Assessing planetary habitability. Giovanni Vladilo INAF - Osservatorio Astronomico di Trieste

Transcription

1 Assessing planetary habitability Giovanni Vladilo INAF - Osservatorio Astronomico di Trieste

2 Personal background interstellar dust: abundance and chemical evolution

3 Recent interest habitability of different types of astrophysical environments Present talk focussed on Planetary habitability... not enough time to present Galactic habitability

4 Assessing the habitability of terrestrial planets by means of Energy Balance Models Gaia Ferri (1,2), Giuseppe Murante (3), Antonello Provenzale (4), Laura Silva (1), Giovanni Vladilo (1,2) (1) INAF - Osservatorio Astronomico di Trieste, (2) University of Trieste, Department of Physics, (3) INAF - Osservatorio Astronomico di Torino, (4) Institute of Atmospheric Sciences and Climate (ISAC)-CNR, Torino

5 Goals Estimate the mean surface temperature of the planet, T Use T as an estimator of habitability

6 Planetary Energy Balance OUTGOING RADIATION Long wavelength INCOMING RADIATION Short wavelength S: stellar radiation A: planetary albedo

7 One-dimensional Energy Balance Models OUTGOING RADIATION INCOMING RADIATION HORIZONTAL TRANSPORT Use Ti(t) as an estimator of habitability

8 OUTGOING RADIATION INCOMING RADIATION Temporal evolution Diffusion coefficient In spite of its simplicity the model can capture some important planetary feedbacks

9 Why Energy Balance Models? Energy Balance Models vs Global Circulation Models Fast simulations Moderate number of parameters Schematic geography Extremely time-consuming Huge number of input parameters Detailed knowledge of geography

10 Why Energy Balance Models? Fast simulations Moderate number of parameters Schematic geography Energy Balance Models vs Global Circulation Models Ideal when experimental data are scarce Extremely time-consuming Huge number of input parameters Detailed knowledge of geography

11 Energy Balance Models ideal for estimating planetary habitability Habitability outside the Solar System Extrasolar planets Habitability in the Solar System Primitive Earth Primitive Mars

12 Main model parameters Astronomical Stellar flux Orbital parameters (a, e...) Planetary Rotational period Axis inclination Ocean fraction Atmospheric parameters Heat capacity Heat diffusion...

13 Main model parameters Astronomical Relatively good observational constraints, even for exoplanets Planetary Very few observational constraints Stellar flux Orbital parameters (a, e...) Rotational period Axis inclination Ocean fraction Atmospheric parameters Heat capacity Heat diffusion...

14 The Energy Balance Model code Validation Based on the detailed comparison with previous results (Spiegel et al. 2008) New implementations Elliptical planetary orbits (most previous codes assume circular orbits) Detailed treatment of planetary albedo Recepy for outgoing IR flux proposed by Williams & Kasting (1997)

15 Tuning of the model parameters Comparison with experimental data of terrestrial planets Earth, Mars Diagnostic tools Temperature - latitude profiles Albedo - latitude profiles...

16 Mean annual temperature versus latitude Data: NASA Mars-GRAM (Global Reference Atmospheric Model) 2010 Model: black-body outgo + albedo from Mars GRAM Mars linea continua: Modello EBM di Marte croci: Misure medie annuali Marte

17 Mean annual temperature versus latitude Data: ERA Interim 2m temperature profiles average Validation of a model presented by Spiegel et al. (2008) Earth

18 Mean seasonal temperature versus latitude Data: ERA Interim 2m temperature profiles average Validation of a model presented by Spiegel et al. (2008) Earth

19 Liquid water criterion Quantifying habitability

20 Fractional habitability Mean annual habitability at a given latitude Mean global habitability at a given time Mean global annual habitability

21 map obtained from 210 simulations Map of fractional habitability in the plane (a,e) for Earth-like planets Based on the Earth-like model presented by Spiegel et al. (2008) fhab Explanation of the trend

22 Map of fractional habitability in the plane (a,e) for Earth-like planets Based on the Earth-like model presented by Spiegel et al. (2008) fhab The Earth lies at the edge of the fractional habitability map

23 Map of fractional habitability in the plane (a,e) for Earth-like planets Based on the Earth-like model presented by Spiegel et al. (2008) Venus is close to the hot edge of the fractional habitability map fhab Mars is far away from the cold edge of the fractional habitability map

