Earth-grazing meteoroid of 13 October 1990
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On 13 October 1990,
meteoroid A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micr ...
EN131090, with an estimated mass of 44 kg, entered the
Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
above
Czechoslovakia , rue, Чеськословеньско, , yi, טשעכאסלאוואקיי, , common_name = Czechoslovakia , life_span = 1918–19391945–1992 , p1 = Austria-Hungary , image_p1 ...
and
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populous ...
and, after a few seconds, returned to space.
Observations Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The ...
of such events are quite rare; this was the second recorded using scientific astronomical instruments (after the 1972 Great Daylight Fireball) and the first recorded from two distant positions, which enabled the calculation of several of its orbital characteristics. The encounter with Earth significantly changed its orbit and, to a smaller extent, some of its physical properties (
mass Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different elementar ...
and structure of its outer layer).


Observations

Visual observations were reported by three independent Czech observers: astronomer
Petr Pravec Petr Pravec (born September 17, 1967) is a Czech astronomer and a discoverer of minor planets, born in Třinec, Czech Republic. Pravec is a prolific discoverer of binary asteroids, expert in photometric observations and rotational lightcurves a ...
, Pavel Klásek, and Lucie Bulíčková. According to their report, the event started at 03:27:16±3 UTThe record is in
Universal Time Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with ...
(UT), local
Central European Time Central European Time (CET) is a standard time which is 1 hour ahead of Coordinated Universal Time (UTC). The time offset from UTC can be written as UTC+01:00. It is used in most parts of Europe and in a few North African countries. CET i ...
(CET) was 1 hour later.
and the observed bright
meteor A meteoroid () is a small rocky or metallic body in outer space. Meteoroids are defined as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide. Objects smaller than this are classified as micr ...
( fireball) moved from south to north. It left a track that was visible for 10 seconds. Most data about the encounter were acquired using photographic observations by cameras of the
European Fireball Network European Fireball Network is an international organization based in Central Europe (Germany and Czech Republic). Its purpose is systematic and simultaneous night observation of meteors and other nebular objects. Description The network was initia ...
. It was the first event of this type recorded by cameras from two distant locations, at
Červená hora Červená Hora (german: Rothenburg) is a municipality and village in Náchod District in the Hradec Králové Region of the Czech Republic. It has about 200 inhabitants. Demographics References

Villages in Náchod District {{Hrade ...
and Svratouch (both in the present-day
Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...
), which enabled the calculation of the meteoroid's orbital characteristics by geometrical methods. Both were equipped with all-sky fisheye objectives. The Červená hora image was especially valuable. It recorded the fireball's trajectory over approximately 110°, starting 51° above the southern horizon, passing the
zenith The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" ...
just 1° westward and disappearing only 19° above the northern horizon (thus crossing about 60% of the sky). Its camera was also equipped with a rotating shutter that interrupted the exposure 12.5 times per second and divided the captured track of the fireball, allowing the determination of its speed. Over the last 4°, the fireball's
angular velocity In physics, angular velocity or rotational velocity ( or ), also known as angular frequency vector,(UP1) is a pseudovector representation of how fast the angular position or orientation of an object changes with time (i.e. how quickly an objec ...
was lower than the resolution of the instrument. The Svratouch image recorded the trajectory only for about 15°, beginning at 30° above the northwest horizon, and the pictured fireball was quite weak. Despite this, the data were sufficient for the calculations. Gotfred M. Kristensen also detected the fireball in
Havdrup Havdrup is a small railway town straddling the boundary between Solrød and Roskilde municipalities, some 30 km southwest of Copenhagen, Denmark. Havdrup station serves the Little South railway line between Roskilde and Køge. Havdrup had a popul ...
, Denmark, using a pen recorder connected to a
radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. Th ...
for 78 seconds, at 03:27:24±6 UT.


