Shoemaker-Levy redirects here. For other Shoemaker-Levy comets see List of periodic comets. Periodic comets are defined for these purposes as those Comets having orbital periods of less than 200 years (also known as "short-period comets" or which

SL9 (Shoemaker-Levy)

Image of Comet Shoemaker-Levy 9, taken on May 17, 1994. Events 1521 - Edward Stafford 3rd Duke of Buckingham, is executed for Treason. Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar)
Discovery
Discovered by:	Carolyn Shoemaker Eugene M. Shoemaker David Levy
Discovery date:	March 24, 1993
Orbital characteristics A
Inclination:	94. Carolyn Jean Spellmann Shoemaker (born June 24, 1929, in Gallup New Mexico) is a co-discoverer of Comet Shoemaker-Levy 9 and is the widow Eugene Merle Shoemaker (or Gene Shoemaker ( April 28, 1928  &ndash July 18, 1997) was one of the founders of the fields of Planetary Biography Levy was born in Montreal, Quebec, Canada, on May 22, 1948. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar) Inclination in general is the Angle between a Reference plane and another plane or axis of direction 23333°

Comet Shoemaker-Levy 9 (SL9, formally designated D/1993 F2) was a comet that collided with Jupiter in 1994, providing the first direct observation of the collision of two solar system objects, not including collisions involving Earth. In ancient times only the Sun and Moon, a few hundred Stars and the most easily visible Planets had names A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — The Solar System consists of the Sun and those celestial objects bound to it by Gravity. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 This generated a large amount of coverage in the popular media, and SL9 was closely observed by astronomers worldwide. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The comet provided many revelations about Jupiter and its atmosphere and highlighted Jupiter's role in reducing space debris in the inner solar system. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " Space debris or orbital debris, also called space junk and space waste are the objects in Orbit around Earth created by humans that no

The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy. Carolyn Jean Spellmann Shoemaker (born June 24, 1929, in Gallup New Mexico) is a co-discoverer of Comet Shoemaker-Levy 9 and is the widow Eugene Merle Shoemaker (or Gene Shoemaker ( April 28, 1928  &ndash July 18, 1997) was one of the founders of the fields of Planetary Biography Levy was born in Montreal, Quebec, Canada, on May 22, 1948. Shoemaker-Levy 9 was located on the night of March 24, 1993, in a photograph taken with the 0. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar) 4 metre Schmidt telescope at the Mount Palomar Observatory in California. A Schmidt camera, also referred to as the Schmidt telescope, is an astronomical Camera designed to provide wide fields of view with limited Palomar Observatory is a privately owned Observatory located in San Diego County California, 90 miles (145 Km) Southeast of Mount Wilson California ( is a US state on the West Coast of the United States, along the Pacific Ocean. It was the first comet observed to be orbiting a planet rather than the Sun. The Sun (Sol is the Star at the center of the Solar System. ^[1]

SL9 was in pieces ranging in size up to 2 kilometres in diameter, and is believed to have been pulled apart by Jupiter's tidal forces during a close encounter in July 1992. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced These fragments collided with Jupiter's southern hemisphere between July 16 and July 22, 1994, at a speed of approximately 60 kilometres per second (37 miles per second). Events 622 - The beginning of the Islamic calendar. 1054 - Three Roman legates fractured relations between the Western and Events 1099 - First Crusade: Godfrey of Bouillon is elected the first Defender of the Holy Sepulchre of The Kingdom of Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) The prominent scars from the impacts could be seen on Jupiter for many months after the impact, and observers described them as more easily visible than the Great Red Spot.

Discovery

Comet Shoemaker-Levy 9 (SL9) was discovered on the night of March 24, 1993 by the Shoemakers and Levy, in a photograph taken with the 0. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar) 4 metre Schmidt telescope at the Mount Palomar Observatory in California, while conducting a program of observations designed to uncover near-Earth objects. A Schmidt camera, also referred to as the Schmidt telescope, is an astronomical Camera designed to provide wide fields of view with limited Palomar Observatory is a privately owned Observatory located in San Diego County California, 90 miles (145 Km) Southeast of Mount Wilson California ( is a US state on the West Coast of the United States, along the Pacific Ocean. Near-Earth objects ( NEOs) are Asteroids Comets and large Meteoroids whose orbits bring them close ( Perihelion distance AU Unlike all other comets discovered before then, it was orbiting Jupiter rather than the Sun. The Sun (Sol is the Star at the center of the Solar System. The comet was thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program. Serendipity is the effect by which one accidentally discovers something fortunate especially while looking for something else entirely

