Comet Encke , or Encke's Comet (official designation: 2P/Encke), is a periodic comet that completes an orbit of the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

once every 3.3 years. (This is the shortest period of a reasonably bright comet; the faint

main-belt comet Active asteroids are Small Solar System body, small Solar System bodies that have asteroid-like orbits but show comet-like visual characteristics. That is, they show a Coma (cometary), coma, comet tail, tail, or other visual evidence of mass-loss ...

311P/PanSTARRS has a period of 3.2 years.) Encke was first recorded by

Pierre Méchain Pierre François André Méchain (; 16 August 1744 – 20 September 1804) was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets. Life Pierre Méchain was bo ...

on 17 January 1786, but it was not recognized as a periodic comet until 1819 when its orbit was computed by

Johann Franz Encke Johann Franz Encke (; 23 September 179126 August 1865) was a German astronomer. Among his activities, he worked on the calculation of the periods of comets and asteroids, measured the distance from the Earth to the Sun, and made observations ...

. Like

Halley's Comet Halley's Comet is the only known List of periodic comets, short-period comet that is consistently visible to the naked eye from Earth, appearing every 72–80 years, though with the majority of recorded apparitions (25 of 30) occurring after ...

, it is unusual in its being named after the calculator of its orbit rather than its discoverer. Like most comets, it has a very low

albedo Albedo ( ; ) is the fraction of sunlight that is Diffuse reflection, diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects ...

, reflecting only 4.6% of the light its

nucleus Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucleu ...

receives, although comets generate a large

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...

and tail that can make them much more visible during their

perihelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

(closest approach to the Sun). The diameter of the nucleus of Encke's Comet is 4.8 km.

Discovery

As its official designation implies, Encke's Comet was the first periodic comet discovered after

(designated 1P/Halley). It was independently observed by several astronomers, the first two being

and

Charles Messier Charles Messier (; 26 June 1730 – 12 April 1817) was a French astronomer. He published an astronomical catalogue consisting of 110 nebulae and star clusters, which came to be known as the ''Messier objects'', referred to with th ...

in 1786. It was next observed by

Caroline Herschel Caroline Lucretia Herschel ( , ; 16 March 1750 – 9 January 1848) was a German astronomer, whose most significant contributions to astronomy were the discoveries of several comets, including the periodic comet 35P/Herschel–Rigollet, which b ...

in 1795 and was "discovered" for a third time by

Jean-Louis Pons Jean-Louis Pons (24 December 176114 October 1831) was a French astronomer. Despite humble beginnings and being self-taught, he went on to become the greatest visual comet discoverer of all time: between 1801 and 1827 Pons discovered thirty-seven ...

in 1818. Its orbit was calculated by

, 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 Carl Ludwig Christian Rümker (28 May 1788 – 21 December 1862) was a German astronomer. Early life (1788-1821) Rümker was born in Burg Stargard, in Mecklenburg, Germany, the son of J. F. Rümker, a court-councillor. He showed an aptitude for ...

at Parramatta Observatory on 2 June 1822.

Orbit

Comets are in unstable orbits that evolve over time due to perturbations and

outgassing Outgassing (sometimes called offgassing, particularly when in reference to indoor air quality) is the release of a gas that was dissolved, trapped, frozen, or absorbed in some material. Outgassing can include sublimation and evaporation (whic ...

. Given Encke's low

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

near the

ecliptic The ecliptic or ecliptic plane is the orbital plane of Earth's orbit, Earth around the Sun. It was a central concept in a number of ancient sciences, providing the framework for key measurements in astronomy, astrology and calendar-making. Fr ...

and brief

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 ...

of 3 years, the orbit of Encke is frequently perturbed by the inner planets. Encke is currently close to a 7:2

mean motion resonance In celestial mechanics, orbital resonance occurs when orbiting bodies exert regular, periodic gravitational influence on each other, usually because their orbital periods are related by a ratio of small integers. Most commonly, this relations ...

with

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, and it is possible that some of the larger fragments shed by the comet, or released by a larger progenitor of the comet, are trapped in this resonance. Encke's orbit gets as close as to Earth (

minimum orbit intersection distance Minimum orbit intersection distance (MOID) is a measure used in astronomy to assess potential close approaches and collision risks between astronomical objects. It is defined as the distance between the closest points of the osculating orbits o ...

). 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. On 18 November 2013, it passed from Mercury. Close approaches to Earth usually occur every 33 years. Comet Encke has a

(closest approach to the Sun) of , and at perihelion Comet Encke passes the Sun at . Between 1769 and 2103, Comet Encke's perihelion distance only varies from 0.330 AU (in 2050) and 0.347 AU (in 1782). Of the numbered comets less than 321P, only 96P/Machholz gets closer to the Sun.

