Activity

Summary

The aim of this activity is to understand the effect the mass and velocity of an impacting object has on the resulting crater, in terms of diameter, depth and ejecta rays and relate this information to the craters on the surfaces of Earth and the Moon.

Goals

After carrying out this activity, students will be able to recognise and describe how impact craters are formed on Earth and how the varying parameters effect the size and energy of an impact.

Planning

Background

Many of the features we see gracing the Moon’s surface are ‘impact craters’ formed when impactors smashed into the lunar surface. The resulting explosion and excavation of material at the impacted site creates piles of rock (called ejecta) around the circular hole as well as bright streaks of target material (called rays) thrown for great distances.

Two common methods of craters formation in nature are:
1) impact of a projectile on the surface and 2) collapse of the top of a volcano creating a crater termed caldera.

The factors affecting the appearance of impact craters and ejecta are the size and velocity of the impactor, and the geology of the target surface.

By recording the number, size and extent of erosion of craters, lunar geologists can determine the ages of different surface units on the Moon and can piece together the geologic history. This technique works because older surfaces are exposed to impacting meteorites for a longer period of time than are younger surfaces.

Impact craters are not unique to the Moon. They are found on all the terrestrial planets (Mercury, Venus, Earth and Mars) and on many moons of the outer planets.

On Earth, impact craters are not as easily recognized because of weathering and erosion. Famous impact craters on Earth are Meteor Crater in Arizona, U.S.A.; Manicouagan in Quebec, Canada; Sudbury in Ontario, Canada; Ries Crater in Germany, and Chicxulub on the Yucatan coast in Mexico.

Characteristic of Impact Craters

Typical characteristics of a lunar impact crater are:

• Floor: bowl shaped or flat, characteristically below surrounding ground level unless filled in with lava.
• Ejecta rays: blanket of material surrounding the crater that was excavated during the impact event. Ejecta becomes thinner away from the crater. 
bright streaks starting from a crater and extending away for great distances. See Copernicus crater for another example.
• Raised rim: rock thrown out of the crater and deposited as a ring-shaped pile of debris at the crater’s edge during the explosion and excavcation of an impact event.
• Walls: characteristically steep and may have giant stairs called terraces.
• Central uplifts: mountains formed because of the huge increase and rapid decrease in pressure during the impact event. They occur only in the center of craters that are larger than 40 km diameter. 

Instructions

Introduction

In this activity we will be using a specially written web application called the Impact Calculator. This can be found at http://simulator.down2earth.eu

Note: You will need to have Flash Player 9 (or higher) installed for it to run in your web browser (you will be directed to download the necessary plugin, if it is not installed). 

Full Description

1. Open the Impact Calculator. Selecting a language and click start. 
2. You will be presented with a choice of 6 parameters which must be set before you can simulate an impact. 

3. Once you have chosen your parameters, click submit and place your impact crater at your preferred location around the World to find out how much damage you have done.

Making Impact Craters

Now we are going to see if we can reproduce the real impact craters we see on Earth. 

Use the data listed on the Making Impact Craters Worksheet to work out the parameters responsible for each crater and calculate the effects of each event. These values provided are estimates based on the real scientific investigations of these known impact craters on the Earth.  

Make sure you set your distance from impact as 500km to ensure that you are not destroyed by the larger impact events!

Next Steps