Encounter data

The meteoroid grazed Earth's atmosphere quite gently (in comparison to, for example, the 1972 Great Daylight Fireball above the United States and Canada). It became visible north of
Uherský Brod Uherský Brod (; german: Ungarisch Brod) is a town in Uherské Hradiště District in the Zlín Region of the Czech Republic. It has about 16,000 inhabitants. The historic town centre is well preserved and is protected by law as an urban monument ...
, Czechoslovakia, at a height of 103.7 km, approaching the Earth's surface to 98.67 km northeast of
Wrocław Wrocław (; german: Breslau, or . ; Silesian German: ''Brassel'') is a city in southwestern Poland and the largest city in the historical region of Silesia. It lies on the banks of the River Oder in the Silesian Lowlands of Central Europe, rou ...
, Poland, and disappearing from sight at a height of 100.4 km north of
Poznań Poznań () is a city on the River Warta in west-central Poland, within the Greater Poland region. The city is an important cultural and business centre, and one of Poland's most populous regions with many regional customs such as Saint John ...
, Poland. It would probably still have been visible until it reached a height of 110 km above the southern
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
. The meteoroid's
absolute magnitude Absolute magnitude () is a measure of the luminosity of a celestial object on an inverse Logarithmic scale, logarithmic Magnitude (astronomy), astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent mag ...
(the
apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's li ...
it would have at an altitude of 100 km at the observer's zenith) was approximately −6 and did not vary significantly during the few seconds of observation. It traveled a distance of 409 km in 9.8 seconds during the time it was observed. It moved at a speed of 41.74 km per second, which did not change measurably during the flight. Jiří Borovička and Zdeněk Ceplecha from the
Ondřejov Observatory The Ondřejov Observatory (; cs, Observatoř Ondřejov) is the principal observatory of the Astronomical Institute () of the Academy of Sciences of the Czech Republic. It is located near the village of Ondřejov, southeast of Prague, Czech ...
in Czechoslovakia estimated that the deceleration caused by the
friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
of the atmosphere reached only 1.7 m/s2 at the fireball's
perigee An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...
(closest approach to Earth), and its velocity was reduced by only 0.012 km per second (less than 0.03%). This corresponds well with
computer simulation Computer simulation is the process of mathematical modelling, performed on a computer, which is designed to predict the behaviour of, or the outcome of, a real-world or physical system. The reliability of some mathematical models can be dete ...
s provided by D. W. Olson, R. L. Doescher and K. M. Watson at the
Southwest Texas State University Texas State University is a public university, public research university in San Marcos, Texas. Since its establishment in 1899, the university has grown to the second largest university in the Greater Austin, Greater Austin metropolitan area ...
, who concluded that the deceleration was less than 0.5 m/s2 except for a few seconds near perigee. This small loss of speed, 12 m per second, corresponded to a loss of kinetic
specific energy Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...
(in the earth's frame of reference) of 0.5 MJ/kg, which was converted to heat (and perhaps sound). The change in the object's velocity vector due to Earth's gravity during the hours it was in the earth's vicinity was on the order of kilometres per second (see ). The software also calculated the fireball's instantaneous apparent magnitude at the ground. The computation started and ended with heights of approximately 250 km, long before and after the cameras of the European Fireball Network could observe it. Its apparent magnitude started at a value of +5.7 and it became brighter quite quickly. The program gave an apparent magnitude of −5.7 when it was seen by one camera and −6.3 at perigee. The fireball subsequently dimmed, with an apparent magnitude of −5.4 when it was last seen by the cameras and a final calculated value of +6.0 at a height of 257 km. These values are not entirely certain, because the program worked with the simplified assumption that the
luminous efficacy Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI). Depending on context, the power can be either the ...
of the fireball did not change along the track. The starting apparent magnitude is not far from the
naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
visibility limits. For example, faint
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
s of the magnitude +6 can be observed only in dark rural areas approximately 150 km away from large cities. This magnitude corresponds to the apparent magnitude of
Uranus Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
. At its brightest, it was several times as bright as the maximum brightness of
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
.


