Materials Needed

• Substrate Tray Setup (from Lesson 1): Deep baking pan/bin filled with 2–3 inches of flour, topped with a dusted contrast layer of cocoa powder.
• Additional Stratigraphy Layer: 1/4 cup of blue/red sugar sprinkles, colored sand, or crushed graham crackers (to add a third hidden sub-surface geological layer).
• Launch Guide / Ramp: Cardboard mailing tube, split wrapping paper tube, or a rigid ruler/flat board to guide angled launches.
• Angle Measurement Tool: Protractor (digital protractor app or printed paper protractor).
• Standard Impactor: Keep the same medium glass marble or steel ball bearing used in Lesson 1 (maintaining mass as a constant variable).
• Measurement Tools: Metric ruler, toothpick (depth gauge), and string (to trace outer ejecta boundaries).
• Degradation Tools: Straw (to simulate wind erosion) and a spray bottle with water fine-mist setting (to simulate rain/weathering).
• Data Collection: Lab notebook or Phase II Data Sheet (provided below) and pencil.

Learning Objectives & Success Criteria

1. Review & Introduction (10 Minutes)

Bridge from Lesson 1: Reviewing Vertical Impact Physics

In our previous lesson, we established how mass and drop height (velocity) increase the kinetic energy ($KE = \frac{1}{2}mv^2$) of an impact, resulting in wider and deeper craters with symmetrical ejecta rays radiating 360 degrees around the rim.

Review Check-In:

• Question: When we dropped our marble straight down (90° angle) in Lesson 1, what shape was the crater rim? (Answer: Circular).
• Question: What did the dark cocoa and white flour reveal about sub-surface rock? (Answer: Deep material gets blasted out as bright ejecta rays over the surface layer).

The Hook: Space Collision Trajectories

Look at high-resolution satellite imagery of the Moon's Messier Crater or Mars's Orcus Patera. Instead of round circles, these craters look like elongated ovals or teardrops, and their ejecta rays shoot out sideways like giant butterfly wings, leaving the space directly behind and ahead completely empty! Why?

In the real solar system, space rocks rarely fall at a perfect 90° vertical angle. In fact, the most mathematically common collision angle across space is 45 degrees, with many meteors striking at shallow angles below 20 degrees! Today, building on our crater dynamics knowledge, we will investigate what happens when space rocks strike at an angle, and how weather on active planets erases these cosmic crime scenes over time.

2. The Body: I Do, We Do, You Do Model

Step 1: "I Do" - Teacher/Parent Demonstration (10 Minutes)

Now that we understand vertical impacts, let's look at trajectory dynamics and multi-layered crusts (stratigraphy).

Key Vocabulary Definitions:

• Oblique Impact: An impact that strikes a planetary surface at an angle non-perpendicular (less than 90°) to the surface.
• Ellipticity Ratio: Major Axis Length divided by Minor Axis Width ($L / W$). A perfect circle has a ratio of 1.0; elongated ovals have ratios greater than 1.0.
• Butterfly Ejecta Pattern: Asymmetrical ejecta distribution produced by shallow impacts (<15°-30°), where material is thrown perpendicular to the flight path, resembling butterfly wings.
• Crater Degradation: The process by which wind, water, tectonic movement, or secondary impacts soften, fill in, and erode crater structures over geological time.

Demonstrating Angled Trajectory Setup:

1. Target Layering Upgrade: To the existing flour substrate, the educator adds a thin layer of blue sprinkles/colored sand, followed by the top dusting of cocoa powder. "This represents three layers of planetary geology: topsoil (cocoa), sub-crustal sediment (sprinkles), and deep bedrock (flour)."
2. Pro-Angle Guide Setup: Place a protractor at the edge of the tray. Align the tube guide at a 45-degree angle pointing toward the center of the pan.
3. Demonstration Release: Roll the medium marble down the tube at 45°.
4. Observation: Point out the change in ejecta spread. Ejecta travels forward (down-range) and sideways, but creates an ejecta-free zone (zone of avoidance) directly behind the launcher (up-range).

Step 2: "We Do" - Guided Trajectory & Measurement Practice (15 Minutes)

Let's practice controlling trajectory angle while keeping drop distance (velocity) and mass constant.

Controlled Setup Protocol:

• Constant Variables: Impactor mass (same marble), total path length inside launch tube (30 cm tube length).
• Modified Variable: Launch Angle ($90^\circ$, $45^\circ$, $20^\circ$).

