Solar System Essay, Research Paper

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.