EN131090 (meteoroid)

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All-sky photo with the grazing meteoroid from October 13, 1990 (the faint, almost vertical track to the right of the cushion), taken in Červená hora, Czechoslovakia. The light trail on the left is the moon.

On October 13, 1990 the meteoroid EN131090 entered the earth's atmosphere with an estimated mass of 44  kilograms over Czechoslovakia and Poland and returned to space after a few seconds. Observations of such events are very rare; this was the second recording made with scientific astronomical instruments (after the fireball of August 10, 1972 ) and the first recording from two distant positions that enabled the calculation of several of its orbit features. The encounter with the earth changed its orbit significantly, and to a lesser extent, changed some of its physical properties, such as the mass and structure of its outer layer.

Observations

Visual observations were reported by three independent Czech observers: the astronomers Petr Pravec , Pavel Klásek and Lucie Bulíčková. According to their report, the event started at 03:27:16 ± 3 UT and the bright meteor observed was moving from south to north. It left a trail that was visible for 10 seconds.

Most of the data about the encounter was captured with photographic observations from cameras of the fireball network . It was the first event of its kind recorded by cameras from two remote locations in Červená Hora and Svratouch (both in the Czech Republic ), and it made it possible to calculate the orbit characteristics of the meteoroid using geometric methods. Both were equipped with all-sky fisheye lenses.

The picture of Červená hora was particularly valuable. It recorded the fireball's trajectory over approximately 110 °, beginning 51 ° above the southern horizon, passed the zenith just 1 ° to the west, and disappeared only 19 ° above the northern horizon (crossing about 60% of the sky). The camera was equipped with a rotating shutter that interrupted the exposure 12.5 times per second and divided the recorded trail of the fireball, which made it possible to determine the speed. For the last 4 ° the angular velocity of the fireball was slower than the resolution of the instrument. The Svratouch image only recorded the trajectory for about 15 °, starting at 30 ° above the northwest horizon, and the fireball pictured was quite faint. Nevertheless, the data was sufficient for the calculations.

Gotfred M. Kristensen detected the fireball in Havdrup, Denmark, using a radio receiver with an attached measuring recorder for 78 seconds, at 03:27:24 ± 6 UT.

Encounter dates

Part of the trail of the meteoroid over Czechoslovakia and Poland, recorded by cameras of the fireball network.

The meteoroid grazed the earth's atmosphere quite flat, for example in comparison to the fireball of August 10, 1972 over the USA and Canada. It was visible north of Uherský Brod in Czechoslovakia at an altitude of 103.7 kilometers, approached the surface of the earth to 98.67 kilometers northeast of Wrocław in Poland and disappeared at an altitude of 100.4 kilometers north of Poznan in Poland. It would probably have been visible until it reached an altitude of 110 kilometers above the southern Baltic Sea .

The absolute magnitude of the meteoroid (the apparent magnitude it would have at a height of 100 kilometers at the zenith of the observer) was approximately -6 and did not vary significantly during the few seconds of observation. During the observation period, he covered a distance of 409 kilometers in 9.8 seconds. It moved at a speed of 41.74 kilometers per second, which did not change measurably during the flight. Jiří Borovička and Zdeněk Ceplecha from the Ondřejov Observatory in Czechoslovakia estimated that the deceleration of the fireball caused by the friction of the atmosphere at perigee , the point of closest approach to the earth, was only 1.7 meters per second square and its speed was only 0.012 kilometers per second Second or less than 0.03%. This corresponds well to the computer simulations by DW Olson, RL Doescher, and KM Watson of Texas State University , who concluded that the delay was less than 0.5 meters per second square other than a few seconds near the perigee. This small loss of speed of about 12 meters per second corresponded to a loss of kinetic specific energy (compared to the reference system of the earth) of 0.5 megajoules per kilogram, which was converted into heat and possibly sound. The change in the velocity vector of the object due to Earth's gravity during the hours near Earth was on the order of kilometers per second (see #Orbit ).

The software also calculated the instantaneous apparent size of the fireball on the ground. The calculation began and ended at altitudes of about 150 miles long before and after the fireball network cameras were able to observe them. Its apparent size started at a value of +5.7 and got lighter fairly quickly. The program gave an apparent size of -5.7 when viewed by a camera and -6.3 at perigee. The fireball was then dimmed to an apparent size of -5.4 when last seen by the cameras and a final calculated value of +6.0 at an altitude of 150 miles. These values ​​are not certain because the program operated on the simplified assumption that the light output of the fireball along the route has not changed. The initial apparent brightness is not far from the limits of visibility to the naked eye. For example, faint +6 stars can only be observed in dark rural areas that are approximately 150 kilometers from major cities. This size corresponds to the apparent brightness of Uranus . At its brightest it was several times as bright as the maximum brightness of Venus .

Encounter data from EN131090
Parameters of the meteoroid Beginning perigee The End
speed 47.1 km / s 47.1 km / s 47.1 km / s
height 103.7 km 98.67 km 100.4 km
Coordinates 49.050 N, 17.650 O 51.350 N, 17.200 O 51.683 N, 17.067 O
Absolute brightness -5.6 -6.2 -6.1
Apparent brightness -5.7 -6.3 -5.4

Physical Properties

The meteoroid was a type I fireball, that is, an ordinary chondrite . When it entered the Earth's atmosphere, its mass was about 44 kilograms, which was estimated based on the measured values ​​of its absolute size and speed. From the known density of common chondrites (3.40 ± 0.15 grams per cubic centimeter for common chondrites of the H group, 3.40 ± 0.15 grams per cubic centimeter for the L group and 3.29 ± 0.17 grams per Cubic centimeters for the LL group) results in an approximate diameter of the meteoroid between 28.5 and 30 centimeters. During the encounter he lost about 350 grams. Computer simulations showed that it lost mass around the time it became visible to the fireball network cameras at an altitude of 100.6 kilometers. The loss of mass took 35 seconds to reach an altitude of 215.7 kilometers. Its surface melted and re-solidified after exiting, meaning that its surface became a typical meteoroid fusion crust.

