most people aren't that familiar with our own planet's neighborhood, the solar system. ask random friends to name the planets in order from the sun outward, and you'll see what i mean. of those who can, when the notion of debris fields is mentioned, their automatic response will be the asteroid belt which lies between the orbits of mars and jupiter. a smaller number will recall that far, far outside the orbits of the major planets exists a sphere of billions of asteroid-sized objects known collectively as the oort cloud, long thought to be the source area for the comets which periodically are pulled by the sun's gravity into a monumental elliptical orbit which invades the inner solar system, e.g. halley's comet or the recent comet hale-bopp.
it turns out that most comets probably originate in debris fields which lie much closer than the oort cloud. these fields are differentiated by their position relative to the orbit of our outermost planet, neptune. (yes, my children, pluto has been demoted from planet to dwarf planet status, and small wonder -- as it were.)
follow along. inside neptune's orbit are cis-neptunian objects, residing between the orbits of neptune and jupiter.
outside neptune's orbit are layered torus- or cloud-like gatherings called trans-neptunian objects, arranged in outward order as follows -- the kuiper belt, scattered disk objects, a few smaller assortments, and finally our old friend the oort cloud. it all makes for a much more complicated collection of objects which orbit our sun than most people ever imagined. following are illustrations of these complex assemblies, from inner to outer. as always, click on any image to enlarge it.
THE MARS-JUPITER ASTEROID FIELD
TRANS-NEPTUNIAN OBJECTS (TNOs)
SIZE COMPARISONS FOR LARGEST TNOs
THE OORT CLOUD
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