Comet Shoemaker–Levy 9

Comet Shoemaker–Levy 9 (formally designated D/1993 F2) was a comet that broke apart in July 1992 and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of Solar System objects.[4] This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide. The collision provided new information about Jupiter and highlighted its possible role in reducing space debris in the inner Solar System.

The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy in 1993.[5] Shoemaker–Levy 9 had been captured by Jupiter and was orbiting the planet at the time. It was located on the night of March 24 in a photograph taken with the 46 cm (18 in) Schmidt telescope at the Palomar Observatory in California. It was the first comet observed to be orbiting a planet, and had probably been captured by Jupiter around 20–30 years earlier.

Calculations showed that its unusual fragmented form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker–Levy 9 passed within Jupiter's Roche limit, and Jupiter's tidal forces had acted to pull apart the comet. The comet was later observed as a series of fragments ranging up to 2 km (1.2 mi) in diameter. These fragments collided with Jupiter's southern hemisphere between July 16 and 22, 1994 at a speed of approximately 60 km/s (37 mi/s) (Jupiter's escape velocity) or 216,000 km/h (134,000 mph). The prominent scars from the impacts were more easily visible than the Great Red Spot and persisted for many months.

D/1993 F2 (Shoemaker–Levy)
Hubble Space Telescope
Shoemaker–Levy 9, disrupted comet on a collision course[1]
(total of 21 fragments, taken on May 17, 1994)
Discovery
Discovered byCarolyn Shoemaker
Eugene Shoemaker
David Levy
Discovery dateMarch 24, 1993
Orbital characteristics A
Inclination94.2°
Dimensions1.8 km (1.1 mi)[2][3]

Discovery

While conducting a program of observations designed to uncover near-Earth objects, the Shoemakers and Levy discovered Comet Shoemaker–Levy 9 on the night of March 24, 1993 in a photograph taken with the 0.46 m (1.5 ft) Schmidt telescope at the Palomar Observatory in California. The comet was thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program.[6]

Comet Shoemaker–Levy 9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, hence its name. It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature. The discovery was announced in IAU Circular 5725 on March 27, 1993.[5]

The discovery image gave the first hint that comet Shoemaker–Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region about 50 arcseconds long and 10 arcseconds wide. Brian G. 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 although this could of course be a line of sight effect, its apparent motion in the sky suggested that it was physically close to it.[5] 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.

Jupiter-orbiting comet

Orbital studies of the new comet soon revealed that it was orbiting Jupiter rather than the Sun, unlike all other comets known at the time. Its orbit around Jupiter was very loosely bound, with a period of about 2 years and an apoapsis (the point in the orbit farthest from the planet) of 0.33 astronomical units (49 million kilometres; 31 million miles). Its orbit around the planet was highly eccentric (e = 0.9986).[7]

Tracing back the comet's orbital motion revealed that it had been orbiting Jupiter for some time. It is 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.[8] Several other observers found images of the comet in precovery images obtained before March 24, including Kin 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.[9] No precovery images dating back to earlier than March 1993 have been found. 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.[10]

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). 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 Jove-centric orbit of very high eccentricity—that is to say, the ellipse was nearly flattened out.[11]

The comet had apparently passed extremely close to Jupiter on July 7, 1992, just over 40,000 km (25,000 mi) above its cloud tops—a smaller distance than Jupiter's radius of 70,000 km (43,000 mi), 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.[11] 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. 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.[12]

More exciting for planetary astronomers was that the best orbital calculations suggested that the comet would pass within 45,000 km (28,000 mi) of the center 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.[13] Studies suggested that the train of nuclei would plow into Jupiter's atmosphere over a period of about five days.[11]

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.[7]

Astronomers estimated that the visible fragments of SL9 ranged in size from a few hundred metres (around 1,000 ft) to two kilometres (1.2 mi) across, suggesting that the original comet may have had a nucleus up to 5 km (3.1 mi) across—somewhat larger than Comet Hyakutake, which became very bright when it passed close to the Earth in 1996. 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.[14] The most optimistic prediction was that large, asymmetric ballistic fireballs would rise above the limb of Jupiter and into sunlight to be visible from Earth.[15] 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. However, given that observing such a collision was completely unprecedented, astronomers were cautious with their predictions of what the event might reveal.[7]

