Asteroid, Meteor, Comets

7/29/2019 Asteroid, Meteor, Comets

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Chapter 9

Remnants of Rock and IceAsteroids, Comets, and Pluto


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9.1 Asteroids and Meteorites

Our Goals for Learning

Why is there an asteroid belt?

How are meteorites related to asteroids?


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Asteroid

Facts

Asteroids are rocky leftovers of planet formation.

Largest is Ceres, diameter ~1,000 km 150,000 in catalogs, and probably over a million with

diameter >1 km.

Small asteroids are more common than large asteroids.

All the asteroids in the solar system wouldnt add up toeven a small terrestrial planet.


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Asteroids are cratered and not round


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Why is there an asteroid belt?


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More than

150,000

asteroids at

theirpredicted

locations for

Jan 1 2004

On this

scale,

asteroids are

muchsmaller than

the dots used

to represent

them


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Why are there very few asteroids

beyond Jupiters orbit?

A. There was no rocky material beyond Jupiters

orbit.B. The heaviest rocks sank towards the center of the

solar system.

C. Ice could form in the outer solar system.

D. A passing star probably stripped away all ofthose asteroids, even if they were there at onetime.


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Why are there very few asteroids

beyond Jupiters orbit?

A. There was no rocky material beyond Jupiters

orbit.B. The heaviest rocks sank towards the center of the

solar system.

C. Ice could form in the outer solar system.

D. A passing star probably stripped away all ofthose asteroids, even if they were there at onetime.


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Which explanation seems to be

the most plausible?A. The belt is where all the asteroids

happened to form.

B. The belt is the remnant of a large

terrestrial planet that used to be between

Mars and Jupiter.

C. The belt is where all the asteroidshappened to survive.


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Which explanation seems to be

the most plausible?A. The belt is where all the asteroids

happened to form.

B. The belt is the remnant of a large

terrestrial planet that used to be between

Mars and Jupiter.

C. The belt is where all the asteroidshappened to survive. But WHY didnt they

form a little planet?


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Rocky planetesimals

survived in the asteroid

belt between Mars andJupiter because they did

not accrete into a planet.

Jupiters gravity, stirs

up the asteroid orbits

and prevents their

planet formation.


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How are meteorites related to

asteroids?


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How are meteorites related to

asteroids?

Meteorites are pieces of asteroids - orsometimes planets or the Moon.


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Meteor: The bright tail of hot debris from the rock

Meteorite: A rock from space that reaches Earths surface


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Peekskill, NY:

October 9, 1992


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Pieces of Asteroids:Meteorite

Types1) Primitive: Unchanged in composition

since they first formed 4.6 billion years

ago.

2) Processed: Younger, have experienced

processes like volcanism ordifferentiation.


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Primitive Meteorites: simple, all

ingredients mixed together


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Processed Meteorites:

shattered fragments of larger objects

Iron

from acore

Volcanic rock from a cru

or mantle


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What do we learn from

meteorites? primitive meteorites tell us when solar

system formation began.

Processed meteorites tell us what asteroidsare like on the inside.

Processed meteorites provide direct proof

that differentiation and volcanism happenedon asteroids.


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Meteorites from Moon and Mars

A few meteorites arrive from the Moon and Mars

Composition differs from the asteroid fragments.

A cheap (but slow) way to acquire moon rocks andMars rocks.

One Mars meteorite generated a stir when scientists

claimed evidence for microscopic life in it.


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What have we learned? Why is there an asteroid belt?

Orbital resonances with Jupiterdisrupted the orbits of

planetesimals, preventing them

from accreting into a planet.

Those that were not ejected

from this region make up the

asteroid belt today. Most

asteroids in other regions of the

inner solar system accreted into

one of the planets.

How are meteorites related toasteroids?

Most meteorites are pieces of

asteroids. Primitive meteoritesare essentially unchanged sincethe birth of the solar system.Processed meteorites arefragments of larger asteroids

that underwent differentiation.


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9.2 Comets


How do comets get their tails?

