Making an Impact

Arizona's Meteor Crater

Looking around our solar system, we see evidence of impactors that have cratered the landscapes of Mars, Mercury, our Moon, and even planet Earth. What are the characteristics of impact craters and how are they formed? Using classroom models and simulations, we can investigate the factors the affect impact craters.

One of the best ways to begin a discussion of craters is by dissecting an image of a crater. Arizona's Meteor Crater provides a launching point for a study of craters and the impactors that formed them.

• How big is this crater? How wide? How deep? What evidence for scale do we see in the image?
• What are some physical features of this crater? (raised rim, steep walls, ejected material, central uplift)
• How big was the impactor?
• How fast was the impactor traveling?
• At what angle did the impactor hit?
• When did the impact happen?
• Where is the impactor?
• Why is this crater so well preserved?

From a discussion of these questions, we can begin to formulate research questions about the factors that affect impact craters:

• How does the diameter of an impactor affect the diameter and depth of a crater?
• How does the mass of an impactor affect the diameter and depth of a crater?
• How does the speed of an impactor affect the diameter and depth of a crater?
• How does the angle of an impactor affect the diameter and depth of a crater?

Impact Craters Lab

From our research questions, we can begin to plan our experiment. The lab investigation we conduct is modeled after an activity designed by NASA, outlined in their Exploring the Moon Educator Guide. Materials needed for this lab activity include Moon material (sand), impactors (marbles and golf balls), pans, balances, and metric rulers. Students test their hypotheses under controlled conditions in an attempt to better understand how an impact crater, such as the one in Arizona, could have formed and the energy involved in the impact.

Why is it important for us to understand craters? A study of geologic history reminds us that Earth has been hit by many impactors in the past. The largest of these impactors have repeatedly reset the evolutionary clock on our planet—mass extinctions of species such as dinosaurs are the result of planetary bombardment by rocks from space. It is only a matter of time before the next impactor threatens Earth.

If a large impactor is headed our way, is there anything we can do about it? While Hollywood-style scenarios involving nuclear missiles, massive explosions, and Bruce Willis single-handedly saving the day are exciting on the big screen, these solution just don't work out mathematically in real life (sorry…). For us to be prepared for a large impactor is a two-step process. We must first catalog the threat by surveying the skies around us and accurately tracking potential impactors. NASA and other organizations have begun to do this, but have not yet found everything—it is a massive undertaking. Second, we must be prepared not to simply blow an object out of space, but to gently finesse it into an orbit that harmlessly bypasses our planet. While the Hollywood excitement level is not as high, the chances for success (and the survival of our species) are much improved.

Universe Today has an excellent analysis of the many ways to deflect an asteroid, and Bad Astronomer Phil Plait explains the process of nudging a space rock out of our way should it come to pass close by. Additionally, there are multiple online resources for simulating impacts, including the Impact Calculator and Impact Earth.

Finally, while impacts have altered the landscapes of countless objects in our solar system and have changed the course of evolutionary history on planet Earth numerous times, they have also had one major positive side effect: the next time you look up in the sky and see the beautiful Moon, be awed by the massive impact between Earth and another long-gone planet-sized body that led to the Moon's formation some 4 billion years ago. Goodnight, Moon!