Comet ISON, formally known as C/2012 S1, was a sungrazing comet from the Oort cloud which was discovered on 21 September 2012 by Vitaly Nevsky (Віталь Неўскі, Vitebsk,

Belarus Belarus, officially the Republic of Belarus, is a landlocked country in Eastern Europe. It is bordered by Russia to the east and northeast, Ukraine to the south, Poland to the west, and Lithuania and Latvia to the northwest. Belarus spans an a ...

) and Artyom Novichonok (Артём Новичонок, Kondopoga,

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

History

The discovery was made using the reflector of the International Scientific Optical Network (ISON) near Kislovodsk, Russia. Data processing was carried out by automated asteroid-discovery program CoLiTec. Precovery images by the Mount Lemmon Survey from 28 December 2011 and by

Pan-STARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; List of observatory codes, obs. code: IAU code#F51, F51 and Pan-STARRS2 obs. code: IAU code#F52, F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical ...

from 28 January 2012 were quickly located. Follow-up observations were made on 22 September 2012 by a team from Remanzacco Observatory in Italy using the iTelescope network. The discovery was announced by 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 ...

on 24 September. Observations by

Swift Swift or SWIFT most commonly refers to: * SWIFT, an international organization facilitating transactions between banks ** SWIFT code * Swift (programming language) * Swift (bird), a family of birds It may also refer to: Organizations * SWIF ...

in January 2013 suggested that Comet ISON's nucleus was around in diameter. Later estimates were that the nucleus was only about in diameter. Mars Reconnaissance Orbiter (MRO) observations suggested the nucleus was smaller than in diameter. Shortly after Comet ISON's discovery, the media reported that it might become brighter than the full Moon. However, as events transpired, it never became bright enough to be readily visible to the naked eye. Furthermore, it broke apart as it passed close to the Sun. Reports on 28 November 2013 (the day of perihelion passage) indicated that Comet ISON had partially or completely disintegrated due to the Sun's heat and tidal forces. However, later that day CIOC (NASA Comet ISON Observing Campaign) members discovered a

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 ...

-like feature, suggesting a small fragment of it may have survived perihelion. On 29 November 2013, the coma dimmed to an

apparent magnitude Apparent magnitude () is a measure of the Irradiance, brightness of a star, astronomical object or other celestial objects like artificial satellites. Its value depends on its intrinsic luminosity, its distance, and any extinction (astronomy), ...

of 5. By the end of 30 November 2013, the coma had further faded to below naked-eye visibility at magnitude 7. On 1 December 2013, the coma continued to fade even further as it finished traversing the Solar and Heliospheric Observatory's view. On 2 December 2013, the CIOC announced that Comet ISON had fully disintegrated. The

Hubble Space Telescope The Hubble Space Telescope (HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the Orbiting Solar Observatory, first space telescope, but it is one of the largest and most ...

failed to detect fragments of ISON on 18 December 2013. On 8 May 2014, a detailed examination of the disintegration was published, suggesting that the comet had fully disintegrated hours before perihelion.

Discovery

During routine observations on 21 November 2012, Vitali Nevski and Artyom Novichonok monitored areas of Gemini and

Cancer Cancer is a group of diseases involving Cell growth#Disorders, abnormal cell growth with the potential to Invasion (cancer), invade or Metastasis, spread to other parts of the body. These contrast with benign tumors, which do not spread. Po ...

after their observations were delayed by clouded weather for much of the night. The team used ISON's reflector near Kislovodsk, Russia, and CCD imaging to carry out their observations. Shortly after their session, Nevski processed data using CoLiTec, an automated asteroid discovery

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

program. In analysis he noted an unusually bright object with slow apparent movement, indicating a position outside the orbit 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 ...

based on the use of four 100-second CCD exposures. At the time of discovery, the object's

ranged from 19.1 to as bright as 18.8.Astronomical magnitudes decrease as brightness increases, from large positive values, through zero, to negative values for very bright objects. The group reported their discovery to the Central Bureau for Astronomical Telegrams as an asteroidal object, which was subsequently forwarded to the

. However, the group later reported that the object had a cometary appearance with a

approximately 8 arcseconds across. The object's position and cometary appearance was confirmed by several other unaffiliated observers, and as such the comet was named ''ISON'', after the international observational project and in accordance with

International Astronomical Union The International Astronomical Union (IAU; , UAI) is an international non-governmental organization (INGO) with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreach, education, and developmen ...

naming guidelines. Comet ISON was precovered in analysis of Mount Lemmon Observatory imagery by Gareth V. Williams and

imagery in Haleakalā. Precovery images from Mount Lemmon were first taken on 28 December 2011 and indicated that the comet had an estimated apparent magnitude ranging from 19.5 to 19.9. Images from Pan-STARRS were taken on 28 January 2012 and in those images the comet had an estimated apparent magnitude ranging from 19.8 to 20.6.