Impacts

Hubble Space Telescope Image of Fragment BDGLNQ12R Impacts
Jupiter in ultraviolet (about 2.5 hours after R's impact). The black dot near the top is Io transiting Jupiter.[16]
Max Planck Institute Shoemaker–Levy 9
Jupiter in infrared, Shoemaker–Levy 9 collision (left), Io (right)

Anticipation grew 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. Although the impacts took place on the side of Jupiter hidden from Earth, Galileo, then at a distance of 1.6 AU (240 million km; 150 million mi) from the planet, was able to see the impacts as they occurred. Jupiter's rapid rotation brought the impact sites into view for terrestrial observers a few minutes after the collisions.[17]

Two other space probes made observations at the time of the impact: the Ulysses spacecraft, primarily designed for solar observations, was pointed towards Jupiter from its location 2.6 AU (390 million km; 240 million mi) away, and the distant Voyager 2 probe, some 44 AU (6.6 billion km; 4.1 billion mi) 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 and make observations with its ultraviolet spectrometer.[18]

Impact fireball appears over the limb of Jupiter
Hubble Space Telescope images of a fireball from the first impact appearing over the limb of the planet

The first impact occurred at 20:13 UTC on July 16, 1994, when fragment A of the nucleus entered Jupiter's southern hemisphere at a speed of about 60 km/s (35 mi/s).[4] Instruments on Galileo detected a fireball that reached a peak temperature of about 24,000 K (23,700 °C; 42,700 °F), compared to the typical Jovian cloudtop temperature of about 130 K (−143 °C; −226 °F), before expanding and cooling rapidly to about 1,500 K (1,230 °C; 2,240 °F) after 40 seconds. The plume from the fireball quickly reached a height of over 3,000 km (1,900 mi).[19] 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.[20]

Despite published predictions,[15] astronomers had not expected to see the fireballs from the impacts[21] and did not have any idea in advance how visible the other 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 (3,700 mi) (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.[22]

Over the next six days, 21 distinct impacts were observed, with the largest coming on July 18 at 07:33 UTC when fragment G struck Jupiter. This impact created a giant dark spot over 12,000 km (7,500 mi) across, and was estimated to have released an energy equivalent to 6,000,000 megatons of TNT (600 times the world's nuclear arsenal).[23] 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.[24]

Observations and discoveries

Chemical studies

Jupiter showing SL9 impact sites
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. Other molecules detected included ammonia (NH3) and hydrogen sulfide (H2S). 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.[25]

As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with abundances consistent with what would be found in a cometary nucleus. Although a substantial amount of 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.[26]

Waves

As predicted beforehand, the collisions generated enormous waves that swept across Jupiter at speeds of 450 m/s (1,476 ft/s) and were observed for over two hours after the largest impacts. The waves were thought to be travelling within a stable layer acting as a waveguide, and some scientists thought the stable layer must lie within the hypothesised tropospheric water cloud. 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.[27]

Other observations

SL9ImpactGalileo
A sequence of Galileo images, taken several seconds apart, showing the appearance of the fireball of fragment W on the dark side of Jupiter

Radio observations revealed a sharp increase in continuum emission at a wavelength of 21 cm (8.3 in) after the largest impacts, which peaked at 120% of the normal emission from the planet. This was thought to be due to synchrotron radiation, caused by the injection of relativistic electrons—electrons with velocities near the speed of light—into the Jovian magnetosphere by the impacts.[28]

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. 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. 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.[29]

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. 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.[30]

Voyager 2 failed to detect anything with calculations showing that the fireballs were just below the craft’s limit of detection.[31] Ulysses also failed to detect anything.[18]

Post-impact analysis

Impact site of fragment G
A reddish, asymmetric ejecta pattern

Several models were devised to compute the density and size of Shoemaker–Levy 9. Its average density was calculated to be about 0.5 g/cm3 (0.018 lb/cu in); the breakup of a much less dense comet would not have resembled the observed string of objects. The size of the parent comet was calculated to be about 1.8 km (1.1 mi) in diameter.[2][3] These predictions were among the few that were actually confirmed by subsequent observation.[32]

One of the surprises of the impacts was the small amount of water revealed compared to prior predictions.[33] 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 30 kilopascals to a few tens of megapascals (from 0.3 to a few hundred bar),[26] with some predictions that the comet would penetrate a layer of water and create a bluish shroud over that region of Jupiter.[14]

