Unit 2 Lesson 6 Small Bodies in the Solar System
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Unit 2 Lesson 6 Small Bodies in the Solar System
Bigger Is Not Better
Where are small bodies in the solar
system?
• Scientists estimate that there are up to a trillion
small bodies in the solar system. They lack
atmospheres and have weak surface gravity.
• The largest of the small bodies, the dwarf planets,
are found in regions known as the asteroid belt
and Kuiper belt.
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Unit 2 Lesson 6 Small Bodies in the Solar System
Where are small bodies in the solar
system?
• The Kuiper belt is located beyond the orbit of
Neptune. It contains Kuiper belt objects and
comets.
• Comets are also located in the Oort cloud, which
is a region that surrounds the solar system and
extends almost halfway to the nearest star.
• Two other types of small bodies, asteroids and
meteoroids, are located mostly between the orbits
of Venus and Neptune.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What are dwarf planets?
• A dwarf planet is a celestial body that orbits the
sun and is round because of its own gravity.
• A dwarf planet does not have the mass to have
cleared other bodies out of its orbit around the
sun.
• Five dwarf planets have been identified: Ceres,
Pluto, Eris, Haumea, and Makemake.
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Unit 2 Lesson 6 Small Bodies in the Solar System
KBOs
What are Kuiper belt objects?
• The Kuiper belt is a region of the solar system
that begins just beyond the orbit of Neptune.
• The Kuiper belt extends outward to about twice
the orbit of Neptune, a distance of about 55
astronomical units (AU).
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Unit 2 Lesson 6 Small Bodies in the Solar System
What are Kuiper Belt objects?
• A Kuiper belt object (KBO) is any of the minor
bodies in the Kuiper belt. They are made of
methane ice, ammonia ice, and water ice.
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Unit 2 Lesson 6 Small Bodies in the Solar System
Pluto: From Planet to KBO
• Until 2006, Pluto was considered to be the ninth
planet in the solar system.
• Beginning in 1992, Kuiper belt objects began to be
discovered beyond Neptune’s orbit, some of which
had similar size and composition as Pluto.
• In 2006, Pluto was redefined as a “dwarf planet”
by the International Astronomical Union.
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Unit 2 Lesson 6 Small Bodies in the Solar System
Pluto: From Planet to KBO
• Many large KBOs have satellites.
• Pluto, the second-largest KBO, has Charon as its
largest satellite.
• Some KBOs and their satellites, such as Pluto and
Charon, orbit each other.
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Unit 2 Lesson 6 Small Bodies in the Solar System
KBOs
What do we know about comets?
• A comet is a small body of ice, rock, and dust
that follows a highly elliptical orbit around the
sun.
• All comets have a nucleus that is composed of ice
and rock. Most comet nuclei are between 1 km
and 10 km in diameter.
• If a comet approaches the sun, solar radiation and
heating cause the comet’s ice to change to gas.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about comets?
• A coma is a spherical cloud of gas and dust that
comes off the nucleus.
• The ion tail of a comet is gas that has been
ionized by the sun. This ion tail always points
away from the sun.
• A second tail made of dust and gas curves
backward along the comet’s orbit. This dust tail
can be millions of kilometers long.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about comets?
• How does a comet change as it orbits the sun?
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about comets?
• Collisions between objects in the Kuiper belt
produce fragments that become short-period
comets.
• Short-period comets take fewer than 200 years to
orbit the sun.
• Short-period comets have short life spans. Every
time a comet passes the sun, it may lose a layer
as much as 1 m thick.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about comets?
• Long-period comets come from the Oort cloud.
They may take up to hundreds of thousands of
years to orbit the sun.
• The Oort cloud is a spherical region that
surrounds the solar system.
• Comets can form in the Oort cloud when two
objects collide, or when the gravity of a nearby
star sends an object into the inner solar system.
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Unit 2 Lesson 6 Small Bodies in the Solar System
On the Rocks
What do we know about asteroids?
• An asteroid is a small, irregularly shaped, rocky
object that orbits the sun.
• Most asteroids are located in the asteroid belt
between the orbits of Mars and Jupiter.
• The asteroid belt contains hundreds of thousands
of asteroids, called main-belt asteroids.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about asteroids?
• Groups of asteroids are also located in the orbits
of Jupiter and Neptune (called Trojan asteroids)
and in the Kuiper belt.
• Some asteroids are called near-Earth asteroids.
These asteroids cross the orbits of Earth and
Venus.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about asteroids?
• Where are most asteroids located in the solar
system?
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about asteroids?
• The composition of asteroids varies.
• Some are rich in carbon.
• Others are rocky, with cores of iron and nickel.
• Some have a rocky core surrounded largely by
ice.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about asteroids?
• Some asteroids appear to be piles of rock loosely
held together.
• Others contain economic minerals such as gold,
iron, nickel, cobalt, and platinum.
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Unit 2 Lesson 6 Small Bodies in the Solar System
Burned Out
What do we know about meteoroids,
meteors, and meteorites?
• A meteoroid is a rocky body, ranging in size from
that of a sand grain to that of a boulder, which
travels through space.
• A bright streak of light that results when a
meteoroid burns up in Earth’s atmosphere is
called a meteor.
• A meteorite is a meteoroid that reaches Earth’s
surface without burning up.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about meteoroids,
meteors, and meteorites?
• Meteoroids come from the asteroid belt, Mars, the
moon, and comets.
• Most meteoroids that enter Earth’s atmosphere do
not reach Earth’s surface. Many explode in the
upper atmosphere; others skip back into space.
• Large meteoroids that enter Earth’s lower
atmosphere or strike Earth’s surface can be
destructive.
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Unit 2 Lesson 6 Small Bodies in the Solar System
What do we know about meteoroids,
meteors, and meteorites?
• Meteorites can be divided into three general
groups. Stony meteorites, made of silicate
minerals, are the most common form.
• Iron meteorites, composed of iron and nickel,
form a much smaller group of meteorites.
• Stony-iron meteorites, composed of silicate
minerals, iron, and nickel, are the rarest group of
meteorites.
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