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SATELLITE SENSOR DETECTION OF A MAJOR METEOR EVENT IN THE UNITED STATES ON 27 MARCH 2003: THE PARK FOREST, ILLINOIS BOLIDE

D. W. Pack,1 B. B. Yoo,2 and E. Tagliaferri3

1Space Science Applications LaboratoryLaboratory Operations

2Astrodynamics DepartmentSystems Engineering Division

3Space-Based Surveillance DivisionThe Aerospace Corporation

El Segundo, CA

R. E. Spalding Sandia National Laboratories

P. BrownUniversity of Western Ontario

Abstract

A major meteor explosion in Earth’s atmosphere occurred over Park Forest, Illinois on 27 March 2003 at 05:50 UT (11:50 PM local time). The event resulted in a large-scale meteorite fall over the southern suburbs of Chicago. This is the largest meteorite fall over a densely populated area in modern history. Several buildings had their roofs penetrated, though no injuries resulted. The explosive disintegration of the meteor lit up the night sky to daylight levels. Large sonic booms were heard over a wide area. Occurring during Operation Iraqi Freedom, many witnesses worried this meteor disintegration was some kind of massive explosion or nuclear event. The meteor explosion was detected by space-based infrared and visible sensors operated by the Department of Defense (DoD) and Department of Energy (DoE), as well as by ground-based infrasonic arrays, seismic stations, video cameras, and video camera microphones. A number of meteorites were recovered, and the object was classified as a type L-5 chondrite (stony meteor). The Park Forest event is one of only four meteors detected by satellite sensors that also resulted in a collected meteorite fall. A collaborative effort is underway between The Aerospace Corporation, Sandia National Laboratories, and the University of Western Ontario to fuse and analyze the space- and ground-based data. This report summarizes the analysis of the satellite data to determine the energy, temporal signature, trajectory, velocity, mass, and size of this extraordinary meteor. The total energy release was determined to be on the order of a 0.34 kT nuclear event. The derived velocity of the meteor was 20 ± 1 km/s, decelerating to 14 km/s

at lower altitude. The preatmospheric mass of the stony object is estimated as 7.8 tons, and its diameter is estimated as 1.6 m.

Introduction

In recent years, a number of DoD satellite sightings of large Earth-impacting meteoroids have been reported and published.1–6 This research is motivated by the ability of large meteor explosions in Earth’s atmosphere to mimic nuclear events and by the desire to better characterize the frequency of Earth impact of small asteroids.1,7 The satellite results have added to our knowledge of the frequency and manner with which objects in the 0.3-m-diameter size range and up impact Earth’s atmosphere. Objects of this size impact the Earth’s atmosphere infrequently enough (50–60 times per year) that a detection and measurement program must strive for very wide area or global coverage and constant, long-term monitoring in order to make progress. Fortunately, satellite-based sensors operated by the DoD and the DoE enable such a research effort. In recent years, proliferation of infrasonic stations built for Comprehensive Test Ban Treaty monitoring has added ground-based sensor capabilities that complement the space-based sensors.6 While distinguishing meteors from other phenomena, such as nuclear detonations, is of interest to the U.S. military, meteor detection and reporting currently is not an operational mission. To implement continuous, scientifically oriented use of these sensors, The Aerospace Corporation and Sandia National Laboratories have constructed a data receiving station devoted to applied research purposes.

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Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

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DoE Sensor Normalized LightcurveAlley Security Video Normalized Intensity

Time Normalized to Peak (Seconds)

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Feature 1

Main Peak

Feature 2

Figure 1. Comparison of normalized DoE sensor and security camera lightcurves. The video data distort the relative peak intensities due to the difficulty of the auto-gain mechanism tracking such a fast bright transient event. The time plotted is relative to 05:50:26.400 UT

For a handful of past events sufficient data were gathered to estimate meteor velocities, trajectories, and their orbits prior to Earth impact. To date, all of the bodies were in orbits consistent with Apollo-type Earth-crossing asteroids; objects with their aphelion in the asteroid belt and their perihelion inside Earth’s orbit.

This report summarizes the satellite data analysis for the 27 March 2003 Park Forest bolide. Meteor energy, trajectory, velocity, and the mass and size of the object are derived from the satellite data. In addition to the satellite data, the Park Forest bolide was measured with ground-based infrasonic, seismic, and video sensors, and meteorites were recovered. The combined data set will make this event the most thoroughly studied bolide to date.

