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Lesson Plan One: Cosmic Collisions and Risk Assessment
*All requirements in this section are quoted directly from the new Science 9 curriculum from Alberta Learning. The full curriculum can be seen here.
Unit C: Environmental Chemistry; Unit E: Space Exploration.
Background information for the teacher can be found here.
Outline the activity
Students create their own impacts using ordinary materials, and observe and measure results with a variety of impacting bodies and velocities Materials Flour, pepper or paprika, sand, shoeboxes, waterproof containers, rocks, marbles, golf balls, tennis balls, hockey pucks.
Teacher notes and debriefing
The effect of impacts is straightforward physics which can be demonstrated with this exercise. On a global scale, impact craters have a diameter roughly 20 times the size of the impacting body, subject to its density and velocity, and a truly major impact might trigger secondary seismic activity such as a volcanic eruption or earthquake. An impact in the ocean (a 2 in 3 chance) would result in a tsunami which would threaten the coast lines in all directions.
Have students complete a short essay about the possible effects of a 2 km asteroid striking:
For further discussion
Note that discussion points have application in:
Discussion One: Evaluate the experiment.
In what ways did the "flour bed" experiment simulate what would happen in the event of a major impact? In what ways was it different?
The splash of water or flour would be roughly similar; however in the experiment the impacting marble would survive intact. In reality, the impactor would be obliterated like a mosquito on a windshield, leaving only an unsightly mess in its aftermath. Indeed, the crucial clue that led Luis Alvarez to his dinosaur-extinction-through-cosmic-impact theory was a layer of Iridium deposited at the geological layer known as the K-T Boundary. Iridium is a rare element on Earth; in this case its source surely would have been the impacting body itself. Other particulates from the impactor would be buried in the crater floor or thrown out in its splash ejecta.
How could the experiment be altered to better represent what happens to the impacting body? As a thought experiment only (!), students may be asked to visualize a raw egg being dropped on concrete from a great height.
The Moon provides countless examples of actual craters caused by impacts. Students are encouraged to view them through a telescope if possible, or certainly to view photographs of them. How do they resemble the crater from the experiment? How do they differ?
The question of how accurately the experiment resembles nature is a critical thinking skill that is fundamental to all science.
Discussion 2: Risk assessment
What is the risk of Earth being devastated by a late planetesimal in the 21st century? And can we do anything to improve those odds?
The chances of Earth being hit by an asteroid at some point in the future is 100%. How big an asteroid? How often? When?
There are as yet, no certain answers to these questions. However, students are encouraged to consider as many factors as possible that would be necessary to address this risk. [Again, this is consistent with the requirements of Unit C: Environmental Chemistry, specifically 'hazards, probabilities and risk assessment', as well as Unit E: Space Exploration, specifically 'investigate predictions about the motion, alignment, and collision of bodies in space'.]
The chances of an individual asteroid hitting Earth were recently compared (in a NASA release) to that of winning the lottery. Let's call it Canada's own 6/49, where an individual ticket has a 1 in 13,983,816 chance of being the right one. These are of course terribly long odds, but what would your chances be if you had 100,000 lottery tickets? 100 million? If you bought 1,000 tickets every week, how long would it take you to win? When it comes to cashing in The Big One on a global scale, the numbers aren't quite so well-defined, however these are the types of quantitative questions which must be considered.
Ever more frequently in the news these days are reports of asteroids perhaps hitting Earth at some finite date in the future, or narrowly missing in the here and now. There are currently over 450 objects on the list of Potentially Hazardous Asteroids (PHAs), each of which has a tiny but non-zero chance of some day encountering Earth. While probably less than 10% of the true total, this list is growing extremely rapidly; over half of its entries date since 2000. Earth is not suddenly encountering new perils, we are simply doing a much better job of identifying them. An entire program, the LIncoln Near Earth Asteroid Research, or Project LINEAR, is dedicated to discovering Earth-crossing asteroids, and has succeeded in discovering numerous comets as well. This low-budget program is proving the worth of remote sensing technology, and is in the early stages of building an important data set: what is the number and nature of Earth-crossing asteroids, and what are their trajectories?
Another question to consider is, what would happen if one hit? Asteroids and comets come in different sizes, densities, relative speeds, and impact angles. Earth offers a variety of possible impact sites: oceans, mountains, tundra, deserts, populated areas. Discuss in light of the "flour bed" experiment.
Discussion Three: Risk assessment 2
Some researchers have already compiled actuarial statistics of 'death by asteroid'. One study from the University of Arizona compiled the following estimated risks of death for an American over a 50-year period:
The probability of impact-related deaths may seem surprisingly large given they're hardly the stuff of everyday news items. (Indeed, students are encouraged to critique the study itself: are the conclusions realistic?) What tips the scales is that a single event can have global implications, unlike most forms of natural disaster - flood, hurricane, tornado, volcano, mudslide, earthquake - which are regional in nature. Another vital distinction is the potential to limit or prevent such a disaster, if the potential 'doomsday asteroid' is spotted early enough.
Again, students are asked to consider the options. Popular among these will be to 'nuke it', but it's not that simple; a nuclear device which breaks the asteroid apart could simply assure several smaller but still catastrophic impacts instead of one, actually increasing the area of destruction. Alternatively, a nuclear device set off to one side of the asteroid will alter its velocity by an infinitesimal amount, which with enough lead time would be sufficient to deflect the object out of harms way. Other possible solutions include lassoing the object, putting a rocket motor on it, putting an ion drive motor on it, putting a solar sail on it, or indeed any propulsion system which could influence the object's momentum. A large-scale mining operation could alter the asteroids mass and momentum while yielding valuable minerals. More conservatively, an accurate prediction of the time and location of an impact would allow for a mass evacuation of the target area. Brainstorm. This can be a fun activity in which the most improbable suggestion could in fact be the solution. Or, that same improbable suggestion could become the plot line of a major Hollywood motion picture! Consider the movies 'Deep Impact' and 'Armageddon', released nearly simultaneously in the summer of 1998. How realistically do they portray the threat of impact? How realistic are the dramatized attempts to Save The Planet?
Students may also consider the economic implications, including the costs of scaling up the PHA detection program and the cost of a mission or missions designed to avert an impact as compared to the potential cost of a regional or global catastrophe. Consider that the budget for each of the Hollywood films cited above dwarfs that of current PHA searches such as Project LINEAR.
While we're sure Earth will be impacted eventually, the chances of it occurring 'tomorrow' are vanishingly small. Should we continue to simply trust our luck? Or do we need to train Bruce Willis to go blow it up?
“Potentially Hazardous Asteroids” http://neo.jpl.nasa.gov/neo/pha.html
“Asteroid and Comet Impact Hazards” http://impact.arc.nasa.gov/
“The Astronomy of ‘Armageddon’” http://www.badastronomy.com/bad/movies/armpitageddon.html
“The Astronomy of ‘Deep Impact’” http://www.badastronomy.com/bad/movies/di2.html