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 (36 psi), well above the expected depth of the water layer. The smaller fragments were probably destroyed before they even reached the cloud layer.[26]

Longer-term effects

The visible scars from the impacts could be seen on Jupiter for many months. They were extremely prominent, and observers described them as even more easily visible 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 although the Great Red Spot is notable for its striking color, no spots of the size and darkness of those caused by the SL9 impacts have ever been recorded before.[34]

Spectroscopic observers found that ammonia and carbon disulfide 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.[35]

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 to 20,000 km (9,300 to 12,400 mi) wide, but dropped back to normal levels within a week of the impact. At smaller sites, temperatures 10 K (18 °F) higher than the surroundings persisted for almost two weeks.[36] 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.[37]

Frequency of impacts

Chain of impact craters on Ganymede
A chain of craters on Ganymede, probably caused by a similar impact event. The picture covers an area approximately 190 km (120 mi) across

SL9 is not unique in having orbited Jupiter for a time; five comets, (including 82P/Gehrels, 147P/Kushida–Muramatsu, and 111P/Helin–Roman–Crockett) are known to have been temporarily captured by the planet.[38][39] Cometary orbits around Jupiter are 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).

By far the most massive planet in the Solar System, Jupiter can capture objects relatively frequently, but the size of SL9 makes it a rarity: one post-impact study estimated that comets 0.3 km (0.19 mi) in diameter impact the planet once in approximately 500 years and those 1.6 km (0.99 mi) in diameter do so just once in every 6,000 years.[40]

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.[41] 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. The impact of SL9 strongly implied that the chains were due to trains of disrupted cometary fragments crashing into the satellites.[42]

Impact of July 19, 2009

On July 19, 2009, exactly 15 years after the SL9 impacts, a new black spot about the size of the Pacific Ocean appeared in Jupiter's southern hemisphere. Thermal infrared measurements showed the impact site was warm and spectroscopic analysis detected the production of excess hot ammonia and silica-rich dust in the upper regions of Jupiter's atmosphere. Scientists have concluded that another impact event had occurred, but this time a more compact and strong object, probably a small undiscovered asteroid, was the cause.[43]

Jupiter as a "cosmic vacuum cleaner"

The impact of SL9 highlighted Jupiter's role as a "cosmic vacuum cleaner" (or in deference to the ancients' planetary correspondences to the major organs in the human body, a "cosmic liver") for the inner Solar System (Jupiter Barrier). 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 2,000–8,000 times higher than the rate on Earth.[44]

The extinction of the dinosaurs at the end of the Cretaceous period is generally thought to have been caused by the Cretaceous–Paleogene impact event, which created the Chicxulub crater,[45] demonstrating that impacts are a serious threat to life on Earth. Astronomers have speculated that without Jupiter to mop up potential impactors, extinction events might have been more frequent on Earth, and complex life might not have been able to develop.[46] This is part of the argument used in the Rare Earth hypothesis.

In 2009, it was shown that the presence of a smaller planet at Jupiter's position in the Solar System might increase the impact rate of comets on the Earth significantly. A planet of Jupiter's mass still seems to provide increased protection against asteroids, but the total effect on all orbital bodies within the Solar System is unclear.[47][48] Computer simulations in 2016 have continued to erode the theory.[49]

See also

References

Notes

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Bibliography

  • Chodas P. W., and Yeomans D. K. (1996), The Orbital Motion and Impact Circumstances of Comet Shoemaker–Levy 9, in The Collision of Comet Shoemaker–Levy 9 and Jupiter, edited by K. S. Noll, P. D. Feldman, and H. A. Weaver, Cambridge University Press, pp. 1–30
  • Chodas P. W. (2002), Communication of Orbital Elements to Selden E. Ball, Jr. Accessed February 21, 2006

External links

118P/Shoemaker–Levy

118P/Shoemaker–Levy (also known as periodic comet Shoemaker–Levy 4) is a comet discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy.During the 2010 apparition the comet became as bright as apparent magnitude 11.5.The comet nucleus is estimated to be 4.8 kilometers in diameter.On December 3, 2015, comet Shoemaker–Levy 4 will pass 0.0442 AU (6,610,000 km; 4,110,000 mi) from asteroid 4 Vesta.This comet should not be confused with Comet Shoemaker–Levy 9 (D/1993 F2) which spectacularly crashed into Jupiter in 1994.

