Transcript Ch 9(10-14-10)

Comets Asteroids and Meteorites
Ch 9
Ch 8 and 9 HW posted and due
Mon Oct. 18
COMETS AND THEIR
COMPOSITION
(Ch. 9 part I)
OUTLINE
I. Nature of Comets
II. Comets and the Origin of Earth’s Water
III. Dust Composition
VI. Summary
(you need to take notes only on slides with blue titles)
Comet Hale-Bopp in 1997
I. Nature of Comets
 Comets from the Greek “”
(kometes). Long-haired ones.
 Ancient greeks considered comets
atmospheric phenomena, not part of the
“perfect” heavens.
Question 1
 A comet is:
A. A piece of interplanetary material that burns in
the Earth’s atmosphere
B. An object made of ices and dust in orbit around
the Sun
C. A shooting Star
D. A rocky object that formed between Mars and
Jupiter
I. Nature of Comets
 Today we know comets are “dirty icebergs”
in orbit around our Sun.
 About ½ of a comet’s mass is water ice, the
rest is cosmic dust and other ices.
 Comet Orbits: generally very elliptical
I. Nature of Comets (Cont.)
 The nucleus is where all cometary activity
originates.
 When a comet is far from the Sun it is an inert
object.
 When a comet approaches the Sun the ices in
the nucleus sublimate and create a cloud of gas
and dust called the coma.
 Sunlight and the solar wind push the dust and
gas away from the sun creating the two tails.
Question 2
The tails of comets are always directly behind the
nucleus. a) True b) False
Comet Hale-Bopp
(Image by Elizabeth Warner on March 8, 1997)
Ion Tail
Dust Tail
Coma
Comet Ikeya-Zhang
(March 11 ‘02 images from Sky and Telescope)
DS1 Spacecraft Image of Comet
Borrelly in September 2001
Image of Comet Wild 2 from NASA's Stardust
spacecraft. January 2, 2004
Deep Impact Spacecraft Image of
Comet Tempel 1 in July 2005
Deep Impact Spacecraft Image of
Comet Tempel 1 in July 2005
I. Nature of Comets (Cont.)
 Our solar system formed about 4.6 billion
years ago from the solar nebula.
 The planets and Sun have been extensively
processed since they formed.
 However, comets have remained relatively
pristine for the past 4.6 billion years.
 Why?
•Comets are small and
•stay far from the Sun most of the time.
Nature of Comets (Cont.)
 Two Known Sources of Comets
• Oort Cloud (spherical shell ~ 50,000-100,000 AU)
• Kuiper Belt (disk ~ 30-50 AU)
(Astronomical Unit [AU] = Earth-Sun Distance)
 Active comets do not last more than about 100,000
years in the inner solar system because they lose
material every time they pass near the Sun
Oort Cloud
Sun
•
~105 AU
About 1/3
distance to
nearest star
Kuiper Belt
~50 AU
•
Sun
Neptune’s Orbit
Comets
can come
from the
Oort
Cloud and
from the
Kuiper
belt
Jovian planets
protect Earth
from most of
bombardment
Fig 9.25
Outer Solar System
Outer Solar System
Collision in the Kuiper Belt
Paiting by Daniel D. Durda
Comet SL9 caused a string of violent
impacts on Jupiter in 1994,
reminding us that catastrophic
collisions still happen.
Tidal forces tore it apart during
previous encounter with Jupiter
COMPOSITION OF COMET GAS
Deuterium Abundance:
• Why study it?
• Chemical signature that can help us understand
the possible links between comet water and
Earth’s water
III. COMPOSITION (Cont.)
Deuterium Atom
P
N
Hydrogen Atom
P
+
+
e
-
e
Normal and “Heavy” Water
H2O
HDO
O
H
O
H
H
D
COMPOSITION OF COMET GAS
Deuterium Abundance:
• The deuterium to hydrogen ratio has been
measured in the water vapor in the coma of
three comets: Halley, Hyakutake, and HaleBopp
• These vales are plotted in the next slide
Deuterium/Hydrogen Ratios
10-3
•HA •HB •HY
10-4
Earth Oceans
Solar Nebula
10-5
D/H Ratios
10-3
Comets
10-4
•HA •HB •HY
C Chondrites (H2O-rich meteorites)
Cores of
Molecular
Clouds
Earth
Oceans
Solar
10-5
Nebula
III.COMPOSITION (Cont.)
