Amber Reed Notes

Chapter 9:

Asteroids, comets and dwarfs planets: Their nature,orbits and impacts
9.1
Why is there an asteroid belt?

Discovering asteroids:
-asteroids leave trails in long-exposure images because if this orbital motion around the sun
Asteroid fat s:
-asteroids are rocky leftovers of planter formation
-largest is Ceres the diameter is ~1000km
-there are 150,000 listed in catalogs and probably over a millions with diameter>1km
-small asteroids are more common than larger ones
-all asteroids in the solar system wouldn't add up to even Smallest terrestrial planet 
-astroids are cratered and  not round

Asteroids with moons:
-some large asteroids ave thief own moons
-asteroid Ida has tiny moon naked Dactyl

Asteroid orbits:
-most asteroids orbit in a belt between Jupiter and mars 
-Trojan asteroids follow Jupiter's orbits
-orbits of near-Earth asteroids cross Earth's orbit

Orbital resonances :
- asteroids in orbital resonance with Jupiter experience periodic nudges
-eventually those nudges move asteroids out of resonant orbits leaving gaps in the belt 

Origin of assorted belt
-rocky plant estimates between mars and Jupiter did not accrete into a planet

How are meteorites related to asteroids?

Origin of meteorites  :
-most meteorites are pieces of asteroids

-Meteorites is a air k from Alsace that falls through earths atmosphere
-meteor is the bright trail left by meteorite

Meteorite types:
-Primitive: unchanged in composition since they first formed 4.6 billion years ago
-Processed:younger have experienced processes such as volcanism or differentiation 

Primitive meteorites :
-Stony primitive meteorite is made of rocky material embedded with shiny metal flakes
-Carbon rich primitive meteorite also is rocky but dark carbon compounds and small whitish  spheres

Processed  meteorites :
-metal rich Processed meteorites are made of iron and other metals that came From Shattered asteroids core
-rocky processed meteorite Resembles volcanic rocks found on earth

Meteorites from moon and mars:
- a few meteorites arrive on earth form moon and mars
-composition differs from the asteroid fragments 
- this is a cheap( but slow) way to acquire moon rocks and mars rocks 

9.2
Comets

How do comets get their tails?

Comet facts:
-formed beyond the frost line, comets are icy counterparts to asteroids
-the nucleus of a comet is Ike a " dirty snowball"
-most comets do not have tails
-most comets remain perpetually for sun in outer solar system
-only comets that enter in inner solar system grow tails 

Nucleus of comet:
-a "dirty snowball"
-source of material for comets tail

Anatomy of a comet:
-coma is atmosphere that comes from heated nucleus 
-plasma tail is gas escaping from coma, pushed by solar wind
-dust tail is pushed by photons

Deep Impact:
Mission to study nucleus of comets Tempel 1
-projectile hit surface on July 4, 2005
-many telescopes studied aftermath of impact 

-Comets eject small particles that follow the comet around in its orbit and cause meteor showers when Earth crosses the comet's orbit 
-Meteorite in a shower appear to emanate from the same are of sky because of earths motion through space 

Where do comets come from?

-only a tiny number of the comets enter the inner solar system; most stay far from the sun
Oort Cloud:comets on random orbits extending to about 50,000 AU
Kuiper Belt: comets on orderly orbits at 30-100AU in disk of solar system 

How did they get there?
-Kuiper belt formed in the Kuiper belt
-flat plane aligned with the plane of planetary orbits
-orbiting in the same direction as the planets

9.3 
Pluto: lone dog no more

How big can a comet be?
Pluto's orbit:
-pluto's orbit is tilted and significantly elliptical
-neptune orbits three times during the time Pluto  orbits twice

Is Pluto a planet?
-much smaller than the eight major planets
-not a gas giant lie the outer planets
-has an icy composition like a comet
-has a very elliptical inclined orbit
-Pluto has more in common with comets than with the eight major planets 
Icy bodies:
-there are many i y objects like Pluto in ellitpcal ink end oribits beyond Neptune
-the largest ones are mom arable in size to earth's moon

In 2006 the international astronomical union decked to call Pluto and objects lie, it " dwarf planets"

What are Pluto and other large objects of the Kuiper belt like?

-It's largest moon, Charon us nearly as large as Pluto itself 
-Pluto is very cold (40k)
-Pluto has a thin nitrogen atmosphere that refreezes onto the surface as pluto's orbit takes it farther from the sun

Other Kuiper Belt Objects:
- most have been dies rovers very recently so little is known

9.4
Cosmic collisions:small bodies vs the planets:

Have we ever witnessed a major impact?

-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 a previous encounter with Jupiter  

Did an impact kill the dinosaurs?

Mass extinctions :
-fossil record shows occasional large dips in the diversity of species:mass extinctions
-the most recent was 65million years ago, ending the reign of the dinosaurs 

Iridium: evidence of an impact :
- Iridium  is very rare in earth surface rocks but is often found in meteorites
-Luis and Walter Alvarez found a worldwide layer containing iridium laid down 65 million years ago probably by a meteorite impact
-dinosaur fossils all lie below this layer

Iridium layer:
-no dinosaur fossils in upper rock layers
-thin layer contain ing the rare elect iridium 
-dinosaur fossils in lower rock layers 

Consequences of an impact:
-a meteorite 10km in size would send large amounts of debris into the atmosphere
-debris would reduce the mount of sunlight renting Earth's surface
-the resulting climate change may have caused mass extinction

-geologists found a large subsurface crater about 65 million years old in Mexico
-comet or asteroid about 10km in diameter approaches Earth
-size if crater suggest impacting object was ~10km in diameter
-impact of such a large object would have ejected debris high into Earth's atmosphere
 
Is the impact threat a real danger of just media hype?

-asteroids and comets have hit Earth
-major impact is only a matter of time:not IF but WHEN
- major impacts are very rare
-extinction level events~millions of years
-major damage ~tens to hundreds of years 

the Asteroid with our name on it:

-we haven't 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 killer comet

How do other planets affect impact rates and life on Earth?
Influence of Jovian planets:
-the gravity of a Jovian planet (especially Jupiter) can redirect a comet 
Jupiter has directed some comets towards Earth but has ejected many more into the Oort Cloud 

Was Jupiter  necessary for life on Earth?
-impacts can extinguish life

Amber Reed