129P/Shoemaker–Levy

129P/Shoemaker–Levy, also known as Shoemaker–Levy 3, is a periodic comet in the Solar System. It fits the definition of an Encke-type comet with (TJupiter > 3; a < aJupiter), and is a quasi-Hilda comet.This comet should not be confused with Comet Shoemaker–Levy 9 (D/1993 F2), which spectacularly crashed into Jupiter in 1994.

138P/Shoemaker–Levy

138P/Shoemaker–Levy, also known as Shoemaker–Levy 7, is a faint periodic comet in the solar system. The comet last came to perihelion on 11 June 2012, but only brightened to about apparent magnitude 20.5.There were 4 recovery images of 138P on 8 August 2018 by Pan-STARRS when the comet had a magnitude of about 21.5. The comet comes to perihelion on 2 May 2019.

This comet should not be confused with Comet Shoemaker–Levy 9 (D/1993 F2), which crashed into Jupiter in 1994.

147P/Kushida–Muramatsu

147P/Kushida–Muramatsu is a quasi-Hilda comet discovered in 1993 by Japanese astronomers Yoshio Kushida and Osamu Muramatsu.

According to calculations made by Katsuhiko Ohtsuka of the Tokyo Meteor Network and David Asher of Armagh Observatory, Kushida–Muramatsu was temporarily captured by Jupiter as an irregular moon between May 14, 1949, and July 15, 1962, (12.17+0.29−0.27 years). It is the fifth such object known to have been captured.It is thought that quasi-Hilda comets may be escaped Hilda asteroids. Comet Shoemaker–Levy 9 is a more famous example of a quasi-Hilda comet.

2017 UV43

2017 UV43 is a centaur from the outer Solar System, approximately 8 kilometers (5 miles) in diameter. It was first observed by the Mount Lemmon Survey on 13 March 2005. The unusual minor planet follows an orbit similar to those of the fragments of comet Shoemaker–Levy 9. This minor planet has neither been numbered nor named.

38th parallel structures

The 38th parallel structures, also known as the 38th parallel lineament, are a series of circular depressions or deformations stretching 700 km (435 mi) across southern Illinois and Missouri into eastern Kansas at a latitude of roughly 38 degrees north.

Rampino and Volk (1996) postulated that these structures could be the remains of a serial meteorite strike in the late Mississippian or early Pennsylvanian periods. Difficulty in determining the age of many of the structures and doubts about the exogenic origins of several of them leave some geologists skeptical of this hypothesis. As of 2016, only two of the structures, Crooked Creek (320 ± 80 Ma) and Decaturville (< 300 Ma), are listed as confirmed in the Earth Impact Database.There is evidence that at least some of them, such as Hicks Dome, are volcanic in origin. They are associated with faults and fractured rock, and are accompanied by igneous rocks and mineral deposits. Hicks Dome is a structural dome which has its central Devonian core displaced upward some 4,000 feet (1,200 m) in relation to the surrounding strata. The dome has small associated igneous dikes around its flanks.Interest in the possibility of serial impacts on Earth was piqued by observations of comet Shoemaker–Levy 9 impacting on Jupiter in 1994. It is estimated, however, that the likelihood of such an event on Earth is vanishingly small because the Earth's weaker gravitational field is much less able than Jupiter's to pull a speeding object close enough to be torn apart by tidal forces. However, evidence of serial impacts on the Moon can be seen in several chains of craters.

Carolyn S. Shoemaker

Carolyn Jean Spellmann Shoemaker (born June 24, 1929) is an American astronomer and is a co-discoverer of Comet Shoemaker–Levy 9. She once held the record for most comets discovered by an individual.Although Carolyn had earned degrees in history, political science and English literature, she had almost no interest in science until after she met and married Eugene M. ("Gene") Shoemaker in 1950-51). She said later that his explanations of his work thrilled her. Despite her relative inexperience and her lack of a relevant scientific degree, Caltech had no objection to her joining Gene's team at the California Institute of Technology as a research assistant. Carolyn had already showed herself to be unusually patient, and she had already demonstrated exceptional stereoscopic vision, both qualities were extremely valuable in a career looking for objects in near-earth space.

