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Class 3 : Solar system formation, and the variety of surface-types. Finish discussion from last class… Recap about the patterns that we find in the solar system Theory for Solar System formation How do we test this theory? Varieties of surfaces in the solar system Classifying surfaces The processes at work

Recap: Characteristics of the solar system All planets (apart from Pluto) orbit in the same plane… solar system is flat

All planets orbit the Sun in same sense. The Sun and all planets (apart from Venus and Uranus) rotate in the same sense as the planets orbit the Sun. Inner planets are small and rocky, but outer planets are large and gassy. There are also asteroids and comets All asteroid and short-period comets are usually in planetary plane and orbit in same sense Long period comets are random in direction and sense.

I: Solar system formation How did all of this come to be? A good theory needs to Explain the facts we just listed. Be as simple as possible (but consistent with the laws of nature). Be testable. Our best theory is the Collapsing Gas Cloud theory.

Phase I (started 5 billion years ago) Gas Cloud starts to collapse in on itself due to its own gravitational pull. As it collapses, it rotates faster and flattens Phase II (lasted 100 million years) The central part of the gas cloud forms the Sun – nuclear reactions start in its core. Phase III Dust grains and ice crystals start to condense out of flattened gas disk Grains grow via collisions to form planetesimals (objects the size of the Moon)

Stage V – 4.5 billion yrs ago to present Stage IV Planets grow by successive bombardment of planetesimals Eventually, there are no more planetesimals left Outer massive planets grab the remains of the gas from the cloud Stage V – 4.5 billion yrs ago to present Planets formed Still some debris around (asteroids and comets) that occasionally hit the planets.

Questions… How would we ever test our theory for the formation of the solar system? The effects of impacts on planetary surfaces in the Solar System

The Moon (near side) The Moon (far side) Europa (a moon of Jupiter)

Callisto (a moon of Jupiter) Gaspra (an asteroid) Io (a moon of Jupiter) Triton (a moon of Neptune) Titan (a moon of Saturn)

Thanks Submitted by Abhishek Mumbai

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