D/1770 L1, popularly known as Lexell's Comet after its orbit computer

Anders Johan Lexell Anders Johan Lexell (24 December 1740 – ) was a Finnish-Swedish astronomer, mathematician, and physicist who spent most of his life in Imperial Russia, where he was known as Andrei Ivanovich Leksel (Андрей Иванович Лексе ...

, was a

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

discovered by

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

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''. Messier's purpose f ...

in June 1770.Other comets named after their orbit computer, rather than discoverer, are

27P/Crommelin Comet Crommelin, also known as Comet Pons-Coggia-Winnecke-Forbes, is a periodic comet with an orbital period of almost 28 years. It fits the classical definition of a Halley-type comet with (20 years <

2P/Encke 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 ...

and 1P/Halley –

Halley's Comet Halley's Comet or Comet Halley, officially designated 1P/Halley, is a short-period comet visible from Earth every 75–79 years. Halley is the only known short-period comet that is regularly visible to the naked eye from Earth, and thus the o ...

. It is notable for having passed closer to

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

than any other comet in

recorded history Recorded history or written history describes the historical events that have been recorded in a written form or other documented communication which are subsequently evaluated by historians using the historical method. For broader world hist ...

, approaching to a distance of only ,Kronk, G.
Cometography: D/1770 L1 (Lexell)
', accessed November 20, 2008.Kronk, G.

', accessed November 20, 20, 2008. It was thought that C/1491 B1 may have approached even closer on February 20, 1491, but its orbit was retracted in 2002 due to a misunderstanding of the records. Se
Approximate Orbits of Ancient and Medieval Comets: 3. Remarks and Discussion
/ref> or six times the distance from the Earth to the Moon. The comet has not been seen since 1770 and is considered a

lost comet A lost comet is one which was not detected during its most recent perihelion passage. This generally happens when data is insufficient to reliably calculate the comet's location or if the solar elongation is unfavorable near perihelion passage. T ...

. Lexell's Comet's 1770 passing still holds the record of closest observed approach of Earth by a comet. However, if approaches deduced from orbit calculations are included, it may have been beaten by a small

sungrazing comet A sungrazing comet is a comet that passes extremely close to the Sun at perihelion – sometimes within a few thousand kilometres of the Sun's surface. Although small sungrazers can completely evaporate during such a close approach to the Sun, la ...

P/1999 J6 (SOHO) C/1999 J6 (SOHO) is a small comet, notable for being among those that made a close approach to the Earth. It was first observed by the space-based Solar and Heliospheric Observatory (SOHO) on 10 May 1995. It is next expected to come to perihelion ...

, which may have passed even closer at about from Earth on June 12, 1999, but the uncertainties are around ±1.5 million km as the P/1999 J6 approach was unobserved.

Discovery

The comet was discovered on June 14, 1770, in the constellation Sagittarius by Messier, who had just completed an observation of

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 mass more than two and a half times that of all the other planets in the Solar System combined, but ...

and was examining several

nebulae A nebula ('cloud' or 'fog' in Latin; pl. nebulae, nebulæ or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral or molecular hydrogen and also cosmic dust. Nebulae are often star-forming region ...

. At this time it was very faint, but his observations over the course of the next few days showed that it rapidly grew in size, its

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

reaching 27

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

s across by June 24: by this time it was of

magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...

+2. The comet was also noted by several other astronomers. The comet was observed in

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. Surviving records identify it as an astronomical and historical phenomenon. It was observed in the

Hejaz The Hejaz (, also ; ar, ٱلْحِجَاز, al-Ḥijāz, lit=the Barrier, ) is a region in the west of Saudi Arabia. It includes the cities of Mecca, Medina, Jeddah, Tabuk, Yanbu, Taif, and Baljurashi. It is also known as the "Western Provin ...

in Safar 1184 AH (June 1770), where some believed it to be the comet predicted by the poet al-Fasi, portending future events.

Close approach to Earth

On July 1, 1770, the comet passed 0.015

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbits t ...

s from Earth, or approximately 6 times the radius of the Moon's orbit.

measured the coma as 2° 23' across, around four times the apparent angular size of the Moon. An English astronomer at the time noted the comet crossing over 42° of sky in 24 hours; he described the

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 Nucle ...

as being as large as

, "surrounded with a coma of silver light, the brightest part of which was as large as the moon's orb". Messier was the last astronomer to observe the comet as it moved away 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 ...

, on October 3, 1770.

Orbit

Scientists at the time largely believed that comets originated outside the solar system, and therefore initial attempts to model the comet's orbit assumed a

parabolic trajectory In astrodynamics or celestial mechanics a parabolic trajectory is a Kepler orbit with the eccentricity equal to 1 and is an unbound orbit that is exactly on the border between elliptical and hyperbolic. When moving away from the source it is ca ...

, which indicated a

perihelion 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 ...

date (the date of the closest approach to the Sun) of August 9–10. When it turned out that the parabolic solution was not a good fit to the comet's orbit, Anders Johan Lexell suggested that the comet followed an

elliptical orbit In astrodynamics or celestial mechanics, an elliptic orbit or elliptical orbit is a Kepler orbit with an eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. In a stricter sense, it ...

. His calculations, made over a period of several years, gave a perihelion of August 13–14 and an orbital period of 5.58 years. Lexell also noted that, despite this short-period orbit, by far the shortest known at the time, the comet was unlikely to have been seen previously because its orbit had been radically altered in March 1767 by the gravitational forces of

.Leverington, D. ''Babylon to Voyager and Beyond: A History of Planetary Astronomy'', Cambridge University Press, 2003, p.193 It is, therefore, the earliest identified

Jupiter family comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena are ...

(as well as the first known

near-Earth object A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...

