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

Comets from the Greek “  ” (kometes). Long-haired ones. Ancient greeks considered comets atmospheric phenomena, not part of the “perfect” heavens. I. Nature of Comets

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 Question 1

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

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. I. Nature of Comets (Cont.)

The tails of comets are always directly behind the nucleus. a) True b) False Question 2

Comet Hale-Bopp Ion Tail Dust Tail (Image by Elizabeth Warner on March 8, 1997) 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

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. I. Nature of Comets (Cont.)

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

Oort Cloud ~10 5 AU Sun About 1/3 distance to nearest star

Kuiper Belt ~50 AU Sun Neptune’s Orbit

Jovian planets protect Earth from most of bombardment Fig 9.25 Comets can come from the Oort Cloud and from the Kuiper belt

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 AtomHydrogen Atom PN + e - P + e -

OO HHHD H2OH2O HDO Normal and “Heavy” Water

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 Earth Oceans Solar Nebula HB HY HA

D/H Ratios Earth Oceans Cores of Molecular Clouds HB HY HA C Chondrites (H 2 O-rich meteorites) Comets Solar Nebula

III.COMPOSITION (Cont.) D/H Ratios in Comet Water: Consistent with comets providing at least some of Earth’s H 2 O

The contents of H 2 O 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 IV. Comets and Origin of Earth’s Water

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

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 IV. Comets and Origin of Earth’s Water

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 H 2 O 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. V. COMPOSITION OF THE DUST

VI.SUMMARY Comets are composed mainly of H 2 O 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.Introduction II.Asteroids Orbits, sizes, composition III. Meteorites Irons Stony-Irons Stones IV.Origin of Meteorites V. Meteorites and the Solar System VI.Summary

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 I.INTRODUCCION

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 II.ASTEROIDS

Irons Stony-Irons Stones (~75% of all meteorites) III. Types of Meteorites Iron Iron and stone Stone Diferenciated AsteroidNon-diferenciated Asteroid

Irons Stony-Irons Stones (~75% of all meteorites) III. Types of 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

Irons are excavated by collisions Stony-Irons are excavated by collisions III. Types of Meteorites Iron Iron and stone Stone Diferenciated AsteroidNon-diferenciated Asteroid

IV. Meteorites and the Solar System Age of Solar System (4.6x10 9 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.