Guided Measurement Technique:

1. Hold the guide tube at exactly 45 degrees using the protractor. Place the lower exit of the tube precisely 10 cm above the substrate surface.
2. The learner releases the marble through the tube.
3. Measuring Ellipticity ($L / W$):
   • Measure the crater's longest axis along the path of travel (Length = $L$).
   • Measure the crater's widest axis perpendicular to the path (Width = $W$).
   • Calculate: $L \div W = \text{Ellipticity Ratio}$.
4. Ejecta Mapping: Use string to trace the boundary of the ejecta blanket. Notice if the rays form a full circle or spread sideways like wings. Record observations together on the data sheet.

Step 3: "You Do" - Independent Investigation & Resurfacing Challenge (25 Minutes)

Run two connected experiments to explore trajectory angles and planetary degradation.

Part A: The Impact Angle Experiment

Reset your surface (smooth flour, sprinkle layer, cocoa dusting). Test three distinct launch angles with the same impactor:

• Trial 1: $90^\circ$ Drop (Vertical Control - repeat from Lesson 1).
• Trial 2: $45^\circ$ Medium Angled Launch.
• Trial 3: $20^\circ$ Shallow Oblique Launch.

Part B: The Planetary Weathering & Degradation Challenge

Select your shallow angle ($20^\circ$) crater from Trial 3. You will now simulate how weather erases craters on Earth and Mars over millions of years!

• Stage 1 (Fresh Crater): Document the sharp rim, deep basin, distinct colors of ejected layers (flour and sprinkles), and ray patterns.
• Stage 2 (Aeolian/Wind Erosion): Take a drinking straw and blow 5 gentle puffs of air across the crater at a low angle. Observe which features disappear first (thin ejecta rays disappear, rim rounds out).
• Stage 3 (Aqueous/Rain Erosion): Spray 3 fine mists of water over the crater using the spray bottle. Observe how water pooling fills the basin, erodes steep rim walls, and flattens topography.

Student Data Table: Angled Trajectory & Degradation Analysis

3. Conclusion & Reflection (10 Minutes)

Guided Review & Synthesis Questions

1. Trajectory Trends: What happened to the Ellipticity Ratio ($L / W$) as the impact angle decreased from $90^\circ$ down to $20^\circ$? At what angle did you notice the ejecta rays stop forming behind the impact point?
2. Sub-surface Geological Excavation: Did the oblique impacts expose the colorful sprinkle layer differently than the vertical drops in Lesson 1? (Notice how lower angles excavate shallower sub-surface layers).
3. Planetary Investigation Application: Scientists discovered the hidden 180-km Chicxulub impact crater (the asteroid that ended the dinosaurs) beneath Mexico's Yucatán peninsula despite millions of years of erosion. Based on our straw and spray bottle simulation, which crater features survive the longest against weathering—the thin ejecta rays, or the underlying rim/basin structures?

4. Assessment & Evaluation

Formative Assessment (During Activity)

Observe angle measurement alignment with protractors and launcher height control. Verify that students maintain a uniform drop/roll distance inside the tube to ensure velocity remains constant while changing only the launch angle.

Summative Assessment: Planetary Geologist Report

Complete the following task in your lab notebook:

Task 1: Ejecta Diagram Analysis

Draw a top-down aerial map comparing a $90^\circ$ impact ejecta blanket to a $20^\circ$ impact ejecta blanket. Label the Direction of Impactor Travel, Down-range Ejecta Fan, Butterfly Rays, and Up-range Exclusion Zone (Gap).

Task 2: Relative Aging Sequence

Below are cross-section descriptions of three craters discovered on Mars. Sequence them from 1 (Youngest / Fresh) to 3 (Oldest / Highly Degraded) based on your Stage 1–3 degradation experiment, and justify your answer in 2 sentences:

• Crater Alpha: Has steep $30^\circ$ rim walls, bright white ejecta rays visible for 5 kilometers, and a deep central basin displaying excavated underlying geological layers.
• Crater Beta: Smooth, shallow basin filled with wind-blown sediment; faint, smooth rim with zero visible ejecta rays surrounding it.
• Crater Gamma: Noticeable rim, minor erosion on wall edges, rays are faintly visible near the rim edge but faded further out.

5. Adaptability & Differentiation Options