Jiri Borovicka, Ondrejov Observatory

March 4, 1997


This report contains the final adjustment of the Honduran fireball trajectory using the visual data obtained during the expedition on February 10-24, 1997. The inferences on the possible meteorite falls, meteoroid heliocentric orbit and mass are also given. The accompanied events (sounds, dust trail) have not been analyzed yet.

Available data

All data used for the trajectory construction are visual observations of causal eyewitnesses. The fireball was seen by Marco Antonio Gonzalez, an amateur astronomer in Villa Nueva, Guatemala, who drew the path relative to stars and gave additional information. Other data were obtained by interviewing local people at the sites where they saw the fireball. The indicated positions on the fireball path were normally measured by a compass and an elevation measuring device. A 7 degree magnetic correction was added to the compass data.

In addition to the Gonzalez' observation, another two good observations from rather distant sites, San Pedro Sula and Comayagua, were obtained. These three observations provided a general characteristics of the fireball trajectory, i.e. the movement from the South to the North with a relatively small slope. Most of other data were obtained from people located near the trajectory. Here the fireball was extremely bright and moving high in the sky. Under these conditions many people did not remember the trajectory well a are giving almost random directions. Large selection of the data was needed. Only the data consistent with the general characteristics of the trajectory were used for the trajectory refinement. From 105 measurements obtained, only 32 were used in the final calculation. Fortunately, the sites are well spread around the trajectory and restrict the possible solutions rather well.

Only the fireball observations were used for trajectory computation. Indirect evidences (e.g. sound directions) were not used. The straight least-squares method of Borovicka (1990, Bull. Astron. Inst. Czech. 41, 391) was used for the computation.

The luminous trajectory   (see also maps )

The final trajectory below is in agreement with the preliminary trajectory. However, the last week of the expedition showed that the luminous trajectory continued farther to the North and to lower heights than assumed previously.

the apparent radiant:

azimuth = 357 deg +/- 10 deg (astronomical)
zenith distance = 71 deg +/- 5 deg

right ascension = 39 deg +/- 17 deg
declination = -55 deg +/- 5 deg

the end of the luminous trajectory:

longitude = -88 deg 52.4' +/- 1.5'
latitude = +15 deg 17' +/- 2'
height = 11 km +/- 3 km

The fireball was first noticed at the height of about 70 km at -88 deg 48' W and 13 deg 49' N. It then moved to the North with a slope of about 19 deg to the horizontal. Several people noticed severe fragmentation near the end of the trajectory. According to our estimates the fragmentation occurred at the height of 15 km at -88 deg 52' W and 15 deg 10' N. The largest piece then continued to the end point given above, where it ceased to be visible.

The time of the fireball appearance

Three people gave the time with the precision of one minute. Unfortunately, the times differ significantly: 21:56, 22:03 and 22:10 local time. We assumed the time 22:05 +/- 5 min, i.e. November 23, 1996, 04:05 UT. This time was used to convert the azimuth and zenith distance of the radiant to the right ascension as given above.

Fireball maximal brightness

Meteor absolute magnitude is defined as its stellar magnitude when seen from the distance of 100 km. Bright fireballs can be compared with the Moon. In this case the Moon was two days before the full Moon (95% illumination, magnitude about -12) and was staying near the zenith. The fireball was certainly much brighter than the Moon. Many people confirmed that the landscape was illuminated like in a clear day during the fireball passage. Probably the most restrictive is the Gonzalez' observation.

Gonzalez was looking into his telescope when he noticed a bright illumination. This means that the fireball was significantly brighter than the Moon at that time, probably about -14 mag. At that time, the fireball was at the height of 60 km, 200 km distant from the observer and less than 20 deg above the horizon. The correction to the atmospheric extinction and the recomputation to the 100 km distance gives -16 absolute magnitude. However, this was still the beginning of the fireball. The experience with photographic fireballs as well as the theory of fireball radiation shows that the maximum light could be reached at about 20-25 km of height, where the fireball could be at least by 3 mag but more probably by 5 magnitudes brighter than at 60 km. We therefore estimate the fireball peak brightness between -19 and -21 mag.

People located near the trajectory experienced the fireball maximum luminosity from the distance of 25 km only. The apparent magnitude may have reached -24 mag which is comparable to the Sun (-26 mag). Some people really mentioned that they were unable to follow the object for its extreme brightness. Only the non-detection of the fireball by the satellite based detectors casts some doubts on the fireball brightness.

Fireball duration and velocity

The estimates concerning fireball duration are unreliable. Gonzalez mentioned that he followed the object for more than 10 sec. He recorded the trajectory of total length of 120 km, so the average velocity was probably lower than 12 km/s. As the fireball is being decelerated during the flight, we consider the initial velocity of 15 km/s as reasonable. The minimal initial velocity for an object on a heliocentric orbit is 11.2 km/s. Velocity higher than 18 km/s is improbable.

