1. Comets Asteroids and Meteorites Ch 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 Earth’s 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 Earth’s 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 comet’s 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

12. (Image by Elizabeth Warner on March 8, 1997)
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 AU)
Kuiper Belt (disk ~ 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. About 1/3 distance to nearest star
Oort Cloud
Sun
~105 AU
About 1/3 distance to nearest star

21. Kuiper Belt
~50 AU
Sun
Neptune’s 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 Belt Paiting 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

29. 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

30. III. COMPOSITION (Cont.)
Deuterium Atom
Hydrogen Atom P N + e -

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
10-5

34. C Chondrites (H2O-rich meteorites)
D/H Ratios
10-3
Cores of
Molecular
Clouds
•HB
•HA
Comets
•HY
Earth
Oceans
C Chondrites (H2O-rich meteorites)
10-4
Solar
Nebula
10-5

35. III. COMPOSITION (Cont.)
D/H Ratios in Comet Water:
Consistent with comets providing at least some of Earth’s H2O

36. 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

37. Water contents of meteorites (which come from asteroids)
Wet
Dry

38. 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

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 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.

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 Earth’s water and organic molecules

41. Asteroids and Meteorites Ch9 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 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

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 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.