Impacts 4 Flashcards
Meteoroids
- small rocks (< 1m)
- from asteroid belt
- Meteors as enter Earth’s atmos
- Meteorite if survives entry as intact rock and hits earth
Bolides
a type of Meteoroid, fireballs that explode in the atmosphere
Asteroids
- large rocks (> 1m)
- smaller than a planet
- from asteroid belt
Comets
- Rock with ice
- leftovers from planet formation
- near sun, has a tail of gas/dust particles
- from Kuiper Belt or Oort Cloud
Why do impact craters appear rare on Earth compared to the moon?
- The moon protects the Earth by blocking many incoming asteroids and comets
- rain/wind/ice erodes the craters on Earth
- Plate tectonics and volcanism remove evidence of craters
- Earth’s atmosphere shields cuz most impactors burn up before impact
moon has larger surface area but that doesn’t rlly mean more meteors will hit
Describe the raup and sepkoski hypothesis
1984
- suggested there might be ~25 Myr cycle in impacts and extinctions
- due to gravitational disruption of the Oort Cloud caused by…
- Nemesis
- Planet 9
- Moving through Galactic Plane
- Coincidence?
-> NASA thinks there is no cyclicality in past extinctions
List and describe some recent impacts and near misses
- Tunguska Russia - 1908 June 30
- Chelyabinsk Russia - 2013 Feb 15
- Asteroid 2019OK - 2019 July 25
- Asteroid 2005YU55 - 2011 Nov 8
- Eastern Mediterranean Event - 2002 June 6
- Asteroid 99942 Apophis
- will approach Earth on April 13, 2019
Briefly describe what is being done right now (impacts)
- Torino Scale
- 5 and above is threatening - Spaceguard Survey
- tracks large objects near earth - NEO Surveyor spacecraft to be launched 2026
- infrared telescope to survey for danger rocks - Double Asteroid Redirection Test - 2022
- an impactor crashed into Dimorphos and altered the orbit by a little
List possible mitigation strategies
- Fragmentation
- Rapid Orbit Adjustment
- Gradual Orbit Adjustment
- Ablation
- Ride the solar winds
Describe the Asteroid Belt
- btwn Mars and Jupiter
- rocky/metallic rocks, some are dwarf planets like Ceres
- four largest asteroids:
Ceres Vesta Palla Hygiea
Kuiper belt
- just past Neptune orbit
- larger than asteroid belt
- ices like water, methane, ammonia
- more dwarf planets like Pluto
- some of our moons are thought to have originated here
Oort Cloud
- 1000x farther from the sun. halfway to Alpha Centauri
- edge of solar system
- mostly ices
Meteor influx
- logarithmic relationship between obj size and avg recurrence time
- 100 billion meteoroids enter earth everyday
- on average: 10km obj impact earth every 100 Million yrs
-> smaller = more common, larger = less common
impacts on earth vs moon
190 compared to like 9k
Earth: near northern hemisphere, all on land
Shoemaker’s Hypothesis
- sudden geological changes can arise from asteroid strikes
- over geological timescales, asteroid strikes are common
- impact craters form large, circular structures
-> associated with ejecta, shocked quartz, iridium
What crater did the shoemakers study?
Ries Crater in Germany
- building stone was suevite (rock mixed with partly melted materials)
- 14 Ma created by 1.5km asteroid
What crater did the shoemakers study?
Ries Crater in Germany
- building stone was suevite (rock mixed with partly melted materials)
- 14 Ma created by 1.5km asteroid
R&S Nemesis
companion star
- Sun has nemesis beyond Oort Cloud, orbit comes close ever 25 Myr
- Gravitational effects kick comets to inner solar system
- no evidence at all
R&S Planet 9
Distant planet far beyond Neptune shift the Oort Cloud as it orbits sun
- no evidence, probably unlikely
R&S Galactic Plane
Solar system orbit centre of galaxy
- galaxy has thickness of stars/stuff
- move through dense part may disrupt Oort cloud
R&S Coincidence?
- dating of extinctions and impacts not always accurate
- spacing not always consistent
- probably more impacts we didn’t know about cuz oceans
- other factors also cause extinctions
Civilization ending impacts occur randomly every ~___ yrs
1 million
Recent impacts: Tunguska, Russia
1908 June 30
- no impact crater or material found, could’ve bounced back out
- air blast of smt with diameter 70m
- largest historical impact that levelled 3km of forest, sent a shockwave around Earth twice
Recent impacts: Chelyabinks Russia
2013 Feb 15
- bolide
- 20m diameter asteroid explode in atmosphere 30km above ground
- entered atmosphere at 19km/s from direction of sun
Near misses: Asteroid 2019OK
2019 July 25
- 100m diameter
- passed within 73k km of Earth (1/5 moons orbit, 2x orbit of satellites :O)
Near misses: Asteroid 2005YU55
2011 Nov 8
- 360m diameter
- passed within 325k km (4/5th of moon’s orbit)
- discovered 6 yrs before passed earth
Near misses: Eastern Mediterranean Event
2002 June 6
- meteor air burst above Mediterranean Sea in Europe
- unknown obj, no fragments found
- similar to small nuclear bomb
Future event: Asteroid Apophis
will approach Earth on April 13, 2029
- 370m diameter
- will pass within 32k km (closer than satellites!)
- but NASA doesn’t think it will hit earth
Comet Shoemaker Levy 9
1993
discovered by shoemaker and David levy
- Jupiter gravity broke comet apart in 1992 and collided 2 yrs later
- if this hit earth, would’ve wiped out life to microbial level
- ppl started taking impacts very seriously
What acts as a cosmic vacuum cleaner
Jupiter, because it has large gravitational pull
Impact hazard is unique cuz
potentially most devastating but can be entirely avoided
-> Important factor is time
Mitigation - Fragmentation
blow asteroid up
- landing on an asteroid (possible), drilling into it
- risk of multiple impacts
- takes long time to prepare
Mitigation - Rapid Orbit Adjustment
- smash a nuclear warhead / projectile into asteroid
- needs a warning period
Mitigation - Gradual Orbit Adjustment
- excavate material off the asteroid
- use chemical. electric, nuclear propulsion
- needs warning period
- predictable method
Mitigation - Ablation
- flash-vaporize away the asteroid mass or deflect its path
- focus sunlight on surface of asteroid / use lasers
- need satellite in orbit around asteroid (possible)
Mitigation - Ride solar winds
- install solar sails on asteroid
- radiative pressure from sunlight will deflect it
- requires very long warning time
- NASA scout mission will test in 2023
Mitigation - Reality
all methods require research, lots of warning time, and lots of money
we have other problems to deal with…
