1. Astronomy190 - Topics in Astronomy
Astronomy and Astrobiology
Lecture 16 : Habitable Zone I
Ty Robinson

2. Questions of the Day
How is the Habitable Zone defined and why is it a useful concept?
How does the size and shape of the Habitable Zone change with different star types?
How could tidal effects impact habitability?
Readings for this week: Ch , 11.1

3. Surface Habitability Factors
What determines habitability?
stellar lifetime UV
stellar energy received
greenhouse gases
UV shield
Star - lifetime, UV
Orbital distance - stellar flux received
Planetary neighbors - stable orbit, impacts
Composition - made with water?
Mass - tectonics, magnetic field
Atmosphere - greenhouse, UV shield
impacts
stable orbit
formed w/water
tectonics
magnetic field

4. Habitable Zone (HZ) = the region around a
Definition of HZ
Habitable Zone (HZ) = the region around a
star where an Earth-like planet could sustain
liquid water on its surface

5. Earth vs. Moon
habitable
not habitable

6. Habitable Worlds in the Solar System

7. Free Floating Planets

8. HZ for Other Liquids
ethane

9. liquid over a wide range of temperatures
Why Water?
liquid over a wide range of temperatures
liquid at relatively high temperatures
abundant
solid water less dense than liquid water
relatively high specific heat
polar molecule

10. Terrestrial Planet Finder
TPF-Coronagraph, Interferometer - primary mission length = ~5yrs

11. hot surface temperature cold small large separation = 1au separation
The HZ around the Sun I
hot
surface temperature
cold
small
large
separation = 1au
separation

12. hot surface temperature cold small large separation
The HZ around the Sun II
hot
surface temperature
cold
small
large
separation

13. The HZ around the Sun III
hot
surface temperature
cold
small
large
separation

14. hot surface temperature cold small large separation
The HZ around the Sun IV
hot
surface temperature
cold
small
large
separation

15. hot surface temperature cold small large separation = 1au separation
The HZ around the Sun V
hot
surface temperature
cold
small
large
separation = 1au
separation

16. hot surface temperature cold small large separation
The HZ around the Sun VI
hot
surface temperature
cold
small
large
separation

17. The HZ around the Sun VII
hot
surface temperature
cold
small
large
separation

18. The HZ around the Sun VIII
hot
surface temperature
cold
small
large
separation

19. Question
Given what you know about our Solar System, estimate the limits for the inner and outer edge of the HZ around our Sun. Be quantitative!
hot
0 - 1 AU
1 - 2 AU
surface temperature AU
1.5 AU
1 - 5 AU
cold AU ? ?
small
large
separation

20. The HZ around the Sun

21. Question Short lifetime Intense UV
HR Diagram
Question
What are two reasons why we tend to rule out O, B and A stars
as targets for searching for habitable planets?
Short lifetime
Intense UV

22. The HZ around other Stars I
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

23. The HZ around other Stars II
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

24. The HZ around other Stars III
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

25. The HZ around other Stars IV
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

26. The HZ around other Stars V
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

27. The HZ around other Stars VI
hot
surface temperature
cold
small
large
separation = 1au
brightness of star

28. Question
Which type of star of main-sequence star is the Habitable Zone closest to? F G K M

29. The HZ around other Stars

30. HZ Plot

31. Why might a tidally locked planet be uninhabitable?
Tidal Locking
Question
Why might a tidally locked
planet be uninhabitable?

32. A Tidally Locked Jupiter

33. Planet around M-Star standard HZ HZ, only tidal heating Circularity

34. Questions of the Day
How is the Habitable Zone defined and why is it a useful concept?
How does the size and shape of the Habitable Zone change with different star types?
How could tidal effects impact habitability?

35. Quiz
1 - Describe the process that generates the energy which drives hydrothermal activity on icy worlds.
2 - Explain why the Habitable Zone is located further from a main-sequence F star than from a main sequence M star.
3 - What is one thing you did not understand from
today’s lecture?