Chapter 9

What is the largest known asteroid in our solar system
Ceres
If all the material in the asteroid belt were to be combined to produce a planet, how big would it be?
about 1500 km in diameter, less than half the diameter of the Moon
An asteroid is
a planetesimal moving in an orbit around the Sun.
The asteroid belt exists between the orbits of the planets
Mars and Jupiter.
What is the average distance between asteroids?
many times the distance between Earth and the Moon
Where do the Trojan asteroids orbit the Sun?
in circular orbits at the same orbital distance as Jupiter
The major difference between the orbital paths of comets that we see in the inner solar system and those of the asteroids in the asteroid belt is that
cometary orbits are highly elliptical and at random inclinations to the ecliptic plane compared with the circular orbits of asteroids in the ecliptic plane.
The most likely origin of the “dirty snowballs” that become comets when they are deflected into orbits that bring them closer to the Sun is the
Kuiper belt and Oort cloud surrounding the solar system.
The Kuiper belt is
a flat or donut-shaped distribution of distant comets around the Sun, extending out about 500 AU.
The Oort cloud is
a spherical distribution of distant comets around the Sun, extending out about 50,000 AU.
Most comet nuclei are believed to be
pieces of dusty ice left over from the formation of the solar system.
The nucleus of Comet Halley, as seen on close-up photographs taken by the Giotto spacecraft, is
potato-shaped and darker than coal.
The measured diameter of the core of Comet Halley is about
10 km
Comet tails are the result of
melting and evaporation of ices from the comet core.
The gas and ion tail of a comet
is always blown away from the comet in the anti-Sun direction by the solar wind.
The ionized gas tail of a comet is always aligned along the
comet-Sun line.
Dust grains released by the melting of ice in a comet nucleus
become a uniform, curved tail moving away from the comet under radiation pressure from sunlight.
The orbits of periodic comets
can extend far out beyond the orbit of Pluto and can be oriented in any direction in the solar system.
The orbits of comets are
randomly oriented in the solar system and can extend far beyond the orbit of Pluto

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