Heliocentric orbit

The heliocentric orbit can be computed from the radiant position and the initial velocity. We give here the orbits for three possible velocities:

assumed velocity perihelion distance semimajor axis inclination argument of perihelion ascending node
12.0 km/s 0.98 AU 1.1 AU 8 deg 336 deg 61.194 deg
+/- 0.7 0.01 0.1 3 22 0.001
15 0.987 1.5 16 0 61.195
+/- 1 0.001 0.3 3 8 0.001
18 0.986 2.4 20 5 61.196
+/- 1 0.004 1.0 3 7 0.001

It can be seen that the perihelion does not depend on the velocity and certainly was between 0.98 and 0.99 AU, i.e. just inside the Earth's orbit. The semimajor axis depends on the velocity, most probably was around 1.5 AU. Inclination was almost certainly between 10 and 20 degrees. The ascending node is given by the time of collision with the Earth. In general, the orbit resembles the orbits of the Lost City (q=0.967 a=1.66 i=12.0) and Innisfree (q=0.986 a=1.87 i=12.3) photographed meteorite falls and is therefore not exceptional.

Initial and terminal mass

Obviously, there are not enough data to compute the initial and terminal mass of the meteoroid. Moreover, the radiation mechanism and dynamics of very bright fireballs are not completely understood yet. For the present fireball, the most important fact is that it penetrated down to 11 +/- 3 km of height. From this, order of magnitude mass estimates were obtained assuming a spherical shape and a density of 3.7 g/cm3 of the meteoroid (ordinary chondrite). The initial mass was estimated to about 20 metric tons (initial diameter of 2.2 m) or more.

The mass of the largest survived fragment (the largest meteorite) was estimated assuming the meteoroid fragmentation at 15 km of height and a continuation of the fragment luminous path down to 11 km. The corresponding mass is about 500 kg (60 cm diameter). This is, however, rather upper limit for the largest meteorite. Subsequent fragmentation events were quite possible and the resulting mass of the meteorites can be considerably less. On the other hand, the production of meteorites of the mass of tens of kilograms is almost certain.

The location of the meteorites

The area of meteorite falls from deeply penetrating fireballs with a small slope is usually quite large. Early fragmentation starts at the heights above 30 km and the meteorites can be spread in a ellipse along the trajectory with the largest pieces being located at the end of the ellipse. The suspected area for the Honduran fireball lies between the longitudes 88 deg 50' and 88 deg 54' W and latitudes 14 deg 55' to 15 deg 25' N (7 km wide and 55 km long).

The most probable area for a big meteorite (500 kg, if it exists) is near the point 88 deg 53' W and 15 deg 24' N, which is in Guatemala. The meteorite would reach this point by a 1-minute dark flight starting at the end of the luminous trajectory given above. The expected velocity at the impact is 180 m/s with the angle 10 deg to the vertical. Wind was neglected in the computation.

Prospects of meteorite recovery

No meteorite has been recovered yet. Small meteorites are expected to be located in the southern part of the suspected area, large in the north. Most of the area lies in Honduras (up to 15 deg 14' N), the northern part is in Guatemala.

The Honduran part is generally hilly but relatively densely populated. The south of the area has not-so-high but steep hills. The vegetation is not particularly dense here. A whistling sound was reported from the village of Santa Elena located in this part.

The largest village in the suspected area is San Antonio at 15 deg 01' N. There is a small flat area to the north of San Antonio (several square kilometers, altitude around 600 m). The region further to the North as far as the Guatemalan border is filled by the mountains in the surroundings of Cerro Azul (2300 m) and El Caribe (1700 m). Originally, this was a region of rain forest. Nowadays, the area is largely deforested, new villages are being built and cultivated fields have been formed in the mountains. Nevertheless, most of the area has rich vegetation and steep slopes inconvenient for a systematic meteorite search. Possible whistling sound was reported in La Elenciona. One man mentioned black stones found (and thrown away) near Pena Blanca.

The mountains continue on the Guatemalan side of the border as far as about 15 deg 18' N. Here the mountains are generally inhabited and hardly accessible. People live in the valley of the Motagua river further to the north. The villages are located just below the mountains. The valley is flat, wide and humid (altitude below 100 m). It is used for agriculture. There are pastures with sparse trees and banana plantations. This is the region where the largest meteorites could be expected. The area is relatively convenient for a systematic search, but none has been performed. People reported no meteorites.


The trajectory of the Honduran fireball was determined with the precision usual for visual observations. The characteristics of the heliocentric orbit were derived. The area of possible meteorite falls is huge. Nevertheless, the largest meteorites of the order of 100 kg mass can be located in the Motagua valley in Guatemala. An inspection of several squares kilometers around the point of 88 deg 53' western longitude and 15 deg 24' northern latitude would be useful.
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