 D/H Ratios in Comet Water:
• Consistent with comets providing at least some
of Earth’s H2O
IV. Comets and Origin of Earth’s Water
 The contents of H2O in meteorites indicates a
decrese in water abundance in the asteroid belt
with decreasing heliocentric distance
 Meteorites believed to have originated in the
innermost part of the asteroid belt are the
driest known material in the solar system
 This suggests that the planetesimals formed in
Earth’s zone should have had an even lower
water content
Water contents of meteorites
(which come from asteroids)
Wet
Dry
IV. Comets and Origin of Earth’s Water
 Why is Earth rich in water and where did
this water come from?
 Comet impacts?
 Asteroid impacts?
 Probably both: The composition Earth’s
water is consistent with a cometary origin of
at least some of it. In addition, some
asteroids can have as much as 15% water
V. COMPOSITION OF THE DUST
 Cometary dust is approximately 50% silicates
(minerals) and 50% organic solids (organic
solids are made up of molecules with many
carbon atoms).
 If comets contributed a significant fraction of
Earth’s H2O they probably also contributed
significant quantities of organic molecules.
 Hence, comets may have played a role in the
origin of life on Earth.
 However, there is no evidence that comets
bring living organisms to Earth.
VI. SUMMARY
 Comets are composed mainly of H2O ice plus
cosmic dust and other ices
 The main features of a comet are the nucleus,
coma and tails
 There are two known sources of comets: Oort
Cloud and Kuiper Belt
 The chemical composition of comets (rich in
deuterium) is consistent with a cometary
origin of at least some of Earth’s water and
organic molecules
Asteroids and Meteorites
Ch9 part II
Asteroids and Meteorites Outline
I.
II.
Introduction
Asteroids
•
Orbits, sizes, composition
III. Meteorites
•
•
•
Irons
Stony-Irons
Stones
IV. Origin of Meteorites
V. Meteorites and the Solar System
VI. Summary
I. INTRODUCCION
 Asteroids, comets and meteorites are the
smallest members of the solar system
 All these objects tell us much about how the
rest of the solar sytem formed
II. ASTEROIDS
 Most have orbits between between Mars and
Jupiter
 Some have orbits that cross Earth’s, these are
known as Earth-crossing asteroids
 They have collided with Earth and they are
likely to do so again.
 The largest asteroid is Ceres
III. Types of Meteorites
 Irons
 Stony-Irons
 Stones (~75% of all meteorites)
Iron
Iron and stone
Stone
Diferenciated Asteroid
Non-diferenciated Asteroid
III. Types of Meteorites
 Irons
 Stony-Irons
 Stones (~75% of all meteorites)
Iron Meteorite
Stony-Iron
Stony Meteorite
III. Origin of Meteorites
 Asteroids (more than 95%)
• Asteroids collide with each other and breakup,
some of those fragments become meteorites
 Mars (a few percent)
• Impacts on Mars kick martian material into
space and some ends up falling on Earth
 Moon (a few percent)
• Also because of impacts
III. Types of Meteorites
 Irons are excavated by collisions
 Stony-Irons are excavated by collisions
Iron
Iron and stone
Stone
Diferenciated Asteroid
Non-diferenciated Asteroid
IV. Meteorites and the Solar System
 Age of Solar System (4.6x109 years)
determined from radioactive dating of
meteorites
 Meteorites and Planets:
• Information about asteroids, Mars,
Moon.
• Information about interior of Earth, e.g.,
iron core.
V. Summary of Asteroids and Meteorites
 Most asteroids orbit the Sun between Mars and Jupiter
 Some asteroids cross Earth’s orbit and collide w/ Earth
 Ceres is the largest asteroid
 There are several types of asteroids
 Meteorites are solid objects from space that reach the
Earth’s surface
 Most meteorites are from asteroids, a few are from
Mars and the Moon. Most meteors are from comets
 Three types of meteorites: Irons, Stony-irons, Stones
 Meteorites tell us about the rest of the solar system.