ASTRONOMY MIDTERM

3 types of Spectra

Continuous, Emission-line, absorption-line

Continuous Spectrum

Emission-Line Spectrum

Produced by downward transistions

Absorption-Line Spectrum

Produced by upward transitions

Light tells us…

chemical composition, temperature, speed

a light source moving toward you has wavelengths shifted to

shorter values (blueshifted)

a light source moving away from you has wavelengths shifted to

longer values (redshifted)

two main functions of a telescope

light-collecting area, angular resolution

Larger diameter telescopes leads to

larger light-collecting area and better “angular resolution”

Two main types of telescopes

reflecting and refracting

Sun

• over 99.8% of solar system’s mass

• made mostly of H/He gas

• converts 4 million tons of mass into energy each second

Mercury

• made of metal and rock

• desolate, cratered; no atmosphere

• very hot and very cold

Venus

• nearly identical in size to earth; surface hidden by clouds

• very hot due to extreme greenhouse effect

• even hotter than mercury: 470 degrees C day and night

• dense, heavy atmosphere; rains sulfuric acid

Earth

• only surface liquid water in the solar system

• a surprisingly large moon

Mars

• giant volcanos, a huge canyon, polar caps, and more

• water flowed in the distant past: why not now? Could there have been life in the past?

• thin atmosphere

Jupiter

• Much farther from sun than terrestrial worlds (5 au)

• mostly H/He; no solid surface

• 300 times more massive than earth

• many moons, rings

Jupiter’s moons

Io, Europa, Ganymede, Callisto

Saturn

• giant and gaseous like Jupiter

• spectacular rings

• many moons, including cloudy Titan

• Cassini spacecraft currently studying it

Uranus

• smaller than Jupiter/Saturn; much larger than earth

• Made of H/He gas and hydrogen compounds

• Extreme axis tilt

• moons and rings

Neptune

• similar to Uranus (except for axis tilt)

• many moons (including triton)

4 observations that lead to our model of the formation of the Solar System (nebular theory)

Orderly Pattern of Motion of Large bodies

Two major Planet Types

Swarms of Smaller Bodies

Exceptions to identified patterns

Terrestrial planets

rocky, relatively small, and close to the sun

Jovian Planets

gaseous, larger, and farther from the Sun

Conservation of Energy: As gravity causes the solar nebula to contract…

it heats up

Inside the Frostline

too hot for hydrogen compounds to form ices; only rock and metals solidified

Outside the frostline

cold enough for ices of hydrogen compounds to form

Accretion

gravity draws planetesimals together to form planets

Final step in formation of solar system

radiation and outflowing matter from the sun— the solar wind— blew away the leftover gases

Where do asteroids come from?

Leftover planetesimals from the inner solar system

Where do comets come from?

leftover planetesimals from the outer solar system

Giant Impact theory

Leading theory is the Earth’s moon formed from a giant impact early on (might also explain the different rotation axes of Uranus)

Order of the formation of the solar system

Contraction of large cloud of gas and dust —> formation of a flattened, spinning disk —> condensation of solid particles —> accretion of planetesimals into large objects —> clearing the remaining gas in the disk by the solar wind

Nebular Theory

our solar system formed from a collapsed giant cloud of interstellar gas

The theory of the formation of the solar system begins when a giant gas cloud begins to contract. What physics principle best explains why the cloud collapses?

The law of gravity

Four terrestrial planets

Mercury, Venus, Earth, Mars

Jovian Planets

Jupiter, Uranus, Neptune, Saturn

Earths interior consists of…

Core, Mantle, Crust, Lithosphere

Lithosphere

a planet’s outer layer of cool, rigid rock that floats on the warmer, softer mantle rock that lies beneath

Sources of Internal Heat

1. Gravitational potential energy of accreting planetesimals

2. Differentiation

3. Radioactivity (still an active heat source)

What do the moon and mercury have in common

both geologically “dead”

