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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 warms and begins to release gases when passing close to the Sun, a process called outgassing. This produces an extended, gravitationally unbound atmosphere or Coma (cometary), coma surrounding ...
discovered by
astronomer An astronomer is a scientist in the field of astronomy who focuses on a specific question or field outside the scope of Earth. Astronomers observe astronomical objects, such as stars, planets, natural satellite, moons, comets and galaxy, galax ...
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 June 1770.Other comets named after their orbit computer, rather than discoverer, are 27P/Crommelin,
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 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 notable for having passed closer to
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
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 h ...
, 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. ...
. 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, P/1999 J6 (SOHO), 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 Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...
and was examining several
nebulae A nebula (; 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 regions, such as in the Pillars of Creation in th ...
. 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 Nociception, respond normally to Pain, painful stimuli, light, or sound, lacks a normal Circadian rhythm, sleep-wake cycle and does not initiate ...
reaching 27
arcminute 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 ...
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 is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
. Surviving records identify it as an astronomical and historical phenomenon. It was observed in the
Hejaz Hejaz is a Historical region, historical region of the Arabian Peninsula that includes the majority of the western region of Saudi Arabia, covering the cities of Mecca, Medina, Jeddah, Tabuk, Saudi Arabia, Tabuk, Yanbu, Taif and Al Bahah, Al-B ...
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 AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...
s from Earth, or approximately 6 times the radius of the Moon's orbit.
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 ...
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 Nucleu ...
as being as large as
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 ...
, "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 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 ...
, on October 3, 1770.


Orbit

Scientists at the time largely believed that comets originated outside 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 "Sola ...
, 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 Orbital eccentricity, eccentricity equal to 1 and is an unbound orbit that is exactly on the border between elliptical and hyperbolic. When moving away f ...
, which indicated a
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 ...
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 elliptical orbit or eccentric orbit is an orbit with an orbital eccentricity, eccentricity of less than 1; this includes the special case of a circular orbit, with eccentricity equal to 0. Some or ...
. 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
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 ...
.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 (as well as the first known
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 ...
).Valsecchi, G
'A comet heading towards Earth: the first NEO'
, in

', Issue 2, accessed November 21, 2008
After conducting further work in cooperation with
Pierre-Simon Laplace Pierre-Simon, Marquis de Laplace (; ; 23 March 1749 – 5 March 1827) was a French polymath, a scholar whose work has been instrumental in the fields of physics, astronomy, mathematics, engineering, statistics, and philosophy. He summariz ...
, Lexell 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 "Sola ...
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 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 (; 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 only mathematics. ...
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 or radiuses) 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 radius of a regular polygon is the line segment or ...
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: Science, technology, and astronomy * '' Chaos: Making a New Science'', a 1987 book by James Gleick * Chaos (company), a Bulgarian rendering and simulation software company * ''Chaos'' (genus), a genus of amoebae * ...
. 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.


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 (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.


See also

* P/2016 BA14 (the closest comet flyby since Lexell, in 2016)


Notes


References

* Hall, John Whitney. (1955). ''
Tanuma Okitsugu (September 11, 1719 – August 25, 1788) 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 son exercised tremendo ...
, 1719–1788: Forerunner of Modern Japan.'' Cambridge:
Harvard University Press Harvard University Press (HUP) is an academic publishing house established on January 13, 1913, as a division of Harvard University. It is a member of the Association of University Presses. Its director since 2017 is George Andreou. The pres ...

OCLC 445621


External links


D/1770 L1 (Lexell) Orbit Diagram
NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...
JPL * * {{DEFAULTSORT:Lexell, 1770 L1 C Near-Earth comets 529668 529668 529668 20100506 17700614 Discoveries by Charles Messier