SpaceImpacts

50 %
50 %
Information about SpaceImpacts
Travel-Nature

Published on March 12, 2008

Author: Joshua

Source: authorstream.com

ESCI 108 - Lecture #17 Bill Leeman - Extraterrestrial Impactors:  "The Aztecs had believed the world would end in one of four ways: earthquake, fire, flood, or jaguars falling from the sky. Here there would be no fire. Nor earthquake nor flood, now that he thought of it. Leaving only the jaguars ... " - Kim Stanley Robinson, Red Mars, p. 14 ESCI 108 - Lecture #17 Bill Leeman - Extraterrestrial Impactors Types/sources of space objects:  Types/sources of space objects Planets - inner rocky, outer ice & gas types Asteroids (remains of rocky planets) sources of many rocky or metallic meteoroids Oort cloud sources of many comets (‘dirty snowballs’) Meteors (‘shooting stars’) vs. meteorites or cosmic dust Fig. 15.1:  Fig. 15.1 Slide5:  Orientale multi-ring basin, Moon (note smaller, later impact craters) 1300 km Slide6:  Manicouagan impact crater, N. Quebec (formed ca. 214 Ma) 75 km Slide7:  Orbits of Apollo and Amor asteroids intersect Earth’s orbit Slide8:  Orbit of Halley’s comet Slide9:  Numbers of Near-Earth Asteroids (NEAs) Slide10:  Inputs from space Study questions:  Study questions Why are impact scars so well preserved on the Moon (and other rocky planets such as Mercury or Venus), whereas they are rather inconspicuous and seemingly rare on the Earth? How would you distinguish craters formed by meteorite impact from those that are volcanic in origin? Roughly, how many impact sites currently are recognized on the Earth's surface? Where are they concentrated, and why? What are the differences between meteorites, asteroids, and comets? Why do comets have tails, and why do they always point directly away from the Sun? Assuming they have the same diameter, what are the relative impact hazards posed by impacts of these types of objects? Where do each of these types of objects likely originate? (multiple possibilities for some) How large must a meteoroid be (give diameter in metric units) for it to pass effectively through the atmosphere without burning up? Draw a cross section of an impact crater produced by a 10 km-diameter asteroid that hits the Earth's surface with a velocity of 20,000 mph (12,000 kph). What is the so-called "iridium anomaly" and what is its significance at the 'K-T boundary'? More study questions:  More study questions Make a comprehensive list of evidence that would convince scientists that a specific area (e.g., Chicxulub) was the site of an ancient asteroid impact. Describe a reasonable sequence of life-threatening events that might accompany the collision of a 10 km-diameter asteroid with the Earth (what would the last dinosaurs have experienced)? There are many large impact craters on Earth whose formation apparently did not coincide with mass extinctions. Explain why this may be. Some of the largest impact craters (multi-ring basins) on the Moon exceed 1000 km in diameter. What are the odds that such a large event (previous question) might occur today (i.e., how frequent is such an event in recent geologic time)? Ditto for a 10 km-diameter impactor? Ditto for a person being struck (killed) by a meteoroid? A comet recently collided with a planet in our solar system. What was the name of the comet and the planet it struck? What was the extent of damage that occurred? How would such and event affect the Earth today? From the perspective of loss of human life, where on Earth would be the 'safest' impact site to park a 1 km-diameter asteroid? For your chosen site, what kinds of global effects would you expect? Explain your reasoning. If impact by a large asteroid was inevitable in the US, what would you advise our government to do about it? Would your advice differ if we had an advance warning of five years, one year, one month? Explain. Why are impact scars so well preserved on the Moon (and other rocky planets such as Mercury or Venus), whereas they are rather inconspicuous and seemingly rare on the Earth?:  Why are impact scars so well preserved on the Moon (and other rocky planets such as Mercury or Venus), whereas they are rather inconspicuous and seemingly rare on the Earth? Development of impact craters:  Development of impact craters How do impact craters differ from volcanic craters? A comet recently collided with a planet in our solar system. What was the name of the comet and the planet it struck? What was the extent of damage that occurred? How would such and event affect the Earth today?:  A comet recently collided with a planet in our solar system. What was the name of the comet and the planet it struck? What was the extent of damage that occurred? How would such and event affect the Earth today? Multiple impact sites formed by fragments (up to 1 km diam) of Levy-Shoemaker comet (July, 1994). Maximum ‘crater’ diameter = that of Earth!!! Types of Near-Earth Objects (NEOs):  Types of Near-Earth Objects (NEOs) About 2,000 objects massive enough (1 km diameter) to cause global catastrophe are known to cross Earth's orbit. Such an impacting object could wipe out 25% of humanity. About 10,000 objects of 500 m size cross Earth's orbit. About 300,000 objects of 100 m size cross Earth's orbit. About 150 million objects of 10 m size cross Earth's orbit. Some 70% of potential impactors are asteroids; the rest are comets. About 50% of the Earth-crossing asteroids most likely are extinct or dormant comets. Frequency of impactors:  Frequency of impactors Pea-size meteroids--10/hr Walnut-size--1/hr Grapefruit-size--1/10 hrs Basketball-size--1/mo 50-m rock that would wipe out an area the size of New Jersey--1/century 1-km asteroid--1/100,000 yrs 2-km asteroid--1/500,000 yrs A "nemesis" parabolic comet impactor would give us only a 6-month warning. Describe a reasonable sequence of life-threatening events that might accompany the collision of a 10 km-diameter asteroid with the Earth (what would the last dinosaurs have experienced)?:  Describe a reasonable sequence of life-threatening events that might accompany the collision of a 10 km-diameter asteroid with the Earth (what would the last dinosaurs have experienced)? Earth impact effects program - do your own simulation… http://www.lpl.arizona.edu/impacteffects/ Try different parameters (size, density, velocity of impactor; target type, etc.) For the K-T event, consider a 10 km metallic meteorite traveling at ca. 20-50 km/sec, with a sedimentary rock target. For different diameter objects, compare the predicted frequency of such events. Effects of a ‘small’ impact event (ca. 1000 yr frequency):  Effects of a ‘small’ impact event (ca. 1000 yr frequency) Consider a 45 meter iron asteroid impact where you are 1km away from ground zero is, apart from the obvious fact that you would be vapourised instantly: The air blast will arrive at approximately 3.3 seconds. Max wind velocity: 1113.0 m/s = 2489.7 mph Sound Intensity: 128 dB (Dangerously Loud) Multistory wall-bearing buildings will collapse. Wood frame buildings will almost completely collapse. Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse. Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use. Up to 90 percent of trees blown down; remainder stripped of branches and leaves. Game over for any area which is hit by such a small - 20m across - body Frequency-energy relations of impact events:  Frequency-energy relations of impact events Global impact crater sites http://www.unb.ca/passc/ImpactDatabase/index www.html:  Global impact crater sites http://www.unb.ca/passc/ImpactDatabase/index www.html Roughly, how many impact sites currently are recognized on the Earth's surface? Where are they concentrated, and why? N. American impact crater sites:  N. American impact crater sites Texas sites: Site Diameter #5 2.4 km #34 12.7 km #41 0.2 km #48 13 km Devastation 8km from ground zero of the 1908 Tunguska event, which was the result of a small asteroid exploding in the atmosphere. Such events occur on time-scales of hundreds of years. :  Devastation 8km from ground zero of the 1908 Tunguska event, which was the result of a small asteroid exploding in the atmosphere. Such events occur on time-scales of hundreds of years. Slide24:  http://www.lpl.arizona.edu/SIC/impact_cratering/Chicxulub/Chicx_title.html Size of Chicxulub multi-ring basin:  Size of Chicxulub multi-ring basin Location of Chicxulub impact site:  Location of Chicxulub impact site Slide27:  http://www.space.com/scienceastronomy/planetearth/asteroid_jello_001122.html Sequence of events following Chicxulub impact A perspective plot of the ~180 km-diameter Chicxulub crater with a cutaway view showing a cross section of the crater as revealed by seismic reflection data. This view is looking to the south; the Yucatán coastline is shown by a thin dark line. Note the different horizontal and vertical scales such that the cross section has a vertical exaggeration of approximately ten times. http://miac.uqac.ca/MIAC/chicxulub.htm:  A perspective plot of the ~180 km-diameter Chicxulub crater with a cutaway view showing a cross section of the crater as revealed by seismic reflection data. This view is looking to the south; the Yucatán coastline is shown by a thin dark line. Note the different horizontal and vertical scales such that the cross section has a vertical exaggeration of approximately ten times. http://miac.uqac.ca/MIAC/chicxulub.htm Slide29:  Impact Hazards Large impact events have the capacity to blow out a hole in the atmosphere above the impact site, permitting some impact materials to be dispersed globally by the impact fireball, which rises above the atmosphere. The K-T event, that produced the now-buried 180 km diameter Chicxulub impact structure in the Yucatan, Mexico, is the only clear case where a large-scale impact event is associated with a biostratigraphic boundary. Estimates of the terrestrial cratering rate suggest the frequency of K-T-sized events on Earth is ca. one every 50-100 Myrs. Smaller, but still significant impact events, occur on shorter time scales and will affect the terrestrial climate and biosphere to varying degrees. The formation of impact craters as small as 20 km could produce light reductions and temperature disruptions similar to a nuclear winter. Such impacts occur on Earth with a frequency of two or three every million years. The most recent known structure in this size range is Zhamanshin in Kazaksthan, with a diameter of 15 km and an age of 1 million years. Impacts of this scale are not likely to have a serious affect upon the biosphere and cause mass extinctions. The most fragile component of the present environment, however, is modern human civilization, which is highly dependent on an organized and technologically complex infrastructure for its survival. There is little doubt that if civilization lasts long enough, it will suffer severely or may even be destroyed by an impact event. Impacts may also induce chemical changes in the atmosphere. These are related to the vaporization of the impacting body and a portion of the target. Considering only the contribution from the impacting body, recent calculations indicate that even relatively small impacting bodies, < 0.5 km in diameter that produce impact craters on the scale of 10 km in diameter, would inject 5 times more sulphur into the stratosphere than its present content. Larger impact events occurring on the time-scale of a million years will inject enough sulphur to produce a drop in temperature of several degrees and a major climatic shift. Slide30:  In marine impacts there is also another consideration; namely, the generation of a tsunami. For example, an impact anywhere in the Atlantic Ocean by a body 400 m in diameter would devastate the coasts on both sides of the ocean with wave runups of over 60 m. Iron impacting bodies up to 20 m will deposit their energy in the atmosphere and not reach the surface; whereas, comets as large as 200 m will deposit their energy in the atmosphere. Such air burst explosions, fortunately, are not efficient at delivering their energy to the ground, because some of initial energy is blown into space. The Tunguska event in 1908 was due to the atmospheric explosion of a relatively small, approximately few tens of metres, body at an altitude of 10 km. The air blast resulted in the devastation of 2000 sq. km of Siberian forest but no loss of human life due to the very sparse population. Events such as Tunguska occur on a time-scale of 100's of years. Impact is a random process not only in space but also in time. The next large impact with the Earth could be an "impact-winter"-producing event or even a K-T-sized event. To emphasize this point, in March 1989 an asteroidal body named 1989 FC passed within 700,000 km of the Earth. This Earth-crossing body was not discovered until it had passed the Earth. It is estimated to be in the 0.5 km size-range, capable of producing a Zhamanshin-sized crater or a devastating tsunami. Although 700,000 km is a considerable distance, it translates to a miss of the Earth by only a few hours, when orbital velocities are considered. At present, no systems or procedures are in place, specifically for mitigating the effects of an impact. Things to think about:  Things to think about How unique are mass extinction events? What factors do they have in common? Are we presently living in a mass extinction event?

