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Asteroids
Astronomy 311
Professor Lee Carkner
Lecture 15
Where is the water on Mars?
a)
b)
c)
d)
e)
Underground
In the atmosphere
In the polar caps
a and b only
a and c only
What is currently the principle
resurfacing agent on Mars?
a)
b)
c)
d)
e)
Water
Volcanism
Wind and dust
Glaciers
Impacts
Which of the following correctly
orders Mars missions from oldest to
most recent?
a)
b)
c)
d)
e)
Phoenix, Spirit, Viking, Mariner 4
Viking, Spirit, Phoenix, Mariner 4
Mariner 4, Viking, Spirit, Phoenix
Mariner 4, Spirit, Phoenix, Viking
Spirit, Mariner 4, Viking, Phoenix
What two compounds likely make
up the ice caps of Mars?
a)
b)
c)
d)
e)
Water and methane
Carbon dioxide and water
Carbon dioxide and ammonia
Ammonia and methane
Water and methane
Temperature of Mars
Temp of Mars from radiation balance
TM = [RS/(2 DS)]½ TS
TM = [6.96X108 / (2)(1.5)(1.496X1011)]½ (5778)
TM = 227.7 K
TF = 1.8TK -460 = (1.8)(227.7)-460 = -50.1 F
How good is this estimate?
Principle source of error is that we have ignored the
effects of Mars’s atmosphere
Since atmosphere is very thin, error is small
How hot must Sun be for liquid water on Mars?
 TM = [RS/(2 DS)]½ TS
TS = TM /{[RS/(2 DS)]½}
TS =(227.7) / {[6.96X108 / (2)(1.5)(1.496X1011)]½}
TS= 6926.2 K
Quiz #2 Friday
Quiz 2 similar format as Quiz 1
~20 multiple choice/matching
~4 short answer
Covers lectures 9-15
bring pencil and calculator
Rocks in Space
Asteroid --
Meteoroid -- a small piece of rock in space
Meteor -- the flash of light when a
meteoroid hits the Earth’s atmosphere

sometimes called a falling or shooting star
Meteorite -- a meteoroid that hits the
ground
Types of Meteorites
Meteorites are classified based on their
composition

Irons are composed of metal
Chondrites are composed of silicates (rock)

Irons make up only ~5% of falls
But, irons are much easier to find

Chondrites look a lot like normal Earth rocks
What are the properties of chondrites and
irons and how can you identify them?
Iron Meteorites

Have small depressions on surface caused by
heat of passage through atmosphere

Often show Widmanstatten patterns when
etched with acid

Helps to distinguish true meteorites from
terrestrial rocks
Widmanstatten Patterns
Chondrite (Stony) Meteorites
Composed of silicates

Contain chondrules, small glassy inclusions
of material that were heated and quickly
cooled

Chondrites are old
Carbonaceous chondrites also contain
volatiles (water and carbon compounds) and
thus represent unprocessed material from the
very early solar nebula
Chondrules
The Missing Planet
In the 18th century astronomers noticed
that there was a gap between Mars and
Jupiter with no planets

This turned out to be a small planet
(diameter 918 km) which he named Ceres

This is the asteroid belt
The Asteroid Belt
Asteroid Myths
Are the asteroids debris from a planet
that exploded?

Is the asteroid belt dangerous to travel
through?

There is on average about one million
kilometers between asteroids
Asteroid Facts
Size: Ceres (918 km), Pallas (522 km),
about 200 larger than 100 km, most are
less than 1 km
Orbit:
Description: very small, irregularly
shaped, cratered
Formation of the Asteroid Belt

Jupiter’s gravity:
Ejected most near-by planetesimals

Alters the orbits of the remaining asteroids
Studying Asteroids
Several asteroids have been observed at
close range

In 2005 the Japanese mission Hayabusa
studied asteroid Itokawa and tried to
collect a sample for return to Earth
Asteroid Features
Only Ceres, Pallas and Vesta (the 3
largest asteroids) have enough gravity
to form a sphere

Asteroids show many craters

During the heavy bombardment period
asteroid collisions must have been frequent
Composition of Asteroids
Asteroids are divided into three major
groups based on composition
S Type

C Type

M type
composed of iron and nickel
Formation of Asteroids

C type asteroids are found in the outer
belt where temperatures are lower
Need low temperatures to keep volatiles
Formation of Meteoroids
Some asteroids became large enough to
differentiate

decay of radioactive materials provided the heat
These asteroids were then broken up by collisions

Fragments of the crust form achondritic stonys
Asteroids that never differentiated formed
chondrites
NEOs
 Some asteroids cross the Earth’s orbit and are called Near
Earth Objects (NEO)

About 1 big one every few hundred years
 Consequences of impacts
Local damage and small climate change

Very large tidal waves

Mass extinctions

What Use is an Asteroid?
Mining

Space Habitats

Spaceships
Put engines on the space colony
Providing Material for Life in Space

Summary
Asteroids are small bodies that orbit the Sun
Most are in the asteroid belt between Mars
and Jupiter (2-3.5 AU)
Jupiter’s gravity prevented the asteroids
from forming a planet
Description:
Small (most less than 1 km)
Max size is few hundred km
Irregularly shaped
Heavily cratered
Summary: Meteoroids
Iron
made of metal
formed from core of
asteroids (M type)
Achondrites (Stony)
made of rock with
no inclusions
made from crust of
asteroids (S type)
Chondrites (Stony)
made of rock with
small inclusions
made from
undifferentiated
asteroids (S and C
type)