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Habitable Exomoons. Rory Barnes with lots of help from René Heller. Habitable Exomoons are Awesome!. Rory Barnes with lots of help from René Heller. What is an exomoon ?. Exomoons !?. You’re gonna talk about habitable exomoons !?. We don’t even understand

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Habitable Exomoons

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Habitable Exomoons

Rory Barnes

with lots of help from

René Heller


Habitable Exomoons

are Awesome!

Rory Barnes

with lots of help from

René Heller


What is an exomoon?


Exomoons!?

You’re gonna

talk about

habitable exomoons!?

We don’t even understand

habitable exoplanets!


The Habitable Zone is about Surface Energy Flux

~300 W/m2

~30 W/m2


Keplercould

find an

exomoon.


Keplercould

find an

exomoon.

See the

exomoon?


Exomoon Transits and Timing Variations

Kipping et al. (2012)


Exomoon Transits and Timing Variations

Direct

Detection

Kipping et al. (2012)


Exomoon Transits and Timing Variations

TTV

Kipping et al. (2012)


Exomoon Habitability

I. Formation

A. Inside Circumplanetary Disk

B. Capture

C. Planet Migration

II. Radiation

A. Starlight

B. Reflected Light

C. Planetary Thermal Emission

D. Eclipses

III. Tidal Heating


The Scale of the Galilean Satellites

Callisto

27 RJup

Europa

10 RJup

Io

6 RJup

Ganymede

16 RJup


Canup & Ward (`06)

transform disks into

moons

Total mass of

moons ~10-4 of planet

Earth = 0.003 Jupiter


Williams, AsBio, submitted


Capture Possibilities

Williams, AsBio, submitted


Capture Possibilities

Williams, AsBio, submitted


Capture Possibilities

Planet has to move

to 1 AU!

Williams, AsBio, submitted


Planet

Satellite Semi-Major Axis (AU)

Planetary Semi-Major Axis (AU)

Galilean Moons

Jupiter’s Radius

Time (Years)

Namouni (2010)


Instabilities

due to planet’s

shrinking

gravitational

influence

Satellite Semi-Major Axis (AU)

Planetary Semi-Major Axis (AU)

Jupiter’s Radius

Time (Years)

Namouni (2010)


Moons

still safe

at 1 AU

Satellite Semi-Major Axis (AU)

Planetary Semi-Major Axis (AU)

Jupiter’s Radius

Time (Years)

Namouni (2010)


Exomoon Formation/Composition

May form with planet (<10 Myr)

- Icy worlds (volatile rich)

- But small

May be captured

- Requires precise encounters

- Captured body must have water

- Terrestrial planets need ~100 Myr to form

Moon must survive migration to HZ


The Radiation Environment of Exomoons

Heller & Barnes (2013)


Starlight Only – The Habitable Zone


Reflected Light – Almost Negligible

Multiply your HZ

boundary by this factor

For F star, outer HZ

pushed out by ~0.01 AU

at aps < 5 RJup

Heller & Barnes (2013)


Reflected Light – Almost Negligible

Multiply your HZ

boundary by this factor

For F star, outer HZ

pushed out by ~0.01 AU

at aps < 5 RJup

There is a “Reflection Correction”

for habitable exomoons

Heller & Barnes (2013)


Thermal Emission

Heat from star (almost negligible)

Heat from Contraction (important early)

Longitude

Heller & Barnes (2013)


Planets Cool with Time*

* adopted from Baraffe+ (1997, 2003)


A Moon at Europa’s Orbit

Run. Grnhs Limit


Time in a Runaway Greenhouse


Time in a Runaway Greenhouse

The moon could lose its

water early.

There is a “Cooling Edge”

for habitable exomoons


Eclipses

Longitude

Heller & Barnes (2013)


Eclipses

No Eclipses

Eclipses

Stellar radiation dominates

With eclipse -> sub-planetary point is cold

No eclipse -> sub-planetary point is hot

Heller & Barnes (2013)


Radiation

The HZ applies

Reflection Correction

Cooling Edge

Eclipses could affect local climate


Tidal Heating

Caused by gravitational flexing of the crust

Source of tectonics on Io, Europa and Enceladus

Could be very large for large moons

Could also produce exo-Europas

Could sustain plate tectonics indefinitely


Earth orbiting Jupiter orbiting the Sun

Tidal Greenhouse

Tidal/Radiation

Greenhouse

Super-Io

Tidal Earth

No Tidal Heating


Earth orbiting Jupiter orbiting the Sun


Earth orbiting Jupiter orbiting the Sun


Earth orbiting Jupiter orbiting the Sun

There is a “Tidal Heating Edge”

to exomoon habitability


Conclusions

Large exomoons probably rare

Kepler can detect, but hard

Planets add energy to the classical HZ

A reflection correction pushes HZ out (slightly)

Thermal radiation causes a cooling edge

Eclipses could alter weather

A tidal heating edge could sterilize close moons

Tidal heating could sustain star-free habitats


For more info:

Heller & Barnes, 2013.

“Exomoon Habitability

constrained by

illumination and

tidal heating.” AsBio,

13, 18-46.


Tidally Heated to Habitable?

Reynolds, McKay & Kasting (1987)


Radiative + Tidal HZs

Reynolds, McKay & Kasting (1987)


Orbits After Capture

Porter & Grundy (2011)


Reflected and Thermal Light (“inplanation”)

Heller & Barnes (2013)


Heller & Barnes (2013)


Heller & Barnes (2013)


Heller & Barnes (2013)


Heller & Barnes (2013)


Heller & Barnes (2013)


Heller & Barnes (2013)


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