Week 10

Question 1

Space Junk

Answer 1

• Uncountable amounts of ice, rock, dust, and other debris float between planets
• Earth is constantly being bombarded with debris, most of which burns up in the atmosphere
• Meteor Impacts cause incredible amounts of damage
• Earth is at constant threat from impactors, though the occurrence of these catastrophic meteor impacts is very low
  The figure right shows a few important meteor impacts in pink, and the amount of energy released by each

Question 2

The Asteroid Belt

Answer 2

• Located between Mars and Jupiter, the Asteroid Belt produces most of the large space debris impacting Earth
• Mostly rock that wasn’t accreted into a planet when the Solar System was forming
• Occasionally, the strong gravity of Jupiter will pull a large, rocky meteoroid from the Asteroid Belt and fling it in any direction
• Many of these asteroids are made of some of the oldest, most primitive material in the universe
• These space-rocks are called Chondritic Meteorites
• The defining feature of these meteorites are chondrules, which are small beads of glass-like rock

Question 3

Near Earth Objects

Answer 3

• Sudbury, ON is a city famously built within a huge, 200km-diameter meteor crater
• This is the largest meteor crater on land anywhere on Earth, produced by a meteorite 10 – 16km across that struck Sudbury 1.85 Gyr ago
• The complex impact structure resultant of the catastrophe has driven a booming mining and tourist industry for decades

Question 4

Comets

Answer 4

• Large chunks of ice and dust
• The Oort Cloud marks the outer reaches of our Milky Way galaxy, where estimates of a trillion comets orbit
• Comet Hale-Bopp passed near Earth in 1997, and was 40km wide, one easily able to decimate the planet
• Halley’s Comet was one of the first to be recognized, thanks to its cyclical orbit that passes Earth every 74 - 79 years
• We’ve found that almost any object weighing over 1g and is less than 1mm across is able to impact Earth without burning up in the atmosphere!

Question 5

Impacts and Craters

Answer 5

Most material hurtling through space is moving at high-velocity, so when material moving ~1200km/h hits the atmosphere, the friction of the impact with the atmosphere produces a deafening sonic boom

Question 6

Impactor

Answer 6

• Varying impactor sizes and speeds can affect the morphology, or shape, of impact craters
  As an object impacts the Earth, the kinetic energy of the impactor is transferred to the ground, allowing the impactor to bury itself before a large shockwave ejects material away from the impact
• Craters are often 15-20x larger than the impactor producing them

Question 7

Ejecta Blanket

Answer 7

The ejecta blanket is thickest near the rim of the crater, overlaying darker, older material with this new, light-colored dust layer

Question 8

2 Types of Craters

Answer 8

Simple Craters
Complex Craters

Question 9

Simple Craters

Answer 9

Less than 4km diameter, these deep bowl-like structures are well-rounded and show overturned rocks near the rims

Question 10

Complex Craters

Answer 10

More than 4km diameter, these produce much larger rims due to crater rims slumping inwards, and produce central peaks, or regions of uplift

Question 11

Brecciated Rocks

Answer 11

Brecciation indicates these rocks were broken violently, and that resultant high-temperatures caused slight melting of the rocks

Question 12

Impact Identifiers

Answer 12

Shatter Cone
Shocker Minerals
Tektites

Question 13

Shatter Cone

Answer 13

The shock wave from impact is often enough to alter rocks in strange ways, such as how shatter cones show converging fractures indicating the direction the shockwave was travelling

Question 14

Shocked Minerals

Answer 14

Mineral crystals such as quartz can be shocked, changing their physical appearance; as well, different minerals can form, such as how quartz will alter to coesite and stishovite under high-stress

Question 15

Tektites

Answer 15

Small spherules made of glassy rock, indicating very strong melting of a rock and quick cooling to a new material

Question 16

Meteorite Classification

Answer 16

Stoney Meteorites
Stoney-Iron Meteorites
Iron Meteorites

Question 17

Stone Meteorites

Answer 17

(Aerolites) This class of rocky meteorite contains a low metal content; composing ~92.8% of all meteorites
- Chondrites: a further breakdown of stoney meteorites, chondrites are meteorites containing silicate minerals and chondrules
- Achondrites: these are chondrites containing silicate minerals and no chondrules

Question 18

Stoney-Iron Meteorites

Answer 18

• (Siderolites) These meteorites are 50% silicate rock and 50% nickel and iron; make up ~1.5% of all meteorites
• The composition is most like the material at Earth’s Core-Mantle boundary

Question 19

Iron Meteorites

Answer 19

• (Siderites) These are primarily iron and nickel, though can contain other rare metals; makes up ~5.7% of all meteorites
• This composition is almost certainly the metallic core of a large, differentiated body

Question 20

Chondrules

Answer 20

• Chondrules are small spherules found in chondrites
• These crystals represent some of the oldest material in the solar system, dating back to nearly the “Big Bang” itself!
• Most are ~0.5 – 1.5mm, with a glassy texture representing very rapid cooling
• The composition of chondrules is quite unlike the average composition of the chondrites they’re found within

Question 21

Near-Earth Objects (NEOs)

Answer 21

• Any object that passes close to Earth, either in a cyclical or irregular orbit, is deemed a ‘Near-Earth Object’
• We use the term PHA (Potentially Hazardous Asteroid) for asteroids that:
• A) is at least 150m in diameter; and,
• B) comes within 0.05AU (7,480,000km) of the Earth
• Of all the NEOs identified, more than 900 asteroids are more than 1km diameter
• An impactor this large is believed to easily decimate ~25% of the world’s population

Question 22

Earth’s Near-Misses

Answer 22

• Earth has been bombarded with impactors over its lifetime, some of cataclysmic size
  ~4.3 – 4.5Gyr ago, an object the size of Mars slammed into Earth, rupturing the planet to its core and ejecting large volumes of material into space
• Some material was caught in Earth’s orbit, which coalesced into the Moon
• 4179 Toutatis passes Earth regularly and closely
• The orbit of Toutatis and Earth are very similar, though computer projections do not forecast a collision anytime soon
• If Toutatis were to have its orbit altered by gravity or a collision with another object, it could be thrown towards Earth
  It is believed Toutatis has the killing potential of the KT Boundary Impact, which killed 75% of life on Earth and produced a devastating nuclear winter