128
G. Vladilo et al.
biological origin. Searching for atmospheric biosignatures is one of the top priorities
of exoplanetary observations that will be carried out with the next generation astronomical facilities in space (e.g. JWST) and on ground (e.g. E-ELT). The detection of
atmospheric bio-signatures in rocky planets is extremely challenging and requires a
careful pre-selection of suitable targets. In turn, this requires a modelization of the
surface and atmospheric properties of the planet, starting from the modest amount of
experimental data that can be obtained from the observational methods of exoplanets [3]. Modelling the surface conditions is essential to characterize the habitability
of the planet and to understand if surface life, if present, can generate atmospheric
signatures. Modelling the atmosphere is necessary not only to estimate the impact
of atmospheric feedbacks on the climate and habitability, but also to calculate the
optical depth of atmospheric biosignatures that could be detected with spectroscopic
methods. The modelization of surface and atmospheric properties of exoplanets can
be accomplished with the aid of dedicated climate models that we briefly discuss in
the second part of this presentation.
14.2 Thermal Limits of Multicellular Life
Life has several requirements that may be used to define criteria of habitability.
These requirements include, among others, the existence of suitable energy sources,
physical conditions, protection from ionizing radiation, and an appropriate set of
chemical constituents. The thermodynamical conditions that allow water to be present
in liquid phase on the planetary surface are commonly used to define the liquidwater criterion which, with the aid of climate models, is applied to estimate the
extension of the habitable zone (HZ) around planet-hosting stars [4, 5]. The liquidwater criterion provides temperature limits that can be parametrized as a function of
surface atmospheric pressure to define a pressure-dependent HZ [6].
Beside its importance for the potential existence of liquid water, the ambient
temperature can be used to set thermal limits of habitability based on the temperature
dependence of biological processes [7]. Terrestrial life is characterized by thermal
limits of survival, metabolism, and reproduction that are specific for different types
of organisms [8]. Here we consider the thermal limits of multicellular organisms
with active metabolism. We focus on multicellular organisms because they represent
a necessary step along the evolutionary pathways that lead to the emergence of life
with neural connections and brains, i.e. the type of life which is of interest for SETI.
We focus on organisms with active metabolism because this is the only type of life
that can generate a detectable chemical imprint in the exoplanetary atmosphere.
Among terrestrial organisms, poikilotherms are of special interest for setting thermal limits of habitability because their internal temperature depends directly on and
varies with ambient temperature [1, 7]. Conversely, homeotherms do not provide
straightforward limits of ambient temperature because they are able to stabilize their
internal conditions over a broad range of external temperatures [9]. Homeotherms
are interesting in the context of SETI, because a tight control of the internal body
G. Vladilo et al.
biological origin. Searching for atmospheric biosignatures is one of the top priorities
of exoplanetary observations that will be carried out with the next generation astronomical facilities in space (e.g. JWST) and on ground (e.g. E-ELT). The detection of
atmospheric bio-signatures in rocky planets is extremely challenging and requires a
careful pre-selection of suitable targets. In turn, this requires a modelization of the
surface and atmospheric properties of the planet, starting from the modest amount of
experimental data that can be obtained from the observational methods of exoplanets [3]. Modelling the surface conditions is essential to characterize the habitability
of the planet and to understand if surface life, if present, can generate atmospheric
signatures. Modelling the atmosphere is necessary not only to estimate the impact
of atmospheric feedbacks on the climate and habitability, but also to calculate the
optical depth of atmospheric biosignatures that could be detected with spectroscopic
methods. The modelization of surface and atmospheric properties of exoplanets can
be accomplished with the aid of dedicated climate models that we briefly discuss in
the second part of this presentation.
14.2 Thermal Limits of Multicellular Life
Life has several requirements that may be used to define criteria of habitability.
These requirements include, among others, the existence of suitable energy sources,
physical conditions, protection from ionizing radiation, and an appropriate set of
chemical constituents. The thermodynamical conditions that allow water to be present
in liquid phase on the planetary surface are commonly used to define the liquidwater criterion which, with the aid of climate models, is applied to estimate the
extension of the habitable zone (HZ) around planet-hosting stars [4, 5]. The liquidwater criterion provides temperature limits that can be parametrized as a function of
surface atmospheric pressure to define a pressure-dependent HZ [6].
Beside its importance for the potential existence of liquid water, the ambient
temperature can be used to set thermal limits of habitability based on the temperature
dependence of biological processes [7]. Terrestrial life is characterized by thermal
limits of survival, metabolism, and reproduction that are specific for different types
of organisms [8]. Here we consider the thermal limits of multicellular organisms
with active metabolism. We focus on multicellular organisms because they represent
a necessary step along the evolutionary pathways that lead to the emergence of life
with neural connections and brains, i.e. the type of life which is of interest for SETI.
We focus on organisms with active metabolism because this is the only type of life
that can generate a detectable chemical imprint in the exoplanetary atmosphere.
Among terrestrial organisms, poikilotherms are of special interest for setting thermal limits of habitability because their internal temperature depends directly on and
varies with ambient temperature [1, 7]. Conversely, homeotherms do not provide
straightforward limits of ambient temperature because they are able to stabilize their
internal conditions over a broad range of external temperatures [9]. Homeotherms
are interesting in the context of SETI, because a tight control of the internal body