Comets Asteroids and Meteorites Ch 9 Ch 8 and 9 HW posted and due Mon March. 14

COMETS AND THEIR COMPOSITION (Ch. 9 part II)

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)

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 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

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

(Image by Elizabeth Warner on March 8, 1997) 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

About 1/3 distance to nearest star 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 Hydrogen Atom P N + e -

Normal and “Heavy” Water H2O HDO O O H 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 Hale-Bopp These vales are plotted in the next slide

Deuterium/Hydrogen Ratios 10-3 •HB •HA •HY Earth Oceans 10-4 Solar Nebula 10-5

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

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 III

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

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 Differenciated Asteroid Non-differenciated 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 Differenciated Asteroid Non-differenciated 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.