EX L3: Impacts and Mankind

Question 1

What material could generally impact our planet?

Answer 1

Comets, asteroids

Question 2

What are comets?

Answer 2

Material left over from the formation of the Solar System. Composed of icy material and other debris. (“dirty snowballs” in space) As comets travel towards the Sun (as they fracture and disintegrate), the ices vaporize producing the comet’s tail (hundreds of millions of km long)

Question 3

How often does comet Halley come into view of the Earth?

Answer 3

Every 74-79 years

Question 4

When was Hale-Bopp comet visible? When will it return again?

Answer 4

It was visible in 1997. It will return in 2380 years.

Question 5

What is the Leonid Meteor Shower. How is it produced?

Answer 5

It is an annual event which is visible in Canadian skies in November. This rain of “shooting stars” is produced as Earth passes through the debris left by comet Temple-Tuttle. Temple-Tuttle orbits around the sun.

Question 6

What are the two comet “stores” in the Solar System?

Answer 6

The Kuiper belt and the Oort cloud

Question 7

What is the Kuiper belt? How many comets does it have?

Answer 7

It exists in an area from about the orbit of Neptune to about 50 au’s out (1au = 150 million km). It has around 1 billion comets greater than 5 km in diameter.

Question 8

What is the Oort cloud? How many comets does it contain?

Answer 8

a cloud of comets that exists way beyond the Kuiper belt and is only weakly associated with our Sun. It contains more than 200 comets with a diameter greater than 500km. It also has many smaller comets.

Question 9

What were comets possibly responsible for bringing into Earth?

Answer 9

They may have brought much of the water and some of the organic compounds that would lead to the development of life on Earth.

Question 10

Where are asteroids mainly found?

Answer 10

in a belt between the orbit of Mars and Jupiter.

Question 11

_______ may represent the material that might have formed another planet early in the history of the Solar System if it were not for the gravitational effects of Jupiter.

Answer 11

Asteroids

Question 12

Describe the range of asteroids that may be out there.

Answer 12

Some are solid, rocky to metallic. Other are little more than “rubble piles” in space.

Question 13

Collisions between ____ could potentially cause them to be redirected into Earth-crossing ____.

Answer 13

asteroids; orbits

Question 14

Describe the asteroids currently in Earth-crossing orbits.

Answer 14

A few are over 500km in diameter. About 1000 have diameters greater than 30 km, and 1 million have diameters over 1 km.

Question 15

How many objects enter our atmosphere every 24 hours? Describe them.

Answer 15

100 billion. Most burn out at a distance of 60 km above the Earth’s surface. They usually travel around 11 to 30 km/s (at these speeds, atmosphere acts like a brick wall. If object enters at a shallow angle, it may skip like stone upon a pond and fly back out to space)

Question 16

Define meteoroid

Answer 16

small rocky, iron or icy debris flying in space. From microns to 1 meter in size.

Question 17

Define asteroid

Answer 17

A Solar System body larger than a meteoroid, smaller than a planet, from 1 meter to hundreds of kilometers. No tail.

Question 18

Define meteor

Answer 18

small sand-to-dust sized meteoroids that emit light in the mesosphere and stratosphere. A large meteor may break apart in aerial burst or crash into Earth.

Question 19

Define meteor showers

Answer 19

Event that occurs during the same time each year when the Earth passes through a region having a great concentration of debris, such as particles left by a comet. From Earth, it looks like meteors radiate from the same point in the night sky.

Question 20

Define fireball

Answer 20

A meteor brighter than the planet Venus.

Question 21

Define bolide

Answer 21

a large fireball meteor that explodes in the atmosphere

Question 22

Define meteorite

Answer 22

a fragment of meteoroid or an asteroid that survives passage through the atmosphere and hits the ground. From a few grams to several dozen of tonnes heavy.

Question 23

Which layers of atmosphere do meteors emit light?

Answer 23

Mesosphere and stratosphere

Question 24

How can we guess that our planet suffered multiple impacts?

Answer 24

By observing the craters on the moon and nearby planets (Mercury)

Question 25

Why is the evidence of early impacts on Earth missing?