Crater chain

A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena (plural catenae), as specified by the International Astronomical Union's rules on planetary nomenclature.Many examples of such chains are thought to have been formed by the impact of a body that was broken up by tidal forces into a string of smaller objects following roughly the same orbit. An example of such a tidally disrupted body that was observed prior to its impact on Jupiter is Comet Shoemaker-Levy 9. During the Voyager observations of the Jupiter system, planetary scientists identified 13 crater chains on Callisto and three on Ganymede (except those formed by secondary craters). Later some of these chains turned out to be secondary or tectonic features, but some other chains were discovered. As of 1996, 8 primary chains on Callisto and 3 on Ganymede were confirmed.Other cases, such as many of those on Mars, represent chains of collapse pits associated with grabens (see, for example, the Tithoniae Catenae near Tithonium Chasma).

Crater chains seen on the Moon often radiate from larger craters, and in such cases are thought to be either caused by secondary impacts of the larger crater's ejecta or by volcanic venting activity along a rift.

David H. Levy

David H. Levy (born May 22, 1948) is a Canadian astronomer, science writer and discoverer of comets and minor planets, who co-discovered Comet Shoemaker–Levy 9 in 1993, which collided with the planet Jupiter in 1994.

Erich Meyer

Erich Meyer (born August 6, 1951) is an Austrian engineer, amateur astronomer and discoverer of asteroids.

Erwin Obermair

Erwin Obermair (29 August 1946 in Hargelsberg – 15 January 2017 in Linz) was an Austrian amateur astronomer and co-discoverer of asteroids.

Together with his college and amateur astronomer Erich Meyer, Obermair built the private observatory Meyer/Obermair (540) in Davidschlag (municipality Kirchschlag bei Linz, Austria), in 1978. He co-discovered a total of 7 asteroids at this observatory, all together with Meyer. Furthermore, he was involved in three other discoveries of asteroids between 1996 and 2005, which were assigned as site discoveries to the observatory Davidschlag by the International Astronomical Union.Obermair was a member of the Astronomical Society of Linz (Linzer Astronomische Gemeinschaft), from 1974 until his death he was vice president of that association. His most important observations include precisie astrometry of the comet Shoemaker–Levy 9, which he observerd together with Erich Meyer and Herbert Raab in 1993. These observations have significantly contributed to the subsequent prediction of the impact of this comet on the planet Jupiter.On 4 April 1997, Obermair was presented the Decoration of Honour in Silver of the Republic of Austria. The main-belt asteroid 9236 Obermair, discovered by his college Erich Meyer at Linz in 1997, was named in his honor. Naming citation was published on 4 May 1999 (M.P.C. 34629).

Eugene Merle Shoemaker

Eugene Merle Shoemaker (April 28, 1928 – July 18, 1997), also known as Gene Shoemaker, was an American geologist and one of the founders of the field of planetary science. He is best known for co-discovering the Comet Shoemaker–Levy 9 with his wife Carolyn S. Shoemaker and David H. Levy. This comet hit Jupiter in July 1994: the impact was televised around the world.

Shoemaker was also well known for his studies of terrestrial craters, such as Barringer Meteor Crater in Arizona. Shoemaker was also the first director of the United States Geological Survey's Astrogeology Research Program.

Herbert Raab

Herbert Raab (born January 24, 1969 in Linz, Austria) is an Austrian software engineer, amateur astronomer and discoverer of astronomical objects.He finished his studies of computer science at the Johannes Kepler University of Linz in 1995 as a graduate engineer. In 2012, he received the Master of Science in Management for Engineers at the LIMAK business school in Linz, where he also graduated as Master of Business Administration in 2013. He works as a software engineer in the field of commercial software.In 1983, he joined the Astronomical Society of Linz (Linzer Astronomische Gemeinschaft), and has been president of the society from 1996 until 2017. Since 1990, he has been developing the widely used software Astrometrica, which is used for astrometric and photometric analysis of images of asteroids and comets. Raab's most important observations include precise astrometry of the comet Shoemaker–Levy 9, which he observed together with Erich Meyer and Erwin Obermair in 1993. These observations have significantly contributed to the subsequent prediction of the impact of this comet on the planet Jupiter.On August 10, 1997, he discovered the asteroid 13682 Pressberger together with Erich Meyer at the private observatory Meyer/Obermair in Davidschlag (municipality Kirchschlag bei Linz, Austria). Furthermore, he was involved in three other discoveries of asteroids which were assigned as site discoveries to the observatory Davidschlag by the International Astronomical Union (see Category:Discoveries by the Davidschlag Observatory). During the Occultation of the star HIP 76293 by the asteroid 1177 Gonnessia on May 18, 2007, Raab discovered that the star is a close double star, whose components have a separation of just 0.04".In May 1996, asteroid 3184 Raab was named in his honor, following a proposal of Brian G. Marsden and Gareth V. Williams from the Minor Planet Center (M.P.C. 27124). On April 4, 1997, Raab was presented the Gold Medal for Services to the Republic of Austria.