Visible Lightcurve Data

Visible light satellite sensors operated by the DoE for nuclear monitoring purposes routinely record high-energy meteor events such as the Park Forest bolide. Useful information about the meteor flaring and breakup is contained in the intensity vs. time data from these sensors. The Park Forest event was also detected by a number of ground-based video cameras. The University of Western Ontario gathered and digitized a number of these ground-based videos, some of which

directly imaged the meteor and some of which recorded reflected and scattered light. Lightcurves were derived by integrating ground-based video camera frames. The various videos showed similar results for high-intensity features. Normalized lightcurves derived from the DoE visible light sensors and the highest quality digitized ground-based video are plotted in Figure 1. Three distinct intensity features are readily apparent. There is excellent correlation of the three main temporal features between the space sensor and ground-based video data, with the peaks matching to within ±1 video frame (±1/30th of a second). From the DoE sensor data, the peak intensity was 4.2 x 1010 W/sr. The total radiated energy was 1.42 x 1011 J. These optical intensity and energy results assume that the emitting source is a 6000K blackbody as in past work.1,4 Theoretical models suggest that the efficiency of conversion of kinetic energy into optical energy is 10–15% for bolides of chondritic composition with energies in the range of the Park Forest event.8 Assuming the efficiency of conversion of kinetic energy to light to be 10%, the initial energy of the body was on the order of 1.42 x 1012 J, equivalent to a 0.34 kT nuclear event. Figures 2–5 show still images of the meteor and the largest explosion from surveillancevideo cameras. These images clearly demonstrate that the Park Forest bolide was an extremely impressive event as viewed from the Chicago area.

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Figure 2. A police squad car camera in South Haven, Michigan images the Park Forest Meteor as it sinks to the tree line. The observer is 150 km away across Lake Michigan. The time stamp is incorrect and is offset by approximately one hour. (Video image courtesy of the South Haven, MI Police Department.)

Figure 3. The Park Forest Meteor lights up the night sky as viewed from the same police video camera. (Video image courtesy of the South Haven, MI Police Department.)

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Figure 4. The Park Forest Meteor is imaged in the windshield of a car parked facing southwest in nearby Crown Point, Indiana. It is beginning to light up the night sky. The time stamp is somewhat in error. (Video image courtesy of the Adler Planetarium, Chicago, IL.

Figure 5. The Park Forest Meteor turns night into day in Crown Point, Indiana. (Video image courtesy of the Adler Planetarium, Chicago, IL.)

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Infrared Data

An accurate trajectory for the meteor has been generated from DoD IR sensor measurements. This is plotted in Figure 6. DoD IR sensors scanned the emissive track from the passage of the meteor through the atmosphere. The first IR measurement was timed 0.60 s following the main peak of the visible lightcurve. This is about 0.03 s after the final flare feature, so the timing was excellent for measuring the emission left from the passage of the object through the atmosphere. The second IR measurement was taken 0.84 s following the peak optical signal. The derived flight path angle was –62.3° from the local geocentric horizontal. The flight path azimuth was 22.3° (the object traveled from the SW to the NE). The straight-line intersection of the track with the WGS-84 ellipsoid is at a geodetic latitude of 41.56° N and a longitude of 87.67° W. Park Forest, IL is located at 41.48°N, 87.69°W. The emissive track was approximately 22 km long, and extended from 38.0

km to 18.5 km altitude above the Earth’s surface (WGS-84 ellipsoid). Three distinct intensity peaks were evident along the track at 36.5 km, 28.2 km, and 21.5 km altitude. Correlating these with the three temporal features evident in the light curves allows velocity to be estimated over intervals along the track. Here, the assumption is made that the flares observed in the light curve correspond to the bright features along the emissive track. Making such a correlation, the average velocity of the object between intensity features is calculated and displayed in Table 1.

The velocity and deceleration measured are physically reasonable based on past observations and modeling. A self-consistent check on the results above is to estimate the average meteor velocity along its entire track from the total length of the emissive streak divided by the duration of the meteor lightcurve signal. The accuracy of this method depends on the fortuitous timing of the infrared scanning of the meteor track.

Figure 6. The emissive track of the 27 March 2003 Park Forest bolide projected into the three planes. The circles denote the location of intensity peaks along the track. The derived flight path angle was –62.3° from the local geocentric horizontal. The flight path azimuth was 22.3° (the object traveled from the SW to the NE).

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Applying this approach *yields 18 km/s, which is in good agreement with the 17 km/s result from the 36.5–21.5 km segment of the track. From the high-altitude results in Table 1, the best estimate of the initial velocity of the object is a lower limit of 20 km/s. The object decelerated to 14 km/s at lower altitudes. Deceleration modeling will allow the estimate of the initial velocity to be refined and an orbit determined for this Earth-crossing asteroid.

