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Lecture 12

ASTA01H3 Lecture Notes - Lecture 12: Carolyn S. Shoemaker, Comet Nucleus, Space Debris

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Kristen Menou

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The planets revolve around the Sun in orbits that lie close to a common plane
The orbit around the Sun of Mercury, the planet closest to the Sun, is tipped 7.0°to
Eath’s oit. The est of the plaets’ oital plaes ae ilied yo oe than 3.4°
The rotation of the Sun and planets on their axes also seems related to the same overall
direction of motion.
The “u otates ith its euato ilied 7.2° to elipti, ost plaets’ euatos ae
tipped less than 30°
However, the rotations of Venus and Uranus are peculiar.
Compared with the other planets, Venus rotates backward. Uranus rotates on its sides,
with the equator almost perpendicular to its orbit
ealy all the oos i the sola syste, iludig Eath’s oo, oit aoud thei
planets counterclockwise
With only a few exceptions, most of which are understood, revolution and rotation in
the solar system follow a common theme.
Two kinds of planets - 1. Four small Earth-like worlds, called terrestrial planets and Four
giant Jupiter-like worlds.
There are three important points to note about these categories
One, they are distinguished by their location.
Two, almost every solid surface in the solar system is covered with craters:
Terrestrial planets and moons have solid surfaces, while giat plaets do’t hae a
visible surface
Three, the planets are distinguished by properties such as composition, rings, and
moons, rocky and gaseous
The first asteroid was Ceres, ~500 km diameter body discovered in 1801
It is covered by ice and clay, and may have liquid water between the rocky core and icy
The solar system is littered with three kinds contains four kinds of space debris (officially
known as minor bodies):
Asteroids, Comets, Meteoroids and Planetoids (dwarf planets) like Pluto, Eris, Sedna,
Quaoar and other large, round bodies
Asteroids Minor planets
Most of them orbit the Sun in a belt between the orbits of Mars and Jupiter.
Roughly 20 000 asteroids asteroid belt (white) have been catalogued
Most in asteroid belt
They are smaller than the Moon
Asteroids are as old as planets, actually planets formed from asteroid-like primitive
bodies called planetesimals
About 2000 follow orbits that bring them into the inner solar system, where they can
occasionally collide with a planet.
About 200 asteroids are more than 100 km in diameter.
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