Habitable Exomoons
description
Transcript of Habitable Exomoons
Habitable Exomoons
Rory Barnes
with lots of help fromRené Heller
Habitable Exomoonsare Awesome!
Rory Barnes
with lots of help fromRené Heller
What is an exomoon?
Exomoons!?
You’re gonna talk abouthabitable exomoons!?
We don’t even understandhabitable exoplanets!
The Habitable Zone is about Surface Energy Flux
~300 W/m2
~30 W/m2
Kepler couldfind an exomoon.
Kepler couldfind an exomoon.
See theexomoon?
Exomoon Transits and Timing Variations
Kipping et al. (2012)
Exomoon Transits and Timing Variations
Kipping et al. (2012)
DirectDetection
Exomoon Transits and Timing Variations
Kipping et al. (2012)
TTV
Exomoon HabitabilityI. Formation A. Inside Circumplanetary Disk B. Capture C. Planet MigrationII. Radiation A. Starlight B. Reflected Light C. Planetary Thermal Emission D. EclipsesIII. Tidal Heating
The Scale of the Galilean Satellites
Io6 RJup
Europa10 RJup
Ganymede16 RJup
Callisto27 RJup
Canup & Ward (`06)transform disks into
moons
Total mass ofmoons ~10-4 of planet
Earth = 0.003 Jupiter
Williams, AsBio, submitted
Capture Possibilities
Williams, AsBio, submitted
Capture Possibilities
Williams, AsBio, submitted
Capture Possibilities
Williams, AsBio, submitted
Planet has to moveto 1 AU!
Plan
etar
y Se
mi-M
ajor
Axi
s (AU
)
Sate
llite
Sem
i-Maj
or A
xis (
AU)
Time (Years)
Planet
Galilean Moons
Jupiter’s Radius
Namouni (2010)
Plan
etar
y Se
mi-M
ajor
Axi
s (AU
)
Sate
llite
Sem
i-Maj
or A
xis (
AU)
Time (Years)
Jupiter’s Radius
Instabilities due to planet’sshrinkinggravitational influence
Namouni (2010)
Plan
etar
y Se
mi-M
ajor
Axi
s (AU
)
Sate
llite
Sem
i-Maj
or A
xis (
AU)
Time (Years)
Jupiter’s Radius
Namouni (2010)
Moons still safeat 1 AU
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 AUat 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 AUat aps < 5 RJup
There is a “Reflection Correction”for habitable exomoons
Heller & Barnes (2013)
Thermal EmissionHeat 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 itswater early.
There is a “Cooling Edge”for habitable exomoons
Eclipses
LongitudeHeller & Barnes (2013)
EclipsesEclipses No Eclipses
Stellar radiation dominatesWith eclipse -> sub-planetary point is coldNo eclipse -> sub-planetary point is hot
Heller & Barnes (2013)
Radiation
The HZ appliesReflection CorrectionCooling EdgeEclipses could affect local climate
Tidal Heating
Caused by gravitational flexing of the crustSource of tectonics on Io, Europa and EnceladusCould be very large for large moonsCould also produce exo-EuropasCould sustain plate tectonics indefinitely
Tidal GreenhouseTidal/RadiationGreenhouseSuper-IoTidal EarthNo Tidal Heating
Earth orbiting Jupiter orbiting the Sun
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 rareKepler can detect, but hardPlanets add energy to the classical HZA reflection correction pushes HZ out (slightly)Thermal radiation causes a cooling edgeEclipses could alter weatherA tidal heating edge could sterilize close moonsTidal heating could sustain star-free habitats
For more info:
Heller & Barnes, 2013.“Exomoon Habitabilityconstrained by illumination andtidal 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)