Physical characteristics

The meteoroid was a type I fireball, i.e. an
ordinary chondrite The ordinary chondrites (sometimes called the O chondrites) are a class of stony chondritic meteorites. They are by far the most numerous group, comprising 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are th ...
. When it entered Earth's atmosphere its mass was about 44 kg, which was estimated on the basis of the measured values of its absolute magnitude and velocity. From the known bulk densities of ordinary chondrites (3.40 ± 0.15 g/cm3 for H group ordinary chondrites, 3.40 ± 0.15 g/cm3 for L group and 3.29 ± 0.17 g/cm3 for LL group) we get the approximate diameter of the meteoroid between 28.5 and 30 cm. During the encounter it lost approximately 350 g of mass. Computer simulations showed that it started losing mass approximately at the moment it became visible to the cameras of the European Fireball Network, at a height of 100.6 km. Losing of mass lasted 35 seconds, until it reached a height of 215.7 km. Its surface melted and solidified again after leaving, which means its surface became a typical meteoritic
fusion crust This is a glossary of terms used in meteoritics, the science of meteorites. # * 2 Pallas – an asteroid from the asteroid belt and one of the likely parent bodies of the CR meteorites. * 4 Vesta – second-largest asteroid in the asteroid be ...
. The meteoroid was not dangerous to life on Earth. Even if it had headed towards lower parts of the atmosphere it would have heated so much that it would have exploded high above the ground and only some small particles (
meteorite A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
s) eventually might have made it to Earth's surface.


Orbit

Because the fireball was recorded by two cameras of the European Fireball Network, it was possible to calculate the trajectory of its flight through the atmosphere, and afterward also the characteristics of both its pre- and post-encounter
orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...
in the Solar System. The calculations were published by Czech astronomers Pavel Spurný, Zdeněk Ceplecha, and Jiří Borovička of the Ondřejov Observatory, who specialize in meteor observations. They demonstrated that the swing by the earth significantly altered the meteoroid's orbit. Its
aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any ellip ...
(the farthest it travels from the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
) and
orbital period The orbital period (also revolution period) is the amount of time a given astronomical object takes to complete one orbit around another object. In astronomy, it usually applies to planets or asteroids orbiting the Sun, moons orbiting planets ...
were lowered to almost half of their original values. The object was initially in a highly inclined orbit (71°) and ended in an orbit with a slightly higher inclination (74°). Approximately every 2.5 or 2.6 years, the object comes back to the point in the solar system where the 1990 encounter occurred, and the earth comes back to the same point every year. The period is not known precisely enough to predict when the next encounter between the two will occur.


Similar events

Although entries of meteoroids into Earth's atmosphere are very common, recording a similar flight through the upper layers of the atmosphere is quite rare. Probably the first one reliably verified happened on 20 July 1860 above the American state of New York. The Czechoslovak–Polish fireball is sometimes compared to the 1972 Great Daylight Fireball above
Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
, the United States, and
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
, Canada, which is the first scientifically observed and studied event of this type. The 1972 fireball was more than a thousand times as massive and it got 40 km closer to Earth's surface. Observational data from both of them helped to develop a method for computing the grazing trajectories of such bodies, which was later used when calculating the trajectory of another Earth-grazing meteoroid, observed on 29 March 2006 above Japan.


Notes


References


External links

* {{DEFAULTSORT:19901013 * Meteoroids Astronomical objects discovered in 1990 Earth-grazing fireballs
1990 File:1990 Events Collage.png, From left, clockwise: The 1990 FIFA World Cup is played in Italy; The Human Genome Project is launched; Voyager I takes the famous Pale Blue Dot image- speaking on the fragility of Humankind, humanity on Earth, Astroph ...
1990 in Czechoslovakia 1990 in Poland 1990 in science Astronomy in Czechoslovakia Astronomy in Poland October 1990 events