).Valsecchi, G
'A comet heading towards Earth: the first NEO'
, in

', Issue 2, accessed November 21, 2008 The comet was never seen again. Lexell, after conducting further work in cooperation with

Pierre-Simon Laplace Pierre-Simon, marquis de Laplace (; ; 23 March 1749 – 5 March 1827) was a French scholar and polymath whose work was important to the development of engineering, mathematics, statistics, physics, astronomy, and philosophy. He summarized ...

, argued that a subsequent interaction with Jupiter in July 1779 had further perturbed its orbit, either placing it too far from Earth to be seen or perhaps ejecting it from the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...

altogether. The comet likely no longer approaches any closer to the Sun than Jupiter's orbit. Although Comet Lexell was never seen again, it remained interesting to astronomers. The Paris Academy of Sciences offered a prize for an investigation into the orbit of the comet.

Johann Karl Burckhardt Johann Karl Burckhardt (30 April 1773 – 22 June 1825) was a German-born astronomer and mathematician. He later became a naturalized French citizen and became known as Jean Charles Burckhardt. He is remembered in particular for his work in funda ...

won in 1801, and confirmed the calculations of Lexell. He calculated that the 1779 close approach to Jupiter drastically altered its orbit and left it with a perihelion of 3.33 AU. In the 1840s,

Urbain Le Verrier Urbain Jean Joseph Le Verrier FRS (FOR) HFRSE (; 11 March 1811 – 23 September 1877) was a French astronomer and mathematician who specialized in celestial mechanics and is best known for predicting the existence and position of Neptune using ...

carried out further work on the comet's orbit and demonstrated that despite potentially approaching Jupiter as close as three and a half

radii In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

from the planet's centre the comet could never have become a satellite of Jupiter.Valsecchi, G
'Le Verrier's computations and the concept of Chaos'
, in

'', Issue 3, accessed February 11, 2011 He showed that after the second encounter with Jupiter many different trajectories were possible, given the uncertainties of the observations, and the comet could even have been ejected from the Solar System. This foreshadowed the modern scientific idea of

chaos Chaos or CHAOS may refer to: Arts, entertainment and media Fictional elements * Chaos (''Kinnikuman'') * Chaos (''Sailor Moon'') * Chaos (''Sesame Park'') * Chaos (''Warhammer'') * Chaos, in ''Fabula Nova Crystallis Final Fantasy'' * Cha ...

. Lexell's work on the orbit of the comet is considered to be the beginning of modern understanding of

orbit determination Orbit determination is the estimation of orbits of objects such as moons, planets, and spacecraft. One major application is to allow tracking newly observed asteroids and verify that they have not been previously discovered. The basic methods wer ...

.Valsecchi, G. '236 Years Ago...' in ''Near Earth Objects, Our Celestial Neighbors: Opportunity and Risk : Proceedings of the 236th Symposium of the International Astronomical Union'', Cambridge University Press, 2006, xvii–xviii

2018 recalculation

In a 2018 paper, Quan-Zhi Ye et al. used recorded observations of the comet to recalculate the orbit, finding Le Verrier's 1844 calculations to be highly accurate. They simulated the orbit forwards to the year 2000, finding that 98% of possible orbits remained orbiting the Sun, 85% with a perihelion nearer than the asteroid belt, and 40% crossing Earth's orbit. The numbers remain consistent even when including non-gravitational parameters caused by pressures from a comet's jets. Based on its apparent brightness in 1770, they estimate the comet to be between 4 and 50 kilometers in diameter, most likely less than 30. Additionally, based on a lack of meteor showers, they suggest that the comet may have ceased major activity before 1800 AD.

Identification

The aforementioned 2018 paper also attempted to identify if any discovered object may be a remnant of Lexell's comet. With an assumed size of >4 kilometers, it is highly unlikely that this comet would remain in the inner solar system and be undiscovered. Most new asteroids discovered even in the asteroid belt (as of 2018) are only 1–4 kilometers across. If Lexell's comet remains in the inner Solar System, it would most likely be an unidentified asteroid. The paper identified four potential asteroids which could be related: (99.2% chance), (74% chance), (0.2% chance), and (~0% chance). The

longitude of perihelion In celestial mechanics, the longitude of the periapsis, also called longitude of the pericenter, of an orbiting body is the longitude (measured from the point of the vernal equinox) at which the periapsis (closest approach to the central body) woul ...

(a value that does not evolve much even over an extended period of time) of these asteroids are 2.32°, 6.22°, 356.98°, and 351.62°, respectively. For comparison, the longitude of perihelion of Lexell's comet was 359.48 ± 0.24°. They find that is very likely to be a remnant of Lexell's comet, although due to a number of close approaches with Jupiter as well as uncertain non-gravitational parameters, a definite link cannot be made. will pass about from Venus on November 3, 2184.

Notes

References

* Hall, John Whitney. (1955). ''

Tanuma Okitsugu (September 11, 1719, in Edo, Japan – August 25, 1788, in Edo) was a chamberlain (''sobashū'') and a senior counselor (''rōjū'') to the ''shōgun'' Tokugawa Ieharu of the Tokugawa Shogunate, in the Edo period of Japan. Tanuma and his s ...

, 1719–1788: Forerunner of Modern Japan.'' Cambridge:

Harvard University Press Harvard University Press (HUP) is a publishing house established on January 13, 1913, as a division of Harvard University, and focused on academic publishing. It is a member of the Association of American University Presses. After the retirem ...

OCLC 445621

External links

D/1770 L1 (Lexell) Orbit Diagram

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...

JPL * * {{DEFAULTSORT:Lexell, 1770 L1 Lost comets 529668 529668 529668 20100506 17700614