Comets Asteroids and Meteorites Ch 9

1
Comets Asteroids and MeteoritesCh 9
Ch 8 and 9 HW posted and due Mon March. 14
2
COMETS AND THEIR COMPOSITION(Ch. 9 part II)
3
OUTLINE

• I. Nature of Comets
• II. Comets and the Origin of Earths Water
• III. Dust Composition
• Summary
• (you need to take notes only on slides with blue
  titles)

4
Comet Hale-Bopp in 1997
5
I. Nature of Comets

• Comets from the Greek ??????? (kometes).
  Long-haired ones.
• Ancient greeks considered comets atmospheric
  phenomena, not part of the perfect heavens.

6
Question 1

• A comet is
• A piece of interplanetary material that burns in
  the Earths atmosphere
• An object made of ices and dust in orbit around
  the Sun
• A shooting Star
• A rocky object that formed between Mars and
  Jupiter

7
I. Nature of Comets

• Today we know comets are dirty icebergs in
  orbit around our Sun.
• About ½ of a comets mass is water ice, the rest
  is cosmic dust and other ices.
• Comet Orbits generally very elliptical

8
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.

9
Question 2

• The tails of comets are always directly behind
  the nucleus. a) True b) False

10
(No Transcript)
11
(No Transcript)
12
Comet Hale-Bopp
(Image by Elizabeth Warner on March 8, 1997)
Ion Tail
Dust Tail
Coma
13
Comet Ikeya-Zhang(March 11 02 images from Sky
and Telescope)
14
DS1 Spacecraft Image of Comet Borrelly in
September 2001
15
Image of Comet Wild 2 from NASA's Stardust
spacecraft. January 2, 2004
16
Deep Impact Spacecraft Image of Comet Tempel 1 in
July 2005
17
Deep Impact Spacecraft Image of Comet Tempel 1 in
July 2005
18
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.

19
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

20
Oort Cloud

Sun
105 AU
About 1/3 distance to nearest star
21
Kuiper Belt

Neptunes Orbit
22
Comets can come from the Oort Cloud and from the
Kuiper belt
Jovian planets protect Earth from most of
bombardment
Fig 9.25
23
Outer Solar System
24
Outer Solar System
25
Collision in the Kuiper BeltPaiting by Daniel D.
Durda
26
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
27
(No Transcript)
28
(No Transcript)
29
COMPOSITION OF COMET GAS

• Deuterium Abundance
• Why study it?
• Chemical signature that can help us understand
  the possible links between comet water and
  Earths water

30
III. COMPOSITION (Cont.)
31
Normal and Heavy Water
H2O
HDO
O
O
H
H
H
D
32
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 Hale-Bopp
• These vales are plotted in the next slide

33
Deuterium/Hydrogen Ratios
10-3
HB
HA
HY
Earth Oceans
10-4
Solar Nebula
34
D/H Ratios
10-3
Cores of Molecular Clouds
HB
HA
Comets
HY
Earth Oceans
C Chondrites (H2O-rich meteorites)
10-4
Solar Nebula
35
III. COMPOSITION (Cont.)

• D/H Ratios in Comet Water
• Consistent with comets providing at least some of
  Earths H2O

36
IV. Comets and Origin of Earths 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
  Earths zone should have had an even lower water
  content

37
Water contents of meteorites (which come from
asteroids)
Wet Dry
38
IV. Comets and Origin of Earths Water

• Why is Earth rich in water and where did this
  water come from?
• Comet impacts?
• Asteroid impacts?
• Probably both The composition Earths water is
  consistent with a cometary origin of at least
  some of it. In addition, some asteroids can have
  as much as 15 water

39
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
  Earths 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.

40
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 Earths water and organic
  molecules

41
Asteroids and MeteoritesCh9 part III
42
Asteroids and Meteorites Outline

• I. Introduction
• Asteroids
• Orbits, sizes, composition
• III. Meteorites
• Irons
• Stony-Irons
• Stones
• IV. Origin of Meteorites
• V. Meteorites and the Solar System
• VI. Summary

43
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

44
II. ASTEROIDS

• Most have orbits between between Mars and Jupiter
• Some have orbits that cross Earths, 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

45
III. Types of Meteorites

• Irons
• Stony-Irons
• Stones (75 of all meteorites)

Iron
Iron and stone
Stone
Differenciated Asteroid
Non-differenciated Asteroid
46
III. Types of Meteorites

• Irons
• Stony-Irons
• Stones (75 of all meteorites)

47
Iron Meteorite
48
Stony-Iron
49
Stony Meteorite
50
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

51
III. Types of Meteorites

• Irons are excavated by collisions
• Stony-Irons are excavated by collisions

Iron
Iron and stone
Stone
Differenciated Asteroid
Non-differenciated Asteroid
52
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.

53
V. Summary of Asteroids and Meteorites

• Most asteroids orbit the Sun between Mars and
  Jupiter
• Some asteroids cross Earths 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 Earths 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.