Courses › Computational astrophysics › Module 5: Habitability › Lesson 9
Lesson 9: Habitable Zone
Where liquid water could exist, and why that isn't enough
🎯 Objectives
- Define the habitable zone and its conservative and optimistic limits
- Calculate the light a planet receives
- Combine habitable zone and magnetic protection
🧪 Exercise
- Calculate the light a planet at 2 AU from a star with 4 times the Sun's luminosity receives (S = L/a²).
- With the Sun's conservative zone (0.95–1.68 AU), would it fall inside if the star were like the Sun?
- Explain in your own words why Mars is in the habitable zone but is not habitable today.
⚠️ Model limits
- The limits from Kopparapu et al. (2014) are for a one-Earth-mass planet with a water and CO₂ atmosphere; they do not account for 3D clouds or other atmospheres.
- TRAPPIST-1 (2566 K) is slightly below the formula's validity range (2600–7200 K), so its limits are a mild extrapolation.
- The stellar parameters are published values (they do not come from MHD-INT's database, which only stores each star's mass).
📚 References
- Kopparapu et al. (2014), Habitable zones around main-sequence stars: dependence on planetary mass, ApJ 787, L29.
- Agol et al. (2021), Refining the transit-timing and photometric analysis of TRAPPIST-1, PSJ 2, 1.
- Pineda et al. (2021), The M-dwarf Ultraviolet Spectroscopic Sample I, ApJ 918, 40.
- Berger et al. (2018), Revised radii of Kepler stars and planets using Gaia DR2, ApJ 866, 99.
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