SL9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, hence its name. However, it was their eleventh discovery in all, because they had also discovered two non-periodic comets, which use a different nomenclature. The discovery was announced in IAU Circular 5725 on March 27, 1993. The International Astronomical Union Circulars ( IAUC s are notices that give information about astronomical phenomena Events 196 BC - Ptolemy V ascends to the throne of Egypt. 1309 - Pope Clement V excommunicates Year 1993 ( MCMXCIII) was a Common year starting on Friday (link will display full 1993 Gregorian calendar) Subsequently, several other observers found the comet in images obtained before March 24, including K. Endate from a photograph exposed on March 15, S. Otomo on March 17, and a team led by Eleanor Helin from images on March 19 [1]. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland Kin Endate (円館 金 born 1960 is a Japanese Astronomer. He was born at Iwaizumi Iwate. Events 44 BC - Julius Caesar, Dictator of the Roman Republic, is stabbed to death by Marcus Junius Brutus, Satoru Otomo (大友哲 also Satoshi Otomo, is a Japanese Astronomer. Events 45 BC - In his last victory Julius Caesar defeats the Pompeian forces of Titus Labienus and Pompey the Younger Events 1279 - A Mongolian victory in the Battle of Yamen ends the Song Dynasty in China.

The discovery image gave the first hint that SL9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region about 50 arcseconds long and 10 arcseconds wide. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. Brian Marsden of the Central Bureau for Astronomical Telegrams noted that the comet lay only about 4 degrees from Jupiter as seen from Earth, and that while this could of course be a projection effect, its apparent motion suggested that it was physically close to the giant planet [2]. Brian Geoffrey Marsden (born 5 August 1937 is a British Astronomer, the longtime director of the Minor Planet Center (MPC at the Harvard-Smithsonian Center This article describes the unit of angle For other meanings see Degree. Apparent motion occurs when a stimulus is flashed in one location followed by another identical stimulus flashed in another location Because of this, he suggested that the Shoemakers and David Levy had discovered the fragments of a comet that had been disrupted by Jupiter's gravity. Gravitation is a natural Phenomenon by which objects with Mass attract one another

A Jupiter-orbiting comet

Orbital studies of the new comet soon revealed that, unlike all other comets discovered before then, it was orbiting Jupiter rather than the Sun. The Sun (Sol is the Star at the center of the Solar System. Its orbit around Jupiter was very loosely bound, with a period of about 2 years and an apojove (furthest distance from Jupiter) of 0. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 33 Astronomical Units (AU) (49. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the 4 million km). Its orbit around the planet was highly eccentric (e = 0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 9986).

Tracing back the comet's orbital motion revealed that it had been orbiting Jupiter for some time. It seems most likely that it was captured from a solar orbit in the early 1970s, although the capture may have occurred as early as the mid-1960s. ^[2] No precovery images dating back to earlier than March 1993 have been found so far. Precovery (prediscovery is a term used in Astronomy that describes the process of finding the Image of an object (usually a Minor planet, but sometimes Before the comet was captured by Jupiter, it was probably a short-period comet with an aphelion just inside Jupiter's orbit, and a perihelion interior to the asteroid belt. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The asteroid belt is the region of the Solar System located roughly between the orbits of the Planets Mars and Jupiter. ^[3]

The volume of space within which an object can be said to orbit Jupiter is defined by Jupiter's Hill sphere (also called the Roche sphere). A Hill sphere is roughly the volume around an Astronomical body (such as a Planet) where it dominates in attraction of Satellites to that body rather When the comet passed Jupiter in the late 1960s or early 1970s, it happened to be near its aphelion, and found itself slightly within Jupiter's Hill sphere. Jupiter's gravity nudged the comet towards it. Because the comet's motion with respect to Jupiter was very small, it fell almost straight toward Jupiter, which is why it ended up on a Jupiter-centric orbit of very high eccentricity —that is to say, the ellipse was nearly flattened out.

