Comet Shoemaker-Levy 9 , comet that collided with Jupiter in 1994 providing the first direct observation of an extraterrestrial collision between objects in the Solar System
Summary
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- 1 Discovery
- 2 Orbiting a planet
- 3 Impact predictions
- 4 Impacts
- 5 Observation
- 6 Discoveries made
- 1 Chemical studies
- 2 Other remarks
- 7 Long-term effects
- 8 The frequency of impacts
- 9 Jupiter as a “cosmic vacuum cleaner”
- 10 Fun facts
- 11 The SL9 in popular culture
- 12 Sources
Discovery
Although the purpose was to discover objects close to Earth, the Shoemaker and Levy couple discovered the Shoemaker-Levy 9 on March 24, 1993 thanks to a photograph of the catadioptric telescope at the Palomar Observatory, being a scientific discovery made thanks to a serendipity, however, was quickly overshadowed by the major discoveries for which the research was planned.The Shoemaker-Levy 9 was the ninth periodic comet (a comet whose orbital period is less than or equal to 200 years and its orbit is a very ellipse eccentric) discovered by Levy and the Shoemakers, hence its name, being the eleventh discovered by the three, although two of them were not newspapers, receiving different names. The event was noted in IAU Circular 5725 of March 27, 1993.Brian Marsden of the Central Bureau for Astronomical Telegrams noted that the comet was only 4 ° from Jupiter and that its apparent motion indicated that it was approaching that planet, and because of this he suggested that the Shoemakers and Levy had discovered an object that was in actually a series of multiple fragments of a comet torn apart by Jupiter’s gravity .
Orbiting a planet
Orbital studies of newly discovered comet quickly revealed that unlike all other comets found previously, the SL9 was spinning around Jupiter, and not around the sun . Its orbit around the planet was too narrow and unstable, with an orbital periodof approximately 2 years, a perihelion of scarce 0.33 ua (49 Gm) and an eccentricity of e = 0.9986. Tracing back the orbital motion of the comet, it was found that it had been orbiting Jupiter for some time, where it most likely had been captured from a solar orbit in the early 1970s, although it may well have happened much earlier, in the mid-1960s. Through more exhaustive analysis of images taken before March 24 (precovery method), some observers also found the comet, including Kin Endate through a photograph from March 15; Satoru Otomo with a March 17th and the team led by Eleanor Helinwith images from March 19. SL9 has also been found in images prior to March 1993. Before the comet was captured by Jupiter, it was probably a short period comet with an aphelion in the orbit of Jupiter, and a perihelion in the interior of the asteroid belt. . The volume of space for an object to be said to have been in the orbit of a planet is defined by the Hill Sphereof the same. Once the comet approached Jupiter between the mid-1960s and early 1970s, it came close to its aphelion and encountered Jupiter’s Hill sphere; When this happened, the planet’s gravity pulled the comet towards itself, pulling it. Because the comet’s motion was very small relative to that of the planet, Shoemaker Levy 9 plunged into Jupiter’s atmosphere in an almost rectilinear motion, causing it to end up in orbit around the planet’s core with a fairly high eccentricity, that is, with a fairly small curvature. Apparently, Shoemaker Levy 9 had passed especially close to Jupiter on July 7, 1992, only 40,000 km above the planet’s clouds, much closer than Metis and at a small distance compared to the radius of 70.Roche limit of the planet within which the tidal force is strong enough to fragment any body held together solely by its own gravity. While the comet had had close approaches to Jupiter previously, the July 7 encounter appeared to be the closest, and the comet’s partition is thought to have occurred at that time. Each of the pieces to which the comet had been reduced was named with a letter of the alphabet, from “fragment A” to “fragment W,” an established practice for the time of finding fractional comets. In the image taken by the Hubble Space Telescopein the boreal summer of 1994, four sections barely separated by 1000 km were distinguished. The fragments are scattered over 160,000 km, each of them gleaming when illuminated by sunlight and surrounded by dust. Astronomers described them as a string of pearls, in the same way, impacts would envelop Jupiter like a necklace. It was even more exciting for astronomers when the orbit of the remaining pieces of the comet was tracked into the future, since it was considered likely that they could pass 45,000 km from the center of Jupiter, a distance even less than the radius of the planet, es In other words, that in a period of approximately five days, the fragments would end up crossing the planet’s atmosphere, all in July 1994. To know the possible effects of the impact, it was essential to determine the mass of the fragments, as well as the speed that they would reach when they hit the planet. According to Hubble observations, the eleven largest fragments were between 2.5 and 4.3 km in diameter. The energy of the impact is proportional to the mass of the fragment and therefore is proportional to the cube of its diameter.
