Astronomy Chapter 8

Outer Solar System objects

Objects beyond the inner planets including comets, asteroids, Kuiper Belt objects, and Oort Cloud bodies

Leftover objects in Solar System

Objects in the outer Solar System are remnants from formation and preserve early conditions

Importance of comets and asteroids

They provide information about early Solar System conditions and can impact Earth

Extinction events cause

Asteroids and comets have caused major extinctions through collisions with Earth

Pluto classification change

Pluto was reclassified from a planet to a dwarf planet

Reason Pluto is a dwarf planet

It does not dominate its orbital region and shares space with similar objects

Kuiper Belt definition

A disk-like region beyond Neptune containing icy bodies

Oort Cloud definition

A spherical cloud of icy objects surrounding the Solar System at great distances

Asteroids definition

Rocky objects orbiting the Sun, mostly in the asteroid belt

Meteoroids definition

Small chunks of rock smaller than asteroids

Comets definition

Icy bodies that form tails when near the Sun

Effect of collisions on Earth

Collisions with debris can significantly change life on Earth

Size range of giant planets

Giant planets are about 4–11 times Earth’s diameter

Size range of terrestrial planets

Terrestrial planets range from Earth size down to about 40% Earth’s diameter

Pluto size relative to Earth

Pluto is about 20% the diameter of Earth

Pluto diameter

About 2300 km across

New Horizons mission significance

Provided detailed images and data of Pluto in 2015

Comets historical perception

Comets were often viewed as omens, usually bad ones

Comet brightness

Some comets are bright enough to be seen from cities

Example of bright comet

Hale-Bopp was visible over New York City

Asteroids and comets importance

They are storehouses of information about Solar System origins

Monitoring space debris importance

Tracking objects is important to prevent potential collisions with Earth

Pluto orbital shape

Highly elliptical orbit

Pluto orbital inclination

Highly tilted orbit compared to other planets

Pluto orbital period

248 years

Pluto perihelion definition

Point in orbit closest to the Sun

Pluto perihelion year example

Pluto was closest to the Sun in 1989

Pluto orbit crossing

Part of Pluto’s orbit lies inside Neptune’s orbit

Visibility of Pluto

Barely visible with medium telescopes under dark skies

Discovery of Pluto

Clyde Tombaugh discovered Pluto in 1930

Method of Pluto discovery

Detected as a moving dot among stars using photographic plates

Location of Pluto discovery

Lowell Observatory in Arizona

Reason Pluto was searched

Expected to explain irregularities in Uranus’ orbit

Pluto discovery technique

Compared images taken on different nights to detect motion

Pluto moon discovery

Charon discovered in 1978

Importance of Charon

Allowed accurate measurement of Pluto’s mass

Pluto mass difficulty

Hard to determine because of its small size and long orbital period

Incorrect early Pluto mass estimate

Once thought to be 91% of Earth’s mass

Charon mass relative to Pluto

About 12% of Pluto’s mass

Pluto density

1.88 g/cm³

Pluto semimajor axis

39.5 AU

AU definition

Distance from Earth to Sun (~150 million km)

Pluto radius

0.19 Earth radii

Pluto mass

0.0022 Earth masses

Pluto day length

6.39 days

Pluto surface feature

Heart-shaped nitrogen ice glacier

Pluto glacier composition

Nitrogen ice

Source of Pluto glacier

Fed by smaller glaciers

New Horizons mission

First spacecraft to visit Pluto

Kuiper Belt distance from Sun

About 30–50 AU

Oort Cloud distance from Sun

About 2,000–200,000 AU

Main asteroid belt location

Between Mars and Jupiter (~2.1–3.3 AU)

Oort Cloud shape

Spherical cloud

Kuiper Belt shape

Disk-like structure

Inclination distribution in Oort Cloud

Isotropic (random directions)

Evidence for Oort Cloud

Long-period comets have isotropic inclinations

Long-period comets definition

Comets with very large orbital periods and distances

Kuiper Belt object orbits

Provide clues about planetary migration

Planetary migration

The movement of giant planets early in Solar System history

Contact binaries definition

Two objects that have merged together

Example of contact binary

Arrokoth

Kuiper Belt composition

Icy bodies and dwarf planets

Reason Pluto was demoted

Many similar-sized objects exist beyond Neptune

Small Solar System bodies

Asteroids, comets, meteoroids, and Kuiper Belt objects

Difference between asteroid and comet

Asteroids are rocky, comets are icy

Comet tail formation

Caused by solar radiation heating ice and releasing gas and dust

Comet nucleus

Solid icy core of a comet

Comet coma

Cloud of gas and dust around the nucleus

Types of comet tails

Dust tail and ion tail

Ion tail direction

Points directly away from the Sun due to solar wind

Dust tail direction

Follows curved orbit path

Short-period comets origin

Kuiper Belt

Long-period comets origin

Oort Cloud

Asteroid composition

Rocky or metallic materials

Asteroid belt formation

Remnants that never formed into a planet

Why no planet formed in asteroid belt

Jupiter’s gravity prevented accretion

Meteor definition

Streak of light when meteoroid enters atmosphere

Meteorite definition

Object that reaches Earth’s surface

Impact crater formation

Caused by high-speed collisions with Earth

Mass extinction cause example

Large asteroid impacts

Importance of studying impacts

Helps understand risk to Earth

Earth monitoring programs

Track near-Earth objects for potential threats

Near-Earth objects definition

Asteroids or comets with orbits near Earth

Defense strategies for impacts

Possible deflection or disruption methods

Solar System formation evidence

Small bodies preserve original materials

Pluto classification criteria

Orbit, shape, and clearing neighborhood

Dwarf planet definition

Orbits Sun, spherical, but has not cleared orbit

Examples of dwarf planets

Pluto, Eris, Haumea, Makemake

Kuiper Belt significance

Source of short-period comets

Oort Cloud significance

Source of long-period comets

Difference between Kuiper Belt and Oort Cloud

Kuiper Belt is disk-shaped, Oort Cloud is spherical

Importance of orbital inclinations

Reveal structure of distant Solar System regions

Pluto orbital eccentricity

Highly eccentric compared to planets

Pluto orbital resonance

Locked in resonance with Neptune

Meaning of orbital resonance

Regular gravitational interaction between bodies

Pluto brightness variation

Depends on distance from Sun

Reason Pluto brightness changes

Elliptical orbit changes distance

Observation challenges for Pluto

Faint and distant object

Scientific importance of Pluto

Provides insight into outer Solar System formation