The Cosmic Perspective Chapter 12 Lecture 28

Which group of objects orbit farthest from the sun

The Oort Cloud

Comets

Balls of Dust and Ice

Comet Parts

Nucleus

Plasma Tail

Dust Tail

Debris Tail

Nucleus

Solid Center

Plasma Tail

Ionized gas blown by solar wind away from the sun

Solar WInd

Combination of magnetic fields and particles

Dust Tail

Small Particles pushed by pressure of Sunlight

Debris Tail

Larger Particles. Not affected by pressure of sunlight

The life of the comet

Cold just nucleus far from the sun

Warms and forms coma and tails near the sun

The Fate of Comets

Lose all ices - Not a comet anymore

Ejected from Solar System by Jupiter's Gravity

Crash into the sun and planets

Where do comets come from

Kuiper Belt and Oort Cloud

Kuiper Belt

Short period comets in forward orbits

Oort Cloud

Long period comets random orbits. Forward, backward and in between

The distance Oort Cloud of Comets was created

From Close Encounters with the Jovian Planets that flung icy planetesimals out randomly

How Big an Impactor makes a typical shooting star

Sand Grain

An Impact Killed the Dinosaurs". This idea was not widely accepted by scientists at first, but now it is. Why did they change their minds?

The evidence and models matched better and Better

Sedimentary Rock Layer

Iridium and Other Elements

Grains of Shock Quartz

Spherical Rock Droplets

Soot from Forrest fires

Spherical Rock Droplets

Form when drops of molten rock cool and solidify in air

What makes iridium rare in metal rocks

Dense Metal due to large abdundance

Grains of Shock Quartz

Requires very high pressure

About how big was the impactor that killed the dinosaurs?

10 km across

impacts and Mass Extinctions on Earth

debris in atmosphere blocks sunlight; plant die...animals starve

poisonous gases form in atmosphere

Other ancient 'mass extinctions' show an impact cause

Atmospheric Explosion of Small Crater

Takes around one year

Impactor size is from 30 meter to 1 kilometer

Tsunamis, Widespread Devastation, Climate Change

Happens 1 million years

Impactor size from 1 to 10 kilometers

Mass Extintion

Happens every 100 million years

Impactor size from 10 to 100 km

About how often does a 1km object strike Earth, and what happens?

~a million years, tsunamis, climate change

How would things be different if jovian planets had never existed?

Asteroid belt would have formed a planet

•Icy planetesimals not flung into Oort cloud or towards the planets

•Kuiper belt comets not nudged inwards

•Kuiper belt comets not nudged inwards

Perhaps no "hydrogen compounds" for terrestrial planets? Fewer impactors?

Jupiter now protects us from many impactors -but it nudged them our way in the first place!

Pluto

1200 km radius iceball

Probably Looks Most Like Triton, the backwards moon of neptune

How is PLuto different from Kupier belt comets and why?

1

2

3

4

5

Pluto and Neptune

orbit most elliptical and inclined of any planet.

•Orbital resonance between the two prevents collision! but no tidal heating

•>100 other Kuiper belt objects also in orbital resonances with Neptune.

Many 'Plutinos' share its orbit!!!

sublimation atmosphere varies

Eris

Goddess of Discord

Bigger than Pluto; has a moon

•Fits in well with Kuiper belt theories...

Ceres

Largest Astroid

500 km radius

Triton

Neptune's Captured Moon

1350 km Radius

Kuiper Belt object

650 km radius