| 词条 | Comet Encke | ||
| 释义 |
| name=2P/Encke | image= | discoverer=Pierre Méchain; Johann Franz Encke (recognition of periodicity) | discovery_date=17 January 1786[1] | designations=1786 I; 1795; 1805; 1819 I; 1822 II; 1825 III; 1829; 1832 I; 1835 II; 1838; 1842 I; 1845 IV | epoch=September 22, 2006 (JD 2454000.5) | semimajor=2.2178 AU | perihelion=0.3302 AU | aphelion=4.11 AU | eccentricity=0.8471 | period=3.30 a[1] | inclination= 11.76° | tjup= 3.026[1] | last_p=10 March 2017[2][1][3] | next_p=25 June 2020[2] | dimensions = 4.8km[1] }}Comet Encke or Encke's Comet (official designation: 2P/Encke) is a periodic comet that completes an orbit of the Sun once every 3.3 years. (This is the shortest period of a reasonably bright comet; the faint main-belt comet 311P/PANSTARRS has a period of 3.2 years.) Encke was first recorded by Pierre Méchain in 1786, but it was not recognized as a periodic comet until 1819 when its orbit was computed by Johann Franz Encke; like Halley's Comet, it is unusual in being named after the calculator of its orbit rather than its discoverer. Like most comets, it has a very low albedo, reflecting only 4.6% of the light it receives. The diameter of the nucleus of Encke's Comet is 4.8 km.[4] DiscoveryAs its official designation implies, Encke's Comet was the first periodic comet discovered after Halley's Comet (designated 1P/Halley). It was independently observed by several astronomers, the second being Caroline Herschel in 1795 [5] and the third Jean-Louis Pons in 1818.[6] Its orbit was calculated by Johann Franz Encke, who through laborious calculations was able to link observations of comets in 1786 (designated 2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to the same object. In 1819 he published his conclusions in the journal Correspondance astronomique, and predicted correctly its return in 1822 (2P/1822 L1). It was recovered by Carl Ludwig Christian Rümker at Parramatta Observatory on 2 June 1822.[7] OrbitComets are in unstable orbits that evolve over time due to perturbations and outgassing. Given Encke's low orbital inclination near the ecliptic and brief orbital period of 3 years, the orbit of Encke is frequently perturbed by the inner planets.[8] Encke's orbit gets as close as {{convert|0.17309|AU|km mi|abbr=on|lk=on}} to Earth (minimum orbit intersection distance).[8] On 4 July 1997, Encke passed 0.19 AU from Earth, and on June 29, 2172 it will make a close approach of roughly 0.1735 AU.[8] On 18 November 2013, it passed {{convert|0.02496|AU|km mi|abbr=on|lk=off}} from Mercury.[8] Close approaches to Earth usually occur every 33 years. ObservationsThe failed CONTOUR mission was launched to study this comet, and also Schwassmann-Wachmann 3. On April 20, 2007, STEREO-A observed the tail of Comet Encke to be temporarily torn off by magnetic field disturbances caused by a coronal mass ejection (a blast of solar particles from the Sun).[9] The tail grew back due to the continuous shedding of dust and gas by the comet.[10] Meteor showersComet Encke is believed to be the originator of several related meteor showers known as the Taurids (which are encountered as the Northern and Southern Taurids across November, and the Beta Taurids in late June and early July).[11][12] A shower has similarly been reported affecting Mercury.[13] Near-Earth object {{mpl|2004 TG|10}} may be a fragment of Encke.[14]MercuryMeasurements on board the NASA satellite MESSENGER have revealed Encke may contribute to seasonal meteor showers on Mercury. The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument discovered seasonal surges of calcium since the probe began orbiting the planet in March 2011. The spikes in calcium levels are thought to originate from small dust particles hitting the planet and knocking calcium-bearing molecules into the atmosphere in a process called impact vaporization. However, the general background of interplanetary dust in the inner Solar System cannot, by itself, account for the periodic spikes in calcium. This suggests a periodic source of additional dust, for example, a cometary debris field.[15] Effects on EarthMore than one theory has associated Encke's Comet with impacts of cometary material on Earth, and with cultural significance. The Tunguska event of 1908, probably caused by the impact of a cometary body, has also been postulated by Czechoslovakian astronomer Ľubor Kresák as a fragment of Comet Encke.