| 词条 | Earth-grazing meteoroid of 13 October 1990 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
|title = Earth-grazing meteoroid of {{nowrap|13 October 1990}} |image = Earth-grazing meteoroid, 13 October 1990 (2).jpg |image_size = |caption = All-sky photo with the Earth-grazing meteoroid of 13 October 1990 (the faint near-vertical track just to the right of the pole star) taken at Červená hora, Czechoslovakia. The bright track on the left is the Moon. |date = {{start date and age|df=October |1990|10|13}} |time = 03:27:16±3 UT |duration = 9.8 seconds[1] |place = Czechoslovakia, Poland |coordinates = {{Coord|49.050|N|17.650|E|name=begin}} (begin) {{Coord|52.683|N|17.067|E|name=end}} (end) |also known as = |cause = |first reporter = Petr Pravec, Pavel Klásek, Lucie Bulíčková |participants = |outcome = |inquiries = |filmed_by = European Fireball Network |type = Ordinary chondrite }} On 13 October 1990, meteoroid EN131090, with an estimated mass of 44 kg, entered the Earth's atmosphere above Czechoslovakia and Poland and, after a few seconds, returned to space. Observations 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 and structure of its outer layer). ObservationsVisual observations were reported by three independent Czech observers: astronomer Petr Pravec, Pavel Klásek, and Lucie Bulíčková. According to their report, the event started at 03:27:16±3 UT[1] and the observed bright meteor (fireball) moved from south to north. It left a track that was visible for 10 seconds.[3] Most data about the encounter was acquired using photographic observations by cameras of the European Fireball Network. It was the first event of this type recorded by cameras from two distant locations, at Červená hora and Svratouch (both in the present-day Czech Republic), which enabled the calculation of the meteoroid's orbital characteristics by geometrical methods.[3] Both were equipped with all-sky fisheye objectives.[3] 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 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 was lower than the resolution of the instrument.[3] 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 was sufficient for the calculations.[3] Gotfred M. Kristensen also detected the fireball in Havdrup, Denmark, using a pen recorder connected to a radio receiver for 78 seconds, at 03:27:24±6 UT.[1][9] Encounter dataThe 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, Czechoslovakia, at a height of 103.7 km, approaching the Earth's surface to 98.67 km{{#tag:ref|That is just below the Kármán line, lying at the height of 100 km and considered to be the boundary of Earth's atmosphere.[10]|group="note"|name="Kármán"}} northeast of Wrocław, Poland, and disappearing from sight at a height of 100.4 km north of Poznań, Poland. It would probably still have been visible until it reached a height of 110 km above the southern Baltic Sea.[3] The meteoroid's absolute magnitude (the apparent magnitude 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.[13] Jiří Borovička and Zdeněk Ceplecha from the Ondřejov Observatory in Czechoslovakia estimated that the deceleration caused by the friction of the atmosphere reached only 1.7 m/s2 at the fireball's perigee (closest approach to Earth), and its velocity was reduced by only 0.012 km per second (less than 0.03%).[3] This corresponds well with computer simulations provided by D. W. Olson, R. L. Doescher and K. M. Watson at the Southwest Texas State University, who concluded that the deceleration was less than 0.5 m/s2 except for a few seconds near perigee.[15] This small loss of speed, 12 m per second, corresponded to a loss of kinetic specific energy (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 #Orbit). 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 of the fireball did not change along the track.[15] The starting apparent magnitude is not far from the naked eye visibility limits. For example, faint stars 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.[17] At its brightest, it was several times as bright as the maximum brightness of Venus.
Physical characteristicsThe meteoroid was a type I fireball,[3] i.e. an ordinary chondrite.[22] 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. It lost approximately 350 g during the encounter.[3] 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. It lost mass for 25 seconds, until it reached a height of 215.7 km.[15] Its surface melted and solidified again after leaving,[3] which means its surface became a typical meteoritic fusion crust.[1] 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 (meteorites) eventually might have made it to Earth's surface.[27] OrbitBecause 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 the Solar System.[3] The calculations were published by Czech astronomers Pavel Spurný, Zdeněk Ceplecha, and Jiří Borovička of the Ondřejov Observatory,[1][3][13] who specialize in meteor observations. They demonstrated that the swing by the earth significantly altered the meteoroid's orbit. Its aphelion (the farthest it travels from the Sun) and orbital period were lowered to almost half of their original values.[13] 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{{Main article|Earth-grazing fireball}}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.[34] Probably the first one reliably verified happened on 20 July 1860 above the American state of New York.