Impact predictions
Discovering the possibility of an impact between the comet and Jupiter caused a great excitement in the astronomical community, because the encounter of two bodies of that magnitude in the Solar System had never been observed before, which led to it being studied with great precision. the orbit that the fragments would have and it was possible to affirm with total certainty that they would end up hitting the planet. Thus, SL9 would provide astronomers with a unique opportunity to search inside Jupiter’s atmosphere, as the collisions were expected to cause eruptions of material from layers that are normally hidden under clouds. Experts estimated that the size of the visible remains of Shoemaker Levy 9 ranged from a few hundred meters to a couple of kilometers,Comet Hyakutake , which became very bright as it passed close to Earth in 1996. One of the big debates before impact is whether the effects of these would be visible from Earth, or if, for example, they would disintegrate like giant meteoroids. Other suggested effects include that the impacts would generate seismic waves that would spread across the planet, an increase in the amount of fog in the stratosphere due to dust, and an increase in the mass of the ring system. However, because the collisions would be something new, astronomers preferred to be cautious about it.
Impacts
As the date for the collisions approached astronomers readied their telescopes, including the Hubble Space Telescope, ROSAT, X-ray observation satellite and significantly the Galileo space mission, then on its encounter trip with Jupiter set for 1996. The impacts Successive of the 23 fragments were scheduled to take place between 20:00:40 UTC on July 16 (fragment A) and 07:59:45 UTC on July 22 (fragment W).
Observation
The impacts, which occurred in alphabetical order, began with the hit that fragment A hit the southern hemisphere of Jupiter at a speed of approximately 60 km / s, at 20:18 UTC on July 16, 1994. The instruments on the The Galileo mission discovered a fireball that reached a maximum temperature of approximately 24,000 K, which contrasts with the temperature of the upper part of the clouds in the atmosphere, which have, in general, a typical temperature of approximately 130 K, thus, about 40 seconds later the temperature dropped rapidly to about 1,500 K. A few minutes later Galileo and observers from Earth discovered the fireball that the impact had generated when the planet rotated, shortly after the initial impact. As planned, the impacts ended on July 22, when the W fragment struck the planet. Astronomers had expected to see the effects of impacts from Earth, but had no idea how visible the atmospheric effects of each collision would be; the largest of these was generated by fragment G on July 18 at 07:34 UTC. This impact created a giant dark spot more than 12,000 km in diameter, and was estimated to be an energy blast equivalent to 6,000,000 megatons of TNT, six hundred times the Earth’s nuclear arsenal. The black spot that fragment G generated was so dark that it could be seen by amateurs and was able to blind some of the telescopes that were observing it. the largest of these was generated by fragment G on July 18 at 07:34 UTC. This impact created a giant dark spot more than 12,000 km in diameter, and was estimated to be an energy blast equivalent to 6,000,000 megatons of TNT, six hundred times the Earth’s nuclear arsenal. The black spot that fragment G generated was so dark that it could be seen by amateurs and was able to blind some of the telescopes that were observing it. the largest of these was generated by fragment G on July 18 at 07:34 UTC. This impact created a giant dark spot more than 12,000 km in diameter, and was estimated to be an energy blast equivalent to 6,000,000 megatons of TNT, six hundred times the Earth’s nuclear arsenal. The black spot that fragment G generated was so dark that it could be seen by amateurs and was able to blind some of the telescopes that were observing it.
Discoveries made
Astronomers have observed with infrared cameras that transform heat into images. The sequence of events in a collision is: 1. Entry of the fireball into the atmosphere, causing a 30 second flash due to incandescence of cometary material; similar to the one that ignites meteors in Earth’s atmosphere. 2. Flash of one or two minutes with an intensity one million times higher than the first, due to the shock wave and the explosion of the fragment. 3. At six minutes, a colossal fireball that reaches an intensity one hundred million higher than the first and that is decaying as the temperature decreases. Gas balls of mass equal to or greater than 100 million tons reached 300 km in height. 4. The result of the crash is black spots in the atmosphere, which lasted for several months. The spot caused by fragment G has a very dark color 8000 km in diameter and is surrounded by a 25000 km gray halo. The cloud is believed to be contaminated with material from the comet.
Chemical studies
Observers hoped that the impacts would give them a first glimpse of what lies below the clouds that cover Jupiter, when the material below was exposed by fragments of the comet passing through the upper atmosphere. Spectroscopic studies revealed the absorption line in the Jovian spectrum due to sulfur (S2) and carbon sulfide (CS2), the first discovery of these molecules on Jupiter, and only the second discovery of S2 in another astronomical object. Other elements they discovered included ammonia (NH3) and hydrogen sulfide(H2S), and the amount of sulfur indicated that the amounts of these elements were much greater than the amount that would be expected in a nucleus of a small comet, so the material is believed to have come from within Jupiter. This means that the comet has reached the ammonia hydrosulfate layer between 35 and 50 km deep in Jupiter’s atmosphere. If the collision has been this superficial, the large dark spots caused can disappear quickly. To the surprise of astronomers, not compounds were discovered oxygen as the sulfur dioxide . By spectroscopy of the clouds arising after the shock, sodium , helium , lithium ,manganese , iron , silicon and of course sulfur . The first six impacts caused a distortion in methane levelswhich make up 2% of the atmosphere. One of the most surprising elements is that no signs of water have been found or they are in quantities lower than expected, meaning that either the layer of water that exists under the clouds was thinner than expected, or that the fragments of the comet they did not penetrate to the expected depth. Ballistic studies showed that the comet fragments were probably broken and completely dissipated before they reached the water layer. Scientists expected to see bright white clouds at each impact. Only after the Q2 impact did the Andalusian Institute of Astrophysics detect water from the comet and not from Jupiter that it does not contain. This calls into question whether the body that collided was really a comet.or an asteroid because while the first contains water the second does not. Even so, the oxygen that the rock can contain when reacting with the hydrogen in the atmosphere should produce water.