Observations

The comet has been observed at every perihelion since 1818 except 1944. An attempt to photograph the comet close to aphelion was made on 2 July 1913 using the Mount Wilson 60-inch telescope but the resulting photographic plate was lost in the mail. A second attempt using the same telescope was made on 1 September 1913 and this showed an object in about the right position (1.5

arcminutes A minute of arc, arcminute (abbreviated as arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of a degree. Since one degree is of a turn, or complete rotation, one arcminute is of a tu ...

from its then predicted position) but orbital uncertainties made it impossible to be sure of its identity. A recalculation of Encke's orbit in the 1970s resulted in a calculated position only a few arcseconds (2.0 in ascension and 4.6 in declination) from the imaged object meaning the object probably was Encke. In March 1918 the Greenwich 28-inch aperture telescope took observations of Encke (1917c). An observer of Encke's in March 1918 had this to say of the comet on March 12, comparing to the early March 9 observation, "The comet much shaper, brighter, smaller; its diameter was 1 1/2', magnitude 7^.7 (B.D. scale). Its magnitude in the 6-inch Corbett was almost stellar, but in the 28 inch no definitive nucleus could be seen." A number of attempts were made to image the comet around the aphelion of 3 September 1972. Elizabeth Roemer and G. McCorkle photographed the comet on 15 August. R.E. McCrosky and C.-Y. Shao photographed it on 5 September and Elizabeth Roemer this time with M.R. Gonzales photographed the comet on 13 September. In 1980 Encke was the first comet to be detected by radar. In April 1984 the

Pioneer Venus Orbiter The ''Pioneer Venus Orbiter'', also known as ''Pioneer Venus 1'' or ''Pioneer 12'', was a mission to Venus conducted by NASA as part of the Pioneer Venus project. Launched in May 1978 atop an Atlas-Centaur rocket, the spacecraft was inserted into ...

observed the comet in ultra-violet and made measurements of its rate of water loss. The failed ''

CONTOUR Contour may refer to: * Contour (linguistics), a phonetic sound * Pitch contour * Contour (camera system), a 3D digital camera system * Contour Airlines * Contour flying, a form of low level flight * Contour, the KDE Plasma 4 interface for tab ...

'' mission was launched to study this comet, and also Schwassmann–Wachmann 3. On 20 April 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 coronal mass ejection (CME) is a significant ejection of plasma mass from the Sun's corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar activity, but a broadly accepted theoretical understandin ...

(a blast of solar particles from the Sun). The tail grew back due to the continuous shedding of dust and gas by the comet.

Proposed missions

In the 70s Germany proposed using a space probe based on the

Helios In ancient Greek religion and Greek mythology, mythology, Helios (; ; Homeric Greek: ) is the god who personification, personifies the Sun. His name is also Latinized as Helius, and he is often given the epithets Hyperion ("the one above") an ...

probes to explore the comet. In the 1970s the Goddard Space Flight Centre and Jet Propulsion Laboratory proposed to NASA probes that would fly past the comet in 1980. The Goddard Space Flight Centre's proposal was for a pair of probes launched directly towards the comet while the Jet Propulsion Laboratory plan was to use Solar electric propulsion. NASA did not attempt either mission. NASA’s failed

probe was planned to perform a flyby of Encke in November 2003.

Meteor showers

Comet Encke is believed to be the originator of several related

meteor shower A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at ext ...

s known as the

Taurids The Taurids are an annual meteor shower, associated with the comet Encke. The Taurids are actually two separate showers, with a Southern and a Northern component. The Southern Taurids originated from Comet Encke, while the Northern Taurids or ...

(which are encountered as the Northern and Southern Taurids across November, and the

Beta Taurids The Beta Taurids (β–Taurids) are an annual meteor shower belonging to a class of "daytime showers" that peak after sunrise. The Beta Taurids are best observed by radar and radio-echo techniques. The Beta Taurids are normally active from June ...

in late June and early July). A shower has similarly been reported affecting Mercury.

Near-Earth object A near-Earth object (NEO) is any small Solar System body orbiting the Sun whose closest approach to the Sun ( perihelion) is less than 1.3 times the Earth–Sun distance (astronomical unit, AU). This definition applies to the object's orbit a ...

may be a fragment of Encke.

Mercury

Measurements on board the NASA satellite ''

MESSENGER Messenger, Messengers, The Messenger or The Messengers may refer to: People * Courier, a person or company that delivers messages, packages, or mail * Messenger (surname) * Bicycle messenger, a bicyclist who transports packages through cities * M ...

'' 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.

