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.