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Astronomy190 - Topics in Astronomy
Astronomy and Astrobiology
Lecture 16 : Habitable Zone I
Ty Robinson
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. 10.1-10.4, 11.1
Surface Habitability Factors
What determines habitability?stellar lifetime
UV
stellar energy received
impactsstable orbit
formed w/water tectonicsmagnetic field
greenhouse gasesUV shield
Definition of HZ
Habitable Zone (HZ) = the region around a star where an Earth-like planet could sustain
liquid water on its surface
Earth vs. Moon
habitable
not habitable
Habitable Worlds in the Solar System
Free Floating Planets
HZ for Other Liquids
ethane
Why Water?
liquid over a wide range of temperatures
liquid at relatively high temperatures
abundant
solid water less dense than liquid water
polar molecule
relatively high specific heat
Terrestrial Planet Finder
The HZ around the Sun I
separation = 1au
separation
surf
ace
tem
pera
ture
hot
cold
small large
separation
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around the Sun II
separation
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around the Sun III
separation
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around the Sun IV
The HZ around the Sun V
separation = 1au
separation
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around the Sun VI
separation
surf
ace
tem
pera
ture
hot
cold
small large
separation
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around the Sun VII
The HZ around the Sun VIII
separation
surf
ace
tem
pera
ture
hot
cold
small large
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!
separation
surf
ace
tem
pera
ture
hot
cold
small large
? ?
0 - 1 AU
1 - 2 AU
1 - 5 AU
1 - 10 AU
The HZ around the Sun
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 lifetimeIntense UV
The HZ around other Stars I
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around other Stars II
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around other Stars III
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around other Stars IV
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around other Stars V
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
The HZ around other Stars VI
separation = 1au
brightness of star
surf
ace
tem
pera
ture
hot
cold
small large
QuestionWhich type of star of main-sequence star is the
Habitable Zone closest to?
F
G
K
M
The HZ around other Stars
HZ Plot
Tidal Locking
Question
Why might a tidally lockedplanet be uninhabitable?
A Tidally Locked Jupiter
Tidal Heating
Planet around M-Star
Circ
ular
ity
standard HZ
HZ, only tidal heating
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?
Quiz
3 - What is one thing you did not understand from today’s lecture?
2 - Explain why the Habitable Zone is located further from a main-sequence F star than from a main sequence M star.
1 - Describe the process that generates the energy which drives hydrothermal activity on icy worlds.