Where do comets come from?


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How do comets

get their tails?


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Comet Facts

Formed beyond the frostline, comets are icycounterparts to asteroids.

Dirty snowballs = the nucleus Most comets do not have tails.

Most comets remain perpetually frozen in

the outer solar system. Only a few enter theinner solar system, where they can growtails.


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When a comet nears the Sun, its ices can sublimate into

gas and carry off dust, creating a coma and long tails.


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Draw This

Picture


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Comets eject small particles that follow the comet around

in its orbit

This can cause meteor showers when Earth crosses the

comets orbit.


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Meteors in a shower appear to emanate from the same area of skybecause of Earths motion through space


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Where do comets come from?


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Kuiper belt:On orderly orbits

from 30-100 AU in

disk of solar

system

Oort cloud:

On random orbitsextending to about

50,000 AU

Only a tiny number

of comets enter the

inner solar system -

most stay far fromthe Sun


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How did they get there?

Kuiper belt comets align with the plane of

planet orbits

Oort Cloud Comets were kicked out of thesolar system by the gravity from jovian

planets: random orbits


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What have we learned? How do comets get their tails?

The vast majority of comets donot have tails. Only those fewcomets that enter the solarsystem grow tails. As the cometapproaches the Sun its nucleusheats up. Some of the cometsice sublimates into gas, and theescaping gases carry alongsome dust. The gas and dustform a coma and two tails: a

plasma tail of ionized gas and adust tail. Larger particles canalso escape, becoming theparticles that cause meteors andmeteor showers on Earth.


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What have we learned? Where do comets come from?

Comets that enter the solarsystem come from one of tworeservoirs in the outer solarsystem: the Kuiper belt and theOort cloud. The Kuiper belt

comets still reside in the regionbeyond Neptune in which theyformed during the birth of thesolar system. The Oort cloudcomets are thought to have

formed in the region of thejovian planets, and were kickedout to the great distance of theOort cloud by gravitationalencounters with the planets.


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9.3 Pluto: Lone Dog

or Part of a Pack? Our Goals for Learning

What is Pluto like?

Is Pluto a planet or a Kuiper belt comet?


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Pluto: the exception

Not a gas giant like the other outer planets.

Has a very elliptical, inclined orbit.

By far the smallest planet, and smaller than

several moons.

Has a surprisingly large moon Charon, probably

formed by a huge comet collision with Pluto.


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Pluto will never collide with Neptune because

of a 3:2 orbital resonance.
http://orbits_neptune_pluto.htm/


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What is Pluto like?

1978 discovery of Plutos moon Charon:

Plutos mass from Newtons orbital law.

It has a thin nitrogen atmosphere that willrefreeze onto the surface as Plutos orbit

takes it farther from the Sun.

Pluto is the largest Solar System object thathas not been visited by spacecraft.


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HSTs view of Pluto & Charon


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Brightness variations during eclipsing orbits showed

dirty ice - like comets.


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Is Pluto a planet or a Kuiper Belt

comet?


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comet? Pluto is well beyond Neptune, in the Kuiper

Belt.

Inclined orbit is typical of Kuiper Beltcomets.

Composition is typical of Kuiper Belt

comets, but not any of the other planets.


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comet? Kuiper Belt objects have been found that

approach Plutos size.

Kuiper Belt comets have similar orbitalresonances with Neptune.

Kuiper Belt comets can have moons.

Triton (a captured moon) is even larger thanPluto.

What have we learned?


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What have we learned? What is Pluto like?

Pluto is much smaller than

any other planet, with an orbitmore elliptical and moreinclined to the ecliptic planethan that of any other planet.It is made mostly of ices andhas a very thin atmosphere ofgases that are expected tofreeze onto the surface asPluto moves farther from the

Sun in its 248-year orbit. Ithas a moon, Charon, with aslightly lower density thanPluto, suggesting that Charonmay have been formed in a

giant impact.

Is Pluto a planet or a Kuiper

belt comet?

