Page 198 - Science Course 3 (Book 2)

Mo13-L1a: What are the Planets of Our Solar System?

A dwarf planet is a spherical object that orbits the A comet is made of gas, dust, and ice and moves
Sun and is not a moon or another planet. around the Sun in an oval-shaped orbit.

Dwarf planets are in regions of the solar system
where there are many objects orbiting nearby.

Ceres, a dwarf planet, orbits the Sun as planets do.

(Ceres)
Distances between
Millions of small, rocky objects called asteroids orbit objects in the solar
the Sun in the asteroid belt between the orbits of system are extremely
Mars and Jupiter. large.

Asteroids vary in size and are usually not spherical. Astronomers do not
use meters or kilome-
ters to describe these
distances.

A more convenient
unit is used - the as-
tronomical unit (AU).

One AU is Earth’s
average distance
from the Sun—about
150,000,000 km.

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