[35] The Czechoslovak–Polish fireball is sometimes compared to the 1972 Great Daylight Fireball[1] above Utah, the United States, and Alberta, Canada, which is the first scientifically observed and studied event of this type.[34] The 1972 fireball was more than a thousand times as massive and it got 40 km closer to Earth's surface.[1] 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.[39] Notes1. ^1 The record is in Universal Time (UT), local Central European Time (CET) was 1 hour later. 2. ^1 2 3 4 5 {{cite journal | last = Spurný | first = P. | authorlink = | last2 = Ceplecha | first2 = Z. | last3 = Borovička | first3 = J. | title = Earth Grazing Fireball: Czechoslovakia, Poland, October 13, 1990, 03h 27m 16s UT | journal = WGN, Journal of the International Meteor Organization | volume = 19 | issue = 1 | pages = 13 | publisher = | location = | date = February 1991 | bibcode = 1991JIMO...19...13S | issn = | doi = }} 3. ^1 2 3 4 5 6 7 8 9 10 11 12 {{cite journal | last = Borovička | first = J. | authorlink = | last2 = Ceplecha | first2 = Z. | title = Earth-grazing fireball of October 13, 1990 | journal = Astronomy and Astrophysics | volume = 257 | issue = 1 | pages = 323–328 | publisher = | location = | date = April 1992 | bibcode = 1992A&A...257..323B | issn = 0004-6361 | doi = }} 4. ^1 {{cite web | last = Richardson | first = James | title = Fireball FAQs | website = | publisher = American Meteor Society | date = | url = http://www.amsmeteors.org/fireballs/faqf/ | doi = | accessdate = 15 February 2015 }} 5. ^1 2 3 4 5 6 {{cite journal | last = Spurný | first = Pavel | authorlink = | title = Recent fireballs photographed in central Europe | journal = Planetary and Space Science | volume = 42 | issue = 2 | pages = 157–162 | publisher = | location = | date = February 1994 | url = http://www.sciencedirect.com/science/article/pii/0032063394900272 | bibcode = 1994P&SS...42..157S | issn = 0032-0633 | doi = 10.1016/0032-0633(94)90027-2 | accessdate = 19 February 2015 |subscription=yes}} 6. ^1 2 3 4 {{cite journal | last = Olson | first = D. W. | last2 = Doescher | first2 = R. L. | last3 = Watson | first3 = K. M. | title = Computer simulation of Earth-grazing fireballs | journal = WGN, Journal of the International Meteor Organization | volume = 19 | issue = 4 | pages = 130–131 | publisher = | location = | date = August 1991 | bibcode = 1991JIMO...19..130O | issn = | doi = }} 7. ^1 {{cite web|url=http://www.txstate.edu/news/news_releases/news_archive/2010/06/YearOfMeteors060110.html|title=Texas State astronomers solve Walt Whitman meteor mystery|last1=Blaschke|first1=Jayme|date=28 May 2010|website=University News Service|publisher=Texas State University|access-date=11 March 2015}} 8. ^1 2 {{cite web|url=http://www.iau.org/public/themes/neo/nea/|title=Near Earth Asteroids (NEAs): A Chronology of Milestones 1800 – 2200|author=Karel A. van der Hucht|date=7 October 2013|website=|publisher=International Astronomical Union|access-date=11 March 2015}} 9. ^1 {{cite journal | last = Kristensen | first = Gotfred Møbjerg | title = Letters to WGN: Fireballs | journal = WGN, Journal of the International Meteor Organization | volume = 19 | issue = 2 | pages = 29–30 | publisher = | location = | date = April 1991 | url = http://articles.adsabs.harvard.edu/full/seri/JIMO./0019//0000029.000.html | bibcode = | issn = | doi = | accessdate = 3 March 2015}} 10. ^1 {{cite conference | first = S. | last = Abe | first2 = J. | last2 = Borovička | first3 = P. | last3 = Spurný | first4 = P. | last4 = Koten | first5 = Z. | last5 = Ceplecha | author6 = Meteor Network Team in Japan | title = Earth-grazing fireball on March 29, 2006 | booktitle = European Planetary Science Congress 2006 | pages = 486 | publisher = | date = 18–22 September 2006 | location = Berlin | url = http://articles.adsabs.harvard.edu/full/conf/epsc./2006//0000486.001.html | doi = | bibcode = 2006epsc.conf..486A | accessdate = 26 March 2015}} 11. ^1 {{cite web|url=http://www.fai.org/icare-records/100km-altitude-boundary-for-astronautics|title=The 100 km Boundary for Astronautics|author=Dr. S. Sanz Fernández de Córdoba|publisher=Fédération Aéronautique Internationale|date=24 June 2004|accessdate=7 May 2014|deadurl=yes|archiveurl=https://www.webcitation.org/618QHms8h?url=http://www.fai.org/astronautics/100km.asp|archivedate=22 August 2011|df=dmy-all}} 12. ^1 {{cite journal |title=The astronomical magnitude scale |journal=International Comet Quarterly |url=http://www.icq.eps.harvard.edu/MagScale.html |publisher=Earth and Planetary Sciences Department at Harvard University |issn=0736-6922 |accessdate=27 May 2015 |deadurl=yes |archiveurl=https://web.archive.org/web/20150507075446/http://www.icq.eps.harvard.edu/MagScale.html |archivedate=7 May 2015 |df=dmy }} 13. ^1 {{cite web | first = Ross | last = Poggson | url=http://australianmuseum.net.au/meteors-and-meteorites | title=Meteors and Meteorites | date=19 March 2012 | publisher=Australian Museum | access-date=30 May 2015}} References{{Reflist|refs=[2][3][4][5][6][7][8][9][10][11][12][13]}} External links{{GeoGroup}}
11 : Apollo asteroids|Meteoroids|Astronomical objects discovered in 1990|Earth-grazing fireballs|Modern Earth impact events|1990 in Czechoslovakia|1990 in Poland|1990 in science|Astronomy in Czechoslovakia|Astronomy in Poland|October 1990 events |
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