The comet had apparently passed extremely close to Jupiter on July 7, 1992, just over 40,000 km above the planet's cloud tops — a smaller distance than Jupiter's radius of 70,000 km, and well within the orbit of Jupiter's innermost moon Metis and the planet's Roche limit, inside which tidal forces are strong enough to disrupt a body held together only by gravity. Events 1456 - A retrial verdict acquits Joan of Arc of heresy 25 years after her death Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) TemplateInfobox Planet.--> Metis (, or as in Greek Μήτις Determining the Roche limit The Roche limit depends on the rigidity of the satellite The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced Although the comet had approached Jupiter closely before, the July 7 encounter seemed to be by far the closest, and the fragmentation of the comet is thought to have occurred at this time. Events 1456 - A retrial verdict acquits Joan of Arc of heresy 25 years after her death Each fragment of the comet was denoted by a letter of the alphabet, from "fragment A" through to "fragment W", a practice already established from previously observed broken-up comets. An alphabet is a standardized set of letters basic written symbols each of which roughly represents a Phoneme, a Spoken language, either

More exciting for planetary astronomers was that the best orbital solutions suggested that the comet would pass within 45,000 km of the centre of Jupiter, a distance smaller than the planet's radius, meaning that there was an extremely high probability that SL9 would collide with Jupiter in July 1994. Studies suggested that the train of nuclei would plough into Jupiter's atmosphere over a period of about five days.

Predictions for the collision

The discovery that the comet was likely to collide with Jupiter caused great excitement within the astronomical community and beyond, as astronomers had never before seen two significant solar system bodies collide. Intense studies of the comet were undertaken, and as its orbit became more accurately established, the possibility of a collision became a certainty. The collision would provide a unique opportunity for scientists to look inside Jupiter's atmosphere, as the collisions were expected to cause eruptions of material from the layers normally hidden beneath the clouds.

Astronomers estimated that the visible fragments of SL9 ranged in size from a few hundred metres to at most a couple of kilometres across, suggesting that the original comet may have had a nucleus up to 5 km across – somewhat larger than Comet Hyakutake, which became very bright when it passed close to the Earth in 1996. Comet Hyakutake (çʲakɯ̥take formally designated C/1996 B2) is a Comet discovered on January 30 1996 which passed very close to Earth One of the great debates in advance of the impact was whether the effects of the impact of such small bodies would be noticeable from Earth, apart from a flash as they disintegrated like giant meteors.

Other suggested effects of the impacts were seismic waves travelling across the planet, an increase in stratospheric haze on the planet due to dust from the impacts, and an increase in the mass of the Jovian ring system. Seismology (from Greek grc σεισμός seismos, "earthquake" and grc -λογία -logia) is the scientific study of Earthquakes The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. The planet Jupiter has a system of rings known as the rings of Jupiter or the Jovian ring system. However, given that observing such a collision was completely unprecedented, astronomers were cautious with their predictions of what the event might reveal.

Impacts

Jupiter in Ultraviolet (about 2. 5 hours after R's impact)

Anticipation was elevated as the predicted date for the collisions approached, and astronomers trained terrestrial telescopes on Jupiter. Several space observatories did the same, including the Hubble Space Telescope, the ROSAT X-ray observing satellite, and significantly the Galileo spacecraft, then on its way to a rendezvous with Jupiter scheduled for 1995. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ROSAT (short for Rö ntgen' sat' ellit was a German X-ray satellite telescope X-radiation (composed of X-rays) is a form of Electromagnetic radiation. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. Galileo was an Unmanned spacecraft sent by NASA to study the Planet Jupiter and its moons Named after the Astronomer While the impacts would take place on the side of Jupiter hidden from Earth, Galileo, then at a distance of 1. 6 AU from the planet, would be able to see the impacts as they occurred. Jupiter's rapid rotation would bring the impact sites into view for terrestrial observers a few minutes after the collisions.