Orbit

Comet ISON came to perihelion (closest approach to the Sun) on 28 November 2013 at a distance of from the center point of the Sun. Accounting for the solar radius of , Comet ISON passed approximately above the Sun's surface. Its trajectory appeared to be hyperbolic, which suggested that it was a dynamically new comet that took millions of years coming freshly from the Oort cloud or even a candidate interstellar comet.C/2012 S1 (ISON) had an epoch 1600 barycentric semi-major axis o
−145127
and would have an inbound v_infinite of 0.2 km/s at 50000 au:
''v''=42.1219 Near perihelion, generic heliocentric two-body solutions to the

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values be ...

suggested that the comet could be either bound or unbound to the Sun. But for objects at such high eccentricity, the Solar System's barycenter is more stable than a heliocentric solution. The orbit of a long-period comet is properly obtained when the osculating orbit is computed at an

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided b ...

after leaving the planetary region and is calculated with respect to the center of mass of the Solar System. JPL Horizons barycentric orbital elements for epoch 1950 and 2050 both generate a hyperbolic solution with no orbital period. Using an epoch of 1950, the inbound weakly hyperbolic eccentricity of 1.000000086 suggests ISON is of solar origin. On its closest approach, Comet ISON passed about from Mars on 1 October 2013, and the remnants of Comet ISON passed about from Earth on 26 December 2013. Shortly after its discovery, similarities between the

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same o ...

of Comet ISON and the

Great Comet of 1680 C/1680 V1, also called the Great Comet of 1680, Kirch's Comet, and Newton's Comet, was the first comet discovered by telescope. It was discovered by Gottfried Kirch and was one of the brightest comets of the seventeenth century. Overview The c ...

led to speculation that there might be a connection between them. Further observations of ISON, however, showed that the two comets are not related. When Earth passed near the orbit of Comet ISON on 14–15 January 2014, it was predicted that micron-sized dust particles blown by the Sun's radiation might cause a

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 ...

or noctilucent clouds; however, both events were considered unlikely. Because Earth only passed near Comet ISON's orbit, not through the tail, the chances that a meteor shower would occur were slim. In addition, meteor showers from long-period comets that make just one pass into the inner solar system are very rare, if ever recorded. The possibility that small particles left behind on the orbital path—almost one hundred days after the nucleus has passed—could form noctilucent clouds is also slim. No such events are known to have taken place in the past under similar circumstances.

Brightness, observations, and visibility

Discovery while entering inner Solar System

At the time of its discovery, Comet ISON's brightness was approximately

18.8, far too dim to be seen with the

naked eye Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnification, magnifying, Optical telescope#Light-gathering power, light-collecting optical instrument, such as a telescope or microsc ...

, but bright enough to be imaged by amateurs with large telescopes. It then followed the pattern of most comets and increased gradually in brightness on approach to the Sun. At least a dozen spacecraft imaged Comet ISON. It was first imaged by the Swift and Deep Impact spacecraft in January and February 2013, and shown to be active with an extended tail. In April and May 2013 the

(HST) measured Comet ISON's size, and the color, extent, and polarization of its emitted dust. The Spitzer Space Telescope (SST) observed Comet ISON on 13 June and estimated

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

outgassing at about per day. From 5 June to 29 August 2013, Comet ISON had an elongation less than 30° from the Sun. No obvious rotational variability was detected by either Deep Impact, HST, or Spitzer. Amateur astronomer Bruce Gary recovered it on 12 August 2013 when it was 6° above the

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

and 19° from the Sun. Due to it brightening more slowly than predicted, Comet ISON only became visible through small telescopes during early October 2013.

Lead-up to perihelion

On 28 September 2013, NASA launched BRRISON, a stratospheric science balloon carrying a telescope and science instruments designed to capture images and data on Comet ISON from an altitude of However, about two and a half hours after launch, the telescope returned to its stowed position too quickly, driving it past a stow latch. Operators were unable to redeploy the telescope, resulting in mission failure. On 1 October 2013, Comet ISON passed within of Mars. Between 29 September and 2 October, the Mars Reconnaissance Orbiter (MRO) detected Comet ISON. The twin

STEREO Stereophonic sound, commonly shortened to stereo, is a method of sound reproduction that recreates a multi-directional, 3-dimensional audible perspective. This is usually achieved by using two independent audio channels through a configurat ...

