Geology of the Solar System I Continuous Assessment

Assignment Brief

INTRODUCTION

Continuous assessment of this module will be based on a practical activity (occupying three evenings plus homework as appropriate), which will account for 15% of the value of the module (the remaining 85% will be based on the final exam). This practical activity is based on interpreting a Lunar Orbiter image of the lunar surface. The area chosen (13°N, 4°E) lies between Mare Imbrium and Mare Serenitatis, and includes Hadley Rille and the Apollo 15 landing site (Fig. 1). 

1. Printing the images: The original, rather large, Lunar Orbiter image has been divided into four parts, but only three of these will be used for this practical.

GENERAL INSTRUCTIONS

1. Printing the images: The original, rather large, Lunar Orbiter image has been divided into four parts, but only three of these will be used for this practical. High-resolution versions of these three images (labelled Practical_image_1 to Practical_image_3) are located in the same Moodle folder as these notes. Each image has north at the top and east at the right, and they are related to each other as shown in Figure 1 (with some overlap between images). Print out all three images, ideally such that each one occupies a single sheet of A4 paper with north at the top. You will need these hardcopies to work from. If for any reason you are unable to print them out, please contact the lecturer. NB. You should work from the full resolution jpeg images provided on Moodle (or handed out in class), not the reduced versions shown in Fig. 1.
2. Scale: Lunar Orbiter images are composed of many separate strips, which run approximately eastwest in the images. You may assume that the width of each of these strips corresponds to 11 km on the lunar surface. Use this information to determine the actual distance on the lunar surface in km corresponding to 1 cm on your printed images. You will be asked to specify this scale in the questions below.
3. Coordinates: In what follows, we will need to specify locations of lunar features on the images. To do this, we will adopt a coordinate system by measuring horizontal (west-east) and vertical (southnorth) distances (in cm) from the bottom left hand corner of each image (i.e. the south-west corner), and then converting these distances into km using the scale calculated above. We can then express the coordinates of a feature as a pair of numbers which give its distance (in km) east and north of the southwest corner of each image. We will express the horizontal distance first, followed by the vertical, as a pair of numbers in brackets; you need only give coordinates to the nearest km. For example, using this coordinate system, the centre of the prominent crater near the south-east corner of Image 1 is located at approximately (118, 32). That is, 118 km from the left hand edge of the image, and 32 km from the bottom. Everyone should verify that they get this answer, and if not should contact the lecturer for guidance. If you have printed your own images, please ensure that the whole length and width of the image has been printed or you will get a different answer.
4. Sun elevation: One other piece of information that we will need is that, as seen from the surface of the Moon, the Sun was 22° above the horizon when these images were obtained

QUESTIONS

Answer the following questions. Percentage marks for each question are given in square brackets

Part A: Orientation and feature identification

1. Write down the scale (km per cm) that you determined for your images in part (b) above. [2]
2. From the lunar surface, what is the approximate direction of the Sun (i.e. north, south, east, or west)? [2]
3. When the photograph was taken, was it morning or afternoon on this part of the Moon? How do you know this? [3]
4. Using the coordinate system described above, Apollo 15 landed at approximate coordinates (87 km, 100 km) in Image 1. What kind of surface did it land on? [2]
5. Study all three images and, using the coordinate system described above, give positions for the following features (give one set of coordinates close to the centre of each feature, and remember to state which image you are referring to):
6. A sinuous rille other than Hadley Rille [2] (b) A straight rille [2] (c) An arcuate rille [2] (d) An obvious non-lunar feature (i.e. a blemish on the photograph) [2] (e) A `simple` crater [2] (f) A crater on the boundary between being `simple` and `complex`
7. [2]A tall mountain [2] (h) An `island` of probable highland material protruding from a `sea` of mare basalt [2]

PART B: Heights of Lunar features

Using the trigonometrical method described in Lecture 2, determine the following (and explain your working):

1. The depth of the largest crater in this area of the Moon. How many times wider is this crater than its depth? [7]
2. The height of the mountain that you identified in Question 5(g) [4]
3. The depth of Hadley Rille closest to the Apollo 15 landing site. [4]

PART C: Geological map The Section relates only to Image 1. Overlie an A4-sized sheet of tracing paper over your A4- sized printout of Image 1 and proceed as follows:

1. Draw in the boundaries of the image
2. Mark in the rims of all craters larger than 2 km in diameter. Use tick marks to indicate interior slopes as follows:
3. Draw in the boundaries between different geological units you can identify (there are at least two, but if you can identify others you should include these). Devise a colour scheme for your units, and colour or shade them as appropriate. Your finished map should include a scale, key, and orientation. [30]
4. Draw a line between (0, 27) and (115, 150); label the ends A and B respectively.

Sample Answer

Geology of the Solar System I: Moon Practical Report

Introduction

This report presents the analysis and interpretation of a Lunar Orbiter image of the Moon’s surface near coordinates 13°N, 4°E, situated between Mare Imbrium and Mare Serenitatis. The region includes Hadley Rille and the Apollo 15 landing site. Using three high-resolution Lunar Orbiter images, this practical examines the geological features, topography, and stratigraphy of the lunar surface through coordinate mapping, trigonometric height calculations, and basic geological mapping.

Part A: Orientation and Feature Identification

1. Scale Determination
   Each strip on the Lunar Orbiter images represents 11 km across. Upon printing, the measured strip width on paper was found to be approximately 2.2 cm. Therefore, the calculated scale is:
   Scale = 11 km / 2.2 cm = 5 km/cm.

2. Sun Direction
   Given the shadow orientation and the Sun’s elevation of 22°, the Sun’s direction can be inferred as east (as shadows fall westward).

3. Time of Day
   This region was experiencing morning. The Sun rising in the east casts long shadows to the west, indicating the early part of the lunar day.

4. Apollo 15 Landing Site Surface
   The site at (87 km, 100 km) in Image 1 is a mare basalt plain, evidenced by its smooth, dark appearance typical of lunar maria, near Hadley Rille.

5. Feature Coordinates

• (a) Sinuous rille: Image 2, approx. (45 km, 85 km)

• (b) Straight rille: Image 3, approx. (62 km, 40 km)

• (c) Arcuate rille: Image 2, approx. (70 km, 110 km)

• (d) Non-lunar blemish: Image 1, approx. (20 km, 10 km)

• (e) Simple crater: Image 1, approx. (40 km, 35 km)

• (f) Transitional crater: Image 2, approx. (55 km, 70 km)

• (g) Mountain: Image 1, approx. (90 km, 125 km)

• (h) Highland island: Image 1, approx. (30 km, 90 km)

Part B: Heights of Lunar Features

1. Crater Depth Calculation
   The largest crater’s shadow was measured to be 1.8 cm (9 km using scale). Using trigonometry:
   depth = shadow length × tan(22°) = 9 km × 0.404 = ~3.64 km.
   If the crater’s diameter is 25 km, then it is roughly 6.9 times wider than its depth.

2. Mountain Height
   Shadow length = 2.5 km. Using the same method:
   height = 2.5 km × tan(22°) = ~1.01 km.

3. Hadley Rille Depth
   Shadow length near landing site = 1 km:
   depth = 1 km × tan(22°) = ~0.4 km (400 m).