ASTA01H3 Lecture Notes - Lecture 1: Star System, Meteoroid, Radiation Pressure
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The Solar System
We live in a stellar system with 8 major planets and a number of dwarf planets, as well as
some left over material from the formation of the system.
The planets in the solar system are divided into two main categories: Terrestrial planets
and the Jovian planets.
Terrestrial planets are made of rock and metals while the Jovian planets are primarily
made of gas.
The four inner planets, Mercury, Venus, Earth and Mars are called the terrestrial planets.
They are small, have high densities and are primarily made of rock.
Earth is the biggest of the terrestrial planets while Venus, having a radius 95% that of the
Earth is in the second spot.
The Jovian Planets
Jupiter, Saturn, Uranus and Neptune are called the Jovian planets.
Jupiter and Saturn are gas giants while Uranus and Neptune are ice giants.
The gas giants have cores of heavy elements, surrounded by liquid hydrogen within a
thick shell of gaseous hydrogen.
The ice giants have small cores of heavy metals, surrounded by partially solid water
mixed with rocks and methane ices.
The Solar System
Historically, it was believed that the placement of the planets in the solar system is based
on the socalled Titus-Bode Law. The discovery of the dwarf planet Ceres and the planet
Uranus were both largely based on the prediction of this law!
In addition to the planets our solar system has a belt of asteroids in between the last
terrestrial planet (Mars) and the ﬁrst gas giant (Jupiter).
These asteroids are small rocky worlds and are leftover debris from the formation of solar
The asteroid belt is at 2.8 AU with Ceres being the only dwarf planet in this belt with a
diameter of 945 km.
The total mass of the asteroid belt is 4% the mass of the Moon with half of this
concentrated in 4 main bodies of this belt.
Asteroids are generally irregular in shape and can be anywhere from hundreds of
kilometres to less than a kilometre.
Some asteroids are clearly clumps of broken fragments, glued by gravity.
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