits on their optical width. These were generally less than 1 m after correction for instrumental effects. Four meteors were found to have heights near 65 km and very low transverse velocities. These may be indicative of a largely unreported high density asteroidal component at these faint meteor magnitudes.     

Radio and Meteor Science Outcomes From Comparisons of Meteor Radar Observations at AMISR Poker Flat, Sondrestrom, and Arecibo

Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.     

TV Meteor Observations from Modra

We present our experience and initial results of single-station observation using the new fish-eye TV system, as well as double station TV observation of the Geminids 2006 shower. The fixed fish-eye TV system was developed for monitoring meteor activity throughout the year. We discuss the astrometric precision of our observations using the UFOAnalyser software.     

Characterization of the Meteoroid Spatial Flux Density during the 1999 Leonid Storm

The November 18, 1999 Leonid storm was rich in meteors and well observed by airborne intensified video cameras aimed low in the sky which enabled enhanced meteor counts over ground-based observations. The two- and three-dimensional distribution of meteoroids was investigated for signs of clustering that could provide evidence of meteoroid fragmentation shortly after lift-off from the parent comet 55P/Tempel-Tuttle, or much later due to space weathering. Analysis of the video tapes yields a refined estimation of the mass ratio during the peak of s = 1.65 and spatial flux density of 0.5 particles/km² greater than those causing visual magnitude +6.5 during the 5 min centered around the peak of the storm. Furthermore, the projection of the individual trails into three-dimensional Heliocentric coordinates, shows non-homogeneity of the stream on spatial scales from hundreds to thousands of kilometers.     

Physical Characteristics of Kazan Minor Showers as Determined by Correlations with the Arecibo UHF Radar

In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source areas where it is easiest to detect discrete showers with less confusion from the background.     

NEOCAM: The Near Earth Object Chemical Analysis Mission

The prime measurement objective of the Near Earth Object Chemical Analysis Mission (NEOCAM) is to obtain the ultraviolet spectra of meteors entering the terrestrial atmosphere from ∼125 to 300 nm in meteor showers. All of the spectra will be collected using a slitless ultraviolet spectrometer in Earth orbit. Analysis of these spectra will reveal the degree of chemical diversity in the meteors, as observed in a single meteor shower. Such meteors are traceable to a specific parent body and we know exactly when the meteoroids in a particular shower were released from that parent body (Asher, in: Arlt (ed.) Proc. International Meteor Conference, 2000; Lyytinen and van Flandern, Earth Moon Planets 82–83:149–166, 2000). By observing multiple apparitions of meteor showers we can therefore obtain quasi-stratigraphic information on an individual comet or asteroid. We might also be able to measure systematic effects of chemical weathering in meteoroids from specific parent bodies by looking for correlations in the depletions of the more volatile elements as a function of space exposure (Borovička et al., Icarus 174:15–30, 2005). By observing the relation between meteor entry characteristics (such as the rate of deceleration or breakup) and chemistry we can determine if our meteorite collection is deficient in the most volatile-rich samples. Finally, we can obtain a direct measurement of metal deposition into the terrestrial stratosphere that may act to catalyze atmospheric chemical reactions.     

Meteor streams associated with Jupiter family comets

Meteor showers have been observed for a considerable time, and the cause, meteoroids from a meteoroid stream ablating in the Earth's atmosphere, has also been understood for centuries. The connection between meteoroid streams and comets was also established 150 years ago. Since that time our ability both to understand the physics and to numerically model the situation has steadily increased. We will review the current state of knowledge. However, just as there are differences between the behaviour of long period comets, Halley family comets and Jupiter family comets, so also differences exist between the associated meteoroid streams. Streams associated with Jupiter family comets show much more variety in their behaviour, driven by the gravitational perturbations from Jupiter. The more interesting showers associated with Jupiter family comets will be discussed individually.     

Rates of development of tafoni in the Moenkopi and Kaibab formations in Meteor Crater and on the Colorado Plateau,northeastern Arizona

Tafoni are pits formed by non‐uniform weathering in otherwise uniform rock. Two equations have been proposed for the rate of development of tafoni, both based on 2000‐year‐old outcrops from the coast of Japan. We have taken tafoni measurements from the Meteor Crater, Arizona, and vicinity that extend the equations back at least 50 000 years. As reported in earlier studies, we found pit depth to be the best tafone parameter to measure. The size of the pit decreases significantly with increasing inclination of the rock surface; however, the size of the pit can vary greatly for other reasons. In some cases the measurements are statistically significantly different between two stations taken from contiguous areas of similar inclination and aspect in an apparently homogeneous bed. It is clear, however, that over tens of thousands of years tafoni enlarge significantly. Our data are generally log‐normal and all are markedly heteroscedastic. The 1991 equation proposed by Matsukura and Matsuoka does not fit our data. The 1996 equation proposed by Sunamura provides a better fit. We propose a sigmoidal equation D = b1 + e^(b2+(b3/t)) where D is the depth, t is the age, and b1, b2 and b3 vary with lithology. This new equation fits our data far better than the earlier published equations. Copyright © 2002 John Wiley & Sons, Ltd.     

Hydrological changes in the European midlatitudes associated with freshwater outbursts from Lake Agassiz during the Younger Dryas event and the early Holocene

Recent studies of lake-level fluctuations during the last deglaciation in eastern France (Jura Mountains and Pre-Alps) and on the Swiss Plateau show distinct phases of higher water level developing at the beginning and during the latter part of Greenland Stade 1 (i.e., Younger Dryas event) and punctuating the early Holocene period at 11,250-11,050, 10,300-10,000, 9550-9150, 8300-8050, and 7550-7250 cal yr B.P. The phases at 11,250-11,050 and 8300-8050 cal yr B.P. appear to be related to the cool Preboreal Oscillation and the 8200 yr event assumed to be associated with deglaciation events. A comparison of this mid-European lake-level record with the outbursts from proglacial Lake Agassiz in North America suggests that, between 13,000 and 8000 cal yr B.P., phases of positive water balance were the response in west-central Europe to climate cooling episodes, which were induced by perturbation of the thermohaline circulation due to sudden freshwater releases to oceans. This probably was in response to a southward migration of the Atlantic Westerly Jet and its associated cyclonic track. Moreover, it is hypothesized that, during the early Holocene, varying solar activity could have been a crucial factor by amplifying or reducing the possible effects of Lake Agassiz outbursts on the climate.