Add a comment

Related presentations

Related pages

The 3 Biggest Space Impacts Ever - YouTube

Celebrate Asteroid Day by learning about the 3 biggest collisions that Earth has experienced with celestial objects. Dooblydoo thanks to the ...
Read more

Space impacts - sourcecodes.website

Space impacts. sound - transitions movement ... Get creative with Space impacts. Ideal for designing logos, sketching, painting and even making your own ...
Read more

Space Impacts - Desktop Nexus Wallpapers

Space Impacts. Download free Planets wallpapers and desktop backgrounds!
Read more

Impact Frequency | Space Objects : The Global Hazard of ...

This section will include how often space impacts can occur and a debate on the chances of a catostrophic event as a result of these space impacts.
Read more

Space Impacts On Earth's Weather by Sara Mitchell on Prezi

Make your likes visible on Facebook? Connect your Facebook account to Prezi and let your likes appear on your timeline. You can change this under Settings ...
Read more

Space Impacts On Society - Lessons - TES

Lesson description: Welcome to the website of "The Impact of Space Activities upon Society" ... The last ten years have brought about a new era of ...
Read more

NASA 'Twins Study' to Yield Trove of Data About How Space ...

NASA 'Twins Study' to Yield Trove of Data About How Space Impacts the Human Body. By ... Mark Kelly told ABC News last year he wanted to help NASA in its ...
Read more

Ancient plants 'frozen in time' by space impacts - BBC News

Ancient plant material has been preserved in the glass formed by asteroids hitting the Earth, scientists report. The "frozen in aspic" appearance of what ...
Read more

Faces in Spaces on Culture: John Roberts, Herman Miller ...

We selected several Canadian Executive Business Leaders to chat with us about how their corporate space impacts culture. This week we ...
Read more