spacecraft began detecting Comet ISON in the second week of October. October 2013 images of Comet ISON displayed a greenish tint, probably attributable to the release of cyanogen and diatomic carbon. On 31 October 2013, Comet ISON was detected with 10×50 mm binoculars. On 14 November 2013, Comet ISON was reported to be visible to the naked eye by experienced observers located at dark sites. It had an appearance similar to comet C/2013 R1 that was also visible to the naked eye. Comet ISON was not expected to reach the naked-eye magnitude 6 until mid-November, and was not expected to be observable by the general public until it brightened to about magnitude 4. On 17–18 November, when Comet ISON was brighter and much closer to the morning

twilight Twilight is daylight illumination produced by diffuse sky radiation when the Sun is below the horizon as sunlight from the upper atmosphere is scattered in a way that illuminates both the Earth's lower atmosphere and also the Earth's surf ...

, it passed the bright star Spica in the constellation

Virgo Virgo may refer to: Arts and entertainment * Virgo (film), a 1970 Egyptian film * Virgo (character), several Marvel Comics characters * Virgo Asmita, a character in the manga ''Saint Seiya: The Lost Canvas'' * ''Virgo'' (album), by Virgo Four, ...

. But due to the full Moon and glow of twilight, Comet ISON had not become bright enough to be seen without optical aid by the general public. On 22 November, it started to drop below Mercury in the bright twilight.

Perihelion

SOHO SoHo, short for "South of Houston Street, Houston Street", is a neighborhood in Lower Manhattan, New York City. Since the 1970s, the neighborhood has been the location of many artists' lofts and art galleries, art installations such as The Wall ...

started to view it on 27 November, first with the LASCO coronograph. On 27 November ISON brightened to magnitude −2 and passed Delta Scorpii. Around the time it reached perihelion on 28 November 2013, it might have become extremely bright if it had remained fully intact. However, predicting the brightness of a comet is difficult, especially one that passes so close to the Sun and is affected by the forward scattering of light. Originally, media sources predicted that it might become brighter than the full Moon, but based on more recent observations, it was only expected to reach around

−3 to −5, about the same brightness as

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

. In comparison, the brightest comet since 1935 was Comet Ikeya–Seki in 1965 at magnitude −10, which was much brighter than Venus. ISON-Cor2B-20131129 012400

On 29 November 2013, Comet ISON had dimmed to magnitude 5 in the LASCO images. By the end of 30 November 2013, it had further faded below naked-eye visibility at magnitude 7.

After perihelion

In a February 2013 study, 1,897 observations were used to create a

light curve In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

. The resulting plot showed Comet ISON increasing its brightness relatively quickly at R. If this had continued to perihelion, it would have reached magnitude −17 – brighter than the full Moon. It had since exhibited a "slowdown event", however, similar to behavior exhibited by other Oort cloud comets, among them C/2011 L4. Therefore, Comet ISON's brightness increased less quickly than expected and it did not become as bright as some early predictions. Further observations suggested that, even if it had remained intact, it might only brighten to about magnitude −6. The temperature at perihelion had been calculated to reach – sufficient to melt iron. Additionally, it passed within its

Roche limit In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal force ...

, meaning it might disintegrate due to the Sun's gravity. Comet ISON had been expected to be brightest around the time it was closest to the Sun, if it could have been seen; but because it was less than 1° from the Sun at its closest, it would have been difficult to see against the Sun's glare. If it had survived its perihelion passage intact, Comet ISON should have been well-placed for observers in the northern hemisphere during mid to late December 2013. It might even have remained visible to the naked eye until January 2014. As Comet ISON moved north on the celestial sphere it would have passed within 2° of

Polaris Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris (Latinisation of names, Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an ...

on 8 January.

Science results

On 22 May 2014, the Eurasian Astronomical Society and Sternberg Astronomical Institute published preliminary results of observations of the observed meteor shower of Comet ISON from January 2014. Scientists from Ukraine and Belarus were assisted by meteor observation groups around the world. The results confirmed that particles of Comet ISON, which likely sublimated at perihelion, entered Earth's atmosphere as meteor particles. 43 meteor events were recorded after analyzing 54,000 images from 10–17 January 2014. On 11 August 2014, astronomers released studies, using the

Atacama Large Millimeter Array The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The ar ...

(ALMA) for the first time, that detailed the distribution of , , , and

dust Dust is made of particle size, fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian processes, aeolian process), Types of volcan ...

inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).

