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a) beyond the orbit of Neptune.

b) between Earth and the Sun.

c) between Mars and Jupiter.

d) in the orbit of Jupiter, but 60 degrees ahead or behind it.

e) orbiting the jovian planets in captured, retrograde orbits.

Most asteroids are found

Question 7

a) beyond the orbit of Neptune.

b) between Earth and the Sun.

c) between Mars and Jupiter.

d) in the orbit of Jupiter, but 60 degrees ahead or behind it.

e) orbiting the jovian planets in captured, retrograde orbits.

Question 7

Most asteroids are found

The Asteroid Belt is located between

2.1 and 3.3 A U from the Sun.

The Structure of the Solar System

~ 45 AU~ 5 AU

L4

L5

L3

Lagrange Points

Interplanetary Matter: Asteroids

The inner solar system, showing the asteroid belt, Earth-crossing asteroids, and Trojan asteroids

Interplanetary Matter: Asteroids

Large picture: The path of Icarus, an Earth-crossing asteroid

Inset: Ceres, the largest asteroid

Asteroids and meteoroids have rocky composition; asteroids are bigger.

(above) Asteroid Ida with its moon, Dactyl

(below) Asteroid Gaspra

(above) Asteroid Mathilde

Interplanetary Matter: Asteroids

Interplanetary Matter: Asteroids

Asteroid Eros

Comets are icy, with some rocky parts.

The basic components of a comet

Interplanetary Matter: Comets

Interplanetary Matter: Comets

The solar wind means the ion tail always points away from the Sun.

The dust tail also tends to point away from the Sun, but the dust particles are more massive and lag somewhat, forming a curved tail.

Interplanetary Matter: Comets

The internal structure of the cometary nucleus

Oort Cloud

The size, shape, and orientation of cometary orbits depend on their location. Oort cloud comets rarely enter the inner solar system.

Meteor Showers

Meteor showers are associated with comets – they are the debris left over when a comet breaks up.

Meteor Showers

Question 9

Compared to asteroids, comets show all of these properties EXCEPT

a) their densities are higher.

b) their orbits tend to be more elliptical.

c) they tend to be made of ice.

d) they can look fuzzy, whereas asteroids appear as moving points of light.

e) their average distances from the Sun are far greater.

Question 9

Compared to asteroids, comets show all of these properties EXCEPT

Comets have densities much lower than asteroids or

planets.

a) their densities are higher.

b) their orbits tend to be more elliptical.

c) they tend to be made of ice.

d) they can look fuzzy, whereas asteroids appear as moving points of light.

e) their average distances from the Sun are far greater.

What causes a meteor shower?

Question 10a) A comet and an asteroid collide.

b) Earth runs into a stray swarm of asteroids.

c) Earth runs into the debris of an old comet littering its orbit.

d) Meteorites are ejected from the Moon.

e) Debris from a supernova enters Earth’s atmosphere

What causes a meteor shower?

Question 10

Meteor showers can generate a few shooting stars, to hundreds of thousands, seen in an hour.

a) A comet and an asteroid collide.

b) Earth runs into a stray swarm of asteroids.

c) Earth runs into the debris of an old comet littering its orbit.

d) Meteorites are ejected from the Moon.

e) Debris from a supernova enters Earth’s atmosphere

Chapter 5: The Earth

Pale Blue Dot

Earth as seen from Voyager 1, when it was 6 billion km from home.

General Features

Mass: MEarth

= 6 x 1027 g

Radius: REarth

= 6378 km

Density: p = 5.5 g/cm3

Age: 4.6 billion years

Earth's Internal Structure

Crust: thin. Much Si and Al(lots of granite). Two-thirds covered by oceans.

How do we know? Earthquakes. See later

Mantle is mostly solid, mostly basalt (Fe, Mg, Si). Cracks in mantle allow molten material to rise => volcanoes.

Core temperature is 6000 K. Metallic - mostly nickel and iron. Outer core molten, innercore solid.

Atmosphere very thin

Earth's Atmosphere

78% Nitrogen21% Oxygen

gas is ionized by solar radiation

ozone is O3 , which

absorbs solar UV efficiently, thusheating stratosphere

commercial jet altitudes

temperature on a cool day

Original gases disappeared. Atmosphere is mostly due to volcanoes and plants!

Ionosphere

Particles in the upper reaches of the atmosphere are ionized by the sun.

Radio signals below ~20 MHz can “bounce” off the ionosphere allowingCommunication “over the horizon” (or mountains)

EarthquakesThey are vibrations in the solid Earth, or seismic waves.

Two kinds go through Earth, P-waves ("primary") and S-waves ("secondary"):

How do they measure where Earthquakes are centered?

* *

*

seismic stations

Like all waves, seismic waves bend when they encounter changes in density. If density change is gradual, wave path is curved.

S-waves are unable to travel in liquid.

Thus, measurement of seismic wave gives info on density of Earth's interior and which layers are solid/molten.

But faint P wavesseen in shadow zone,refracting off denseinner core

Curved paths ofP and S waves:density must slowlyincrease with depth

Zone with no S waves:must be a liquid corethat stops them

No P waves too:they must bend sharplyat core boundary

Earth's Interior Structure

Average density

CrustMantleCore

5.5 g/cm3

3 g/cm3

5 g/cm3

11 g/cm3

Density increases with depth => "differentiation"

Earth must have been molten once, allowing denser material to sink, as it started to cool and solidify.

Earthquakes and volcanoes are related, and also don't occur at random places. They outline plates.

Plates moving at a few cm/year. "Continental drift" or "plate tectonics"

When plates meet...

1) Head-on collision (Himalayas)

2) "Subduction zone" (one slides under the other) (Andes)

3) "Rift zone" (two plates moving apart) (Mid-Atlantic Ridge)

4) They may just slide past each other (San Andreas Fault)

side view

top view

=> mountain ranges, trenches, earthquakes, volcanoes

Clicker Question:

Sunlight absorbed by the Earth’s surface is reemitted in the form of?

A: radio waves

B: infrared radiation

C: visible radiation

D: ultraviolet radiation

E: X-ray radiation

The Mid-Atlantic Ridge is a rift zone.

What causes the drift?

Convection! Mantle slightly fluid and can support convection. Plates ride on top of convective cells. Lava flows through cell boundaries. Earth loses internal heat this way.

Cycles take ~108 years.

Plates form lithosphere (crust and solid upper mantle).Partially melted, circulating part of mantle is asthenosphere.

Pangaea Theory: 200 million years ago, all the continents were together!