LAST TIME:We explored planetary transits in depth

planetary atmospheres (greenhouse effect),

introduced the term “albedo” …

TODAY:Using transits to infer atmospheric

composition, inferring temperature of earth like planets, and ALIENS.

Homeworks 8-10 pushed back — due on Tuesdays for the rest of the semester.

a=0 (not reflective) a=1 (reflective)

Ftr

Fnotr

= 1�⇣Rp

R?

⌘2

Last time we looked in detail at (a) greenhouse gases & how they work, and (b) how planetary transits work…

How do we learn what an atmosphere is made of?

Putting these tools together can actually allow you to learn about exoplanet atmospheres.

Last time we looked in detail at (a) greenhouse gases & how they work, and (b) how planetary transits work…

How do we learn what an atmosphere is made of?

Putting these tools together can actually allow you to learn about exoplanet atmospheres.

Scenario AScenario B

Consider planet V which has a very thick atmosphere. It’s so thick that it absorbs all light from its star. Another planet, T, has no atmosphere but has the same radius. How would the transit event of these two planets differ?

V

T

Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue light from its star. Suppose this blue light is absorbed by a particular gas in M’s atmosphere. What would its transit look like, and how would its transit differ from V? What kind of measurement is necessary to tell the difference between M and V?

V

M?

DISCUSS IN YOUR GROUP:

Scenario AScenario B

Consider planet V which has a very thick atmosphere. It’s so thick that it absorbs all light from its star. Another planet, T, has no atmosphere but has the same radius. How would the transit event of these two planets differ?

V

T

Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue light from its star. Suppose this blue light is absorbed by a particular gas in M’s atmosphere. What would its transit look like, and how would its transit differ from V? What kind of measurement is necessary to tell the difference between M and V?

V

M?

DISCUSS IN YOUR GROUP:

Scenario AScenario B

Consider planet V which has a very thick atmosphere. It’s so thick that it absorbs all light from its star. Another planet, T, has no atmosphere but has the same radius. How would the transit event of these two planets differ?

V

T

Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue light from its star. Suppose this blue light is absorbed by a particular gas in M’s atmosphere. What would its transit look like, and how would its transit differ from V? What kind of measurement is necessary to tell the difference between M and V?

V

M?

DISCUSS IN YOUR GROUP:

V

M?

After discussing in your group, take a moment to write down what type of

measurements you would take to measure M’s

atmosphere.

Remember: M is still a fruitfly in front of a search light a mile away…

DISCUSS IN YOUR GROUP:Scenario B

Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue light from its star. Suppose this blue light is absorbed by a particular gas in M’s atmosphere. What would its transit look like, and how would its transit differ from V? What kind of measurement is necessary to tell the difference between M and V?

This technique is called Transmission spectroscopy.

V

MIf we know the spectrum of the star very well, we can measure the spectrum of the star during a transit and figure out

the difference between the two spectra to constrain the planet’s atmosphere.

In other words, we measure the depth of the transit as a function of wavelength.

time

This technique is called Transmission spectroscopy.

V

MIf we know the spectrum of the star very well, we can measure the spectrum of the star during a transit and figure out

the difference between the two spectra to constrain the planet’s atmosphere.

In other words, we measure the depth of the transit as a function of wavelength.

time

This technique is called Transmission spectroscopy.

V

MIf we know the spectrum of the star very well, we can measure the spectrum of the star during a transit and figure out

the difference between the two spectra to constrain the planet’s atmosphere.

In other words, we measure the depth of the transit as a function of wavelength.

time

This technique is called Transmission spectroscopy.

V

MIf we know the spectrum of the star very well, we can measure the spectrum of the star during a transit and figure out

the difference between the two spectra to constrain the planet’s atmosphere.

In other words, we measure the depth of the transit as a function of wavelength.

time

This is Pluto as seen from its far side, looking back towards the Sun.

This is Pluto as seen from its far side, looking back towards the Sun.we only see this glow

because Pluto has an

atmosphere.

This is Pluto as seen from its far side, looking back towards the Sun.we only see this glow

because Pluto has an

atmosphere.

if Pluto’s atmosphere

scattered all light equally

the glow would be the

same color of the sun

This is Pluto as seen from its far side, looking back towards the Sun.we only see this glow

because Pluto has an

atmosphere.

if Pluto’s atmosphere

scattered all light equally

the glow would be the

same color of the sun

This is Pluto as seen from its far side, looking back towards the Sun.we only see this glow

because Pluto has an

atmosphere.

if Pluto’s atmosphere

scattered all light equally

the glow would be the

same color of the sun

This is Pluto as seen from its far side, looking back towards the Sun.we only see this glow

because Pluto has an

atmosphere.

if Pluto’s atmosphere

scattered all light equally

the glow would be the

same color of the sun

the sun’s spectrum was taken during this phase when partial light was blocked due to the atmosphere.

Now back to transiting exoplanets…

Now back to transiting exoplanets…

An example transmission spectrum for a hot Jupiter.

GJ1214b; Berta et al. (2012)

GJ1214b; Berta et al. (2012)

An example transmission spectrum for a hot Jupiter.

(Compared to models of atmospheres of different compositions)

The best transmission spectra so far from HST: 10 transiting hot-Jupiters.