Name

Comet ISON's formal designation was C/2012 S1.The "C" indicates that it was non-periodic, followed by the year of discovery. The "S" represents the half-month of discovery – in the case of C/2012 S1, the second half of September – and the number "1" shows that this was the first comet found in that half-month. It was named "ISON" after the organization where its discovery was made, the Russia-based International Scientific Optical Network. The initial report of the object to the Central Bureau for Astronomical Telegrams identified the object as an asteroid, and it was listed on the Near-Earth Object Confirmation Page. Follow-up observations by independent teams were the first to report cometary features. Therefore, under the International Astronomical Union's comet-naming guidelines, Comet ISON was named after the team that discovered it, rather than the individual discoverers.

Media coverage

After it was discovered in 2012, some media sources called Comet ISON the "Comet of the Century" and speculated that it might outshine the full Moon. An ''Astronomy Now'' columnist wrote in September 2012 that "if predictions hold true then Comet ISON will certainly be one of the greatest comets in human history." Astronomer Karl Battams criticized the media's suggestion that Comet ISON would be "brighter than the full Moon", saying that members of the Comet ISON Observing Campaign did not foresee ISON becoming that bright. Comet ISON has been compared to Comet Kohoutek, seen in 1973–1974, another highly anticipated Oort Cloud comet that peaked early and fizzled out.

Notes

References

External links

ISONCampaign.org
the NASA Comet ISON Observing Campaign
Comet ISON
at NASA Solar System Exploration
C/2012 S1 (ISON)
at the IAU

C/2012 S1 (ISON)
at the JPL Small-Body Database Browser

at Aerith.net

at Cometography.com
"Anticipated STEREO observations of Comet ISON"
at NASA's STEREO Science Center
"A Timeline Of Comet ISON's Dangerous Journey"
at NASA.gov

Media

Eyes on Comet ISON
at NASA Solar System Exploration
ScienceCasts: Comet of the Century
by Science@NASA at YouTube.com
story

NASA's Deep Impact Spacecraft Images Comet ISON
by JPL News at YouTube.com
Path of Comet ISON through the SOHO/LASCO fields of view
by Bill Thompson at Sungrazing Comets

by Erik Bryssinck at Astronomie.be

''Minor Planet Electronic Circulars''

(2013 Nov 26 : 6120 obs : Epoch 2013 Dec 14 e=0.9999947 q=0.0124439 includes nongravitational parameters)

(2013 Nov 25 : 5586 obs : Epoch 2013 Dec 14 e=1.0000019 q=0.0124479)

(2013 Sep 30 : 4308 obs : Epoch 2013 Dec 14 e=1.0000020 q=0.0124441)

(2013 Sep 16 : 3997 obs : Epoch 2013 Dec 14 e=1.0000019 q=0.0124442)

(2013 Sep 6 : 3897 obs : Epoch 2013 Dec 14 e=1.0000019 q=0.0124441)

(2013 Apr 23 : 3442 obs : Epoch 2013 Dec 14 e=1.0000020 q=0.0124437)

(2013 Apr 9 : 3307 obs : Epoch 2013 Dec 14 e=1.0000021 q=0.0124435)

(2013 Mar 25 : 3121 obs : Epoch 2013 Dec 14 e=1.0000022 q=0.0124434)

(2013 Mar 18 : 3047 obs : Epoch 2013 Dec 14 e=1.0000022 q=0.0124434)

(2013 Mar 9 : 2799 obs : Epoch 2013 Dec 14 e=1.0000022 q=0.0124437)

(2013 Feb 23 : 2372 obs : Epoch 2013 Dec 14 e=1.0000020 q=0.0124436)

(2013 Feb 12 : 1999 obs : Epoch 2013 Dec 14 e=1.0000019 q=0.0124439)

(2013 Jan 14 : 1418 obs : Epoch 2013 Dec 14 e=1.0000016 q=0.0124445)

(2012 Dec 26 : 1000 obs : Epoch 2013 Dec 14 e=1.0000015 q=0.0124443)

(2012 Dec 11 : 812 obs : Epoch 2013 Dec 14 e=1.0000014 q=0.0124453)

(2012 Nov 27 : 706 obs : Epoch 2013 Dec 14 e=1.0000014 q=0.0124475)

(2012 Nov 15 : 538 obs)

(2012 Oct 26 : 418 obs : Epoch 2013 Dec 14 e=1.0000013 q=0.0124484)

(2012 Oct 12 : 272 obs : Epoch 2013 Dec 14 e=1.0000008 q=0.0124472)

(2012 Oct 3 : 163 obs : Epoch 2013 Dec 14 e=1.0000013 : (1/a)_orig = +0.00005808, (1/a)_fut = +0.00000785) {{DEFAULTSORT:ISON, 2012 S1 Non-periodic comets Hyperbolic comets Destroyed comets 20120921 * * * Sungrazing comets Comets in 2012 Comets in 2013 Oort cloud Articles containing video clips