Comets and KBO's Far outside the orbit of Neptune are an overwhelming number of small icy bodies The Kuiper belt is a ring of icy material located in the plane of the Solar System Comets were known and recognized by ancient astronomers Comets We know today that comets are clumps of icy material from the outer reaches of the Solar System As these objects pass by Earth on their way around the Sun, they produce an amazing display Halley's Comet Edmund Halley theorized that the appearance of a new comet in 1682 was actually the same object seen many times over Researching archival records and ancient texts, Halley realized this comet had been seen every 76 years for centuries Halley's Comet - 1910 1
Orbits of Comets The orbits of comets like Halley's are usually highly elliptical The comet spends most of its time far from the Sun and speeds through the inner Solar System during a brief time Comet Structure The bright head of a comet is the coma, comprised of excited gases released from the nucleus The comet's tail always streams away from the Sun and is surrounded by a thin, invisible hydrogen envelope Comet tails usually show two parts, an ion (gas) tail and a dust tail Comet Tails The ion tail is made up of light gaseous material which is pushed directly away from the Sun by solar wind The dust tail contains heavier, solid material which is swept back as the comet orbits the Sun 2
Both the ion and dust tail form only when the comet approaches the Sun Comet Tails Keep in mind that the tail of a comet ALWAYS trails away from the Sun, even when the comet is moving away from the Sun Comets and Meteor Showers Meteors are the bright, fast streaks of light seen in the sky on any given night Meteors are caused by small dust grains vaporizing in the Earth's atmosphere The leftover dusty material of the comet provides lots of material to 'rain' down on the atmosphere Major meteor showers happen around the same time every year Meteor Showers The name of the shower corresponds to the constellation in which the meteors appear to originate The Leonid meteor shower will peak November 17th Orionid meteor shower in October Material originates from Halley's comet 3
Comets Up-close The last pass of Halley's comet provided multiple spacecraft a chance to get up close and personal with a comet Comets Up-close With each pass, a comet losses more material and becomes more unstable until eventually it disintegrates Visiting a Comet In addition to taking images of the comet, the mission attempted to take samples of material from the comet's tail The probe returned to Earth and (despite a crash landing) some samples remained intact for study 4
Blowing Up a Comet In July of last year,the Deep Impact mission visited the comet Tempel 1 In addition to imaging the comet, this mission also had an impact probe The resulting explosion revealed many details about the comet's density, composition, etc Where Do Comets Come From? The short period comets (<200 years) all originate from outside the orbit of Neptune Objects in this area of the Solar System are called Kuiper belt objects or trans-neptunian objects The Kuiper Belt The Kuiper belt is one of the most recently discovered structures in the Solar System In the past decade, hundreds of objects have been found beyond the orbit of Neptune 5
As the search intensifies, more large Kuiper belt objects (KBO's) are found KBO's Many of these are comparable in size, composition, and orbit to Pluto All are very icy worlds, resembling large comets more than a real planet KBO's The main interest in these distant, desolate worlds is the fact that they have remained relatively untouched since formation Studying these objects will give astronomers a better picture of conditions when the Solar System first formed Long Period Comets These objects originate from distances around 50,000 A.U. and come from random directions toward the Sun While made of similar icy materials, these comets obviously come from a very different location than the Kuiper belt 6
In the 1950's, Jan Oort theorized that these comets must come from a 'cloud' of material surrounding the Sun Most of these comets (perhaps billions in number) never come close to the Sun The Oort Cloud Only the gravitational influence of a passing nearby star can perturb these comets enough to send them into the inner Solar System 7