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 Youre gonna ID: 615318
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Slide1
Habitable
Exomoons
Rory Barnes
with lots of help from
René HellerSlide2
Habitable
Exomoonsare Awesome!
Rory Barnes
with lots of help from
René HellerSlide3
What is an
exomoon?Slide4
Exomoons
!?
You’re
gonna
talk about
habitable
exomoons
!?
We don’t even understand
habitable
exoplanets!Slide5
The Habitable Zone is about Surface Energy Flux
~300 W/m
2
~30 W/m
2Slide6
Kepler
could
find an
exomoon
.Slide7
Kepler
could
find an
exomoon
.
See the
exomoon
?Slide8
Exomoon
Transits and Timing VariationsKipping
et al.
(2012)Slide9
Exomoon
Transits and Timing VariationsKipping
et al.
(2012)
Direct
DetectionSlide10
Exomoon
Transits and Timing VariationsKipping
et al.
(2012)
TTVSlide11
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. EclipsesIII. Tidal HeatingSlide12
The Scale of the Galilean Satellites
Io
6
R
Jup
Europa
10
R
Jup
Ganymede
16
R
Jup
Callisto
27
R
JupSlide13
Canup
& Ward (`06)
transform disks into
moons
Total mass of
moons ~10
-4
of planet
Earth = 0.003 JupiterSlide14
Williams,
AsBio, submittedSlide15
Capture Possibilities
Williams, AsBio, submittedSlide16
Capture Possibilities
Williams, AsBio, submittedSlide17
Capture Possibilities
Williams, AsBio, submitted
Planet has to move
to 1 AU!Slide18
Planetary Semi-Major Axis (AU)
Satellite Semi-Major Axis (AU)
Time (Years)
Planet
Galilean Moons
Jupiter’s Radius
Namouni
(2010)Slide19
Planetary Semi-Major Axis (AU)
Satellite Semi-Major Axis (AU)
Time (Years)
Jupiter’s Radius
Instabilities
due to planet’s
shrinking
gravitational
influence
Namouni
(2010)Slide20
Planetary Semi-Major Axis (AU)
Satellite Semi-Major Axis (AU)
Time (Years)
Jupiter’s Radius
Namouni
(2010)
Moons
still safe
at 1 AUSlide21
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 formMoon must survive migration to HZSlide22
The Radiation Environment of
ExomoonsHeller & Barnes (2013)Slide23
Starlight Only – The Habitable ZoneSlide24
Reflected Light – Almost Negligible
Multiply your HZ
boundary by this factor
For F star, outer HZ
pushed out by ~0.01 AU
at
a
ps
< 5
R
Jup
Heller & Barnes (2013)Slide25
Reflected Light – Almost Negligible
Multiply your HZ
boundary by this factor
For F star, outer HZ
pushed out by ~0.01 AU
at
a
ps
< 5
R
Jup
There is a “Reflection Correction”for habitable
exomoons
Heller & Barnes (2013)Slide26
Thermal Emission
Heat from star (almost negligible)Heat from Contraction (important early)
Longitude
Heller & Barnes (2013)Slide27
Planets Cool with Time*
* adopted from
Baraffe
+ (1997, 2003)Slide28
A Moon at
Europa’s Orbit
Run.
Grnhs
LimitSlide29
Time in a Runaway GreenhouseSlide30
Time in a Runaway Greenhouse
The moon could lose its
water early.
There is a “Cooling Edge”
for habitable
exomoonsSlide31
Eclipses
Longitude
Heller & Barnes (2013)Slide32
Eclipses
Eclipses
No Eclipses
Stellar radiation dominates
With eclipse -> sub-planetary point is cold
No eclipse -> sub-planetary point is hot
Heller & Barnes (2013)Slide33
Radiation
The HZ applies
Reflection Correction
Cooling Edge
Eclipses could affect local climateSlide34
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 indefinitelySlide35
Tidal Greenhouse
Tidal/RadiationGreenhouse
Super-Io
Tidal Earth
No Tidal Heating
Earth orbiting Jupiter orbiting the SunSlide36Slide37
Earth orbiting Jupiter orbiting the SunSlide38
Earth orbiting Jupiter orbiting the SunSlide39
Earth orbiting Jupiter orbiting the Sun
There is a “Tidal Heating Edge”
to
exomoon
habitabilitySlide40
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 habitatsSlide41
For more info:
Heller & Barnes, 2013.“Exomoon Habitabilityconstrained by illumination and
tidal heating.”
AsBio
,
13, 18-46.Slide42
Tidally Heated to Habitable?
Reynolds, McKay & Kasting
(1987)Slide43
Radiative
+ Tidal HZsReynolds, McKay &
Kasting
(1987)Slide44
Orbits After Capture
Porter & Grundy (2011)Slide45
Reflected and Thermal Light (“
inplanation”)
Heller & Barnes (2013)Slide46
Heller & Barnes (2013)Slide47
Heller & Barnes (2013)Slide48
Heller & Barnes (2013)Slide49
Heller & Barnes (2013)Slide50
Heller & Barnes (2013)Slide51
Heller & Barnes (2013)