Two other satellites made observations at the time of the impact: the Ulysses spacecraft, primarily designed for solar observations, was pointed towards Jupiter from its location 2. Ulysses is a robotic Space probe designed to study the Sun at all latitudes The Sun (Sol is the Star at the center of the Solar System. 6 AU away, and the distant Voyager 2 probe, some 44 AU from Jupiter and on its way out of the solar system following its encounter with Neptune in 1989, was programmed to look for radio emission in the 1–390 kHz range. Voyager 2 is an unmanned Interplanetary Spacecraft launched on August 20, 1977. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second.

HST images of a fireball from the first impact appearing over the limb of the planet.

The first impact occurred at 20:15 UTC on July 16, 1994, when fragment A of the nucleus slammed into Jupiter's southern hemisphere at a speed of about 60 km/s. Events 622 - The beginning of the Islamic calendar. 1054 - Three Roman legates fractured relations between the Western and Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) Instruments on Galileo detected a fireball which reached a peak temperature of about 24,000 K, compared to the typical Jovian cloudtop temperature of about 130 K, before expanding and cooling rapidly to about 1500 K after 40 s. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The plume from the fireball quickly reached a height of over 3,000 km. ^[4] A few minutes after the impact fireball was detected, Galileo measured renewed heating, probably due to ejected material falling back onto the planet. Earth-based observers detected the fireball rising over the limb of the planet shortly after the initial impact. ^[5]

Astronomers had expected to see the fireballs from the impacts, but did not have any idea in advance how visible the atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact. The spot was visible even in very small telescopes, and was about 6,000 km (one Earth radius) across. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact.

Over the next 6 days, 21 discrete impacts were observed, with the largest coming on July 18 at 07:34 UTC when fragment G struck Jupiter. Events 390 BC - Roman - Gaulish Wars Battle of the Allia - a Roman army is defeated by raiding Gauls, This impact created a giant dark spot over 12,000 km across, and was estimated to have released an energy equivalent to 6,000,000 megatons of TNT (750 times the world's nuclear arsenal). Two impacts 12 hours apart on July 19 created impact marks of similar size to that caused by fragment G, and impacts continued until July 22, when fragment W struck the planet. Events 711 - Muslim forces under Tariq ibn Ziyad defeat the Visigoths led by their king Roderic. Events 1099 - First Crusade: Godfrey of Bouillon is elected the first Defender of the Holy Sepulchre of The Kingdom of

Observations and discoveries

Chemical studies

Brown spots mark impact sites on Jupiter's southern hemisphere.

Observers hoped that the impacts would give them a first glimpse of Jupiter beneath the cloud tops, as lower material was exposed by the comet fragments punching through the upper atmosphere. Spectroscopic studies revealed absorption lines in the Jovian spectrum due to diatomic sulfur (S₂) and carbon disulfide (CS₂), the first detection of either in Jupiter, and only the second detection of S₂ in any astronomical object. Astronomical spectroscopy is the technique of Spectroscopy used in Astronomy. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range compared Sulfur or sulphur (ˈsʌlfɚ see spelling below) is the Chemical element that has the Atomic number 16 s are significant physical entities, associations or structures which current Science has confirmed to exist in Space. Other molecules detected included ammonia (NH₃) and hydrogen sulfide (H₂S). Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. The amount of sulfur implied by the quantities of these compounds was much greater than the amount that would be expected in a small cometary nucleus, showing that material from within Jupiter was being revealed. Oxygen-bearing molecules such as sulfur dioxide were not detected, to the surprise of astronomers. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the ^[6]

As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with the abundances of these atoms being consistent with what would be found in a cometary nucleus. In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 While substantial water was detected spectroscopically, it was not as much as predicted beforehand, meaning that either the water layer thought to exist below the clouds was thinner than predicted, or that the cometary fragments did not penetrate deeply enough.