The meteoroid was not dangerous to life on earth. Even if it had reached lower parts of the atmosphere, it would have warmed so much that it would have exploded high above the ground and only a few small particles might have made it to the surface of the earth.

orbit

Orbit of the meteoroid before and after the strip of the earth's atmosphere.

Since the fireball had been recorded by two cameras in the fireball network, it was possible to calculate the orbit of its flight through the atmosphere and then also the properties of its orbit before and after the encounter in the solar system. The calculations were published by the Czech astronomers Pavel Spurný, Zdeněk Ceplecha and Jiří Borovička from the Ondřejov Observatory, who specialize in meteoroid observations. They showed that the Earth's gravity redirection changed the orbit of the meteoroid significantly. Its aphelion , that is, its point furthest from the sun, and its orbital period have been reduced to almost half of their original values. The object was originally in a steeply inclined orbit of 71 ° and ended up in an orbit with a slightly higher inclination of 74 °.

Orbital features Before the encounter After the encounter
Major semi-axis 2.72 ± 0.08 AU 1.87 ± 0.03 AU
eccentricity 0.64 ± 0.01 0.473 ± 0.009
Perihelion 0.9923 ± 0.0001 AU 0.9844 ± 0.0002 AU
Aphelion 4.45 ± 0.15 AU 2.76 ± 0.07 AU
Argument of the periapsis 9.6 ± 0.1 ° 16.6 ± 0.2 °
Length of the ascending node 19.671 ° 19.671 °
Orbit inclination 71.4 ± 0.2 ° 74.4 ± 0.2 °
Orbital time 4.5 ± 0.2 years 2.56 ± 0.06 years

Every 2.5 or 2.6 years or so, the object returns to the point in the solar system where the 1990 encounter took place, and Earth returns to the same point every year. The time period is not known accurately enough to predict when the next encounter between the two will take place.

Similar events

Although meteoroid penetration into the Earth's atmosphere is very common, it is quite rare to record a similar flight through the upper layers of the atmosphere. The first reliable check probably happened on July 20, 1860 over the American state of New York. The Czechoslovak-Polish fireball is sometimes compared to the August 10, 1972 fireball over Utah (USA) and Alberta (Canada), the first scientifically observed and studied event of its kind. The 1972 fireball was more than a thousand times as massive and was approaching the earth's surface up to 40 kilometers. Observational data from both events helped develop a method for calculating the trajectories of such bodies, which was later used in calculating the trajectory of another grazing meteoroid observed over Japan on March 29, 2006.

Individual evidence

  1. ↑ a b c d e f g h i j k l m J. Borovička, Z. Ceplecha: Earth-grazing fireball of October 13, 1990 . In: Astronomy and Astrophysics , Volume 257, pp. 323-328, bibcode : 1992A & A ... 257..323B
  2. ^ Gotfred Møbjerg Kristensen: Letters to WGN: Fireballs. In: WGN, Journal of the International Meteor Organization , Volume 19, No. 2, pp. 29-30.
  3. ↑ a b c d e Pavel Spurný: Recent fireballs photographed in central Europe. In: Planetary and Space Science. Volume 42, 1994, pp. 157-162, doi: 10.1016 / 0032-0633 (94) 90027-2 .
  4. ↑ a b c D. W. Olson, RL Doescher, KM Watson: Computer simulation of Earth-grazing fireballs. In: WGN, Journal of the International Meteor Organization , Volume 19 (1991), bibcode : 1991JIMO ... 19..130O , pp. 130-131.
  5. ^ The astronomical magnitude scale. In: International Comet Quarterly , Earth and Planetary Sciences Department at Harvard University, ISSN = 736-6922.
  6. ↑ James Richardson: Fireball FAQs. American Meteor Society, accessed February 15, 2015 .
  7. ^ Sarah L. Wikinson, Mark S. Robinson: Bulk density of ordinary chondrite meteorites and implications for asteroidal internal structure. In: Meteoritics & Planetary Science. Volume 35, 2000, pp. 1203-1213, doi: 10.1111 / j.1945-5100.2000.tb01509.x .
  8. ↑ a b c d P. Spurny, Z. Ceplecha, J. Borovicka: Earth-grazing fireball: Czechoslovakia, Poland, October 13, 1990, 03h27m16sUT. In: WGN, Journal of the International Meteor Organization , Volume 19 (1991), bibcode : 1991JIMO ... 19 ... 13S , p. 13.
  9. ↑ Ross Poggson: Meteors and Meteorites. Australian Museum, March 12, 2012, accessed May 30, 2015 .
  10. ↑ a b Karel A. van der Hucht: Near Earth Asteroids (NEAs): A Chronology of Milestones 1800 - 2200. International Astronomical Union, October 7, 2013, accessed on March 15, 2015 .
  11. ↑ Jayme Blaschke: Texas State astronomers solve Walt Whitman meteor mystery. Texas State University, University News Service, May 28, 2010, accessed March 11, 2015 .
  12. ↑ S. Abe et al. a .: Earth-grazing fireball on March 29, 2006. In: epsc , 2006, bibcode : 2006epsc.conf..486A , p. 486.