Whether Pluto should be

called a planet is a matter

of opinion, but its properties

suggest that it is a Kuiper belt

comet. Its composition andorbital properties match those

of other Kuiper belt comets

and do not fit in with the

other planets. It is the largest

known Kuiper belt comet

today, but there may be larger

ones still awaiting discovery.

9 4 C i C lli i ll


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9.4 Cosmic Collisions: small

bodies vs. the planets


Have we ever witnessed a major impact?

Did an impact kill the dinosaurs?

Is the impact threat a real danger or just media

hype?

How do other planets affect impact rates and life

on Earth?


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Have we ever witnessed a major

impact?


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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


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Impact plume rises

high above Jupiters

surface


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Did an impact kill the dinosaurs?


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Mass Extinctions

Large dips in total species diversity in the

fossil record.

The most recent was 65 million years ago,ending the reign of the dinosaurs.

Was it caused by an impact?

How would it have happened?


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Dinosaur fossils

in lower rocklayers

No dinosaur

fossils in theserock layers

Thin layer

containing iridiumfrom impactor


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Iridium - evidence of an impact

Iridium is very rare in Earth surface rocks

but often found in meteorites.

Luis and Walter Alvarez found a worldwidelayer containing iridium, laid down 65

million years ago.


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Comet or

asteroid about

10km in

diameter

approaches

Earth


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An iridium-rich

sediment layer and

an impact crater onthe Mexican coast

65 million years

ago.

shows that a largeimpact occurred

at the time the

dinosaurs died out,


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The Impact Threat:

Real danger or media hype?


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Facts

Asteroids and comets have hit the Earth.

A major impact is only a matter of time: not IF but

WHEN. Major impact are very rare.

Extinction level events ~ millions of years.

Major damage ~ tens-hundreds of years.


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Tunguska, Siberia: June 30, 1908

The ~40 meter object disintegrated and exploded in the

atmosphere


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Meteor Crater, Arizona: 50,000 years ago (50 meter object)


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An object 1km in size would produce a mile-high tidal wave

This slide is placeholder in case you would like to

download and show the movie noted below (notes

field).


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Impacts will certainly occur in the future, and while the

chance of a major impact in our lifetimes is small, the

effects could be devastating.


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The asteroid with our name on it

We havent seen it yet.

Deflection is more probable with years of

advance warning.Control is critical: breaking a big asteroid into

a bunch of little asteroids is unlikely to help.

We get less advance warning of a killercomet


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What are we doing about it?

Stay tuned to

http://impact.arc.nasa.gov
http://impact.arc.nasa.gov/http://impact.arc.nasa.gov/


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How do other planets

affect impact ratesand life on Earth?


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Gravity from

Jovial planets

can influencethe path of

comets and

Asteroids.

They couldprotect us or

steer one in

our direction

Fig 9.20

W J it f lif


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Was Jupiter necessary for life

on Earth?

Impacts can extinguish

life.

But were they

necessary for life as

we know it?



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What have we learned? Have we ever witnessed

a major impact? In 1994, we observed

the impacts of comet

ShoemakerLevy 9 on

Jupiter. The comet had

fragmented into a string

of individual nuclei, so

there was a string of

impacts that left

Jupiters atmosphere

scarred for months



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What have we learned? Did an impact kill the

dinosaurs? We are not certain whether animpact was the sole cause, buta major impact clearlycoincided with the mass

extinction in which thedinosaurs died out, about 65million years ago. Sedimentsfrom the time show clearevidence of an impact, and an

impact crater of the right agehas been found near the coastof Mexico.


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Is the impact threat a

real danger or just

media hype?

Impacts certainly posea threat, though the

probability of a major

impact in our lifetimes

is fairly low.



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How do other planets affect impact rates and lifeon Earth?

Impacts of asteroids and comets are always linked in at

least some way to the gravitational influences of

Jupiter and the other jovian planets. Thesegravitational influences have shaped the asteroid belt,

the Kuiper belt, and the Oort cloud, and sometimes

still help determine when an object is flung our way.

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Asteroid, Meteor, Comets