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HALLEY'S COMET.
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Essay Subject:
Discovery, composition, nucleus, 1986 passage, probes from Earth, tail, solar wind, general comet data.... More...
4 Pages / 900 Words
6 sources, 9 Citations, APA Format
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Paper Abstract:
Discovery, composition, nucleus, 1986 passage, probes from Earth, tail, solar wind, general comet data.

Paper Introduction:
This paper will discuss Halley's comet using several current sources which deal with topics such as how a comet works, what causes the comet to be what it is, what new discoveries have been made and what research has been done or is being done on Halley's Comet. Very recently has come the first unambiguous evidence of organic molecules in the nucleus of Halley's comet. The evidence from recent examination of the infrared spectrum of the comet shows emission by the carbon-hydrogen bonds of a solid in the dust grains surrounding the nucleus of the comet. The temperature of the dust is about 400 K.(a determination made by Giotto, the European comet probe), and yet the wavelength emissions match those observed from bacteria in the library. A dust analyzer on the Giotto shows that the dust is composed of

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Berry, R. ICE. Henbest, N. 3 -35. References Anonymous. The Giotto probe found that the comet's nucleus was a deep black,with a reflectivity like that of the darkest materials known in the solarsystem, a reflectivity of from one to two percent. Probes face dangersfrom the 21 kilometer per second impacts of cometary dust, as well assubatomic particles and fields generated by comets. Where the solarwind and gases expanding from the comet meet, there is "bow shock." TheSoviet Vega comet probes show that the gas output of the comet's nucleus israpidly changing. The temperature of the dust is about 4 K.(a determinationmade by Giotto, the European comet probe), and yet the wavelength emissionsmatch those observed from bacteria in the library. "Bow shock"need not go ahead of the comet and the nucleus may even rotate, as in CometGiacobini-Zinner, which shows that comets may differ from Halley's comet.Basically, however, all comets are viewed as interactions between thesmall, icy nucleus of the comet and the Sun. The solar wind has a magnetic field which makes ithard for ions from a comet to cross the field and keeps the solar windparticles locked into the field. Astronomy 13, n.12 pp. Tiny gravitational nudges frompassing stars are believed to help comet material reach the solar vicinity.when the comet's orbit brings it toward the sun, the comet's nucleus issubject to effects of the Sun: e.g., warmth, ultraviolet radiation (whichcan deprive molecules of their electrons, turning them into ions), solarwind subatomic particles (mostly protons and electrons traveling at 4 kilometers per second). 5 -55.----------------------- 6 Astronomy 14, n.l pp. 37-4 . (1986, April 17). But it ispuzzling that the magnetosphere boundaries between comets and the solarwind are not as distinct as the planetary magnetosphere boundaries with thesolar wind. New Scientist 11 , n.15 4 p. It is likely that the blackness of the surface is due to anorganic material, perhaps a tar formed from organic molecules. The molecules escapethe comet because it lacks the gravity to retain the molecules. The InternationalCometary Explorer(ICE) was originally investigating the geotail of theEarth and turned onto the comet by NASA as a surrogate for its never-fundedmission to Halley's comet (it was deemed that Halley's comet was adequatelycovered by the European, Russian and Japanese probes). The Giotto spacecraft have confirmed that Halley's comet is at itscenter a small solid nucleus emitting gas and dust. The darkness of the comet surface means that much heatfrom the Sun must be absorbed. Heat, cosmic rays and ultraviolet radiation couldaccount for these observations, since these factors acting on ordinarymolecules could produce the larger organic complexes(Chown, 1986). Very recently has come the first unambiguous evidence of organicmolecules in the nucleus of Halley's comet. This paper will discuss Halley's comet using several current sourceswhich deal with topics such as how a comet works, what causes the comet tobe what it is, what new discoveries have been made and what research hasbeen done or is being done on Halley's Comet. Gazer's Gazette (1986, January). Amoderately-sized comet throws off 1.5 tons of carbon monoxide and water persecond, which results in the loss of an inch or so of the icy crust per daywhen the comet is close to the Sun. Halley draws nearer. Chown, M. While the characteristics of one comet could be anaberration or not representative of comets in general, the study of manycomets is needed to better understand the origin and nature of comets.Thus, the International Cometary Explorer, which studied Comet Giacobini-Zinner has made important contributions to our understanding of comets(Berry, 1985). Organics or organisms in Halley'snucleus. It is presumed thatthe comets formed at about the same time as the solar system. 