LAST TIME: We explored planetary transits in depth

2 Ftr Rp =1 planetary atmospheres Fnotr R? ⇣ ⌘ (greenhouse effect), introduced the term “albedo” …

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

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. How do we learn what an atmosphere is made of?

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

Putting these tools together can actually allow you to learn about exoplanet atmospheres. How do we learn what an atmosphere is made of?

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

Putting these tools together can actually allow you to learn about exoplanet atmospheres. DISCUSS IN YOUR GROUP: Scenario B Scenario A Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue Consider planet V which has a very thick light from its star. Suppose this blue atmosphere. It’s so thick that it absorbs all light is absorbed by a particular gas in light from its star. Another planet, T, has no M’s atmosphere. What would its transit atmosphere but has the same radius. How look like, and how would its transit differ would the transit event of these two planets from V? What kind of measurement is differ? necessary to tell the difference between M and V? T M ?

V V DISCUSS IN YOUR GROUP: Scenario B Scenario A Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue Consider planet V which has a very thick light from its star. Suppose this blue atmosphere. It’s so thick that it absorbs all light is absorbed by a particular gas in light from its star. Another planet, T, has no M’s atmosphere. What would its transit atmosphere but has the same radius. How look like, and how would its transit differ would the transit event of these two planets from V? What kind of measurement is differ? necessary to tell the difference between M and V? T M ?

V V DISCUSS IN YOUR GROUP: Scenario B Scenario A Consider planet V and a new planet M. Planet M’s atmosphere absorbs all blue Consider planet V which has a very thick light from its star. Suppose this blue atmosphere. It’s so thick that it absorbs all light is absorbed by a particular gas in light from its star. Another planet, T, has no M’s atmosphere. What would its transit atmosphere but has the same radius. How look like, and how would its transit differ would the transit event of these two planets from V? What kind of measurement is differ? necessary to tell the difference between M and V? T M ?

V V 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 After discussing in your look like, and how would its transit differ group, take a moment to from V? What kind of measurement is necessary to tell the difference between write down what type of M and V? measurements you would take to measure M’s M atmosphere. ?

Remember: M is still a fruitfly in front V of a search light a mile away… This technique is called Transmission spectroscopy.

If we know the spectrum of the star very well, we can measure the spectrum of M 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 V the transit as a function of wavelength.

time This technique is called Transmission spectroscopy.

If we know the spectrum of the star very well, we can measure the spectrum of M 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 V the transit as a function of wavelength.

time This technique is called Transmission spectroscopy.

If we know the spectrum of the star very well, we can measure the spectrum of M 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 V the transit as a function of wavelength.

time This technique is called Transmission spectroscopy.

If we know the spectrum of the star very well, we can measure the spectrum of M 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 V 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

if Pluto’s atmosphere 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

if Pluto’s atmosphere 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

if Pluto’s atmosphere 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

if Pluto’s atmosphere 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) An example transmission spectrum for a hot Jupiter. (Compared to models of atmospheres of different compositions)

GJ1214b; Berta et al. (2012) 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

= Transmission Spectroscopy

Deduced via addition with the starlight

= (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.

L = luminosity of star, D = distance between Flux absorbed by L star & planet planet and (probably) Fp =(1 a)F =(1 a) 2 turned into thermal 4⇡D energy (heat)

Flux from planet’s star (at the fromgiven star) distance

a 0.3 a 0.6 rocky planets⇠ aren’t especially ⇠ snow and ice are highly reflective, though clouds are reflective at visible wavelengths somewhat note: an atmosphere isn’t needed for albedo to vary! Let’s investigate a tool used in homework #8.

1 a 1/4 T no g h = 280 K 0 0 D2 (from page 274 in the⇣ book) ⌘

a = albedo or reflectivity D = distance from sun to planet in AU

Where does this come from? Formulas you already know! L =4⇡D2F F = T 4 Let’s investigate a tool used in homework #8.

1 a 1/4 T no g h = 280 K 0 0 D2 (from page 274 in the⇣ book) ⌘

a = albedo or reflectivity D = distance from sun to planet in AU

Where does this come from? Formulas you already know! L =4⇡D2F F = T 4 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.

1 a 1/4 T no g h = 280 K 0 0 D2 (from page 274 in the⇣ book) ⌘

a = albedo or reflectivity D = distance from sun to planet in AU

Where does this come from? Formulas you already know! L =4⇡D2F F = T 4 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:

This at least tells us (in the 1/4 1/4 L? (1 a) absence) of the T‘no g h = greenhouse effect, what 0 16⇡ D2 the surface temperature of ⇣ ⌘ ⇣ ⌘ an exoplanet may be! What temperature do you think is best to support life? (if you HAD to guess)

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

This at least tells us (in the 1/4 1/4 L? (1 a) absence) of the T‘no g h = greenhouse effect, what 0 16⇡ D2 the surface temperature of ⇣ ⌘ ⇣ ⌘ an exoplanet may be! 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 water boils 0oC 100oC (273.15 K) (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 boils! water freezes! THE HABITABLE ZONE. THE HABITABLE ZONE. log10(D)

Our solar system’s habitable zone: Earth, maybe Mars. 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? Artist’s impression of a snowball Earth infrared

Shields et al. (2013)

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist What makes habitable zone planets habitable: not having a snowball planet perhaps? Artist’s impression of a snowball Earth snow infrared

Shields et al. (2013)

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist What makes habitable zone planets habitable: not having a snowball planet perhaps? Artist’s impression of a snowball Earth snow infrared

land

Shields et al. (2013)

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist What makes habitable zone planets habitable: not having a snowball planet perhaps? Artist’s impression of a snowball Earth snow infrared

land

Shields et al. (2013)

Aomawa Shields (UCI), exoplanet climatologist/astrophysicist What makes habitable zone planets habitable: not having a snowball planet perhaps? Artist’s impression of a snowball Earth snow infrared

land

Shields et al. (2013)

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… Aomawa Shields (UCI), exoplanet climatologist/astrophysicist 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.