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Exoplanet Transit Detection

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Run the Exoplanet Transit Detection MicroSim in Fullscreen Edit the Exoplanet Transit Detection MicroSim Using the p5.js Editor

Description

This MicroSim demonstrates the transit method for detecting exoplanets—the primary technique used by NASA's Kepler and TESS missions to discover thousands of planets orbiting other stars.

How the Transit Method Works

When a planet passes in front of (transits) its host star from our perspective, it blocks a small fraction of the star's light. By measuring this periodic dimming, astronomers can:

  1. Detect the planet's presence from the periodic brightness dips
  2. Calculate the planet's size from the depth of the dimming
  3. Determine the orbital period from the time between transits

Simulation Components

The simulation is divided into three sections:

Star View (Top)

  • Yellow star at center with realistic glow effect
  • Dark planet orbiting in an edge-on configuration
  • Orbital path shown as dotted ellipse
  • Transit status indicator showing when the planet is transiting

Light Curve Graph (Middle)

  • Real-time brightness plotted over time
  • Y-axis: Relative brightness (1.00 = full brightness)
  • Characteristic dip when planet transits the star
  • Current brightness marked with red dot

Controls (Bottom)

Control Range Effect
Planet Size 5-30% of star Larger planets create deeper transit dips
Orbital Period 2-15 seconds Faster orbits show more frequent transits

Physics Concepts Demonstrated

  1. Transit Depth Formula: The fractional brightness decrease equals the ratio of areas:

\(\(\text{Transit Depth} = \left(\frac{R_{\text{planet}}}{R_{\text{star}}}\right)^2\)\)

  1. Light Curve Analysis: The shape of the brightness dip reveals:
  2. Planet size (depth of dip)
  3. Orbital inclination (shape of ingress/egress)

  4. Orbital period (time between dips)

  5. Detection Limits:

  6. Jupiter-sized planets (~10% of Sun) create ~1% dips (easily detectable)
  7. Earth-sized planets (~1% of Sun) create ~0.01% dips (requires precise instruments)

Real-World Applications

  • Kepler Mission (2009-2018): Discovered 2,700+ confirmed exoplanets
  • TESS Mission (2018-present): Surveying the entire sky for nearby transiting planets
  • James Webb Space Telescope: Studies atmospheres of transiting exoplanets

Lesson Plan

Learning Objectives

By the end of this lesson, students will be able to:

  1. Explain how the transit method detects exoplanets
  2. Calculate expected transit depth from planet/star radius ratio
  3. Interpret light curve data to determine planetary properties
  4. Discuss the limitations of the transit method

Grade Level

High School Physics/Astronomy (Grades 10-12)

Prerequisites

  • Understanding of light and brightness
  • Basic geometry (area of circles)
  • Familiarity with graphs and data interpretation

Duration

45-60 minutes

Activities

Activity 1: Transit Depth Investigation (15 min)

  1. Set planet size to 10% and observe the transit depth
  2. Predict what the transit depth would be for a 20% planet (should be 4× deeper)
  3. Test your prediction by adjusting the slider
  4. Record: Planet Size vs Transit Depth for 5%, 10%, 15%, 20%, 25%

Activity 2: Light Curve Analysis (15 min)

  1. Observe the shape of the light curve during transit
  2. Identify: ingress (planet entering), full transit, egress (planet exiting)
  3. Measure the duration of the flat bottom of the transit
  4. How does orbital period affect the light curve appearance?

Activity 3: Exoplanet Detective (15 min)

Given only a light curve with:

  • Transit depth of 1%
  • Orbital period of 10 seconds

Calculate:

  1. What fraction of the star does the planet cover?
  2. If the star is Sun-sized (696,340 km radius), what is the planet's radius?
  3. How does this compare to Jupiter (69,911 km) or Earth (6,371 km)?

Discussion Questions

  1. Why can we only detect exoplanets whose orbits are edge-on to us?
  2. What percentage of planetary systems would we miss due to orbital inclination?
  3. How would a planet with rings (like Saturn) affect the light curve?
  4. Why is the transit method better for finding large planets close to their stars?

Assessment

  • Students calculate transit depth from radius measurements
  • Students sketch expected light curves for different scenarios
  • Students explain why Kepler discovered mostly "hot Jupiters"

Usability Features

This simulation was designed with the following usability principles:

  1. Clear Visual Hierarchy: Star view on top, light curve below, controls at bottom
  2. Real-Time Feedback: Light curve updates continuously as planet orbits
  3. Labeled Controls: Each slider shows its current value and physical meaning
  4. Status Indicators: Transit detection shown with text and visual highlighting
  5. Educational Annotations: Transit depth percentage calculated and displayed
  6. Space Theme: Dark background appropriate for astronomy content

References

  1. NASA Exoplanet Archive - NASA - Database of all confirmed exoplanets
  2. Kepler Mission - NASA - The spacecraft that revolutionized exoplanet discovery
  3. TESS Mission - MIT/NASA - Current all-sky exoplanet survey
  4. Transit Photometry - Wikipedia - Detailed explanation of the transit detection method
  5. Exoplanet Detection Methods - NASA - Overview of all exoplanet detection techniques