Exoplanet Transit Worksheet
Goal: Explain how astronomers find planets from tiny dips in starlight, and use the transit depth to estimate a planet’s size.
What to do
- Press the “Jupiter-sized” preset, then press Play simulation and watch the light curve as the planet crosses the star. Record the readouts.
- Repeat for the “Earth-sized” and “Grazing transit” presets.
- Press “Earth-sized”, then change Star radius to 0.2 (a small red dwarf). Record the readouts.
Record your results
| Setting | Maximum depth | Radius ratio |
|---|---|---|
| Jupiter-sized | ||
| Earth-sized | ||
| Grazing transit | ||
| Earth-sized, star radius 0.2 |
Questions
How much does a Jupiter-sized planet dim a Sun-like star? How much does an Earth-sized planet dim it?
Show that transit depth ≈ (planet radius ÷ star radius)² for the Jupiter-sized planet.
What happened to the Earth-sized planet’s dip around the small star? Why do astronomers search small stars for Earth-sized planets?
Why is the grazing transit’s dip shallower than the central one, even though the planet is the same size?
Astronomers measure a 1% dip from a Sun-like star. Estimate the planet’s radius in Earth radii. (Hint: Rp ≈ R★ × √depth, and the Sun is about 109 Earth radii wide.)
Can a transit tell you a planet’s mass? What else would astronomers need?
Free from The Astronomy Lab · theastronomylab.com