Table 1. Velocities Calculated from Features in Visible and Infrared Space Sensor Data

Altitude Range (km) Velocity (km/s)36.5 - 28.2 20 ± 136.5 - 21.5 17 ± 128.2 - 21.5 14 ± 1

Estimation of the Mass and Size of the Park Forest Meteor

Employing the velocity derived above and the estimated total kinetic energy of the event allows the meteor’s initial mass to be estimated. With E = 1.42 x 1012 J, and V = 20 km/s, we employ:

m= 2E2

V (1)

to calculate the objects initial mass, m, as 7.1 x 103 kg, or 7.8 tons. The Park Forest object was a stony meteor, recently typed as a type L-5 chondrite from recovered meteorite specimens.9 Assuming a density, �, of 3.5 g/cm3, we calculate an equivalent spherical radius, r:

r = 3

4πm

ρ

1/3

, (2)

and find the object’s radius is 79 cm, or a diameter of 1.6 m. To date, a total of 18 kg of meteorites have been discovered at over 40 sites, on the order of 0.25% of our estimated initial mass. The largest piece recovered to date was 2.7 kg.9

Conclusions

The Park Forest meteor was an extraordinary event, made more so by its occurrence over the suburbs of Chicago, the resulting meteorite fall, its many witnesses, and the combination of satellite sensor data and several types of ground-based observations. This report summarizes the preliminary results from DoD and DoE satellite sensors. The optical energy, trajectory, and

velocity were derived from the space sensor data and used to estimate the total energy, mass, and size of the object. These large meteors, or superbolides, are of concern to the Department of Defense due to their ability to mimic nuclear events. These events occur 50–60 times per year globally and are the single largest source of false alarms for infrasonic nuclear monitoring stations operated by the Comprehensive Test Ban Treaty organization. Thorough study of these bolides is warranted so no confusion results should one explosively disintegrate at an inopportune time in a region where military tensions are high. Further analysis of the Park Forest event will add to our knowledge base of the infrared, visible, infrasonic, and seismic signatures of these extraordinary Earth-crossing objects and serve to train global observers to better recognize and characterize these naturally occurring huge explosive events.

Acknowledgments

Carolyn Lee-Wagner, and Joycelyn Fuqua are acknowledged for their assistance with the extraction of DoD satellite data. Chief Rod Sommerlott of the South Haven, MI Police Department and Dr. Mark Hammergren of the Adler Planetarium are acknowledged for their permission to use images derived from videos of the Park Forest Meteor. This work was funded by The Aerospace Corporation’s internal research and development program.

References

1. E. Tagliaferri, R. Spalding, C. Jacobs, S.P. Worden and A. Erlich 1994. Detection of meteoroid impacts by optical sensors in Earth orbit. In Hazards Due to Comets and Asteroids, (Tom Gehrels Ed.), pp. 199-220. University of Arizona Press, Tuscon.

2. E. Tagliaferri, R. Spalding, C. Jacobs and Z. Ceplecha. 1995. Analysis of the Marshall Islands fireball of February 1, 1994. Earth Moon and Planets 68, 563-572

3. McCord, T.B. J. Morris, D. Persing, E. Tagliaferri, C. Jacobs, R. Spalding, L. Grady and R. Schmidt 1995. Detection of a meteoroid entry into Earth's atmosphere on February 1, 1994. J. Geophys. Res. 100, E2, 3245-3249.

4. P. Brown, A.R. Hildebrand, D.W.E. Green, D. Pagé, C. Jacobs, D. Revelle, E. Tagliaferri and J. Wacker 1996. The fall of the St-Robert

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meteorite. Meteoritics Planet. Sci. 31, 502-517.

5. P. Brown, A. Hildebrand, M. Zolensky, M. Grady, R. Clayton, T. Mayeda, E. Tagliaferri, R. Spalding, N. MacRae, E. Hoffman, D. Mittlefehldt, J. Wacker, J. Bird, M. Campbell, R. Carpenter, H Gingerich, M. Glatiotis, E. Greiner, M. Mazur, P. McCausland, H. Plotkin, and T. Mazur 2000. The fall, recovery, orbit and composition of the Tagish Lake meteorite: a new type of carbonaceous chondrite. Science 290, 320-325.

6. P. Brown, R. Spalding, D. Revelle, E. Tagliaferri, and S. P. Worden, 2002. The flux of small near-Earth objects colliding with the Earth. Nature 420, 294-296.

7. Chyba, C.F. G.E. van der Vink and C.B. Hennet 1998. Monitoring the comprehensive test ban treaty: possible ambiguities due to meteor impacts. Geophys. Res. Lett. 24, 191-194.

8. Nemtchenov, I. et. al. 1997. Assessment of kinetic energy of meteoroids detected by satellite-based light sensors, Icarus 130, 259-274.

9. Simon, S.B. et. al. 2003. The fall, recovery and classification of the Park Forest meteorite, abstract to the 66th Annual Meteoritical Society Meeting (2003).