Effects on Earth

More than one theory has associated Encke's Comet with impacts of cometary material on Earth, and with cultural significance. The

Tunguska event The Tunguska event was a large explosion of between 3 and 50 TNT equivalent, megatons that occurred near the Podkamennaya Tunguska River in Yeniseysk Governorate (now Krasnoyarsk Krai), Russia, on the morning of 30 June 1908. The explosion over ...

of 1908 may have been caused by the impact of a cometary body and has also been postulated by Czechoslovakian astronomer

Ľubor Kresák Ľubor Kresák (23 August 1927 in Topoľčany – 20 January 1994 in Bratislava) was a Slovakia, Slovak astronomer. He discovered two comets: the periodic comet 41P/Tuttle-Giacobini-Kresak and the non-periodic C/1954 M2 (Kresak-Peltier). He a ...

as possibly caused by a fragment of Comet Encke. Hansilk2

A theory holds that the ancient symbol of the

swastika The swastika (卐 or 卍, ) is a symbol used in various Eurasian religions and cultures, as well as a few Indigenous peoples of Africa, African and Indigenous peoples of the Americas, American cultures. In the Western world, it is widely rec ...

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 Fred Lawrence Whipple (November 5, 1906 – August 30, 2004) was an American astronomer, who worked at the Harvard College Observatory for more than 70 years. Among his achievements were asteroid and comet discoveries, the " dirty snowball" hy ...

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. Astronomers planned a 2019 search campaign for fragments of comet Encke which would have been visible from Earth as the Taurid swarm passed between July 5–11, and July 21 – August 10. There were no reports of discoveries of any such objects.

Importance in the scientific history of luminiferous aether

Comet Encke (and

Biela's Comet Biela's Comet or Comet Biela (official designation: 3D/Biela) was a periodic Jupiter-family comet first recorded in 1772 by Montaigne and Messier and finally identified as periodic in 1826 by Wilhelm von Biela. It was subsequently observed ...

) had a role in scientific history in the generally discredited concept of ''

luminiferous aether Luminiferous aether or ether (''luminiferous'' meaning 'light-bearing') was the postulated Transmission medium, medium for the propagation of light. It was invoked to explain the ability of the apparently wave-based light to propagate through empt ...

''. 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 1,200 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. 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 comet's 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. The supposed shortening of the orbit of Encke's Comet demonstrating the existence of ether was mentioned in Edgar Alen Poe's story, "The Unparalleled Adventures Of One Hans Pfaall".

Gallery

File:Comet Encke from MESSENGER.png, A ''

'' image of Comet Encke at its closest approach to Mercury, 17/11/2013 (NASA/JHUAPL/Carnegie Institution of Washington)

References

Citations

Bibliography

* Klačka, Jozef (1999). "Meteor Streams of Comet Encke. Taurid Meteor Complex"
Abstract
* Whipple, F.L. (1940). "Photographic meteor studies. III. The Taurid shower." ''Proc. Amer. Phil. Soc.,'' 83, 711–745. * Master, S. and Woldai, T. (2004) The UMM Al Binni structure in the Mesopotamian marshlands of Southern Iraq, as a postulated late holocene meteorite impact crater : geological setting and new LANDSAT ETM + and Aster satellite imagery. Johannesburg, University of Witwatersrand, Economic Geology Research Institute (EGRI), 2004. EGRI - HALL : information circular 382, p. 21 http://www.itc.nl/library/Papers_2004/tech_rep/woldai_umm.pdf (1.56 MB) * Master, S. and Woldai, T. (2004) Umm al Binni structure, southern Iraq, as a postulated late holocene meteorite impact crater : new satellite imagery and proposals for future research. Presented at the ICSU workshop : comet - asteroid impacts and human society, Santa Cruz de Tenerife, Canary Islands, Spain, November 27- December 2, 2004. p. 20 * Hamacher, D. W. (2005) "The Umm Al Binni Structure and Bronze Age Catastrophes", ''The Artifact: Publications of the El Paso Archaeological Society'', Vol. 43 * Hamacher, D. W. (2006) "Umm al Binni lake: Effects of a possible Holocene bolide impact", ''Astronomical Society of Australia Meeting'' 40, #15

External links

Orbital simulation
from JPL (Java)
Ephemeris

2P/Encke
at the

Minor Planet Center The Minor Planet Center (MPC) is the official body for observing and reporting on minor planets under the auspices of the International Astronomical Union (IAU). Founded in 1947, it operates at the Smithsonian Astrophysical Observatory. Funct ...

's Database
Gary W. Kronk's Cometography page for 2P

by Seiichi Yoshida {{DEFAULTSORT:Encke, 002P Encke-type comets Periodic comets 0002 002P 17860117

1786 Events January–March * January 3 – The third Treaty of Hopewell is signed between the United States and the Choctaw. * January 6 – The outward bound East Indiaman '' Halsewell'' is wrecked on the south coast of Englan ...

002P 002P 002P 002P 002P Articles containing video clips Discoveries by Pierre Méchain Tunguska event