Michael J. Belton

Michael J. S. Belton (September 29, 1934 – June 4, 2018) was President of Belton Space Exploration Initiatives and Emeritus Astronomer at the Kitt Peak National Observatory in Arizona. Belton served as the Chair of the 2002 Planetary Science Decadal Survey guiding NASA and other US Government Agencies plans for solar system exploration. Belton studied first at the University of St. Andrews in Scotland and earned his PhD at the University of California at Berkeley for his doctoral thesis on "The Interaction of Type II Comet Tails with the Interplanetary Medium".Belton was born in Bognor Regis, England. He led the Galileo Imaging Science Team in high-resolution imaging studies of Venus, Jupiter, Jupiter's moons Io, Europa, Ganymede and Callisto, Earth's moon as well as asteroids Ida, Gaspra, and Dactyl. The team also studied the collision of comet Shoemaker-Levy 9 with Jupiter.

Shoemaker (surname)

Ann Shoemaker (1891–1978), American actress

Benjamin Shoemaker (1704–c. 1767), mayor of Philadelphia during the 18th century

Bill Shoemaker (1931–2003), American jockey

Carolyn S. Shoemaker (born 1929), astronomer and co-discoverer of Comet Shoemaker-Levy 9

Charles F. Shoemaker (1841–1913), Commandant from 1895 through 1905 of the United States Revenue Cutter Service

Craig Shoemaker (born 1958), American comedian

Douglas Harlow Shoemaker (1905–1985), last Chief Engineer of the Northern Pacific Railway

Eugene Merle Shoemaker (1928–1997), planetary scientist and co-discoverer of Comet Shoemaker-Levy 9

Francis Shoemaker, member of the U.S. House of Representatives from Minnesota during the 1930s

Henry W. Shoemaker (1880–1958), American folklorist, diplomat, and writer

Jarrod Shoemaker (born 1982), American triathlete

Jenna Shoemaker (born 1984), American professional triathlete

John Shoemaker (born 1956), American baseball coach and manager

Lazarus Denison Shoemaker (1819–1893), member of the U.S. House of Representatives from Pennsylvania during the 1870s

Matt Shoemaker (born 1986) American baseball player

Mike Shoemaker (born 1945), politician from Ohio

Myrl Shoemaker (1913–1985), former lieutenant governor of Ohio and father of Mike Shoemaker

Nelson Shoemaker (1911–2003), former member of the Legislative Assembly of Manitoba, Canada

Robert Alan Shoemaker (born 1928), Canadian mycologist with the standard author abbreviation "Shoemaker"

Robert M. Shoemaker (born 1924), U.S. Army general

Sam Shoemaker (1893–1963), American reverend

Sydney Shoemaker (born 1931), American philosopher

Sylvia Browne (1936–2013), born Sylvia Celeste Shoemaker, American author

Trina Shoemaker, music producer and technician

Dave T. Shoemaker (born 2001), American professional beatboxer

Tanami Road

The Tanami Road, also known as the Tanami Track and the McGuire Track, runs between the Stuart Highway in the Northern Territory and the Great Northern Highway in Western Australia. Its southern junction is 19 km (12 mi) north of Alice Springs and the northern junction is 17 km (11 mi) south west of Halls Creek. It follows a cattle droving route northwest from the MacDonnell Ranges area of central Australia to Halls Creek in the Kimberley.The Tanami Road is the most direct route from Alice Springs to the Kimberley, passing through the Tanami Desert. Along its route are Yuendumu and The Granites gold mine owned by Newmont Mining. In the Northern Territory it passes through land owned by the Aboriginal Warlpiri people, and in Western Australia it passes through pastoral land.

About 20% of the road is bitumen, the remainder is dirt and gravel and, although it is navigable by two-wheel drive vehicles, a four-wheel drive is recommended. Some parts of the road are prone to severe corrugations, making for an uncomfortable and slow drive at times.The mid-way point, Rabbit Flat, formerly a public roadhouse, was closed indefinitely at the end of 2010, so planning for this journey must take the lack of fuel and supplies into account. Tilmouth Well, located 186 km (116 mi) from Alice Springs between Alice Springs and Rabbit Flat, provides fuel service 7 days a week. Carrying adequate fuel and water supplies is essential.

