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Book review - Solar System Evolution

I have just spent the last two months reading  Solar System Evolution - 
a New Perspective by Stuart Ross Taylor, Cambridge Press, 1994.

This book has opened my eyes and made me see the solar system in a new 
way, as the title hints.

The emphasis is mostly made on geochemical descriptions rather than 
astrophysical events, but most aspects of solar system evolution are 
explored.

There are some ideas that come up over and over again:

1) What we don't understand, we simplify. At first this helps sort out 
the details, but if kept for too long it may be a mistake. For example, 
he doesn't think the molecular cloud that was the source for the solar 
system was homogeneous, and the planets certainly didn't condense 
uniformly from the dust.

2) Science is leaving the clockwork universe models. Chaos, turbulence
and 
stochastic processes are the prevalent forces in the dynamics of the 
solar system.

The general argument pushed is that the planets formed from a hierarchy 
of smaller objects - chondrules and dust -> small matrixed objects; 
these accreted to larger rocks and boulders, on and on up until the 
solar system was populated by hundreds of earth sized objects, thousands 
of lunar sized objects, etc. This process was very efficient, the last 
stages of planetary formation were titanic with planet sized object 
colliding.

This process was not uniform, in fact, the inner solar system and outer 
solar system have distinct formation times and special processes related 
to the temperature conditions of the region they formed.

One of the earliest major events was the formation of Jupiter, probably 
in a slush zone of snow and ice. It grew so quickly and cleaned out it's 
feeding zone rather quickly - before the new sun could blow away all the 
hydrogen and helium.

There was very little lateral mixing in the formation of the solar 
system. This is evident today in the zoned nature of the asteroid belt.

Some of the titanic events described:

Mercury loosing its mantle, Venus hit head-on so hard it started 
spinning backwards, Earth hit by a Mars sized object obliquely, causing 
the Moon to be formed, Uranus hit by an earth sized object so that it 
was knocked sideways.

Over and over there was a terrible violence and a dominance of unique, 
stochastic events. The end result is a solar system where every planet 
and satellite is unique.

The author covers some areas in great detail, showing what the major 
arguments are and describing their strengths and weaknesses, and why we 
have attached so much importance to some (wrong) ideas.

Other areas he doesn't cover in so much detail, since they aren't his 
area of specialization or aren't so important to the end result of 
planetary formation and evolution (for example, there isn't a lot of 
material spent on covering chondrule formation).

In the end, he feels that there is no grand unified theory of solar 
system evolution, certainly nothing as orderly as the models of Stellar 
evolution epitomized in the H-S diagram. Each planetary system will 
probably be unique. In fact, since most stars evolve in pairs or 
multiples, planetary systems are a bit rare.

--
Jim Hurley
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