Smaller planets cool off

faster

4 Geological processes

Tectonics, volcanism, erosion, impact cratering

Tectonics

disruption of a planet’s surface by internal stresses

Volcanism

eruption of molten rock onto surface

Erosion

surface changes made by wind, water, or ice

Impact cratering

impacts by asteroids or comets

Rift zones

continental plates pull apart

Subduction zones

when plates run into each other, one is forced beneath the other

The geological age of a planet’s surface can be determined from the relative amount of

Impact craters

Effects of Atmospheres

Erosion, protection from radiation, greenhouse effect

Greenhouse gas

molecules with more than 2 atoms and two different types of elements are effective at absorbing infrared radiation

Global temperatures on earth have been increasing over the past few decades. Based on a great deal of evidence, scientists believe that this global warming is caused by

human activities that are increasing the concentration of greenhouse gases in Earth’s atmosphere

If there were no greenhouse effect on Earth:

Earth’s average temperature would be colder than freezing (-18 degrees C instead of +15 degrees C)

Terrestrial worlds from most geologically active to least

Earth, Venus, Mars, Mercury

Main difference between the earth and mars

mars is smaller

What makes a planet habitable

1. large enough for geological activity to be sustained, and to release and retain water and atmosphere

2. Located at an optimal distance from the sun for liquid water to exist

What is the structure of Jupiter like?

Gaseous on the outside, then liquid hydrogen, more dense metallic hydrogen, rocky/icy/metallic core

All Jovian planet cores all believed to be similar

• made of rock, metal, and hydrogen compounds

• 10x the mass of earth

What causes the distinctive bands of color at different latitudes on jupiter?

Three gases condense in Jupiter’s atmosphere

• ammonia

• ammonium hydrosulfide

• water

High pressure storm on Jupiter

the great red spot

High pressure storm on neptune

the great dark spot

Why are Uranus and Neptune blue?

they absorb red light and reflect blue light

What would increase the tidal heating of a moon

a more elliptical orbit, larger size, orbit around a larger planet

Small Jovian moons

irregular shaped, probably captured asteroids and comets

Larger Jovian Moons

formed like planets out of “mini-solar nebulae” surrounding the Jovian planets

Some larger moons are geologically active. How?

1. Ices melt at lower temperatures than rock

2. there is another heat source: tidal heating

Io- most volcanically active

large tidal forces cause interior to be molten

Europa- “likeliest to have life”

• metallic core, rocky mantle, and a crust made of H2O ice

• evidence of a subsurface ocean of liquid salt water beneath icy crust

• tidal forces crack icy crust

• liquid water could imply life under the icy surface

Ganymede

largest moon in the solar system

Callisto

Furthest of the 4 Galilean moons, weakest tidal forces

What mechanism is most responsible for generating the internal heat of Io that drives its volcanic activity

tidal heating

Titan

Saturns largest moon

Dwarf planet

like pluto; objects that are smaller than planets, orbit the sun, and are large enough to be round

Asteroid

a rocky leftover planetesimal orbiting the sun

Comet

an icy leftover planetesimal orbiting the sun, regardless of its size or whether it has a tail

Meteorite

any piece of rock that fell to the ground from space, regardless of its origin

Meteor

a flash of light in the sky caused by a particle entering the atmosphere, regardless of its origin

Where are most asteroids located?

In the asteroid belt, between mars and Jupiter

Evidence a catastrophic asteroid impact caused dinosaur extinction

the iridium layer, enormous crater

If the hypothesis tracing the extinction of the dinosaurs to an impact is correct, the dinosaurs died off largely because _____

Of global climate effects initiated by dust and smoke that entered the atmosphere after the impact

DART — Double Asteroid Redirection Test

• crash impactor spacecraft into Dimorphos and see its orbital response

Kuiper Belt

Comets on orderly orbits at 30-100 AU in disk of solar system

Oort Cloud

Comets on random orbits extending to about 50,000 AU

Where did Kuiper Belt comets form?

In the Kuiper belt

Where did Oort cloud comets form?

they were once closer to the Sun, but they were kicked farther out by gravitational interactions with Jovian planets

When do meteor showers occur?

Comets leave small particles in their orbit around the sun. Meteor showers occur when earth crosses the comet’s orbit