Answer 25

Processes of erosion and active plate tectonics.

Question 26

What did some think about Meteor Crater (in Arizona) and the craters on the moon?

Answer 26

they were extinct volcanoes, not impact craters.

Question 27

Who is Gene Shoemaker? What did he do?

Answer 27

A founder of planetary science; correctly deduced the nature of craters. He studied features such as the material of ejecta, shocked quartz, and chemical anomalies. It was proof they came from extraterrestrial origins

Question 28

What is the Manicouagan impact crater? How old is it? How big is it now? How big was it before?

Answer 28

It is a significant impact crater in Northern Quebec. It formed ~214 years ago in the Late Triassic. 70km in diameter, but was once 100km before glacial erosion.

Question 29

What other craters is the Manicouagan impact thought to be associated with?

Answer 29

The Saint Martin Crater in Manitoba (40km), Rochechouart Crater in France (25km), and 2 others. Not associated with a major mass extinction event, however.

Question 30

Which two researchers produced the worrying data of mass extinctions in 1984? What did they conclude?

Answer 30

D. Raup and J.J. Sepkoski. They analyzed the number of mass extinctions during the Phanerozoic, and concluded that every 25 million years there was severe stress on the biosphere, sometimes associated with a mass extinction event. Peaks in the extinction rate occur at 26-30 million year intervals.

Question 31

Why is the severe stress Raup and Sepkoski found related to impacts? What may be the culprit for this stress?

Answer 31

No known terrestrial geological process that could cause this frequency of problems for the biosphere. So they suggest it’s an extraterrestrial source, especially comets in the Oort cloud.

Question 32

Describe Raup and Sepkoski’s hypothesis.

Answer 32

every 25-26 million years, something shifts the Oort cloud, causing some comets to fall in towards the Sun, and possibly impact the Earth.

Question 33

What are the hypotheses proposed to account for the “Raup-Sepkoski” periodicity? Describe each.

Answer 33

1. Nemesis-Companion Star: Sun has a companion star beyond the outer limits of Solar System, whose orbit brings it close to the Oort cloud every 25 million years. Gravitational effects of this close pass could cause comets to fall into the inner Solar System. If it were a red dwarf star or black hole, it would be difficult to detect. None have been found yet.
2. Planet X: an astronomical body that causes shifts in the Oort cloud as it orbits around the sun. The body is a planet lying within the bounds of the Oort clouds but outside the Kuiper belt. No evidence found yet.
3. Movement Through the Galactic Plane:
   In addition to traveling around the galaxy, the Solar System is also moving up and down through it. Every 25-26 million years we pass through the densest part of the galaxy, which contains a higher number of stars and also the most gravitational effects. This movement through the dense part of the galactic plane is responsible for the Oort cloud shifting and causing a potential impact related to biosphere crisis.

Question 34

How many years since we passed the densest part of the galaxy? Why is this dangerous?

Answer 34

Approx. 1 million years ago. It takes comets from the Oort cloud 1 million years to reach inner Solar System. If Raup and Sepkoski are correct, we have increased chance of comet impacts.

Question 35

Why is Raup and Sepkoski’s hypothesis controversial?

Answer 35

Many scientists criticize the data, saying that spacing between biosphere crises is not always consistent. They were also critical of the statistics Raup and Sepkoski used in identifying the extinction events.

Question 36

Describe the Tunguska near miss.

Answer 36

June 30 1908: large explosion about 8km above surface due to extraterrestrial object breaking up in the atmosphere. People were knocked off their feet 480km away. Shock wave from blast traveled around Earth twice. It was a fragment of comet Encke, which was passing close by the Earth at the time. Over 80 million trees knocked over area of 2150km^2. Tunguska’s area of devastation can be compared to area of Washington, D.C. or Metro Vancouver.

Question 37

Describe Comet Shoemaker Levy 9

Answer 37

In 1994, the comet was fragmented by Jupiter’s strong gravity and crashed into Jupiter in explosions between 16-22 July 1994.

