Download Small Bodies in the Solar System

Module G: Unit 2, Lesson 6 - Small Bodies in the Solar System
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.
• 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.
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.
What are Kuiper belt objects (KBOs)?
• 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).
• 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.
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.
• 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.
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.
• 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.
• 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.
• 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.
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.
• 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.
• 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.
• Some asteroids appear to be piles of rock loosely held together.
• Others contain economic minerals such as gold, iron, nickel, cobalt, and platinum.
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.
• 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.
• 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.