Assignment 2-Worksheet S2023_Stokes-Schroeter

ERSC 1P94 – Assignment 2, Crater Counting (Stokes & Schroeter) In this lab exercise you will determine the age of a planetary surface using the method of crater counting. Crater counting uses the frequency of occurrence of given size craters (by diameter) to estimate the age of a surface since it was last reworked. You will assess the quantity of craters in 4 size classes of 8 to 16 km , greater than 16 up to 32 km , greater than 32 up to 64 km , and greater than 64 up to 128 km . To do this you will need images of a planetary surface images and a method of measuring/counting the craters, both of which are in this document. The number of craters in a size class (in a normalized area) are then plotted on a chart which is used to read off the likely age. The Images, chart, and questions are in this file. Complete the assignment in Word, then enter your answers and upload your file (saved as a PDF) under Quizzes.  Save this worksheet with all circles, graphs and answers as a PDF before submitting it. Any non-PDF file will receive 0 marks (i.e., a loss of 18 marks). To save as PDF go to File , then Save as , and change the file type to PDF.  Add your surname at the beginning of your pdf’s file name . Here is a link to the Crater Counting Tutorial on YouTube  Your answers depend on the quality of your counts . Even with the generous ranges we accept, poor counting will lose marks. This is how scientific study works; theory alone is not sufficient, application and execution matter just as much.  Below are two cratered-surface images. At the bottom you will see scale bars and a set of circles to use for sizing/counting. Use the scale bars to set the outside of the circle to the right diameter.  Some craters are already sized for you, include them in your counts.  Craters that are less than 8 km across are marked with red dots , do not count those craters , they are too small for our size classes. Do not count things the same size as them.  Count craters where at least 50% of the rim is visible. Instructions : 1) Watch the YouTube tutorial and read the Background & Methods pdf. Review Module 3’s Falling Space Objects , and Examples at the end of this document. 2) Now, on to our Martian images! Click on the image, you will notice the entire image will be selected (little handles appear on the edges). 3) A click on a circle will select the circle and then you can move it ( with your mouse, or using the arrow keys ). Copy the circle and paste it to make a new one (CTRL + C then CTRL + V, or just use CTRL + D). You’re going to want to be zoomed in. 4) Move a circle over a crater of the proper size range. In the example above, the crater is more than 32km but less than 64 km in diameter; it is therefore in the 32-64 km category (red circle). The picture has a 32km green circle to illustrate that the green circle is smaller than the crater and therefore not correct. 5) While a circle is selected, (it still has the little handles for rescaling and moving on it), press CRTL +D (hold control key and press D) to make a second circle of the same size near the first one. Move the second circle to another crater and generate the next circle with CTRL+D again. Move across the image systematically until all craters of that size are filled. Probably best to count whilst using the provided circles (make tic marks on a sheet). You have CTRL + Z to undo a mistake. Notes:  Please be careful not to count ejecta blanket (see Examples & FAQs at the end of this document).  Post your question with a specific title in the Forum.  Relax and count purposefully. Recommended music for crater counting is Gustav Holst’s Jupiter, Bringer of Jollity (or the whole The Planets suite)

ERSC 1P94 – Assignment 2, Crater Counting (Stokes & Schroeter) Image name: Stokes crater , north of the dichotomy. Image Size: 1491 km x 940 km = 1,401,540 km 2 ( 5pts – for outlined craters )