NATS 1880 Lecture Notes - Lecture 10: Solar Wind, Runaway Greenhouse Effect, Planetary Habitability
23 Jun 2018
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Lecture 10: Chapter 10 - The Nature and Evolution of Habitability
Learning Outcomes
- Explain what is meant by "Habitable Zone" and how it changes depending on the
central star!
- Describe the key factors that influence planetary habitability!
- Discuss the long-term future of life on Earth!
- Describe the evidence for climate change on Earth!
!
Important Questions!
1. What is meant by the Habitable Zone and what are its boundaries in the solar
system?!
2. What are the most important factors involved in planetary habitability?!
3. How and why does a Habitable Zone's boundaries change with time?!
4. Is there good evidence for a causal relation between the concentration of carbon
dioxide in the atmosphere and Earth's surface temperature?!
Chapter 10.1
Habitable Zone (HZ):
- Volume within which a planet (similar to Earth) could have surface temperatures that permit
liquid water on its surface. !
- conditions are necessary (we think) but not sufficient to make a world habitable (e.g., Venus,
Europa). !
-observations of extrasolar planets will only permit an assessment of surface life at best; not
subsurface life (if any). !
-HZs can evolve with time (e.g., Mars)!
-Surface temperature of a planet depends on its: !
-technically, simple life can exist outside the habitable zone: e.g., a planet with significant
internal heat or that is ejected from a star’s system with an H atmosphere during formation
("free-floating Earths") !
-may be possible to substitute another liquid medium apart from water with much lower
freezing point !
Chapter 10.2
-Earth and possibly Mars are in the HZ !
-Venus is not at this point !
-Venus is similar to Earth is many ways !
-Why is Venus now so hot? !
-It is closer to the Sun but sunlight is only 1.9 times more intense than on Earth; with same
atmosphere as Earth, it would be only 30° C degrees warmer at the surface, not 450° C
warmer (or 465° C) !