Seismic waves

As predicted beforehand, the collisions generated enormous seismic waves which swept across the planet at speeds of 450 km/s and were observed for over two hours after the largest impacts. Seismic waves are Waves that travel through the Earth, most often as the result of a tectonic Earthquake, sometimes from an Explosion These waves seemed to be gravity waves, but their location was subject to debate. In Fluid dynamics, gravity waves are waves generated in a Fluid medium or at the interface between two media (e The waves were thought to be travelling within a stable layer acting as a waveguide, and some scientists believed the stable layer must lie within the hypothesised tropospheric water cloud. A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and However, other evidence seemed to indicate that the cometary fragments had not reached the water layer, and the waves were instead propagating within the stratosphere. The stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. ^[7]

Other observations

A sequence of Galileo images, taken several seconds apart, showing the appearance of the fireball of fragment G on the dark side of Jupiter. Galileo was an Unmanned spacecraft sent by NASA to study the Planet Jupiter and its moons Named after the Astronomer

Radio observations revealed a sharp increase in continuum emission at a wavelength of 21 cm after the largest impacts, which peaked at 120% of the normal emission from the planet. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. In Physics, a black body is an object that absorbs all light that falls on it A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth This was thought to be due to synchrotron radiation, caused by the injection of relativistic electrons into the Jovian magnetosphere by the impacts. This article concerns the physical phenomenon of synchrotron radiation This page is about the scientific concept of relativity for philosophical or sociological theories about relativity see Relativism. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. ^[8]

About an hour after fragment K entered Jupiter, observers recorded auroral emission near the impact region, as well as at the antipode of the impact site with respect to Jupiter's strong magnetic field. In Mathematics, the antipodal point of a point on the surface of a sphere is the point which is diametrically opposite it — so situated that a line drawn from the In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges The cause of these emissions was difficult to establish due to a lack of knowledge of Jupiter's internal magnetic field and of the geometry of the impact sites. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges One possible explanation was that upwardly accelerating shock waves from the impact accelerated charged particles enough to cause auroral emission, a phenomenon more typically associated with fast-moving solar wind particles striking a planetary atmosphere near a magnetic pole. For the music album by Converter see Shock Front For the 1977 horror film see Shock Waves A shock wave (also called The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. This article is about geographic magnetic and other poles on planets and other astronomical bodies ^[9]

Some astronomers had suggested that the impacts might have a noticeable effect on the Io torus, a torus of high-energy particles connecting Jupiter with the highly volcanic moon Io. In Geometry, a torus (pl tori) is a Surface of revolution generated by revolving a Circle in three dimensional space about an axis Coplanar Plate tectonics and hotspots Divergent plate boundaries At the TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek High resolution spectroscopic studies found that variations in the ion density, rotational velocity, and temperatures at the time of impact and afterwards were within the normal limits. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different Rotational speed (sometimes called speed of revolution) indicates for example how fast a motor is running Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature ^[10]

Post-impact analysis

Fragment G impact site, showing asymmetric ejecta pattern.

One of the surprises of the impacts was the small amount of water revealed compared to prior predictions. Before the impact, models of Jupiter's atmosphere had indicated that the break-up of the largest fragments would occur at atmospheric pressures of anywhere from 300 kilopascals to a few megapascals (from three to a few tens bar), and most astronomers expected that the impacts would penetrate a hypothesised water-rich layer underneath the clouds. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure.

Astronomers did not observe large amounts of water following the collisions, and later impact studies found that fragmentation and destruction of the cometary fragments in an 'airburst' probably occurred at much higher altitudes than previously expected, with even the largest fragments being destroyed when the pressure reached 250 kPa (2. 5 bar), well above the expected depth of the water layer. The smaller fragments were probably destroyed before they even reached the cloud layer. ^[11]

Longer-term effects

The visible scars from the impacts could be seen on Jupiter for many months after the impact. They were extremely prominent, and observers described them as more easily visible even than the Great Red Spot. A search of historical observations revealed that the spots were probably the most prominent transient features ever seen on the planet, and that while the Great Red Spot is notable for its striking colour, no spots of the size and darkness of those caused by the SL9 impacts have ever been recorded before. ^[12]

Spectroscopic observers found that ammonia and carbon sulfide persisted in the atmosphere for at least fourteen months after the collisions, with a considerable amount of ammonia being present in the stratosphere as opposed to its normal location in the troposphere. ^[13]

Counterintuitively, the atmospheric temperature dropped to normal levels much more quickly at the larger impact sites than at the smaller sites: at the larger impact sites, temperatures were elevated over a region 15,000–20,000 km wide, but dropped back to normal levels within a week of the impact. At smaller sites, temperatures 10 K higher than the surroundings persisted for almost two weeks. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic ^[14] Global stratospheric temperatures rose immediately after the impacts, then fell to below pre-impact temperatures 2–3 weeks afterwards, before rising slowly to normal temperatures. ^[15]

Frequency of impacts

A chain of craters on Ganymede, probably caused by a similar impact event. A crater chain is a line of craters along the surface of an astronomical body TemplateInfobox Planet.--> Ganymede (ˈgænɨmiːd, or as Greek The picture covers an area approximately 190 km (120 mi) across.