24 Map of fractional habitability in the plane (a,e) for generic terrestrial planets Based on the Earth-like model presented by Spiegel et al. (2008) Exoplanets can be plotted on this map, or similar ones, to assess their fractional habitability fhab Maps for generic exoplanets can be produced by varying the stellar & planet parameters

25 Habitability maps: the ocean fraction as a free parameter

26 Terrestrial planet with ocean fraction = 0.7 fhab

27 Terrestrial planet with ocean fraction = 0.3 fhab

28 Terrestrial planet with ocean fraction = 0.0 fhab

29 Mean temperature and CO2 pressure on the Earth at the epoch of the origin of life

30 Habitability of the Earth at the epoch of the origin of life In the primitive Earth the solar flux was ~70% of the present value. Modelling the Earth climate with this faint solar flux yields a frozen planet Since liquid water was present, it is commonly assumed that the primitive greenhouse effect was stronger By using Energy Balance Models we are able to estimate the minimum partial pressure of CO2 necessary to make the early Earth habitable

31 Habitability of the Earth at the epoch of the origin of life We built up a simple model representative of the primitive Earth and gradually rised p(co2) starting from the present atmospheric level (3 x 10-4 bar) Preliminary results obtained from an updated EBM originally introduced by Williams & Kasting (1997)

32 Habitability of the Earth at the epoch of the origin of life Solar flux = 0.70 present value Fraction of oceans=0.95 Total atmospheric pressure=1 bar Partial pressure of CO2 = 0.1 bar Rotation period: 24 h Rotation period: 8 h T (K) Preliminary results obtained from an updated EBM originally introduced by Williams & Kasting (1997)

33 Habitability of the Earth at the epoch of the origin of life Solar flux = 0.70 present value Fraction of oceans=0.95 Total atmospheric pressure=1 bar Partial pressure of CO2 = 0.3 bar Rotation period: 24 h Rotation period: 8 h T (K) Preliminary results obtained from an updated EBM originally introduced by Williams & Kasting (1997)

34 Habitability of the Earth at the epoch of the origin of life Solar flux = 0.70 present value Fraction of oceans=0.95 Total atmospheric pressure=1 bar Partial pressure of CO2 = 0.9 bar Rotation period: 24 h Rotation period: 8 h T (K) Preliminary results obtained from an updated EBM originally introduced by Williams & Kasting (1997)

35 Conclusions Energy Balance Models provide a simple tool for investigating the habitability of terrestrial planets Can be employed to cast light on the properties of the Earth at the epoch of the origin of life There is room for including more realistic climate recepies while keeping low the computing time In order to improve the definition of habitability...

36 ... we would like: biologists to give us a set of limits Tmin, Tmax & Pmin, Pmax for life to exist and climatologists to give us a <Tmax> to avoid runaway grenhouse effect Pmax from biology??? Climatological <Tmax>: runaway greenhouse effect

37 Experimental data for exoplanets by combining different techniques (RV & transit) orbital parameters (a, e) mass, radius & mean density

38 Galactic habitability Galaxy simulations as a tool for mapping habitable zones Pierluigi Monaco (2), Giuseppe Murante (3), Luca Tornatore (2), Giovanni Vladilo (1,2) (1) INAF - Osservatorio Astronomico di Trieste, (2) University of Trieste, Department of Physics (3) INAF - Osservatorio Astronomico di Torino

39 basic idea Galactic Habitable Zone Gonzales et al. (2001) planet formation probability Metallicity level planet sterilization probability Rate of supernova explosions In particular regions of the Galaxy the combined probability is optimal for habitability

40 Cosmological SPH N-body simulations Milky Way-like galaxies evolutionary maps of properties relevant for habitability Metallicity level planet formation probability Rate of supernova explosions planet sterilization probability

41 Cosmological SPH N-body simulations Milky Way-like galaxies evolutionary maps of properties relevant for habitability Metallicity level planet formation probability Rate of supernova explosions please contact me if you are interested planet sterilization probability

42 Example of planetary feedback induced by a change of rotational velocity period: 24 h period: 8 h Example: validation of an Earth-like model presented by Spiegel et al. (2008)