Question 38

Did the Tunguska event leave a crater?

Answer 38

No. It exploded 8km in the atmosphere.

Question 39

What is the most important factor in preventing an impact on Earth?

Answer 39

TIME. To know which objects are potential risks, time to make plans and build what is needed for defense.

Question 40

What does the Spaceguard survey or Planetary Defense at NASA do?

Answer 40

It finds and analyzes space objects with diameters greater than 1km.

Question 41

90% of potential impactors are ______ or _______ with another 10% being _______.

Answer 41

near-Earth asteroids

short-period comets

intermediate or long period comets (greater than 200-year return periods)

Question 42

Describe Asteroid 2005 YU55

Answer 42

It’s a good example of what threats of impacts we’re faced with near-Earth objects. It was discovered by NASA in 2005, and if it were on a direct course to Earth, we would only have 6 years to diffuse the threat.

Question 43

What’s the Torino Scale?

Answer 43

Scale/method for categorizing impact hazards. Measures the potential threat of Near-Earth objects (NEO’s) on scale of 0-10. (colors: White, Green, Yellow, Orange, Red)
It can also be correlated between amount of KE, the approx. diameter of meteor, and the probability of impact.

Question 44

What are some impact mitigation strategies proposed? What’s the most important factor in those strategies?

Answer 44

TIME is most important. Need long warning period of potential impact.

1. Fragmentation
2. Sudden Orbit Adjustment
3. Steady State Orbit Adjustment

Question 45

Describe fragmentation as a proposed impact mitigation strategy.

Answer 45

Destroy an incoming impactor with nuclear weapons.

Downfall: may not work for metallic bodies. Even after fragmentation, fragments produced may still impact planet.

Question 46

Describe Sudden Orbit Adjustment as a proposed impact mitigation strategy.

Answer 46

Explode a nuclear warhead in front or on the surface of an approaching body to adjust its trajectory so it is no longer an impact threat. Still an unpredictable solution.

Question 47

Describe Steady State Orbit Adjustment as a proposed impact mitigation strategy.

Answer 47

Requires more warning time, but can permanently adjust orbit of approaching object predictably.

a. Attach chemical or nuclear rocks to object to gently it out of the way.
b. deploy robot “mass drivers” to land on surface to excavate material and launch it off surface (becomes a form of propulsion. slowly changes the approaching object’s trajectory).
c. Ablation systems: irradiate the surface with lasers or focus sunlight with large mirrors. Gases produced by vaporization acts as propellant to adjust trajectory.
d. Attach large solar sails. Large reflective mirrors that catch charged particles from the Sun (solar wind) and act like giant sails in space.

Question 48

Define ablation

Answer 48

removal of material from the surface of an object by vaporization

Question 49

Define air burst

Answer 49

detonation in the atmosphere

Question 50

Define black hole

Answer 50

region of space with extremely powerful gravitational field

Question 51

Define galactic plane

Answer 51

area of galaxy most densely packed with stars

Question 52

Define galaxy

Answer 52

massive gravitationally-bound collection of stars and other matter

Question 53

Define gravity well

Answer 53

gravitational field produced by large body; other space bodies can ‘fall’ into this well

Question 54

Define impactor

Answer 54

anything from outer space that can impact Earth’s surface

Question 55

Define Kuiper Belt

Answer 55

a ring of small Solar System objects including comets

Question 56

Define mass driver

Answer 56

process of removing material of a large space body to cause the body to move

Question 57

Define Near-Earth Object (NEO)

Answer 57

Any Solar System object in an orbit that passes close to Earth

Question 58

Define Nemesis

Answer 58

hypothetical companion star or black hole to our Sun

Question 59

Define Oort Cloud

Answer 59

spherical cloud of comets that surrounds the Sun at about 1 light year distance

Question 60

Define Planet X

Answer 60

hypothetical planet proposed to exist way beyond the orbit of Pluto

Question 61

Define Red Dwarf Star

Answer 61

a star smaller and cooler than the Sun

Question 62

Define Solar System

Answer 62

the Sun and all the other celestial objects gravitationally bound to it.