Section 13: Comets Asteroids and Meteors

Celestial Objects

Comets, Asteroids and meteors

• Used to identity materials and compositions from the formation of the universe

• Transportation of materials to earth

• Potential global catastrophe

Comets

• An icy body from the outer solar system that develops a tail and fuzzy "coma" when it gets close to the Sun

  • Formed beyond the Iceline: making them icy

• Components of a Comet

1. Nucleus: Icy chunk at the center

• Contains dark primitive hydrocarbons and silicates

• Low gravity, low escape velocity → can not hold onto material

2. Coma: The temporary atmosphere of gas and dust that surrounds the nucleus 

• Produced in proximity of the sun (within 3AU)

• Very large 10s-1000s of km in diameter

3. Comet Tails: Formed with a change of orbit and they near the sun releasing volatiles with two distinct tails

1. plasma/ gas or ion tail: 

• Carried straight away from the sun with by streams of ions in the  solar wind emitted by the sun

2. Dust tail: brighter tail 

• Curves as the dust cover the orbit it took

• Pushed  by  radiation  pressure  or  sunlight

• Destination of Comets

1. Impact another object or get tidally ripped apart

2. Speed up and ejected from the solar system forever 

3. Perturbed into a shorter period orbit 

• Cometary Evolution: 

• Solar radiation causes ice and volatile material to sublimate → eroding the nucleus

• Comet will lose most of its volatile material over time and it breaking completely 

• Comets show different regions and eras of the solar system

  • Short-period comets: trace material from the Kuiper Belt (moderately distant, relatively stable region).

  • Long-period comets: trace material from the Oort Cloud (the farthest, ancient reservoir).

Oort Cloud

•  vast, spherical reservoir of icy bodies located far beyond the Kuiper Belt

  • Origin of Long Period comets

    • Have any inclination or direction: Forming a nearly spherical distribution around the solar system

  • At the limit of the sun’s gravitational influence

Formation theory of Oort Cloud

• Oort Cloud comets likely formed closer to the Sun, near the Jovian planets but later gravitational interactions with these massive planets ejected them outward

Perturbations of Oort Cloud

Passing stars or galactic tides disturb the cloud objects sending them into the solar system as comets

Centaurs

• Intermediate point between asteroids and comets in the jovian space 

  • Beyond Jupiter but within neptune

  • Behaviour: 

1. Comet-like activity: with temporary tails when approaching the sun 

2. Unstable orbits: altered by the gravity of giant planets

TNO’s

• Trans Neptunian objects

  • Composition: Icy and rocky bodies — remnants of the early Solar System.

  • Significance: Represent a transition zone between the planets and the distant comet reservoirs.

Kuiper belt Objects (KBOs):

•  subcategory of TNOs

  • Origin of Short period comets: Under 200 year orbital periods 

  • Perturbations: Neptunes gravity perturbs the orbits of KBOs kicking them into the inner solar system appearing as comets

  • Frozen leftovers from planet formation 

Asteroids

are rocky, metallic, or icy bodies that orbit the Sun, primarily found in the main asteroid belt

• Round of potato like shape 

• Formed within the iceline

• Can reach over a km 

  • Would cause a global catastrophe

• Multiple craters and chunks missing 

• Density of an asteroid is less than rocks and metals despite that being its composition → since they are porous and made of multiple rocks 

Asteroids are leftover planetesimals that never merged into planets

• So many collisions due to jupiters gravity it became destructive instead of forming growth

Asteroid belt

•  Found between the gab of mars and jupiter

  • Had a large enough mass to build a terrestrial planet, however, jupiter being a fat ass sucked a lot of its mass in 

    • Not densely packed

Asteroid Capture

•  By different planets or massive objects and become their moons

Trojans Asteroids

• Past the main asteroid belt and closer to Jupiter

  • This and asteroids in the main belt do not concern Earth's safety

Space Guards

• Efforts to watch NEOs

  • NEOs: Near earth Objects (like comets)

  • NEAs: Near Earth Asteroids

    • Asteroids Before Mars: Dangerous to earth

Asteroid orbits today:

•  Avoid unstable orbital resonance that would suck them in

Kirkwood gaps

• Gaps within the asteroid belt where an unstable orbital resonance would be developed 

Families of Asteroids

asteroids that have Similar orbital characteristics, formed from

1. Break up of larger body 

2. Collision of two asteroids

3. Controlled by a resonance with jupiter

Asteroid Classification

1. S-type

2. C-Type

3. M-Type

4. Differentiated

S-type

1.  Stony or silicaceous

• Primitive

• Brighter appearance

• Form from 1Au to 4 AU from the sun

  • Peaking at 2.5

C-Type

1.  Carbonaceous

• Primitive 

• Darker appearance 

• Form from 1.5AU to 5AU from the sun

  • Peaking at 3.5

M-Type

1. Metallic

• From differentiated bodies that are now destroyed

• Shiny and a lot denser

• From from 2AU to 3AU from the sun 

  • Peaking at 2.5

Differentiated

• A rocky body that was once heated enough to partially melt, causing its materials to separate into layers, much like a planet

Vesta an asteroid

• Protoplanet

  • Was differentiated 

  • Was once volcanically active 

  • HED Meteorites: Howardite, Eucrite and Diogenite

    • Match Vesta’s composition so are believed to be from it 

  • As old as the solar system (4.5 billion)

Meteors

• When a meteoroid enters Earth's atmosphere and creates a streak of light

  • Origin: Mainly from comets

    • All meteor showers are comets

  • Observation

    • Seen every 10 mins

    • Pea to golf ball size: burn up and produce a fireball in the atmosphere

    • Larger than a bowling ball → form a meteorite and hit the ground

Meteroid

•  a small (grain- to boulder-sized) particle of debris in the Solar System

“Meteor Shower”

• Actually associated with a comet’s debris trail

  • If  Earth  then  intersects  this  debris  trail of a comet (regardless of the comet still existing), we  see  a  spike  in  meteor  activity that  we  call  a  meteor  shower

  • Parallel Paths: the direction of material falling onto earth

Radiant

• the from which the materials come form seeming like its only from one location in the sky

  • Named based on the constellation they were infront of 

Meteorite

 the parts of the meteor that survives and hits the ground

• Origins: From asteroids

  • Comets can not survive passage through earths atmosphere since its made of ice and it will melt

• Finding meteorites

1. Watching them fall from the sky 

2. Dark stones on top of stone or ice 

• Meteorite CLassification: very dense

1. Irons 

2. Stones

3. Stony irons 

4. Lunar and Martian: from impactors on either the moon or mars and the material ejected from it 

5. Primitive/ Chondrites: Come from asteroids

6. Differentiated/ Achondrites: come  from larger  parent  bodies  that underwent  some differentiation

Carabancous meteorites

• From C-type asteroids 

  • Contain equal amounts of right and left handed molecular symmetry

    • refers to the chirality of molecules, where a chiral molecule is non-superimposable on its mirror image

Widmanstätten Pattern

• FOund only on meteorites

  • A  cut  iron  meteorite, briefly  washed  with  strong  acid

  • Crystals  of pure  iron  nickel  alloy  that  do not  occur  on  Earth  because they  only  occur  under slow  cooling  condition (millions of years)

Meteorology

• Another word for “atmospheric science”; has only little to do with meteors