Since the impact of SL9, two further very small comets have been found to be orbiting Jupiter temporarily- 82P/Gehrels and 111P/Helin-Roman-Crockett ^[3]. Studies have shown that the planet, by far the most massive in the solar system, can capture comets from solar orbit into Jovian orbit rather frequently. The Solar System consists of the Sun and those celestial objects bound to it by Gravity.

Cometary orbits around Jupiter are generally unstable, as they will be highly elliptical and likely to be strongly perturbed by the Sun's gravity at apojove (the furthest point on the orbit from the planet). In Mathematics, an ellipse (from the Greek ἔλλειψις literally absence) is a Conic section, the locus of points in a In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from Studies have estimated that comets probably crash into Jupiter once or twice per century, but the impact of comets the size of SL9 is much less common - probably no more often than once per millennium. A millennium (pl millennia) is a period of Time equal to one thousand Years (from Latin la mille, thousand and la annum

There is very strong evidence that comets have previously been fragmented and collided with Jupiter and its satellites. During the Voyager missions to the planet, planetary scientists identified 13 crater chains on Callisto and three on Ganymede, the origin of which was initially a mystery. A crater chain is a line of craters along the surface of an astronomical body TemplateInfobox Planet.--> Callisto (kəˈlɪstoʊ, or as Greek TemplateInfobox Planet.--> Ganymede (ˈgænɨmiːd, or as Greek Crater chains seen on the Moon often radiate from large craters, and are thought to be caused by secondary impacts of the original ejecta, but the chains on the Jovian moons did not lead back to a larger crater. A gas giant (sometimes also known as a Jovian planet after the planet Jupiter, or giant planet) is a large Planet that is not primarily The impact of SL9 strongly implied that the chains were due to trains of disrupted cometary fragments crashing into the satellites.

Jupiter as a "cosmic vacuum cleaner"

The impact of SL9 highlighted Jupiter's role as a kind of "cosmic vacuum cleaner" for the inner solar system. The planet's strong gravitational influence leads to many small comets and asteroids colliding with the planet, and the rate of cometary impacts on Jupiter is thought to be between two thousand and eight thousand times higher than the rate on Earth. Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but ^[16] If Jupiter were not present, the probability of asteroid impacts with the Solar System's inner planets would be much greater.

The extinction of the dinosaurs at the end of the Cretaceous period is generally believed to have been caused by the impact event which created the Chicxulub crater, demonstrating that impacts are a serious threat to life on Earth. The Cretaceous (kriːˈteɪʃəs, usually abbreviated 'K' for its German translation "Kreide" is a geologic period and system, reaching from the end of See also Impact crater An impact event is the Collision of a large Meteoroid, Asteroid or Comet (generically The Chicxulub Crater (tʃikʃuˈlub is an ancient Impact crater buried underneath the Yucatán Peninsula in Mexico. Astronomers have speculated that without Jupiter to mop up potential impactors, extinction events might have been much more frequent on Earth, and complex life might not have been able to develop. ^[17] This is part of the argument used in the Rare Earth hypothesis. In Planetary astronomy and Astrobiology, the Rare Earth hypothesis argues that the emergence of complex Multicellular life ( Metazoa

References

External links

• Comet Shoemaker-Levy 9 FAQ
• Comet Shoemaker-Levy 9 Photo Gallery
• Downloadable gif Animation showing time course of impact and size relative to earthsize
• http://www.cv.nrao.edu/~pmurphy/patsl9.html
• Jupiter Swallows Comet Shoemaker Levy 9
• Comet Shoemaker-Levy Collision with Jupiter
• National Space Science Data Center information
• A simulation of the orbit of SL-9 showing the passage that fragmented the comet, and the collision 2 years later
• YouTube video animation of impact