exoplanets, extremophiles and habitabilityconference.astro.ufl.edu/starstolife/science_final/... ·...

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EXOPLANETS, EXTREMOPHILES AND

HABITABILITY

Eduardo Janot Pacheco, Luander Bernardes

Institute of Astronomy, Geophysics and Atmospheric Sciences, Department of Astronomy, University of São Paulo, BRAZIL

and

Claudia LageInstitute of Biophysics Carlos Chagas Filho,Rio de Janeiro Federal University, BRAZIL

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PURPOSE OF THE WORK:

ESTIMATE OF

Average Surface Temperature

CO2 Partial Atmospheric Pressure pCO2 as a

free parameter,

For exoplanets in the Habitable Zone (HZ)

For hypothetical moons of gaseous giants known to

be in the HZ

EXOPLANETS + TERRESTRIAL ATMOSPHERE

GREENHOUSE EFFECT

(data base: J. Schneider’s http://exoplanet.eu/)

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INPUT:

The Extrasolar Planet Encyclopedia

Williams (1997) atmospheric model for the Earth

(geodynamic conditions, Si-Ca cycle, albedo...)

Exomoons of gaseous giants in the HZ with an

atmosphere, dynamic stability, geodynamic activity...

RESULTS:

1) more precise determination of HZ

2) New concept: the EXTREMOPHILIC ZONE: EZ

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Energy Budget Equation of the atmospheric model:

L(t) is the stellar luminosity, d the exoplanet orbit size,

A the atmospheric albedo, which is a fonction of the

surface albedo as surface temperature Ts , stellar azimutal

angle µ, CO2 partial pressure p and F the IR flux leaving

the planet.

where

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Basic Equations for the exomoons model:

1) Stable orbital radii (Domingos et al., 2006):

for prograde orbits and

for retrograde orbits. RH is the exoplanet Hill radius.

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Basic Equations for the exomoons model (cont.):

Maximum exomoon mass (Murray & Dermott, 2000; Barnes et al. 2009):

Where f, Qp and k2p are parameters adjusted

empirically, T is the time scale for the moon orbital

decay and a, M and R are the orbital semi-major axis,

masses and radius of the planet and moon.

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EXTREMOPHILES: life under extreme conditions

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Radiococcus radiodurans: endures 10,000 times the

radiation dose lethal for humans

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Experiment on panspermia

+ Solar UV +

Carbon tape

=

Concordia micrometeorite

=100µm

Microastronauts?

Lima et al. 2010; Lima et al. 2011

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ASTROBIOLOGY

THE EXTREMOPHILIC ZONE (EZ), A NEW

CONCEPT :

“EZ IS THE TEMPERATURE REGION AROUND A

STAR WHERE (TERRESTRIAL) EXTREMOPHILES

COULD LIVE ”

EZs are obviously more extended than HZs.

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<

SOME RESULTS

a) for rocky planets supposed to be in

the HZ

b) for hypothetical moons around

gaseous giants in the HZ

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<

Results for the Solar System

Look out!

Earth will be outside both the HZ and

EZ in 1.7 G years from now for any

reasonable CO2 partial pressure. Mars

will then be inside the EZ.

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Habitability in the Solar SystemHZ: 273K<T<373; EZ: 190<T<390

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Habitability in the Solar System (cont.)

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Habitability in the Solar System (cont.)

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<

Results for the Solar System

Look out!

Earth will be outside both the HZ and

EZ in 1.7 G years from now for any

reasonable CO2 partial pressure. Mars

will then be inside the EZ.

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Analysis of habitability for the Gl 581 SystemMayor et al. 2008: “GL 581c is in the HZ”

(GL 581d is a super-Earth with 6 MEarth

)

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Analysis of habitability for the Gl 581 System (cont.)GL581d can hardly be in the HZ

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Analysis of habitability for the Gl 581 System (cont)GL 581 b is in the EZ

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<

Habitability in the planetary system of Gliese 581 (M3V)

Super-Earth planet “d” (6 MEarth) stays in

HZ and EZ from 2.2 G years on. But, it is

outside the HZ for any reasonable CO2

partial pressure. Nevertheless, the planet is

in the EZ even for small CO2 pressures as

e.g. on Earth (3x10-4 bars).

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Analysis of habitability for the HD 37124 SystemG4V star

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Analysis of habitability for the HD 37124 System (cont.)

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Analysis of habitability for the HD 37124 System (cont.)

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Analysis of habitability for the HD 37124 System (cont.)

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<

Planet “c” enters HZ after 6 G years but very

high CO2 partial pressures are needed for it.

It is always in the EZ for any CO2 pressure.

Exomoons with masses capable to maintain plate

tectonics and an atmosphere are able to exist

orbiting HD37124 c.

Habitability in the planetary system of

HD 37124 (G4V)

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HZ

EZ

Habitable and Extremophilic zones for some planetary systems

<

CONCLUSIONS

Using a model of an Earth-like atmosphere and a model for the orbital stability of exomoons, we show that terrestrial extremophile organisms can survive on the surface of planets and moons of extrasolar systems in a region larger than the “classical” HZ. Definition of “Extremophilic Zone” (EZ) Next step: to use  detailed atmospheric models with other free parameters to investigate the possible survival of extremophiles in these environments.

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THANK YOU!