Martha visits every Monday and just stays until noon, period.Oct 11 '04 Write an essay on this topic.The Bottom Line We've learned a LOT about the Solar System---still a LOT to learn! Do others share my fascination with memory aiding mnemonics? This one is an Astronomy 101 crutch to help remember the Solar System: Martha visits every Monday and just stays until noon, period. Mercury, Venus, Earth, Mars, Asteroid belt, Jupiter, Saturn, Uranus, Neptune, Pluto. But recent findings with higher and higher power telescopes are revealing that this view of the Solar System is incomplete and overly simplistic. For example, recent findings raise a question whether Pluto should even be regarded as a planet, since it is just one of many objects of comparable size that make up a region of the Solar System now called the “Edgeworth-Kuiper Belt,” extending some 3.9 to 4.5 billion miles from the sun, 30-50 times as far from the sun as the planet Earth! The Kuiper Belt is believed to contain some 100,000 objects that are at least 30 miles in diameter, some of them three fourths as big as Pluto. The Kuiper Belt was first predicted in the 1940’s and confirmed by observations in 1992. In the last four years, there have been observed and identified seven larger objects in the Kuiper Belt, in addition to Pluto, with diameters ranging from 500 to 1000 miles, and orbits with periods of 250 to 300 years to orbit the sun, at distances from 3.7 to 4.4 billion miles. And even further away lies the planet Sedna, first discovered in November 2003, only one year ago!. It is 1100 miles in diameter, a little smaller than Pluto, and is in an orbit that ranges from 7-90 billion miles from the sun. How and when Sedna may have been formed is still a matter of speculation, and some see it as a part of the Kuiper Belt that somehow had its orbit disturbed and jostled into its present irregular path. Still farther away lies the Oort Cloud, a spherical region of dust and gas, the same stuff from which the planets were originally formed. It forms a sort of bubble around the entire solar system, extending from 10,000 to 100,000 times the distance from the sun to the Earth. The Oort Cloud may contain trillions of significant objects, some of them the size of Mercury or Mars. Comets are thought to originate in the Oort Cloud. The Solar System was formed about 4.5 billion years ago when a cloud of dust and gas collapsed and coalesced into the Sun; the rocky planets of Mercury, Venus, Earth and Mars, and the asteroid belt of some 700,000 objects, ranging in size from less than a mile to 600 miles in diameter; then the gaseous planets of Jupiter, Saturn, Uranus and Neptune; Pluto and the Kuiper Belt; and enveloping it all, the Oort Cloud. It is thought that the Oort Cloud is made up of objects and material preserved in the state it existed at the time the Solar System was formed 4.5 billion years ago! It boggles the mind to realize that the Solar System extends to 100,000 times the distance from the Sun to the Earth. But I suppose it should be no surprise that the influence of the sun’s gravity extends outward until it becomes weaker than the gravitational field of some other nearby star. NASA is planning to launch an explorer to the neighborhood of Pluto in 2005. It will swing around Jupiter in February 2007, and the slingshot effect will accelerate it toward a rendezvous with Pluto in July 2015, where it will take pictures, map surface features, study composition of the planet and its atmosphere with spectroscopy, from its closest approach of about 6000 miles. After 2015 the explorer will continue beyond Pluto into the Kuiper Belt to study at least one of the 30-60 mile diameter objects there for perhaps another decade. Still a lot to learn about our Solar System, and maybe we will soon need a better mnemonic!  |
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