Sing et al. (2015)

There is also “phase-resolved emission spectroscopy”

We can only measure the total light of the whole system as a function of wavelength. But if we do this very precisely and we know the star well…

There is also “phase-resolved emission spectroscopy”

There is also “phase-resolved emission spectroscopy”

Spectroscopy of planets can either be:

Deduced via subtraction from the starlight

Deduced via addition with the starlight

= Transmission Spectroscopy

= (Phase-Resolved) Emission Spectroscopy

last time: albedo ranges from 0 (absorbs all light) to 1 (fully reflective) and the symbol “a” is how we refer to albedo.

a ⇠ 0.6a ⇠ 0.3

Flux absorbed by

planet and (probably)

turned into thermal

energy (heat)

Flux from planet’s star

(at the given distance

from star)

Fp = (1� a)F = (1� a)L

4⇡D2

L = luminosity of star,

D = distance between star & planet

snow and ice are highly reflective at visible wavelengths

rocky planets aren’t especially reflective, though clouds are

somewhatnote: an atmosphere isn’t needed for albedo to vary!

Let’s investigate a tool used in homework #8.

L = 4⇡D2F F = �T 4

T0no g�h

0 = 280K⇣1� a

D2

⌘1/4

(from page 274 in the book)

a = albedo or reflectivityD = distance from sun to planet in AU

Where does this come from? Formulas you already know!

Let’s investigate a tool used in homework #8.

L = 4⇡D2F F = �T 4

T0no g�h

0 = 280K⇣1� a

D2

⌘1/4

(from page 274 in the book)

a = albedo or reflectivityD = distance from sun to planet in AU

Where does this come from? Formulas you already know!

What it MEANS is that the “no greenhouse” temperature is highest when albedo = 0, or when the planet is closer to the sun. The above formula is

only good for our sun. The generic formula is:

Let’s investigate a tool used in homework #8.

L = 4⇡D2F F = �T 4

T0no g�h

0 = 280K⇣1� a

D2

⌘1/4

(from page 274 in the book)

a = albedo or reflectivityD = distance from sun to planet in AU

Where does this come from? Formulas you already know!

What it MEANS is that the “no greenhouse” temperature is highest when albedo = 0, or when the planet is closer to the sun. The above formula is

only good for our sun. The generic formula is:

T‘no g�h

0 =⇣ L?

16⇡�

⌘1/4⇣ (1� a)

D2

⌘1/4

This at least tells us (in the absence) of the

greenhouse effect, what the surface temperature of

an exoplanet may be!

What temperature do you think is best to support life? (if you HAD to guess)

T‘no g�h

0 =⇣ L?

16⇡�

⌘1/4⇣ (1� a)

D2

⌘1/4

This at least tells us (in the absence) of the

greenhouse effect, what the surface temperature of

an exoplanet may be!

(a) ~ 30 K (b) ~300 K (c) ~3000 K (d)~30000 K

WATER: essential for all life or just ours?

WATER: essential for all life or just ours?

WHAT IS THE RANGE OF TEMPERATURES WHERE WATER IS A LIQUID?

water freezes 0oC

(273.15 K)

water boils 100oC

(373.15 K)

GROUP DISCUSSION: DOES THE SIZE OF THE HABITABLE ZONE — AND ITS DISTANCE FROM ITS STAR — DEPEND ON PROPERTIES OF THE STAR?

GROUP DISCUSSION: DOES THE SIZE OF THE HABITABLE ZONE — AND ITS DISTANCE FROM ITS STAR — DEPEND ON PROPERTIES OF THE STAR?

water freezes!water boils!

THE HABITABLE ZONE.

THE HABITABLE ZONE.

Our solar system’s habitable zone: Earth, maybe Mars.

log10(D)

THE HABITABLE ZONE.log10(D)

Super-Earths are incredibly common in the habitable zone. Super-Earths and Neptunes seem to be the most common planet size out there! And yet we have no

Super-Earths in our own Solar System.

Super-Earths are incredibly common in the habitable zone. Super-Earths and Neptunes seem to be the most common planet size out there! And yet we have no

Super-Earths in our own Solar System.

What makes habitable zone planets habitable: not having a snowball planet perhaps?

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist

Shields et al. (2013)

Artist’s impression of a snowball Earth

infrared

What makes habitable zone planets habitable: not having a snowball planet perhaps?

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist

Shields et al. (2013)

Artist’s impression of a snowball Earth

snow infrared

What makes habitable zone planets habitable: not having a snowball planet perhaps?

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist

Shields et al. (2013)

Artist’s impression of a snowball Earth

snow

land

infrared

What makes habitable zone planets habitable: not having a snowball planet perhaps?

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist

Shields et al. (2013)

Artist’s impression of a snowball Earth

snow

land

infrared

What makes habitable zone planets habitable: not having a snowball planet perhaps?

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist

Shields et al. (2013)

Artist’s impression of a snowball Earth

Ice actually can absorb more heat from low-mass stars — stars emitting primarily in the

infrared — compared to land. In other words, harder to freeze, easier to thaw…

snow

land

infrared

ARE WE ALONE?

ARE WE ALONE?

SO, ARE WE ALONE? IS ALIEN COMMUNICATION POSSIBLE AND/OR PROBABLE?

Brainstorm with your groups how you would begin to estimate the

number of civilizations in our own galaxy that we could plausibly

communicate with. What factors do you think you should consider in

your estimate?number of stars in the galaxy ~ 100 billion

THE DRAKE EQUATION.