Other remarks
- Radio observations revealed a marked increase in emission at a wavelength of 21 cm after the largest impacts that peaked at 120% of normal emission from the planet. This was thought to be due to synchrotron radiation, caused by the injection of electrons moving by impacts at relativistic speeds into the Jovian magnetosphere. This change had not been anticipated by scientists because the emissions come from the electron belt around the planet. 2. After the crash, an increase in the northern lights caused by the entry of material into the magnetosphere of the southern hemisphere has been observed. 3. According to the Instituto Astrofísico de Canarias the largest impacts caused a double deflagration, observed at all frequencies, this is associated with changes in luminosity caused by the thermal evolution of the phenomenon. 4. As anticipated in advance, the collisions generated a huge seismic wave that swept across the planet at speeds of 450 km / s and was observed for more than two hours after the largest impacts. These waves appeared to be the gravity wave, traveling within a stable layer that acts as a waveguide, by the supposed water cloud of thetroposphere .
Long-term effects
The scars from the impacts on Jupiter were visible for many months after the impact. They were extremely prominent, and observers described them as more easily visible than the Red Spot. A search for historical observations revealed that the spots were probably the most prominent the planet had ever seen, and that while the Great Red Spot is remarkable for its striking color, no spot the size and darkness of those caused by the impacts of the SL9.
The frequency of impacts
Since the SL9 impact, two very small comets have been found circling Jupiter. Studies have shown that the planet, the largest in the Solar System, captures them quite frequently from the solar orbit. The comet’s orbit around Jupiter is generally unstable, it is highly elliptical, and the comet is strongly disturbed by the Sun’s gravity. Analyzes have estimated the frequency of Jupiter’s fall at once or twice a century, but the impact of comets from the SL9 size is much less common, probably no more than one per millennium. There is very strong evidence of comets that have previously fragmented or collided with Jupiter and its satellites. During Voyager missions to the planet, planetary scientists identified 13 crater chains on the moon Callisto and three on Ganymede, whose origin was initially a mystery. Crater alignments seen on the Moon are often caused by radiating from large craters, or caused by secondary impacts from the original projectile, but crater chains on Jovian moons do not lead to a larger crater. The SL9 impact strongly supported that the strings were due to comets broken by the action of Jupiter and trains of cometary fragments formed by colliding with satellites.
Jupiter as a “cosmic vacuum cleaner”
The SL9 impact highlighted Jupiter’s role as a “cosmic vacuum cleaner” for the inner Solar System. Studies have shown that, due to its gravitational influence, the planet attracts many small comets and asteroids that end up colliding with it, and it is thought that the rate of impact of comets against Jupiter is between two and ten times higher than the same against the planet. Earth. It is not easy for something similar to happen on our planet. If the SL9 collided with Earth the effects would be devastating. “We would not be here talking,” in the words of E. Shoemaker. If Jupiter were not present, these small bodies could collide with the inner planets., and shows that these are a serious threat to life on Earth. Astronomers have speculated that extinction events could have been much more frequent here were it not for Jupiter; and complex life could not have developed. 50,000 years ago a meteorite caused in Arizona ‘s Barringer Crater . It was precisely Eugene Shoemaker who revealed its origin. At the beginning of the last century (1908) in Tunguska ( Siberia ) a comet caused the destruction of a large area of forest.
Fun facts
- In 1992, SL 9 passed Jupiter inside the Roche limit. It broke into at least 21 fragments that scattered several million kilometers throughout its orbit.
- The size and mass of the original body and individual fragments is, as of this writing, still uncertain. A size of 2 to 10 km is estimated for the diameter of the original body and 1 to 3 km for the largest of the fragments.
- Between July 16 and 22, 1994, the fragments hit the upper atmosphere of Jupiter. It was the first time that scientists had the opportunity to witness the collision of two extraterrestrial bodies.
- The impacts were observed with virtually all large telescopes on the ground, thousands of small and amateur telescopes, and several spacecraft including HST and Galileo.
- The photographs were published on the Internet hours after the impacts and caused significant traffic jams in some WWW and ftp sites.
- The effects of the impacts were visible on Jupiter for almost a year after the collision.
- Linear chains of craters have been found on Ganymede and Callisto that are believed to have been formed by the impacts of bodies similar to SL 9.
- The SL 9 is no more, but its scientific legacy will be studied for years.
