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    пллллллллллллллм  плл   млллмллммм   пллллм плллллллмллмммллн лп
        пппллллллллллм он  лллллллллллпплмоллл    лллллм    пплллоп
Mo.iMP  мллм  плллллллнл  оллллллллл    олллл     олллллн      плп
      мллллллл  ллллллллн оллллллллн     ллл       лллллл
     млллллллн  олллллллл олллллллл       п        оллллллм   мл
    млллллллн    лллллллл  ллллллллн               оолллллллллп
   млплллллл мм  ллллллллн ллолллллн               оллллллпп
  млпллллллмллллмолллллллл ол пллллл           м   лнллллл             м
 мл оллллллллллп  ллллллллл плм  плллмм    ммлллп ол олллн         ммлл
лл   ллллллллп    ллллллллллм плм  пплллллллллп мммп ллллмммммммлллллп
 плм   млллп       пллллллллллм  ппмм ппмллпп  пллм   ппплплллллллпп
    ппппп                ппллп      ппппп        ппппппппппппп
          ARRoGANT                CoURiERS      WiTH     ESSaYS

Grade Level:       Type of Work           Subject/Topic is on:
 [x]6-8                 [ ]Class Notes    [Origins of the Solar    ]
 [ ]9-10                [ ]Cliff Notes    [System                  ]
 [ ]11-12               [x]Essay/Report   [                        ]
 [ ]College             [ ]Misc           [                        ]

 Dizzed: o4/95  # of Words:889   School: ?              State: ?
ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>Chop Here>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ>ФФФФФФФФФ
               ORIGIN OF THE SOLAR SYSTEM

     For more than 300 years there has been serious scientific discussion
of the processes and events that led to the formation of the solar system.
For most of this time lack of knowledge about the physical conditions in
the solar system prevented a rigorous approach to the problem.
Explanations were especially sought for the regularity in the directions of
rotation and orbit of objects in the solar system, the slow rotation of the
Sun, and the Titius-Bode law, which states that the radii of the planetary
orbits increase in a regular fashion throughout the solar system. In a
similar fashion, the radii of the orbits of the regular satellites of
Jupiter, Saturn, and Uranus increase in a regular manner. In modern times
the slow rotation of the Sun has been explained as resulting from the
deceleration of its angular motion through its magnetic interaction with
the outflowing solar wind, so that this feature should not have been
considered a constraint on theories of the origin of the solar system.
 
     The many theories concerning the origin of the solar system that have
been advanced during the last three centuries can be classified as either
dualistic or monistic. A common feature of dualistic theories is that
another star once passed close to the Sun, and tidal perturbations between
the two stars drew out filaments of gas from which the planets condensed.
Theories of this type encounter enormous difficulties in trying to account
for modern information about the solar system, and they have generally been
discarded. By contrast, monistic theories envisage a disk of gas and dust,
called the primitive solar nebula, that formed around the Sun. Many of
these theories speculate that the Sun and the planets formed together from
the primeval solar nebula. A photograph taken in 1984 of a nearby star,
Beta Pictoris, appears to show a solar system forming in this way from a
disk of surrounding material.
 
     The large amount of activity that has taken place in the last 20 years
in the renewed exploration of the solar system has also provided a great
impetus for renewed studies of the origin of the system. One important
component of this research has been the detailed studies of the properties
of meteorites that has been made possible by modern laboratory
instrumentation. The distribution and abundance of the elements within
different meteoritic mineral phases has provided much information on the
physical conditions present at the time the solar system began to form.
Recent discoveries of anomalies in the isotopic compositions of the
elements in certain mineral phases in meteorites promise to give
information about the local galactic interstellar environment that led to
the formation of the solar system. Investigations of the properties of
other planets has led to the new science of comparative planetology, in
which the differences observed among the planets not only lead to a better
understanding of the planets, but also pose precise new questions
concerning the mechanisms by which the planets may have been formed.
 
     Studies of the stars within our galaxy have shown that the age of our
galaxy is much greater than the age of the solar system. Therefore,
processes observed in the formation of stars within our galaxy today are
likely to be found relevant to the formation of our solar system. Stars
appear to form in groups or associations, as a result of the gravitational
collapse of clouds of gas and dust in the interstellar medium. Modern
monistic theories envisage the gas and dust in the primitive solar nebula
to be the collapsed remnant of a fragment of an interstellar cloud.
 
     There has been much discussion of how the planets might have formed
from the primeval solar nebula. In recent years attention has focused on
the possibility that two types of gravitational instabilities might have
played an important role in this process. One type is a gravitational
instability in the gas of the primitive solar nebula, from which there
would be formed a giant gaseous protoplanet. From the evolution of such
protoplanets there could arise, in the outer solar system, the giant
planets that are observed today. In the inner solar system, the possibility
exists that giant gaseous protoplanets formed rocky cores at their centers,
which survived the stripping away of the gaseous envelopes caused by
gravitational and thermal forces from the growing Sun.
 
     The other form of gravitational instability involves the condensed
materials in the solar nebula. Small dust particles that may have been
present in the gas of the solar nebula could be expected to settle toward
the midplane of the nebula if the gas were not subject to extensive
turbulent churning. Gravitational instabilities acting on a thin dust layer
might have formed bodies ranging from tens to hundreds of kilometers in
radius. Collisions among these bodies may have played a major role in
accumulations of material to form the planets.
 
     It must be stressed that all theories of the origin of the solar
system currently being formulated respond to and are limited by the rapid
accumulation of facts about planetary bodies within the solar system.
Because of the rapid rate of progress in such studies, it is generally
recognized that such theories are preliminary and simplified, so that ideas
and theories in this area of research can be expected to continue to evolve
rapidly.
