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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
What determines habitability?
stellar lifetime
UV
stellar energy received
greenhouse gases
UV shield
impacts
stable orbit
formed w/water
tectonics
magnetic field
Habitable Zone (HZ) = the region around a
star where an Earth-like planet could sustain
liquid water on its surface
habitable
not habitable
ethane
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
surface temperature
separation = 1au
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
surface temperature
separation = 1au
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
surface temperature
hot
cold
small
large
separation
Question
surface temperature
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
1 - 5 AU
1 - 10 AU
cold
?
?
small
large
separation
The HZ around the Sun
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
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
surface temperature
separation = 1au
hot
cold
small
large
brightness of star
Question
Which type of star of main-sequence star is the
Habitable Zone closest to?
F
G
K
M
The HZ around other Stars
Question
Why might a tidally locked
planet be uninhabitable?
Circularity
Planet around M-Star
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
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?