The astronomer Eugene Shoemaker, best known for his co-discovery of the comet Shoemaker–Levy 9, died in a car accident while travelling along the Tanami Road in 1997.

Weaubleau structure

The Weaubleau structure is a probable meteorite impact site in western Missouri near the towns of Gerster, Iconium, Osceola, and Vista. It is believed to have been caused by a 1,200 feet (370 m) meteoroid between 335 and 340 million years ago during the middle Mississippian Period (Latest Osagean to Earliest Meramecian).

It is listed by the Impact Field Studies Group as a "probable" impact structure.The structure consists of an area of severe structural deformation and extensive brecciation that was poorly understood and had been thought to be the result of either thrusting over a dome or a cryptoexplosive event. A 12 mi (19 km) circular structure was discovered by geologist Kevin R. Evans through examination of digital elevation data. The structure was originally called the Weaubleau-Osceola structure after Weaubleau Creek and Osceola. It is now known as the Weaubleau structure.

Because the site was covered by later Pennsylvanian Period sediments, and only partially exposed to erosion relatively recently, its structure is well preserved, and its age can be determined with fair accuracy. It is one of a series of known or suspected impact sites along the 38th parallel in the states of Illinois, Missouri, and Kansas. These 38th parallel structures are thought to possibly be the result of a serial impact, similar to that of comet Shoemaker-Levy 9 on Jupiter, an extremely unlikely event on Earth. The argument for a serial strike would be greatly strengthened if the ages of the other 38th parallel structures could be constrained to the same period as the Weaubleau structure.The Weaubleau structure is one of the fifty largest known impact craters on earth and the fourth largest in the United States. The three larger ones in the US either have been glaciated and buried (Manson crater), are under water (Chesapeake Bay crater), or have been subjected to orogeny (Beaverhead crater). Therefore, the Weaubleau structure is the largest exposed untectonized impact crater in the US.

Wiesław Z. Wiśniewski

Wiesław Z. Wiśniewski (May 2, 1931 in Poland – February 28, 1994 in Tucson, Arizona, United States) was a Polish astronomer.

Wisniewski was born and educated in Poland. He survived the Nazi occupation and many of his later insights and viewpoints may have grown from the hardships suffered during the war and the years afterwards. He began his career as a high school mathematics teacher before receiving his M.A. degree in astronomy from Poznan University in 1952 and his D.Sc. degree in astronomy from Jagiellonian University, Poland, in 1962. He joined the staff of the Cracow Observatory at Jagiellonian University as a research assistant in 1953. Wisniewski moved to the United States in 1963 to work as an astronomy professor at the newly founded Lunar and Planetary Laboratory at the University of Arizona in Tucson Arizona. Wisniewski returned to Poland in 1967, but eventually made his permanent home in Tucson, Arizona in 1971.His main interests were comets and asteroids. Wisniewski was heavily involved in astronomical photometry which he learned while working with Harold Johnson at the Lunar and Planetary Laboratory. His later years were occupied with observations of asteroids and comets, especially of the light-curves of small asteroids as well as taxonomic measurements of asteroids. At the time of his death, he was actively planning to participate in a network of telescopes to observe the impacts of comet Shoemaker-Levy 9 on Jupiter. He had obtained one of the early high resolution images of the comet on March 28, 1993 while using the Steward Observatory 90 inch telescope.

Zdenek Sekanina

Zdenek Sekanina (born 12 June 1936, Mladá Boleslav, Czechoslovakia (now Czech Republic)) is a Czech-American astronomer and scientist.

In 1959, Sekanina started to study astronomy at Charles University in Prague, where he was graduated in 1963. Since 1980, he has been working at the Jet Propulsion Laboratory.

His main areas of professional study are meteors and interplanetary dust as well as the study of comets. In the course of his investigations, he dealt with Halley's comet, the Tunguska event, as well as the break-up and impact of Comet Shoemaker–Levy 9 on Jupiter.He was involved in the data evaluation of the Giotto, Stardust, and Solar and Heliospheric Observatory missions.

The asteroid 1913 Sekanina was named after him.

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