7-13. Curtain call for Comet Halley. Comets are known to throw off jets of dust and gas that are non-gravitational forces which alter the comet's path. There are small amounts of sodium and sulfur, as well aspositively-charged oxygen atoms, carbon dioxide, hydroxyl radicals andwater molecules (Henbest, 1986). This heat would melt the comet's ice unlessthe surface crust of the comet were very thick to insulate the ices at thecenter (Henbest, 1986). Brightspots observed in the vicinity of the nucleus have been identified as jetsof gas and dust. The nucleus of a comet isbelieved to be 85% water ice with ices of carbon monoxide, methane andammonia, as well as fine dust and rock-sized objects. The evidence from recentexamination of the infrared spectrum of the comet shows emission by thecarbon-hydrogen bonds of a solid in the dust grains surrounding the nucleusof the comet. (1986, March). The halo of gas called the coma forms when the molecules areejected from the comet into space. The ICE probe, which predates the Halley's cometprobes by several months, shows the current comet theory correct in sayingthat the tail of a comet has two lobes with opposite polarities. A dust analyzer on theGiotto shows that the dust is composed of carbon, hydrogen, oxygen, andnitrogen -- but simple hydrocarbons are ruled out because they boil attemperatures lower than 4 K., so the molecules must be large polymers.It might be noted that biological processes are not necessary to explainthese observations since 11-carbon molecules have previously been observedin interstellar space. This April is the last month for viewing of Halley's comet, withviews being best in the Southern Hemisphere. (1985, December). Astronomy 14,n.2, pp.38-49. This molecule outflow that is theproduct of the Sun's energy takes with it some of the dust from the comet'snucleus. To know just what a comet is requires the study of more than justHalley's comet. 23. NewScientist 1 9, n.15 pp. Halley's Comet:more dirt than snow. The nucleiof comets are presumed to have been in cold storage in the depths of spacefor billions of years and to be frozen examples of the primordial materialthat went into forming the outer planets. The gas molecules arebroken down, becoming radicals that are ionized by the ultravioletradiation of the sun and impact from solar wind particles. WithHalley's comet, the brightening tail was evident in October and November,1985 (Anon, 1986). Comets are also more turbulent, more complex and moreenergetic than scientists had realized before the space probes (Berry,1985). When the solar wind piles up in front of the comet,there is "bow shock'.' The magnetic field of the solar wind may fold arounda comet and be assimilated into the cometary plasma (Berry, 1985). The Halley's comet brightening is related to passingclose to the Sun (Gazer's Gazette, 1986). Near comets, magnetic field strengths rise and there are bursts ofelectrons moving with violent energy in all directions. Schaaf, F. (1986, February). (1986, April). The nucleus is lessthan 8 km in width and about 15 km long with a shape comparable to apotato, peanut or banana and surface structures that resemble ring-likedepressions(probably sealed vents that erupted during previous orbits ofthe Sun). The solar wind ionizes the neutralparticles ejected from the comet and the comet particles, which cannotcross the solar wind magnetic field, become part of the solar wind to formthe comet's tail. The brightness of the moon makes it hard to see the comet between the21st and 28th of April, but from the 28th to 3 th of April, Halley's cometis visible low in the western evening sky (Schaaf, 1986). Water molecules are themost abundant molecules given off through the comet's nucleus. Astronomy14, n.4 pp. Comet tails were foundto be many times denser than the solar winds and permeated by magneticfields that are orderly and heavy ions that are mostly water moleculesmissing an electron. As the comet nucleus passes the Sun, theicy surface materials heat up, the molecules vibrate faster and finallyescape the surface in a process called sublimation. Amateur astronomers observeHalley's comet.

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