[16] A theory holds that the ancient symbol of the swastika appeared in a variety of cultures across the world at a similar time, and could have been inspired by the appearance of a comet from head on, as the curved jets would be reminiscent of the swastika shape (see Comets and the swastika motif). Comet Encke has sometimes been identified as the comet in question. In their 1982 book Cosmic Serpent (page 155) Victor Clube and Bill Napier reproduce an ancient Chinese catalogue of cometary shapes from the Mawangdui Silk Texts, which includes a swastika-shaped comet, and suggest that some comet drawings were related to the breakup of the progenitor of Encke and the Taurid meteoroid stream. Fred Whipple in his The Mystery of Comets (1985, page 163) points out that Comet Encke's polar axis is only 5 degrees from its orbital plane: such an orientation is ideal to have presented a pinwheel like aspect to our ancestors when Encke was more active. Importance in the scientific history of luminiferous aetherComet Encke (and Biela's Comet) had a role in scientific history in the generally discredited concept of luminiferous aether. As its orbit was perturbed and shortened, the shortening could only be ascribed to the drag of an "ether" through which it orbited in outer space. One reference reads: Encke's comet is found to lose about two days in each successive period of 1200 days. Biela's comet, with twice that length of period, loses about one day. That is, the successive returns of these bodies is found to be accelerated by this amount. No other cause for this irregularity has been found but the agency of the supposed ether.[17] Encke's pole tumbles in an 81-year period, therefore it will accelerate for half that time, and decelerate for the other half of the time, (since the orientation of the comets rotation to solar heating determines how its orbit changes due to outgassing forward or aft of the comets course). The authors of this 1860 textbook of course could not know that the pole of the comet would tumble as it does over such a long period of time, or that outgassing would induce a thrust to change its course. GalleryReferences1. ^{{Cite magazine |last=Ley |first=Willy |date=September 1968 |title=Mission to a Comet |department=For Your Information |url=https://archive.org/stream/Galaxy_v27n02_1968-09#page/n99/mode/2up |magazine=Galaxy Science Fiction |pages=101–110}} {{Refbegin|2}}2. ^1 {{mpc|2p}} 3. ^2P/Encke past, present and future orbits by Kazuo Kinoshita 4. ^1 2 3 4 {{cite web |type=2017-03-04 last obs |title=JPL Small-Body Database Browser: 2P/Encke |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2P |accessdate=2017-03-13}} 5. ^{{cite book|last=Herschel|first=Caroline Lucretia|editor1-last=Herschel|editor1-first=Mrs. John|title=Memoir and Correspondence of Caroline Herschel|year=1876|publisher=John Murray, Albemarle Street|location=London}} 6. ^{{cite book|title=Biographical Encyclopedia of Astronomers|page =924}} 7. ^{{cite web|last1=Kronk|first1=Gary|title=2P/Encke|url=http://cometography.com/pcomets/002p.html|website=Gary W. Kronk's Cometography|accessdate=5 July 2014}} 8. ^1 2 3 {{cite web |date=2013-08-18|title=JPL Close-Approach Data: 2P/Encke |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2P;cad=1#cad |accessdate=2013-10-06}} 9. ^{{cite web |date=2007-10-01 |title=The Sun Rips Off a Comet's Tail |publisher=Science@NASA |url=https://science.nasa.gov/headlines/y2007/01oct_encke.htm |accessdate=2009-10-20}} 10. ^{{Cite APOD |date=3 October 2007 |title=Comet Encke's Tail Ripped Off |access-date=}} 11. ^http://www.serve.com/~wh6ef/comets/meteors/showers/beta_taurids.html 12. ^Whipple, 1940; Klačka, 1999). 13. ^{{cite journal| author1=Rosemary M. Killen | author2=Joseph M. Hahn | title =Impact Vaporization as a Possible Source of Mercury's Calcium Exosphere | journal =Icarus | volume=250 | pages=230–237 | date = December 10, 2014 | doi =10.1016/j.icarus.2014.11.035|bibcode = 2015Icar..250..230K }} 14. ^{{cite journal |last=Williams |first=V. |author2=Kornoš, L. |author3=Williams, I.P. |title=The Taurid complex meteor showers and asteroids |journal=Contributions of the Astronomical Observatory Skalnaté Pleso |volume=36 |issue=2 |pages=103–117 |year=2006 |arxiv=0905.1639|bibcode = 2006CoSka..36..103P}} 15. ^{{cite web | url=http://www.sci-news.com/astronomy/science-mercury-seasonal-meteor-showers-02350.html | title=Mercury Experiences Seasonal Meteor Showers, Say NASA Scientists | publisher=Sci-News.com | work=Web Article | date=17 December 2014 | accessdate=29 December 2014 | author=M. Killen & Joseph M. Hahn}} 16. ^{{cite journal|bibcode=1978BAICz..29..129K|title=The Tunguska object - A fragment of Comet Encke|author1=Kresak|first1=L'.|volume=29|year=1978|pages=129|journal=Astronomical Institutes of Czechoslovakia}} 17. ^https://archive.org/stream/firstprinciples06sillgoog/firstprinciples06sillgoog_djvu.txt 18. ^{{cite web |url=http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?image_id=1303 |title=Archived copy |accessdate=2014-03-28 |deadurl=yes |archiveurl=https://web.archive.org/web/20131205110226/http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?image_id=1303 |archivedate=2013-12-05 |df= }}
http://www.itc.nl/library/Papers_2004/tech_rep/woldai_umm.pdf (1.56 MB) ×Professor Nayr,Hahs(2002)Geological Researcher at University of Oxford
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8 : Encke-type comets|Periodic comets|Astronomical objects discovered in 1786|1780s in science|Meteor shower progenitors|Comets in 2013|Comets in 2017|Articles containing video clips |
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